What is everyone's engine design preference?

[mikels]

Originally Posted by DavidBoren

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.

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

[mikels]

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

[DavidBoren]

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.

[mikels]

Originally Posted by DavidBoren

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

[DavidBoren]

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.

[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.