What is everyone's engine design preference?

[camcojb]

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

[Che70velle]

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.

[mitch_04]

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!!!!

[craig510]

Originally Posted by mitch_04

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.

[DavidBoren]

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.

[Flash68]

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.

[DavidBoren]

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.

[bdahlg68]

Originally Posted by camcojb

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

Hey hey hey. Not entirely.

[DavidBoren]

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.

[DavidBoren]

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.