What is everyone's engine design preference?
 

What type or design of engine do you prefer, and why?

Inline six because they are smooth and balanced?

Undersquare for n/a efficiency and torque, versus oversquare for boost and high rpm's?

V8 for that all American thumpy idle, or V6 for the packaging?

What engine type do you prefer, and why?

Also, is there a particular design that is better suited for road racing/pro touring? I know that transmission choice and gearing can be tailored to keep any design of motor in its optimum operating range, but is there a good reason to choose a high revving, oversquare, turbo motor over an undersquare stroker with a positive displacement blower?

I would have to say that, on this site, you are going to find mostly V8's for sure. The LS series specifically... they are everywhere, engineered well, parts are available, etc etc etc...

I plan out what my goal is with the vehicle, what I want. I have a '50 Chevy 3600 that will have an inline 6 with fuel injection, well hidden. The idea is an old vehicle with (well hidden) new design. IRS, IFS, etc etc...

I have a '47 that will get an original inline 6, no custom anything. That vehicles a restoration.

I have an '84 Camaro that will be getting a 6.0 LS. It will be boosted (LS's have very strong rotating assembles) and a power house.

I have an '85 C10 that will be getting an inline 5 cylinder. It's more of a "look at me" vehicle, so the originality of a 5 cylinder will fit perfectly with the extreme lowering and custom interior.

So yeah... I'd say match the engine to the design of the project. However, on here, I'm going to go out on a limb and say the LS V8 will be the engine of choice on most builds.

PS. It seems that a lot of people slap in an LS engine "because it works" and call it good. But I asking more of a preference towards one design theory over another, and for what reason.

Example:
I want to build a 359ci LC9 stroker with stock 3.78" bores and a 4" crank. This makes the motor undersquare. The tall, narrow cylinders are better air pumps for naturally aspirated applications, and the long rod design reduces piston speed towards top dead center, which reduces the likelihood of detonation. This should allow for higher compression and more timing.

There is more to that, but I don't want to bore you with a pipe dream engine that I haven't built yet. Those are the kinds of thoughts and explanations I am looking for with this question.

I get that a lot of people just use what works, without having a real preference towards how the results are achieved. But I want to build an engine with the theories I, personally, think makes sense to test whether or not the engine performs how I want it to using the theories I want it to incorporate. If that makes sense.

Building the engine as I want it built, just to see if I want the right things... if the theories that make sense to me actually give the performance I want. Otherwise, I have to re-evaluate my understanding of engines, and how they work, and figure out what it is that I am wrong about. Why what I think should work does (or does not) actually work. That sort of thing.

Anyone else building an engine or picking a particular engine using this approach?

I know you can take inline 6 off the list for this site... :lol:

David, I like the way you think. I'm an engine guy myself, and I'm constantly reading and researching whats out there. I feel that this conversation won't go far on this forum, due to the stupid LS platform being so efficient, and the engineers doing there homework so well, that honestly it's a no brainier for the average guy building a car to choose an LS3, or Ls7 for their project.
My Chevelle, when I bought it had a fresh .030 over 350 with a 350 trans, that worked well, but I wanted to drive this car a lot, so the fuel injection and reliability of the LS series engine was calling my name. Yeah it's mainstream today, but I wanted reliability that an old sbc couldn't give me. Been there done that.
In my younger days, I worked at a shop that built Cup engines, back when people actually outsourced objects in Nascar. Not only did we build engines there, but we raced on the weekends. I was able to learn engine formulas and machine work during the week, and then on the weekend apply what I'd learned. It was a great job for a gearhead like myself.
Later on in life, when funds started to get comfortable, I did my own racing venture, running asphalt late models. I built my own stuff, due to what I'd learned from life's experiences. Absolutely priceless. The engine program that I had to run was perfect for this thread. A lot of homework, trial and error, and money went in to making those engines run. But that was racing.
Not to bust your bubble, but the 4" crank you want to run in your LC9 will increase piston speed, and even with long rods, your piston speed will likely be greater than stock. That block will bore out safely over .100, however.

I understand what you're saying (although I haven't studied engines enough to get very in-depth, I stick to short stroke=high rpm, long stroke=torque).

I would think you need to figure out the exact purpose of the car. Autocross or road track would be a big one. Then build around that. A high RPM screamer would probably be wonderful for a long road track, not as useful on a short turn to turn autocross track. You'd have to have it at high RPM which would make gearing incredibly important, similar to racing a 2-stroke motorcycle.

I, personally, love the planning stages of the build. It's only limited by your imagination and, of course, budget. The better planned out build will always make a guy happier in the end, when everything is perfect! Plan away!!!!

That all depends on the course. The Goodguys layouts generally have 1 or 2 very slow corners so you need to be in first coming out. Unless you are a racing hero (or paddle shifters) you can't shift 4 times a lap, so RPMs are your friend for higher top speeds. I would love to build a high winding small block for my Falcon.

