Short Stroke LS7?

[93Rubie]

Ok, so I got to thinking (i know dangerous idea) this is not exactly C4 related but is Corvette related. So in this age of bigger is better LS7 and LS9 etc...engines, what if you built something smaller? I love the idea of taking a LS7 with its great cylinder heads and 4.125 bore and getting a 3.00 stoke in it. Can you say high rev's? Visions of the 302 reincarnated dance in my head. The high flow heads and the short stoke=high rev's and big power. I think the biggest challenge would be getting the valvetrain to stay in place at 8K RPM. I don't know what the fuel mileage and emissions issues might be with such an idea, and really don't care. This is purely a hotrodding idea and has one goal big HP from a small high winding package, a al 67-69 302. SO what you do think about this, fantasy land or is it technically possible. What do you think of its actuall feasibility. This is all theory at the this time anyway.

 

[Hib Halverson]

The stock LS7 already revs 400-600 rpm higher (7100 rpm) than a stock 302 which floated the valves at 6500 rpm or so.

Reality is that shortening the stroke of the LS7 would not appreciably increase its rpm range or it's rev limit.

The rev limit in that engine is more a function of valve train and accessories than it is bore-stroke ratio. By converting to forged pistons, mechanical lifters and changing the valve spring package, 7500 rpm would not be a problem for an LS7. Much more than that and you risk significant durability problems with alternator, power streering pump and the water pump. If we take the accessory issue off the table, the engine's rotating assembly is good to 8000 rpm, probably 1000-1200 rpm more than the 302's.

Also, if you decreased displalcement but kept those heads, you'd not increase top end power by much and you'd narrorw the engines torque band.

 

[93Rubie]

I figured that the valve train would be the limiting factor. I have always been a fan of small high winding small blocks of any make that is why the thought occured to me. The LS7 maybe a small block but it has big block cubes which is not a bad thing. Those heads wow, I read of 360cfm from them. Imagine the possibilities if you could get that kinda of flow to work on a smaller engine, but would have to have a higher velcotiy in the ports I could imagine. I drove a 5.0 Coyote Mustang the other day, wow 7K right NOW!! Likes to rev, granted it is a DOHC engine. Makes me wonder what a LT5 is like. Maybe some day....Someday all engines will rev like crazy if electro-mechanical valve ever show up on production models. Talk about having your cake and eating it too. For now I guess, I 'll have to stick with my "old school" Gen 2 LT1. :L Heck, the LS makes it look arachic, the next gen LS will make it look pre-historic, I'm sure.

Wow, 8k from a LS7, that is Honda inline 4 VTEC territory. Out of a PRODUCTION pushrod V8. Gotta love it.

 

[Hib Halverson]

Test out your theory.

Put a crankshaft from a 4.8 or a 5.3 into the 7-liter block.

 

[93Rubie]

Haha, if I had the funds I might. Like I said, Hib, just a thought, I had. Those 302's supposedledly where known to be a rev king and made quite a bit of power for their size at the time. I just thought it might be an intresting concept. Not a nesseary one but a interesting one. If I had money I would be dangourous, I would actually get to try all my screwy ideas, some might work out, others not so much.

 

[Jeb]

I understand that Chevy is talking about putting a dual-turbo'd, OHC, 3 point something Litre with a little bittie bore. long stroke (or maybe short stroke) and turn it upwards of 10K RPMs for the next generation Vette. Has anyone else heard or read anything about this?
Damn, I wish I knew something about engines.

 

[Hib Halverson]

Test out your theory.

Put a crankshaft from a 4.8 or a 5.3 into the 7-liter block.

Just kidding....

In practice what wouldn't work because the snout on non-dry sump Gen 3/4 cranks is shorter. Neither of those cranks has a snout long enough to fully engage the two-stage oil pump on LS3 Z51 manuals, LS7s and LS9s.

The 302 of 1967-1969, rated at 290-hp gross but probably making more like 325 gross, was indeed capable of high revs but only in modified form. In stock trim it still floated the valves at 6600-6700 rpm like the other mechanical lifter SBV8s of the era. Where the 302 really made rpm was when modified for SCCA Trans-Am racing with modified oiling system, a 2x4bbl cross ram intake, special valve springs and, later, even roller rockers. Once those mods were made the engines would safely go to 6800 rpm perhaps even 7000 rpm. Today's vintage road racers run them even higher.

 

[Hib Halverson]

I understand that Chevy is talking about putting a dual-turbo'd, OHC, 3 point something Litre with a little bittie bore. long stroke (or maybe short stroke) and turn it upwards of 10K RPMs for the next generation Vette. Has anyone else heard or read anything about this?
Damn, I wish I knew something about engines.

There have been lots of rumors of late about smaller engines coming for Corvette. One rumor is a high-rpm, turbocharged V8 of about 4-liters. Certainly possible but it would cost a lot of money to do that.

