I'm looking at making a road racer/DD out of a Ls engine in a porsche 944. Due to the tranny I can't break 500rwhp. But I'd like it to turn up to 8,500rpm. So is there any point in going forged? As long as I replace the rod bolts I think I should be good? Would the stock pistons handle that kind of rpm and power? What do I have to loose by going this route?

Also, what would it take to get that kind of power....550hp from a ls1? I'm not stroking but I could bore it out to 3.905. What heads, cam, valvetrain, and I think I'll be running a ram air. This is not a drag car so I need this to be able to run daily and on the track.

 

I have limited knowledge in this area and everything I know has been told to me, so take my advice with a grain of salt. For any car, but especially a road racing car, you want the lightest rotating assembly possible that will handle the power. I really dont see a point in going forged on a motor thats never gonna see boost or nitrous. Most of your build is going to be the valvetrain. Definately put hardened pushrods in it and upgrade the springs and lifters and such. The rest of your build is going to be not so much about peak hp but about powerband. A light bolt on n/a lsx motor in your porsche is going to make more than enough power to sling it around a road course at a VERY quick pace.

 

^x2.... You can find very nice lightweight forged rotating assemblies also just in case you wanted to bump up the power and get a diff tranny if it's in ur budget of course but like stated above a ls in that light of a car will be awesome on a rr course given you have the right susp setup etc.

 

stock pistons can handle that power but i have no idea on how much rpm the rotating assembly can handle.

 

I would be looking at destroking the motor and using a larger bore for high rpm operation. Even then I suspect reliabilty would dictate a redline under 8k rpm.

 

thats alot of rpm for a prolonged time. I see rod failures

 

Spinning that high is a tall task. You'll need some serious valve train and likely need spring replacements every 5K miles or so.... maybe even more frequent.

If it were me for a 450-500 whp goal I'd just re-gear the final drive of your transaxle and run a 6500- 7000ish RPM redline and build something around 400 cid engine and you'll make your hp goal with ease and have daily driver reliability out of it and only need a valve spring swap every 30k miles or so.

 

Why do you want to turn 8500RPM? To sound cool? RPM just causes unnecessary wear and tear on your engine, especially on critical areas like valvesprings and rod bolts.

Why not stroke it? The money you'd spend for a valvetrain capable of 8500RPM would be more than that of an entire rotating assembly and turning 8500RPM on a daily driver would be more expensive to maintain as well. You could go with a cheap Callies LSc crank for a 383ci LS1, run a low enough compression for the cheap pump gas, and your engine will be a lot happier, make your 500whp goal, and last longer as well. You wouldn't need to run a solid roller, or mondo triple springs either. Then if you decide to get a manly transmission that can handle more than 500whp, you can basically swap heads and the cam for another 50-100whp.

Not a good idea.

 

Crank 550? Just pick some killer heads and a big cam and keep it under 7Krpm. Over 7K and your inviting migraines.

Get a crate LS6, have a builder go through and replace the bearings and upgrade all the bolts and properly slap it all together.

Your going to open the whole pick 2 of 3 scenario if you want reliability, tracking ability, and lots of power.


FWIW, when my motor broke, why wrist pin seized on factory LS6 rotating assy.




They use a transaxle, pretty tiny unit lol.

 

They use Porsche transaxles on the Factory 5 GTM supercars don't they? SC30 or something like that? I'm sure the turbocharged LS7's I've seen go in those cars make more than 500whp.

 

It is exactly what Cadillac Racing did with its LS6 car in 2004. They won races too, but the redline was limited to 7,600 rpm.

 

Like was asked, why do you want so much RPM?

If you were to get a stock LS6 bottom end and have it gone through like OKcruising said, slap on some AFR 205s, and their 224/228 cam, youll be up there in power, but youll have power all over the place under peak which definitly wont hurt!

 

That was a racecar. This is not a racecar and he didn't mention any rules to limit displacement. You want RPM when you can't increase the displacement, and even then you wear components faster since each part sees more cycles and greater loads.

If you increase displacement, you increase torque. When you increase torque, you automatically increase horsepower. Destroking is simply not cost effective and would be effectively giving up cubic inches (ie torque and horsepower). Like I said, not a good idea.

 

You don't give up displacement - you simply reconfigure the displacement such that it is achieved with a shorter stroke and a larger bore. It allows higher rpm operation with the same displacment. (Cadillac Racing actually increased the displacement from 346 to 349 if I recall correctly) Whether it is a good idea depends on the application. But if you want high rpm operation with the same displacement the over square bore-to-stroke configuration is, in fact, the converntional way to get there. Road racers typically prefer higher rpm because is allows lower gearing for better acceleration.