I am working on a model A which I have a DOHC 4.6 linclon motor for. I got some cams and valve springs for it so it should spin up to 7200. Even if it quits making power at 5900, the extra RPM will keep me off the limiter for a couple more seconds.

Thanks for the replies. And keep them coming.

I hear you about the long stroke increasing piston speed overall, and I figured that it will still be at a higher speed at TDC, than that of the 5.3 piston. But it's no more than that of the other LS engines with a 4" throw, and people spin them plenty fast without detonation issues. So I think I will be ok there. And, I'm looking for torque, with absolutely not a single care of what the peak horsepower ends up being.

Horsepower sells cars, torque wins races.
-Carroll Shelby.

My focus on torque is what led me to the 359 stroker. I'm not all caught up on big cubes or high horsepower. I want a streetable, fun, torquey motor that meets some simple theory criteria I have put together, namely being undersquare.

I want to stay with the 3.78" bore, instead of the 3.9" bore, because the blocks use the same sleeves, so the 4.8/5.3 sleeves have more "meat" than that of the 5.7 sleeves. So the thicker sleeves will handle the extra side load on the pistons from the increased stroke. And the thicker sleeves will handle boost better (if I can ever afford a W180AX for it).

Or at least that's my thoughts on using the 3.78" bore. Wiseco makes forged slugs for the 5.3 with the correct pin height for use with a 4" crank and 6.125" rods, and all the other parts will be stock LS parts.

Interesting thread. At least it doesn't talk about Camaros... yet.

I really became interested in the Nascar stuff after seeing the teams give away their stuff on the used market after their "life cycle" was used up.

But I also wanted/needed something that didn't have to be rebuilt every 500 miles (1 race).

As much as I would love to play with a 9000 rpm motor, I wanted to gain the needed low and mid range torque and bring the powerband down for durability and less maintenance. So a 4" stroke was used instead of the 3.25" that the Cup cars use.

4.170 x 4.0 = 437"

Of course with the small chamber size of the SB2.2 heads (mine are 51cc, many are in the 40 something range) this made piston design pretty much impossible to achieve 11:1 to 12:1 in order to get to pump gas range. So, to minimize the dish in the piston and keep it "acceptable" according to my engine builder we ended up around 13:1 compression. So, the other pump gas came into the picture... E85. Several stations not too far from me. I am good with that.

Even though a .800-.900 lift cam would be right at home with the heads, we decided to use a milder cam (.660ish net lift) with a lower rocker arm ratio (1.7 instead of 1.9 or 2.0). Again, all to keep things lower maintenance.

I really wanted a toned down Nascar motor with all the cool parts and look but not the rebuild cycle. Time will tell but I think we achieved that without giving up the BIG power. In fact the trade off to gain the torque is what I am really excited about.

640 ft #s out of a pump gas SBC. I'll take it. :)

Thank you, Flash. That is exactly the sort of answer I was looking for. I have heard that it is better for the longevity of the valvetrain to let the cam do the work, instead of compensating with higher ratio rockers. That sounds like a nice engine you have put together. 600+ pounds of torque is no joke.

I was also thinking that using the 4" crank, would slide my power band to the left. I might even use a truck cam in it for the initial build. I'm looking for a relatively tame, yet torquey, motor that I don't need to rev the piss out of.

Hey hey hey. Not entirely.

The inline six should never be scratched off the list, in my opinion. Between the 2jz and the 6bt, I think that platform has earned its place and proven its worth. I would love to see more inline six swaps, as even the all aluminum Atlas motor can handle boost and respond well.

Just something interesting I found on a big-bang-theory-esque forum discussing undersquare versus oversquare engines from a physics/math/nerd perspective;

Oversquare engines will last longer because the piston travels a shorter distance, therefore it creates less friction. The larger piston also transfers heat to the cooling system better than a smaller piston does. So an oversquare engine creates less heat through friction and transfers the heat to the cooling system better.

Apparently the heat created by friction in the piston rings increases exponentially with stroke length. So if displacement remains equal, the engine with oversquare architecture will waste less energy, every time.

It's kind of funny, or sad, that reading all the advantages of going with oversquare bore-stroke ratio does little to sway my decision to build an undersquare engine. But, I am sure I will find an excuse to build another one, and I will go the other way with it just for the sake of comparison.

Speaking of comparison, here are the two extremes of what is available using stock LS bores and strokes.

Undersquare:
359ci (3.78" bore X 4" stroke)

And

Oversquare:
353ci (4.125" bore X 3.3" stroke)

I think the difference of six cubic inches in total displacement is negligible, so it would be really cool to build and drive both to see if oversquare versus undersquare makes a difference you can feel.

