Destroked LS2

[RobM]

stroke has alot to do with mechanical advantages, high rpm stability, and piston dwell. cant forget about these!.... discuss... man i love this stuff

[Fuelie Fan]

I'm wondering if you can elaborate on what you mean by high rpm stability?

[RobM]

We a shorter stroked engine generally has less rotating mass than a longer stroke engine, and this mass is generally closer to the axes of the crank than a longer stroked engine. This in turn makes the engine less sensitive to imperfections in the balance of the rotating assembly. Any engine builder will tell you they balance to “0” but it is impossible to balance any thing entirely perfect. How ever the hole in my theory is that the benefit if this concentrated rotating mass can be canceled out due to the higher rpm capabilities of a de-stroked engine. A shorter stroke also makes for slower bearing speeds. which frees up power

[Fuelie Fan]

Once again we need to clarify whether we are talking purely about a change in stroke, or a change in stroke in combination with an increase in redline to achieve comparable max piston speeds.

For the former, then yes you've decreased rod bearing speeds, but crank bearing speeds are the same and all accessory speeds are still the same. That's all well and good, but I guarantee you that the minor rod bearing friction reduction won't offset your loss of displacement! You're better off running different bearing diameters (see nascar running Honda bearings) than reducing stroke if you're looking to reduce friction losses.

If you increase engine speed, your rod bearing speeds will be basically the same as they were before. Meanwhile, you've INCREASED speed of the crank bearings, resulting in a net increase in friction. You're also driving your pump and all accessories faster. And, probably most importantly, your crank is cutting through oil at a much higher rate. You will experience increased losses as you increase engine speed.

[RobM]

i agree with what your saying, i was just bringing some other factors into the mix. this conversation could become endless but thats ok. I mean if you throw rod length into the mix it opens up even more doors of conversation

[68ls1wannabe]

Why the high rpms. V8's are about torque. Longer stroke = more torque. That is what move's the car right. Where can you use 8000 rpm on the street. That high winding motor would get it's ass handed to it by a properly setup turbo motor in a useful powerband. Say 2000 to 6500. I thought the whole idea of the turbo was to pack maximum amouts of air into the cylinders without having to turn the piss out of the motor. Check out ls1tech.com. They argue these ideas constantly.

[Kenova]

I normally try to stay out of discussions like this one, but sometimes I just can't help myself . I haven't had much experience building engines, and I've never seen the inside of a dyno cell, but I have done a pile of reading over the last forty years. What follows is merely what I think I have learned.
First off, torque is primarily a product of displacement. I've seen more than a few tests over the years where different bore and stroke combinations of the same displacement were tested. The torque and horsepower readings are usually within one or two percent, sometimes even closer.
A shorter stroke with longer rods reduces strain on the rod bearings, rod bolts, rods, and wrist pin. The friction from thrust side loading is also reduced. Does this result in more power? Usually not, but if it makes life easier for your engine, why not do it?
Just because an engine has a short stroke and big bore doesn't mean you have to wind it up to the moon. Lord knows there are more than a few Ford 5.0s (3.00s x 4.00b) lugging a variety of trucks and land barges around. How far you wind an engine up depends on how big of a cam you have (and the size of your gonads).
With the advent of modern fuel injection and turbocharging, large displacement engines are not always necessary. Although it will always be easier to get the same torque and horsepower out of a larger engine.
Now for my personal preference. If I were building a turbo engine for street duty, I would use a 4.125" bore so the heads can breath more freely. The crank would be in the neighborhood of 3.25" with 6.125" rods for a displacement of approximately 350 cu.in. With a good turbo system it would make plenty of power for the street and I would have a slightly higher comfort level due to the short stroke and long rods.
Needless to say, all this goes out the window if you must conform to racing class rules.
Ken

[nancejd]

Don't forget that their is a difference between engine torque at the flywheel and torque at the wheels due to gear multiplication. The chief disadvantage I can see with the smaller displacement higher winding motor is that you'd need more gear in the differential to overcome the torque disadvantage, which would result in a higher rotational speed for the driveshat. You'd potentially be a lot closer to the driveshafts critical speed. On the plus side, how much torque do you really want to make a t a low rpm anyway? Can you really hook up a big block on the street? Or most turbo small blocks for that matter? I think something that came out of the hole soft and just kept going could be interesting on the street.

[68ls1wannabe]

I believe one of the best motors to build is the 6.0 LQ4. It's an iron block so no issues with strength. Stpck bore at 4.00. Get a forged eagle rotating assembley, 4.00 crank, rods, pistons. Keep compression at 9:1 for turbo or 11.5:1 NA. Port the stock heads and use comp 921 springs. Lightweight valves "like the LS6". New cam. LS6 intake or if budget permits the FAST 90/90. More power than u know what to do with and getting the job done under 6500 rpm. Say goodbye to those new rear tires.

[Colvindesign]

If this was to go into a very light car, then I'd say go for it and forget the turbos. A LS302 would be sweet.

If this is going into a middleweight to heavyweight car, then forget it, and go for a stroker LS1 or LS2 and your choice on the turbos. I think they have 396 Cube stroker kits, which would also be a sweet displacement number.

However, if you are seriously looking into the destroked LS, I'd do some research and try to get Dyno graphs on the ones that have been built (destroked LSxs that is), this will tell you exactly what you will need to do (gear, trans, etc). If you build something that revs to 9000 rpm and makes 400 peak torque, you need to know what the off idle torque is. If it's 100 off idle, that's a lot different than 200 or more. This means you will need to take it up to 2500 to get moving. A well balanced rotating assembly and a lightweight flywheel will throw the revs up and down faster than you would think, plus if you are going for those high of revs, I would suggest a dry sump, or something more extreme, if you are building it let me know and I'll let you know a secret good for up to 10% increase in power on a high winder.

Anyway, finding out where the torque is, is pretty important. Because if it makes none down low, you can go test drive an S2000 to see what it'd feel like to drive. But if it makes a fair amount down low, regular driving will be fairly normal.