What is everyone's engine design preference?

[Twoblackmarks...]

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.

[DavidBoren]

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.

[DavidBoren]

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.

[DavidBoren]

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?

[mikels]

Originally Posted by DavidBoren

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.

Originally Posted by DavidBoren

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

[clill]

I have no mo money !!!!

[mikels]

Originally Posted by clill

I have no mo money !!!!

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

Dave

[DavidBoren]

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.

[DavidBoren]

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.

[cjsgarage]

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