PS. A "square" bore/stroke motor with a displacement of 356ci (the average displacement of the two engines listed above) would have a bore and stroke of 3.842", just to give you an idea of how over or under "square" each of those engines are.

I mentioned that the oversquare engine will generate less heat due to the shorter stroke causing less friction. It also transfers the heat to the cooling system more efficiently because the larger bore cylinder will expose more surface area.

This is also a detriment to the efficiency of combustion in the cylinder. The flame has to spread across a larger surface. A greater portion of the combustion heat/energy is being transferred to the cooling system, rather than being converted into work. And there is a greater loss in pressure per angle of rotation with a shorter/wider cylinder, regardless of rod ratio.

It seems, in my limited understanding, that any benefits of going oversquare, just to gain larger valves, would be negated by the less efficient combustion characteristics. And oversquare cylinders make less efficient air pumps.

So in a naturally aspirated motor, I am going to build it undersquare to capitalize on the efficiency of the tall/narrow cylinders, both as better air pumps and as offering better combustion characteristics.

The small bores/valves can be ported to flow PLENTY enough for a naturally aspirated 359ci (6.0L) motor. TEA stage 2 flows over 300cfm @ .600, which will do just fine for anything less than 7.0L spinning at less than 7k rpm's.

Any thoughts? Am I missing something entirely? The obvious trend in OEM engines is oversquare, unless you count transverse motors which tend to be undersquare for packaging reasons.

You can't really say reliability or service interval is a determining factor in this case due to the fact that there are a lot of high mileage OEM motors still on the road with 4" stroke crankshafts.

And with compression ratios constantly on the rise, you would think that a longer conrod would be preferable to slow the piston near top dead center for less detonation issues. Undersquare engines tend to have longer rods inherent to their design.

So if you can achieve adequate air flow with smaller valves, what is the advantage of being oversquare? I should say that we are staying below 7500rpm's for the sake of this discussion... I have no interest in tickling 10k rpm's.

David, speaking only of naturally aspirated engines, the over square method of achieving a set cubic inch goal will be more reliable. Increased rod angle is the biggie, with a taller stroke. The more rod angle you have, the more wear you put on the cylinder wall, and the piston rings/skirt, and it also puts more heat in the engine from friction, which is a no no. A bigger piston will run cooler, all things being equal, due to more surface area for oil splash to cool piston from bottom.
These are things to consider if your building a high rpm endurance engine, which your not, so I say build what you'd like, and enjoy it.
Fun fact...in two absolutely identical engines, one having aluminum heads, the other having cast iron heads, the engine with cast iron heads will make more overall power, due to being able to hold heat in the combustion chamber longer...
Totally off topic, but worthy of discussion also. Logically, you'd want aluminum heads over the iron heads, due to weight, and where the weight is at in the vehicle.

Thank you for the input. I have heard that about iron heads making more power due to combustion chamber heat.

And given that this is a discussion of design theory, I see the inherent detriment of increasing stroke. The side loading and friction/heat increase presents a problem to be resolved, for sure. And is probably (obviously?) best left avoided.

In my particular case, I will have an oversized cooling system with electric water pump and fully boxed/ducted radiator, to handle the heat. And I am going to use the small bore block to capitalize on its thicker cylinder sleeves to address the side loading caused by the 4" stroke.

I also will be running an oil cooler, and I have a small quandary about oil squirters...

Are oil squirters piston coolers, or are they just oil heaters?

They use engine oil to cool the piston. Which puts the heat directly into the oil. Are the pistons cooled enough to really make a difference in detonation issues? Doesn't cooling the combustion chamber decrease power output (as discussed above with iron vs aluminum heads)? Doesn't squirting 75psi of oil UP at a piston that is traveling DOWN add resistance/drag that is otherwise not present?

Also, undersquare engines have better combustion due to small chambers, less surface area, blah blah blah. So if oil squirters do detract from the combustion efficiency, due to heat loss in the combustion chamber, this effect would be naturally counteracted by the undersquare small bore combustion efficiency.

If oil squirters are just to stem detonation, then the long rods inherent to an undersquare motor make them (oil squirts) unnecessary. As long rods slow the piston near top dead center, and naturally reduce detonation issues.

Said another way, do the characteristics of an undersquare motor counteract everything oil squirters are trying to accomplish? Or would the longer stroke, and the friction/heat that comes with it, be in a greater need for added piston cooling?

In my opinion, an short stroke high RPM engine is usually much more fun to drive than an long stroke grunty one.

3.78" Bore is very small for an 2 valve 5.8 liter+, it does not matter if you get "better" combustion chamber, because the valve probably is so shrouded by the cylinder wall that you get poor filling and "looses" combustion efficiency by that. So then you probably need to put in smaller valves to unshroud them. And that 300cfm is probably not flowed on a 3.78" bore, I would guess. But I may be wrong.