 

I'm not stroking it and over camming it, its not a drag car. It'll put too much side load on the pistons for full days of road racing. Although I'm not planning on road racing every weekend, I do plan on being on a track for an hour or two at a time without stopping (other than for fuel).

As for the rpm. As Darkman put it, it'll allow for better acceleration out of the corners. Also, I figured that would be the only way I can pull that kind of power from a ls1 engine. I'm completely willing to bore it out. 8,000 isn't an exact number that I need to hit, if 7,600 turns out to be that magic number...so be it.

I was looking at destroking it down to a 3.185 but then you lose a lot of cubes and the cost of getting darton sleeves makes it not really financially feasible. I think with a 3.622 stroke I should be okay with side load but correct me if I'm off. I mean if I can get my hands on something cheap that runs a stroke between 3.3-3.5 that would be wonderful and debatable. But I'm mainly wondering on how durable the stock rods and crank are?

KCS, the transaxle you're thinking costs 5 grand used which is far out of my budget. As for now 500whp is more than I'll need since the car stock is 2,800lbs (2,700 or less when I'm finished).

 

a forged assembly will allow it to hold up better to the rigors of what you are going to do to it.
also if you go with forged pistons, you will be able to hold up to the constant heat and will be less prone to problems caused by a little bit of detonation. on a stock piston it only takes a little bit of detonation to ruin things fast...
typically a forged assembly will also come to the door already really well balanced, which means better power thru the entire powerband.

Be sure to get some good ARP Rod Bolts or Rod Studs and go with Studs for the heads as well.

ls1's dont tend to make power up at 8k rpm's. to get there you will need a pretty healthy sized cam..solid roller specs..at which point, your hope of long valvespring life goes out the door.

as far as power... 550 Crank is easy on an LS1... any cam and decent heads and you are there no problems...

550 to the wheels is a whole different story... you wont get there on motor without a 408 or bigger.

there are upgrades you can do to your transmission to make it handle more power... probably not cheap upgrades...but it can be made stronger.

 

sorry. I meant 550 at the crank. I'll take whatever that converts to on the rear wheels.

 

yeah.. pretty much any Good set of Heads, full bolt-ons and a mid size cam and you are there easy...

I would still go forged for reliability if you can afford it..
but you still wont be making good power at 8k rpms without a really large cam with a large valve relief in the pistons...
talking a high 250's cam on a 116ish lsa.... which might as well be solid roller, and will be hell on the valvesprings

 

You do give up displacement if you go to a larger bore and then destroke it. Just a larger bore alone would be more displacement (say 364ci?), but you're suggesting going the extra effort and destroking it too so that it stays at 346ci. That's giving up displacement.

The point I'm making is why high RPM when you can make the same power at a lower RPM, and more of it everywhere with a larger engine? An over square engine is the ticket for high RPM, but is it really worth it? For gearing?

Too much side loading? From a 4" stroke? Like what's in a stock LS7? A stock LS7 with even shorter rods than an LS1?

You can't bore out an LS1. All you can do is stroke it, which is the easiest way of extracting that power from an LS1. The cam and induction system needed to make power up to 8000RPM is going to sacrifice a lot from lower RPM where you'll be at for daily driving, and will cost a lot more money than if you were to stroke it.

As a daily driver/weekend racer combo, many people optimize their car for where it's driven for maybe 10% of the time...at the track. Then they're unhappy with it because the 90% of the time it is driven for a DD, it's a dog and just miserable. It happens all the time is all I'm saying, and you may learn from the mistakes of others. Or not.

I think you're too worried about side loading. The LS7 uses a 4" stroke with a 6.067" rod and I don't think LS7's have too many side loading issues after track days. A 383 rotating assembly would use a 4" stroke with a 6.125" rod which is theoretically less side loading than the LS7. If you're that worried about side loading, use an LS7 block and then throw in a crank from a 4.8L. You'll get you're 349ci and I assure you, no sideloading issues...

Well hopefully one day you can afford it, or maybe just find a really good deal on one. The option I'm suggesting is that you aren't straining an engine for a magic RPM, but rather having a less radical combo that puts out more overall power, requires less maintenance, and would be more fun to drive to work or to the track. Then when the day comes that you can afford the transaxle we're talking about, you don't have an engine that basically already maxed out, but one that can be improved upon for more power.

 

Sorry I wasn't clear. I meant honing out a ls1 to 3.905 not boring. I was referring to the ls1 when I said I won't stroke it.

It does make a lot of sense to aim it for more of a daily driver rather than a track car. I totally agree with that and I wasn't sure how drivable this car would be.

The problem with ls7's is that they aren't cheap and they don't come up very often at all. Unless I'm completely off my rocker.

What could I reasonably achieve with a ls1/ls2 block since they're cheaper? If I were to stick with just a hone? I think a 383 would be pushing it for side loading..yes?