The other rumor is a V6 twin-turbo. The intel I've seen seems to point at the V6 idea. My guess is GM is working on a further development of the so-called "high feature" V6 currently used in the CTS-V and the Camaro. The engine is a four-cam, 3.6L, 60° V6 with DI, VVT and AFM. It's most aggressive version in current production is the 313hp unit in the Camaro. Add two turbos and you'd have 350-375-hp. My guess is that engine and a 5.5L supercharged V8 with DI, VVT and AFM is what we'll get. My last guess is that both will be flexfuel to please the rabid environmentalists amongst GM's government overseers.

 

[xfirez51]

93 Rubie,Why don't you try an LT-5 and find out what a high revving small block feels like!?Power peaks at somewhere around 6800rpm with torque peak at 52-5300. That's alightly modified LT-5. Essentially porting the top end and headers yields about 400hp at the wheels.Port the heads and a bit larger cams and you're in Z06 territory w a 5.7L motor NA. And the roar of an LT-5 at full bore is something th hear.

 

[Hib Halverson]

93 Rubie,Why don't you try an LT-5 and find out what a high revving small block feels like!?Power peaks at somewhere around 6800rpm with torque peak at 52-5300. That's alightly modified LT-5. Essentially porting the top end and headers yields about 400hp at the wheels.Port the heads and a bit larger cams and you're in Z06 territory w a 5.7L motor NA. And the roar of an LT-5 at full bore is something th hear.

LT5s were, indeed, a great engine for the early 90s, but the idea that engine gets you to "Z06" territory is perhaps a bit of an exaggeration, mainly because while the LT5 had a pretty spectacular specific output for a late-80s design, it was heavy and in a heavy car. Also, there is misunderstanding about where LT5s made peak power and torque. Peak power was 5800-6000 rpm and peak torque was about 5200 rpm. The engines would rev to just short of 7200 rpm, but they didn't make much power up that high. They were better when shifted at 6200-6500.

When run heads up against an 02-04 Z06, a stock 2G ZR-1, has a tough time because of its weight. It is true, that things stack-up better if you have an LT5 of about 500-hp, but even then, the better torque curve of the LS6 and the lighter C5 makes a pretty stout contender. I agree that, if you add more aggressive camshafts to the LT5, you can gain another 25 or so horsepower and then you are close to "C5 Z06 territory."

 

[xfirez51]

I have a dyno sheet showing ~400rwhp @6800rpm on a stock block LT-5 motor with just ported plenum and IH and 1 7/8 Watson headers. Turns out the cam timing was out of phase. I did run a C5Z heads up at Byron last year and walked from him top end. His trap was 113, mine was 117+. One member of our FBI group runs a stock block LT-5
with 11.0's at 129mph (474rwhp). On a road course, I doubt the C4Z would keep up with the C5Z and forget the C6Z. I am not disputing the technology of either the C6Z (would love one) or even the LS-6, but the question in the thread is about high winding small block/small displacement Chevys. No question that Gen III motors give you tons of bang for the buck. No doubt, on the other hand, the LT-5 is a labor DIY love.

 

[93Rubie]

Like I said in one of my posts an LT5....someday. I have never saw one in person and just having something so unuiqe would be really cool. The C4 ZR1's are heavy cars so it does not suprise you may have gotten him on the top end but off the line, no so much. Unless, you got lots of HP, 1/4 mile drag races are won in the first 60 feet. For their day the ZR1 was and is a Beast. I don;t think it was until the C5 206 in 02 that a Corvette was as fast in the modern era as the C4 ZR1. I forgot about the LS7, etc...being dry sump that would make a big difference for sure. Like I said, in theory....

 

[catbert]

Just kidding....

In practice what wouldn't work because the snout on non-dry sump Gen 3/4 cranks is shorter. Neither of those cranks has a snout long enough to fully engage the two-stage oil pump on LS3 Z51 manuals, LS7s and LS9s.

The 302 of 1967-1969, rated at 290-hp gross but probably making more like 325 gross, was indeed capable of high revs but only in modified form. In stock trim it still floated the valves at 6600-6700 rpm like the other mechanical lifter SBV8s of the era. Where the 302 really made rpm was when modified for SCCA Trans-Am racing with modified oiling system, a 2x4bbl cross ram intake, special valve springs and, later, even roller rockers. Once those mods were made the engines would safely go to 6800 rpm perhaps even 7000 rpm. Today's vintage road racers run them even higher.

Roger Penske retained Traco engines to massage the small block TransAm Z motor in early TransAm. Traco breathed their magic and saw 441 to 460 (@7,100 RPM) horsepower in various stages of tune WITH 1 4BBL in 1968. Those numbers come from a car and engine still racing in vintage events.

The 302 Engine