But it depends on if you want an 300HP truck engine or an 300+HP fun engine.

I would take the fun engine, a shorter stroke engine that survives some RPM and abuse much more easily than an long stroke grunty engine that runs out of rpm.

I dont think the heat and resistance is such a big deal, unless you are going to run a lot of track, rod angle this and that, the most important is the guy who put the engine together, like Warren Johnson says " The rod only holds the piston" but of course, there is more to it than that..

Piston squirters are good for piston cooling, an 100HP VW engine from the 80s has that, then I would think an 3-4-500+ HP V8 SHOULD have it, it`s almost only just american V8s that dont have it for some reason. Any engine that is going to run continually at high speed/load likes piston coolers. Before people often cut a groove in the rods to get piston cooling, and lubrication.

I dont think there is anything wrong with a 4" stroke, but team it up with an bigger bore than 3.78 and it would be better. Cubes work, that I have experienced.. I have an 4.25 stroke engine.. But is it made for endurance racing, probably not so much..

If you can I would just go for what you think would work and try it, on a side note, most european engines are long stroke - small bore, but they are small engines that "need" the stroke. They often have short rods to, sometimes because of not much room for long. If you are used to US V8s, many european engines seems not so smart put together, from an performance view....

I think I prefer big bore and stroke engines for autocross and higher, faster revving smaller cube engines for road courses, at least in terms of fun factor. autocross is a lot more stop-turn-go. I have a Camaro with a 454 cube LS7, and it never lugs out of corners versus my Coyote powered Mustang. However, put the two cars on a road course, and the less powerful Coyote motor is way more fun, despite being slower, simply because you can put your foot down and hold on almost all the time.

I am not trying to argue with anything anyone has said. I think Ron nailed my objectives perfectly. I do have a question about using a 4" stroke and this phenomenon that has been brought up multiple times called "running out of steam"...

From what I have seen, on this forum and other places, the LS7 is a staple of the pro touring community. It has been put in plenty of performance cars that have never had a single complaint about running out of steam.

How many rpms do you use on a road course? The obvious answer is all of them. But seriously, is the 7k redline associated with the LS7, and it's 4" crank, not enough?

Ron says, in "C", to build as much power as you can use. I am building a S-10, it's going to weigh 3000# race weight, I don't think I can use a whole LS7. But it's the go-to engine for pro touring and I am building a pro touring S-10. So I am going to subtract one liter of displacement, but keep the things I like (4" stroke = torque, I like torque). And, at the same time, it provides me with an opportunity to test some design theory that I have for some reason attached myself to.

As for what is more fun to drive. I favor torque here as well. I would rather spin my tires rather than spin the crap out of my engine. I don't roast my tires, and I know spinning tires isn't fast. But I prefer the feeling of taking off in a 500hp duramax diesel truck more than the feeling of "launching" with a 500hp evo8.

I would rather have a car that I have to drive with respect, more than a car I have to abuse. Hunter S. Thompson said that men like big guns and fast cars because they push us to our limits, rather than us pushing the machine to its limits. And with rpm motors, it's like you have to keep them at the upper limit for them to be any fun. But with a torque engine, you have to respect the machine.

Maybe I am just retarded. But I'm under the impression that using a 4" stroke crankshaft will in no way limit my useable rpms.

Is 7000rpms not enough?
Are LS7's hard to drive?

cool discussion...I'll bite..
engine RPM and to me drive ratio go hand in hand and is very dependent on the track, for the few PT style cars I have built or advised on what I shoot for is an 70-75 mph speed at limiter in second gear..in order to have this i looked at having a 7200RPM limit on my engine, this allows the car to run small events such as Goodguys tracks in first or second only, for example the track in Nashville this weekend was a first gear track, and the finals track in scottsdale is a 1-2 track because it has a long straight that I just reach limit 7200 in second at the end of it....and for larger tracks like Las Vegas motor speed way or Michigan international...I spend a large amount of time in 2-3,,and forth on large straights.....so to me function over form in the engine department

That's the whole point of this, though. I'm trying to make the form of the motor fit the function of the vehicle.

I am trying to get everything working in concert. Engine design theory and architecture, cam profile and useable powerband, transmission gearing, rear axle ratio, suspension and brakes... Isn't the purpose of starting over to do everything over? Everything, for the most part, on the S-10 is set up from the factory to work as a system. Even though it's made from GM's leftover parts bin, some amount of engineering went into making sure that the parts selected meshed together for its intended purpose.

So, for me to change anything, I need to adjust all things. And since there is no single redeeming quality of the original S-10 worth saving (other than its compact chassis/body), I might as well design a whole new system, including an engine specifically designed for the rpm range and powerband I want, and a suspension set up for exactly how I feel a vehicle should handle.

