i was thinking, since the inception of the L92 heads. just think of what this budget combo would do. it would be a big bore ~346 that would rev to the moon and with the l92s it would probably make power to the moon. think itd be a good combo? ive never heard, read, or seen of anything like this. and seems tht something tht worked for the sbcs should work even better wih the LSx motors.

 

One of the crate engines in our new lineup is a short stroke LS7 5.7L revving to 8000rpm. You could continue that concept with the LS2 and L92 heads, but I think it would get a little pricey and more effective to just do an LS7.

 

ehh, just think how expensive those are to begin with. an ls2/lq9 would make nice budget foundation then the l92s, etc, etc. :dunno: youre the expert not me. just seems to be an awesome budget setup

 

I've always wanted to see this done too....

 

hmmmmm 8krpm V8

i think its a very nice idea, especialy with turbos!

Chris.

 

I too would like someone to chim in, who has done short Stroke engine. 6.0L with 3.28 Stroke or similar. I realize a bigger bore would be ideal 4.125 but it seems to put me over my budget the sleeved LS2 $1600 extra. Most Road race cars have short stroke. I plan on building a short stroke for my future GTM but need a little detailed info. Like would a stock 3.28 stroke crank with stock rods all cryoed be strong enough. What heads would work with a ASA cam @.570 lift.

 

I thought that I'd contribute a little info from one of my former motors.

I ran a solid roller, aluminum rodded, iron block 402ci into 8300rpm many times. I later
pulled it out running perfectly. It was a 4inch stroked 6.0L motor.

I had a Glide behind it, each gear pulled and lasted FOREVER!
People in the stands would come up to me and tell me that the way it sounded, they
would tell me that it sounded like a attack fighter plane, rocket, and some would tell
me they thought it was going to blow up It just kept climbing.

My car had a major vanishing point effect on the top end with the Glide and high rpm
capabilities. It pulled hard on the big end. The Glide would even out the accelleration
the whole way.

You may not have to destroke to run reasonably safe into 8000rpm.


Jay Johnson

 

Sure, the long strokes make great power, but they won't live as long in a road racing application. The high piston speeds accelerate wear and fatigue quickly. Remember they have to hold those revs lap after lap and that's when the effects start to show.
I like the idea of a large bore short stroke setup. There are some cylinder heads on the horizon that will help these setups make the rpm reliably.

Richard

 

Yes but increasing power never increases reliability. At the same overall power level the bigger engine will live longer always. If you are turning the same rpm with the larger stroke engine you are also making much more power. Destoking just reduces power and reliability at any power level.

If you are choosing an arbitrary rpm limit then destroking will take a little wear out of the engine for sure and it will also take the same amount of power out as well. Why do that? Many have built destroked LS1s on this board with the same results. They go slower at a higher rpm but there is nothing special about that!

There's a good reason the LS7 comes with a 4 inch crank. RPM tears stuff up WAY faster than stroke ever will. I'm not saying that you believe all that Richard I was just quoting you on the wear part.

 

Why Short Stroke engines? Because it works in the application it is being run like Road Racing and it also has worked for the 0-100-0 Record holder. SBC 377

 

There is nothing magic about the short stroke. As Erik said, you are compensating in revs for cubes. There are probably three factors:

1. The rotating assembly. Here, we are primarily interested in peak forces on the weak points: wrist pins, piston bosses, connecting rods, but primarily the rod bolts. The forces are higher with a shorter stroke (same bore) adding revs to gain displacement.

2. The valvetrain. With the same swept displacement, basically the the same size components. Here, the shorter stroke is providing a higher load without benefit. Also note, when you move from 6500-7000 to 7500-8500rpm, you move out of the range of hydraulic roller cams to solid roller cams, that can have lifter issues in street use. Schubeck lifters, at $920/set, may be the only fix.

3. Low speed operation. Simply, a street car needs to operate in traffic at under 20, and sometimes under 10mph. Modern multiple cam engines use variable cam timing and lift and variable intake length to provide a wide range operation. Barring that, which to the best of my knowledge is not done in the pushrod OHV world, the low speed operation of the smaller displacement engine is worse. It is my understanding that forced induction can minimize this.

The advantages of smaller displacement/higher revs can come in several ways:

1. So countries have high taxes on larger engines.

2. Many racing classes restrict engine displacement, although increasingly they are also restricting engine speed.

3. It produces the same power (torque at the wheels) with lower forces in the engine and driveline. 400hp at 8200 rpm is 263 lbf-ft of torque, at 7000 it is 300. That is the difference between a 7 L and a 6.2. This can allow lighter components and may fall within the operating range of the only components available.

