How and why?......Suppose I want to turn 12,000rpm, of course I would be looking at upgrading rods and pistons to something stronger and of course lighter, to reduce rotating mass.....but no one sells smaller stroke cranks for LS1's....the only option that I've found is to machine your journals and move your centerline closer to your crank. From what I've heard a .0013" machining can reduce your displacement by roughly 10%, which really is heading in the right direction. Other than that....I'm out of options, Is the crank gonna support that rpm or will it spin itself to death, what are my options here?

 

you could use a 4.8l crank

 

Aww heck man, you can get a custom made crankshaft all day long. That's easy. Deciding on what specification you want in stroke based on alot of other stuff is what you'd need to come up with before you order one. Even a crankshaft maker would go over it with you. You don't need to relocate it in your block either. You'd be looking at custom one off pistons and connecting rods too.

Then, depending on how you'd want your engine to run, you'd get into what kind of cylinder heads and induction. Then that would mean, getting into cam timing. It's just like building a regular stroke LS1.

 

my question to you... Why do you want to spin 12,000 rpms? Just for fun? Racing class displacement limitations? etc..

It can be done... but RPM's and Durability come at the cost of Dollars^2... well at least to do it right.

also.. you will want to look at bearing diameter changes, extreme lightweight vavletrain, some of the best 2v cylinder head ports, etc..

you might want to take some notes from F1 engine design as well as nascar..

 

Heads will be the the key to this project.....Durability and 12,000rpms isn't going to be easy, considering the Valve spring strength needed is going to destroy those lightweight valves when they hit the valve seat....I've taken most of my notes from F1...Using a 1.59" stroke isn't an option...but a 2.5" (that might change)is. I understand I can get a custom crank shaft, but that will be last on my list of options. This project is intended to Race/engineering project. I have yet to see a LSx motor turn that high, and stroker motors are all too common (considering I'm not looking for low end but more high end torque and horsepower).....I want to do this and do it right, I won't cut any corners.

 

sounds like it could be interesting, 2.5 in stroke with say a 4 in bore would probably sound pretty damn sick cracking 11+ grand rpms

 

No other options.......but "buy a custom crank"

 

They're out there.

 

You wouldn't happen to know where I could find one? I've tried searching

 

You're not going to find stuff like that on the internet. Someone won't divulge information like that. You have to do some reading in technical magazines, books and engineering theory journals. These are push rod V8 engines. They're high tech in the advancements now in them compared to the first smallblocks in the 1950's. Then NASCAR guys I heard, can see 9,000 rpms and maybe more. Some drag racers think nothing about pushing one of these engines into well over 10,000rpms. So it can be done.

You're definitely looking at a custom build. You'll need ECM software that is mapped for rpm's like that. You'll need a dry sump and real good oil control. I don't really know where to tell you to go though. You can try Katech on here. They're a sponsor.

 

First question; Why? Just because? There would be a lot of hurdles to get over at an astronomical cost. A science experiment of this magnitude would be a huge undertaking requiring many variations of parts testing. This would quickly be a six figure engine.

I can think of a lot of potential problems including but not limited to:
-high windage
-oiling issues
-valvetrain stability
-actually filling the cylinder with air at 12,000rpm with a 2 valve pushrod engine
-2.500" stroke at 12,000rpm is 5000fpm mean piston speed - a little high
-component longevity - no matter how high quality the parts were to start with, this would be a radical engine

 

You could try a 4.010 bore and 3.000 inch stroke for 303 ci. 8.700 deck height , keep pistons short with 6inch rods with custom pistons with a 1.200 compression height. With a 2:1 rod ratio that should get you to 10,000.

 

i had been thinking about a 4.065 l92 block used with 4.8 crank and stock rods and arp bolts would make for a nice motor even only for atleast 7,500 rpm, at least for a nice street car, nothing radical or really high power
woul run good with a m6 in a lighter car such as fox body or 240sx swap
4.065x3.276=341ci,
5ci smaller than 5.7 ls1 but with a way larger bore
used with some 243 heads, ls6 intake, lt headers 10.75-11.0:1scr. and a GT11 or CheaTR cam it would be very responsive along with a aluminum flywheel
it sure would be fun on the hiway and blvd.

 

Not a good idea!

X10 to what Jason at Katech said!

 

I figured 2.5" stroke was a little high and by a little, I mean 500fpm more than the F1 motors turn and they are pushing it. This thread isn't meant to throw around radical Ideas, but to simply allow me multiply resources to finding a "feasible" route. A 11,000rpm redline with a 2.2" stroke will take me to around 4033fpm (roughly 1000fpm than first stated). Obviously the rotating assembly will be my first issue. I've decided to simply hone instead of bore to maintain the least possible rotating mass. Compression I want to bring up to 11.3:1.

 

The rpm will kill stuff not an arbitrary piston speed. There are million mile diesels that turn very high piston speeds but very low rpm and F1 only lasts a few hundred miles doing similar piston speeds but ten times the rpm.

I can take a 4.000 stroke LSx engine to 7,500 rpm pretty easy and it will live a long time as a bracket motor even with economical parts.

I can take a 2.000 stroke LSx engine to 15,000 rpm and it will blow up in a million pieces with those same parts even though the piston speed is the same.

RPM is WAY more damaging than anything else in an engine and that's why you don't see high rpm on engines that have to last for decades and millions of miles.

The forces on an engine rise at the SQUARE of rpm where as increased forces from stroke are only LINEAR. When you add more stroke the heads don't magically grow better so the rpm decreases as well almost linearly.

...and voila you have a more dependable engine that still turns the same piston speed but at a newer and lower and more reliable rpm.

 

I did a few quick calculations on this.

For an F1 car: Assuming a 39.7mm stroke and a rev limit of 18000rpms, that would mean the pistons are subject to a constant acceleration of 5833 G's. The piston speed is 1429 mpm.

For NASCAR: Assuming a 82.6mm stroke and 9600rpms, that's an average acceleration of 3452 G's. The piston speed is 1585 mpm.

Now before factoring in the weights of rotating assemblies it is obvious that the F1 engine is subject to much larger forces. This is despite the fact that the average piston speed is over 150 meters per minute larger than the F1 car. It's easy to see why rpms are the real killer of engines and not mean piston speed.

 

if you really want to try it (the cheap way)....run a 4.8 crank and rods, then get some custom pistons made. Granted it wont hold together to 12,000 rpm... but I don't see why it would'nt turn 75-7700rpm. It would be different.

 

Yes Landstuhltaylor, and the higher cycle frequency (RPM) wears it down faster too since it's going through double the number of cycles as well at double the rpm during the same time.

 

Additional thoughs on F1 and Cup engines.

Peak piston gs are probably more telling than average gs. F1 is about 10,000g and Cup about half that. F1 pistons are close to being 50% of the mass of Cup pistons so the piston loads are fairly similar. We're talking ~200 gm and ~400 gm pistons.

Interestingly F1 engines and a Cup engines turn roughly the same number of total revs in a race (say 1.5-1.7 million) mainly because of race lengths. F1 engines have to go two races on an engine. They may go to three races. The engine builders spend lots of money and time to keep the engines from losing power over their 2-race lifetime.