When I see a 10k redline, I think "why" because I know it's possible to make the power sooner. And if you can't make enough power to do... ANYTHING you want... before 7500rpms, then you need less mass, not a higher redline.

My idea of reinventing the 6.0L with a 3.8x4.0 architecture vs the 4.0x3.6 bore and stroke is to shift the powerband left, favoring early torque production. The exact same crankshafts are used in OEM engines that spin to 7k rpms. I have no doubts, whatsoever, that any engine built using this crank will be in any way redline limited.

So, it's up to proper cam selection, valvetrain components, and transmission/axle gearing to best utilize a powerband that both comes on early, and can extend to 7k rpms.

Mind you, the torque will come on early compared to a 6.0L with the 3.6" crank. But it won't subtract from the upper limit of the same mid-stroke 6.0L, given proper valvetrain and cam selection... So I literally do not see a downside to building a undersquare 6.0L motor.

All that needs to be done is porting the heads to provide adequate air flow for six liters of displacement spinning at 7k rpms... Which I know is possible, even with the little valves.

Little valves and little pistons are easy to move, so the rotating mass will be able to rev as high as the big LS7 components, even with the LS7 using titanium.

Everyone always says that they want a broad powerband, and yet it seems no attention is ever paid to broadening it to the left. People go through great lengths to expand the powerband to the right, ever increasing the redline. And engine design and architecture reflects the chase for higher redlines with oversquare engines. Yet you can achieve roughly the same effect starting power production earlier.

3000-8500 powerband is 5500 useable rpms...

So is... 1500-7000...

Things that make you say, "hmm..."

As a side note, using head flow numbers from TEA's website regarding their stage two ported 5.3L heads, and an online calculator provided by Wallace racing, the projected redline where head flow can no longer support the displacement at any higher rpms, is 8000. Playing with different VE inputs got readings between 7300 all the way to 9000. So, no matter what, with properly ported heads, the small bore can support six liters of displacement spinning all the way to 8k...

I have no intentions of spinning it that high, but for the sake of this discussion, I thought it to be relevant.

For comparison's sake, the 353ci oversquare engine proposed earlier, 4.125" x 3.3" bore and stroke, using stock LS7 head flow numbers, gives a max redline of 8,300 to 10,900... depending on what VE values you use.

@RodP, I can get 74.5mph in 2nd gear @ 6500rpms with a 1.88:1 second gear and 3.55 rear gears with a 25.7" tire. All of that is theoretical using the Wallace racing online calculator. Rims are based on 2006 z06 18x9 fronts and Toyo R888 275/35R18 tires. Transmission ratio is from the TKO600RR. I would like to use a 5spd transmission and stay around the 3.5:1 range for the rear. So the road race TKO and relatively mild rear gears archives the 70-75 mph in 2nd gear rule.

Same calculator, same tire diameter, same rear gear ratio, same 6500rpms, just changed to the .84:1 OD gear of the TKO600RR, and this predicts a top speed of 166mph. I think that will do just fine.

That's funny Ron. I started with a 377 and quickly discovered that was a big issue on both AutoX and road course. So, I decided to go overboard and skip all steps in between and go with a the big bore big 4" stroke 437"! :lol:

So, what you're saying is.... Sprint Car engines FTW. :thumbsup:

I really wanted to go with a 3.8ish stroke but decided to reuse all the parts with my used SB2.2 "deal" I found... smart? Maybe not... fun? Should be!

You shoulda bought a Miata like that Weld guy.

For 99% of what are people are doing around here, I would have to agree with you.

A true 1500 to 7000 rpm range sounds very difficult to achieve. What would the specs of this engine look like?


Oh, and this is a winner:

Hunter S. Thompson said that men like big guns and fast cars because they push us to our limits, rather than us pushing the machine to its limits.


:bigun2: :thumbsup:

What would a true 1500-7000 motor look like? I don't know. Hopefully it has a 3.78" bore and a 4" stroke. Lol.

But nobody knows what that motor looks like because nobody is working on extending the powerband to the left. We all know what it takes, or at least have an idea of what the motor with the 3000-8500 powerband looks like... if I had to take a guess, I would say it is probably oversquare.

Something like this.........

http://g.foolcdn.com/editorial/image...base_large.jpg

....but you start at zero RPM.

It looks like this:

4.130 bore x 4 stroke
Rev limit @ 7500
Torque is nearly adequate - anywhere

Spent a lot of time optimizing combination for overall powerband.

Dave

The other primary design criteria is DRIVEABILITY!

There are changes that could be made that would further increase power - to the right - but adversely affect driveability, so just not worth it.

Keep in mind this combination is what Mark Stielow runs in his cars, and is able to autocross in 1st gear (3.25 FDR) with precise control.