Factor 3 may make that sort of engine a good choice for a FFR GTM or Ultima, especially using a G50 transaxle. Using a Quaife, ZF, or Mendeola may mitigate that a bit.

P.S.
It seems most modern engines have 82-87mm bores. Does that have something to do with combustion efficency? Hondas with those bores have piston speeds and G-forces exceeding anything we are talking about here. However, the small bores result in relatively light pistons, they use smaller, lighter pins, and short rods with small journals and less weight minimizing the negative rotating assembly issues, an overhead cam 4valve setup minimizing valvetrain speed issues, and a variable cam timing/lift setup minimizing low speed operation issues.

 

Does this engine use the LS7 rotating assembly and valvetrain (with custom crank and pistons) or did you replace it with a more solid setup?

 

LS7 rotating assembly with custom crank/pistons and other upgrades to suit 8000 rpm.

 

DavidNJ basically hit the nail on the head.

The only thing I have to add is that stroking an engine will allow for more TQ and keeping the RPM's down to save the life of the engine, but there is a point of diminishing returns when it comes to stroke. Where that is varies based on the motor.

Practically the only reason that F1 motors rev to 16k+ rpm is because they have to. They have a 3.0L max on displacement. They even have 3.0L V10's. In order to compete they have to. If they could run any displacement, I can gaurantee you that they would balance engine and transaxle integrity instead of spinning to the moon.

I do think it is a good idea for a GTM like previously stated because of the G50 transaxle. They are definately have a much weaker TQ rating than a T56.

In this situation, it would probably be more cost effective to build a high spinning de-stroker than to get a G50 build to handle 500+ ft-lbf tq. You are probably looking at a $15k+ transaxle :-0

 

Those Ti rods, with the HUGE balancing pads, don't look like true high speed stuff. That is where my concern would be...an 8000-8500rpm road racing/oval track engine has a lot of forces on the rod. With the big bore, big pin diameter and big non-piston guided pin length, that could be alot of force swinging around that rod.

 

Erik, I believe we're in agreement. I wasn't debating weather a short stroke will make more or less power than a long stroke engine. I was only touching on the wear related aspect between the two.
Large bore/short stroke engines are dependant on efficient flowing intake and exhaust systems to maintain torque beyond the peak. These engines do have their place in the racing world.
The bore vs. stroke debate will go on for ever, but my experience says it's application dependent.

Richard

 

david, i know honda spend a lot of time and effort balancing their engines! the older vetch generation of engine ran a long stroke to bore ratio and still spun it to 9k! would likr to know if the reason they can do this (on a production engine that will last forever) is due to the lighter wiehgt or the extreme balancing they go through!

thanbks Chris.

 

The C5R and C6R 427 cu in motors are shifted at 6200 RPM's they make their horsepower at a much lower RPM that the motors you are talking about. As far as road racing goes I would say that these are pretty much state of the art when it comes to the LSX series road racing engines. Torque is highly under rated. Of course they are limited by the rules they have to comply too in IMSA. They have restrictions on the size of the intake orifaces. Kind of like restrictor plate racing in NASCAR. But they would make even more power without the ristrictions on them. Don't see any reason to go little when this is a tried and true platform to use...

 

Welp, I don't know if it's been taken into consideration yet, but look at your rod/stroke ratio, as well. Sure, a stroker can be balanced, blueprinted, blah-blah-blah, but with the shorter rods sometimes required to fit a longer stroke in, this creates more side thrust, decreasing engine life. One good thing it does though, is add low-end torque due to the added leverage that comes with more side thrust.

De-stroking a motor allows you to run longer rods, and while this can hurt low-end power, I can't for the life of me think of a short stroke motor built for low-end. The whole big-bore short-stroke long-rod combo is part of why the ol' 426 Hemi was hard to beat in NASCAR. 4.25" bore, 3.75" stroke, and up to 7" long rods, resulting in a 1.87:1 rod/stroke ratio, which is on the extreme high end of the spectrum. for most engines, 1.6:1 to 1.8:1 is an acceptable range, with 1.7:1 giving the best of both worlds.

Oh, and longer rods will allow for higher compression. Years ago, Hot Rod built a GM 352 out of a 400 block, a 327 crank, and Ford 300-6 cyl. rods. At 11:1 CR, it made 412 hp... on 87-octane, 36* total timing, with no pinging at all.

 

Lots of engines rev like the Honda. The M5, new M3, Audi RS4 V-8 are all 8000+rpm engines. Never heard of any balance issues. However, lightweight rods and pistons certainly help. I believe the production engines are around 1350-1400gms bobweight.