Another rev limiter question
Thread Starter
Instructor
Joined: Nov 2012
Posts: 240
Likes: 18
From: Carrollton Illinois
Another rev limiter question
I've got a '94 m6 (early, has pink rods), I'm heading to the dyno to get it dynotuned on Saturday. I'm running the factory bottom end, PAC 1219 springs (installed at 160 closed and ~350 open, tested by head machinist), one piece comp pushrods, guide plates, scorpion 1.5 rrs w/ 7/16 studs, cam specs : 222 and 226 @ 0.050, .530 lift, 113 Lsa. Also running headers but that isn't relevant. I'm assuming I'll make power past 5850 on the factory rev limiter. I figure since the LT4 ran the same bottom end and they ran to 6400 that I can do the same. I know it's mostly controversial but what do you think I can rev it to? When the heads were off the cylinder walls looked great still having the cross etching and no ridge at all.
Thanks!
Colton
Thanks!
Colton
Advanced
Joined: Apr 2012
Posts: 95
Likes: 6
SPECIALLY MACHINED CRANKSHAFT
The crank itself was improved via something called undercutting and rolling. Undercutting is the machining of a groove into the corner of a journal. Though this would seem to weaken the crank at that point, it actually makes it stronger where tensile stress is most likely to cause sudden failure. Rolling the undercut introduces compressive stress to the area. This makes it more durable, because potentially catastrophic tensile stress generated during high RPM operation must first overcome the compressive stress before that area of the crank is subjected to tension. Undercutting, a groove cut into the corner of a journal, looks counterintuitive, but makes a crankshaft stronger where tensile stress is most likely to cause failure. By undercutting and then rolling it, compressive stress is introduced. Tensile stress during high-speed operation first has to overcome the compressive stress before there's any tension on the joint. And as tensile stress is what breaks crankshafts, undercutting and rolling make the crankshaft stronger.
NODULAR IRON MAIN BEARING CAPS
These LT4 components are considerably stronger than their LT1 counterparts and resist failure at higher RPM's.
Thread Starter
Instructor
Joined: Nov 2012
Posts: 240
Likes: 18
From: Carrollton Illinois
Thanks for the great replies! I didn't think the crank was the weak link in the system, I always thought/read that it's the rod bolts that yield first. Our blocks are already 4 bolt mains so I didn't figure cap twist or shifting was an issue either. Has anyone had issues with a stock lt1 crank?
Thread Starter
Instructor
Joined: Nov 2012
Posts: 240
Likes: 18
From: Carrollton Illinois
Thanks everyone for the help, I'll give you all an update. I got it on the dyno and got my tune down. I made 311 at the wheels but it was 95 degrees and high humidity so my tuner thinks its more along the lines of 325 at the wheel in good weather. I turned my fuel cut up to 6400 and we revved it up to 6200. After 5700 the power band flattened out and stayed right around 311 until 6200. I made 345 ft-lbs at the wheels from 2000 all the way until 5700ish and it started falling off slightly, so a really nice usable power band.
Pro
Joined: Mar 2004
Posts: 654
Likes: 18
From: Linthicum MD
Stock LT1 cranks have been known to handle over 600hp. F-body guys do it regularly. The weak links are rod bolts and rings. I thrown my stock bottom end up to 6500rpm with no problem. Pulls like a raped ape.