Combined with 700 rpm idle, pump-gas operation, no sags or other compromises in operation makes this a nearly perfect all-around package.

Dave

That is a very sexy motor. And although impressive, it is more than I personally need. I also have some tingling fear of boosted LS7 blocks. No real reason. Haven't even heard that many horror stories about too much boost grenading the block. I just personally wouldn't do it. Note also, that I chose the small bore block specifically for its thicker cylinder sleeves. From what I understand, the LS7 has such thin sleeves that not even GM would put boost to it, and GM put a turbo on 4.3L V6. Lol.

Sweet engine though. Very impressive curve. Thank you for sharing this.

We've not broke one yet (with ~30 of them running around now starting in 2008). And our guinea pig Mark is not known for driving his cars gently......

The advantage of making really big power is you just can't make it for very long - run out of real estate.

Don't get me wrong, this combination would likely never pass GM's GED (Global Engine Durability) test - that and a 100K mile powertrain warranty prevent factory from ever offering this.

Key is optimized design with combination of high-quality parts and precision machining & assembly. These engines will be very unforgiving for carelessness.

Dave

Relating back to what Hunter Thompson said about big guns and fast cars... These sorts of machines are not intended for the careless.

I am sure that the LS7 blocks hold up fine... All 30 of yours seem to be working. But I am my father's son. And we have a tendency to over-engineer things. We choose our mechanicals based on its ability to survive the apocalypse.

We aren't afraid of maintenance, nor do we shy away from or skimp on routine maintenance. But we prefer machines that can persevere and last. I understand that the parts you select will be a huge factor in long-term reliability, with the single biggest contribution to durability being the quality of prep and assembly.

Because we all know that if it's sloppily put together with poor tolerances, then even the best parts will not be reliable. And likewise, if you take your time and blueprint/ balance even mediocre components and assemble them to the proper tolerances, then you will have a damn dependable motor.

My grandpa won't ever own a motor with an aluminum block. He doesn't trust it. He also won't own a rifle he doesn't trust to work as a club, either. Ask him what he thinks about the M-16, or import cars for that matter (he views both with equal disdain). Lol.

Anyways, for my particular tastes and needs, I want an engine I can rely on and put some real miles through. And I don't need 7.0L for what I'm doing. If an undersquare 359" doesn't do what I expect/ want/ need, I will boost it (like everyone else who doesn't know how to make horsepower like a real man... another piece of wisdom from my grandpa).

As for the reliability issues associated with undersquare architecture, I think I can handle the increased heat load with a more efficient cooling system (larger radiator/ fan, oil cooler and oil squirters, etc). And high quality parts with a damn proper fit and balance should handle everything else.

What is your plan?

1#Do you know what your max RPM will be, or you want it to be?

2#And what max power you want? This could impact max RPM of course.

3#And is it gonna be a carb type intake or injection?

Intake runner length could maybe be an issue to get OPTIMAL, if you are gonna run low RPM and carburetor?

ITBs could maybe flatten out your power curve.

But why not just have a "really big" engine with a small cam, and small runner heads, then you can have that flat power curve in a low RPM?

In my opinion I dont see any problem with an longer stroke than bore, my short deck 1.8Litre VW has 3.18bore 3.40 stroke and short 5.66 rods and makes peak HP at 6100. The stock 2 litre has 3.65 stroke I think. But if the bore gets to small compared to the stroke/total engine size, I would think the valve shrouding or size would limit the power potential. Especially in a 2 Valver.

If you increase the bore too, you would get even more bottom end, and probably more everywhere, so why not more bore too?

(This is like an modern 305 vs 350 discussion, the 305 too has 3.78 bore) I have nothing against 305s though, I like difference.

I am far from building this, I'm really trying to get as much information as I can before I commit to any one thing or another. I figure with the proper amount of research and preparation, I should be able to minimize scope creep during the building phase.

But I don't have any power goals. I'm not chasing numbers. I am studying the different designs of engine architecture and I want to test something out.

The LS motors are the obvious starting point, given that parts interchange so easily and just about any combination of square, oversquare, or undersquare can be achieved using basically stock parts.

My general rule of thumb is that a vehicle should have at least one ft/lb of torque for every ten pounds of race weight. That's all vehicles. For spirited driving/hooning, a daily driven weekend track car should have at least one ft/lb of torque for every 7.5 pounds of race weight. And a track only car should have at least one ft/lb of torque for every five pounds of race weight. Peak horsepower means absolutely nothing to me, as long as it's high enough to get me the torque I want.

Those are arbitrary ratios that I made up some time ago. To me, it makes sense, and it keeps the power goals in proportion to the vehicle. The 4500#, 10 second Hellcat is a 1ft/lb of torque to 7.5# of race weight vehicle, just for reference.

I don't really have power goals outside of making sure my truck can scoot. If the engine I build, by the design I choose, doesn't perform how I want it to, I will do what everyone who fails at building an N/A motor does... boost it.

My plan is to definitely use fuel injection. Probably just a LS2 intake for starters. But I am open to change it to optimize my powerband, for sure.

No horsepower or redline goals, as long as they're high enough to get me the torque I want.

Inch for inch, I think my undersquare six liter motor will be better than the stock 6.0L out of a truck, because the longer stroke should help power come on earlier (juxtaposed with the 3.6 crank), and I will have a higher redline. So, compared to the stock six liter LS, I should see my torque earlier, AND make power higher into the rpm range... with the proper cam, of course.

Even using a stock six liter cam and stock six liter tune, the 4" crank should give a noticeably broader and flatter powerband just because the torque should be showing up earlier, all other things being equal.

Note, I will be using heads ported to flow AT LEAST as well as stock six liter heads. So in a 6.0 vs 6.0 shootout, even if head flow, cam, intake, injectors, and tune are all the same, the only difference being undersquare vs oversquare... My undersquare motor SHOULD have a better (being broader and flatter) powerband with the same top end. If my heads flow the same, despite the smaller valves, and if the 4" crank doesn't lower the redline, then I will lose nothing up top compared to the stock (oversquare) engine. Yet I should gain a noticeable improvement down low.

I do have a question about optimizing induction to compliment engine design.

Do you play to the design's strengths, or use the induction system to make up for weakness

With a stroker motor, you should have all the low end grunt you need as an inherent feature of the design, so do you put a single plane long runner intake on it to help improve the top end, or a dual plane short runner intake to further compliment the low end torque?

Same with adding boost. Do you put a turbo on a high revving short stroke engine to use those extra rpms? Or do you put a positive displacement blower on it to make up for the short throw and add some bottom end?

Or, in the case of my proposed undersquare 359" engine, would a dual plane rpm air gap intake be best to really compliment that 4" crank, and get as much low end as I can... Or do I throw a single plane victor jr intake on it to try get a little more up top? Same question about boost. Trust that the long stroke will provide all the low end I need, and put a turbo to give me some top end? Or just throw a blower on it and have all the low end torque ever?

I suppose it will depend greatly on my intentions. However, I find it very hard to believe that I will require anything extraordinary in terms of the redline for this motor. The supercharged LSA has a 6200rpm redline, the LS7 has a 7k redline, so I will split the difference and establish a theoretical 6600rpm redline for the sake of this discussion. My calculations from the other page put a projected top speed of 166mph @ 6500rpms, which I am okay with.

Any thoughts on induction versus architecture in general? Or in relation to my proposed undersquare six liter?

Just a few thoughts from your comments:

-LS6 intake is superior to LS2 for cathedral port heads. Difference is how they are made (LS6 keeps intake runners isolated from one another entire length, LS2 has small air-gap between upper & lower runner halves.

-Dual plane intake purpose is to increase vacuum signal to carburator. If injected, no reason to use (actually reasons not to use).

-Proper component selection will likely result in nearly identical power bands from either 6.0L combination. If limiting factor is head flow (even with larger bore), not much difference. Longer stroke means more dwell time (and therefore knock sensitivity) - so if running pump-gas, likelyhood of generating substantially more torque with longer stroke is reduced.

-Displacement will win over bore/stroke combination for peak power and bandwidth. 4" stroke 6.0L is 408" motor (if I recall correctly). Issue with 4" stroke on everything short of LS7 is bore depth - 4" stroke will pull piston pin slightly out of bottom of bore at BDC - not so great for piston stability.

-Either combination could turn to 7-7500 with right internals. Need to turn to 7-7500 is dependent on cam, heads, etc.

-'Build' the combinations in Dynomation or other capable modeling software and compare. Program is much less expensive than parts (and can infinite number of combinations for free).

-Many people forget that the engine is a 'system' and neglect to select proper combination of parts for optimization.

-Assuming you have a 'limit' to your budget, you will be restricted at absolute optimization of all components. Again, that's why suggestion of running math models prior to parts purchase to see what is best 'bang-for-buck'.

-Forced induction requires same attention to detail as N/A. Either turbo or supercharged you need to look at everything and balance package for your intended usage.

-I always focus on breadth of powerband - and if for street use, who cares if you give up 20-50hp at top end to improve bottom end. You spend very little time at high revs (even on an aggressively driven street car). Example: We changed cam's in a build we did for friend of mine (built LS7). Gave up ~50 hp @ 7200 rpm for a gain of 100 #/ft @ 2000. SO MUCH better overall package for his street driven (occasionally track, autocross) car.

-Glad to read you are not 'chasing the internet pissing contest of peak HP' - that's a sure way to end up with a pathetic combination that is miserable to live with on daily basis.

-One last note: The power curve I posted earlier was the result of 6 years of continuous optimization of our 7.0 SC package. 1st version made 780hp/830tq. Now @ 1010hp/1020tq. But devil is in the details - and takes time (and money!!) to ferret those out.

Dave

I have no mo money !!!!

Bummer..... Then how are we going to do the 1 MW engine for you?

Dave

Wow, once again I get surprised by how little I actually know. I honestly didn't know that dual plane intakes have no use on a efi motor. Man, I don't know ****.

And that's why I'm here posing these questions. The TEA stage two ported 5.3 heads flow to 320 @ .600, so that would be my ultimate determining factor. The heads support six liters of displacement up to 8k rpms with those numbers, according to the Wallace racing online calculator.

I'm not building a racecar, to tell the truth. It's a 1982 2wd S10. I wanted to see what the lowest displacement motor I could build with the longest OEM stroke available in the LS platform. I actually chose to build the smallest 4" crank LS possible, on purpose.

This will be my first time completely building an engine, as I'd you can't tell. So I chose to build it small. With a displacement handicap, as I learn more and develop more as a driver... If I outgrow what the 3.78 bore is capable of providing, then I will build a new, obviously larger, motor utilizing everything I have learned.

For now, given that the only 4" stroke kit for the 3.78" bore is all forged, and how easily boost can be added, even with the 10:1 compression ratio the wiseco pistons have, I am sure I could get more than enough power to kill myself in a 3000# truck, even out of a small bore six liter.

So I will probably be playing with this combination for a while. Hopefully I can get something half as respectable as yours in the next decade or so.

Also, I am getting conflicting information regarding possible knock issues.

Everything I read, up to this point, says that the long rods inherent to a long stroke will slow the piston near top dead center. This will provide the increased dwell time at TDC, as you stated.

But I read that decreases the risk of detonation, so I would appreciate some clarification, please.

Does the piston slowing down near TDC simply increase the amount of time it is possible for detonation to occur? Or does something about the piston slowing down actually cause or invite detonation to occur?

My understanding of it, from what I have read, and how it was explained to me, is that the reduced rate of compression decreases the likelihood of detonation. Am I wrong?

I can see detonation issues being inherent to the small bore size, as we discussed earlier... Less surface area to dissipate heat into the cooling system. More latent heat in the engine raises the risk of detonation.

It could be argued that I will see no benefits of what long conrods can provide because my 4" stroke gives me a 1.53:1 rod ratio, which isn't great. So my rod angles are still relatively severe, so I probably won't see any decrease in piston speed near top dead center. If anything, it may act like a short rod motor and increase in speed at TDC.

If it has more to do with the rod ratio than the actual length of the rod, then I probably won't see any increase in dwell at top dead center. And therefore, I probably won't have the detonation issues you warn of.

However, I am still in need of some clarification on this.

Does increasing dwell CAUSE detonation, or simply increase the amount of time it may occur?

When discussing piston speed, does the actual length of the rod matter? Or is it all about the ratio in comparison to the stroke? The change in rod angle determines the relative change in speed, and the ratio is constant in the sense that any length of rod with the same ratio will change the same relative angle, right? So any length of rod with a 1.53:1 ratio will give you the same relative change in speed near top dead center... Correct?

If that's the case, then my stroker is actually more of a short rod motor, because 1.53:1 is kind of low.

David,
I'm struggling to remember everything I've learned (especially just recently) and am no expert by far. But I have taken a few classes from experts and read more than one book on the subject. THANK YOU for starting this thread. It's cool to have insight from giants like Ron Sutton and all the other well-learned ones on this forum.

anywho. One of the points I actually can remember from my last class: High Performance Engine Design and Theory from Allen Osborne was that, the bigger bore always seem to make the better power. And I understand your desire to move the powerband down the RPM range.. but there's a reason NHRA and others are up to 4.7 bores. Something about shrouding the valves.

The other point I remember him saying was, to use the longest rod possible. Not necessarily as a stroker.. he meant pushing the rod up into the piston as far as you can--getting a wrist pin as close to the piston head as possible.

I looked for my notes on the class, but they escape me for the moment.



anyway. What about building the more common over-square engine with camshaft designed to pull the power band a little lower? Just a devil's advocate kind of thing.

It seems like you're pretty set on what you want to do, build the 3.78x4 engine. Maybe you'll have enough parts to build a second one if you use all OEM parts, and you can try oversquare similar displacement as you mentioned on page 1.
I do think Dynomation5 would serve you well at this point. It's made by Motion Software.



More food for thought: This is something I found on another forum:
Where B = bore, S = stroke, N = number of cylinders, and C = a constant for fuel quality, materials, stress levels, etc.:

HP ~ B^1.65 × S^.5 × N × C
(after F. W. Lanchester)

Removing N, most power by far, is big bore + short stroke