The factory PCM has the rev limiter set for 5800rpm for lt1, and 6400 for lt-4, i was playing with my PCM using a HYPERTECH PPM, and 6400 for the stock LT-1 feels reel good, it seems like all my horsepower is up on the top end. Your only above 6000 rpm for a second then your shifting to the next gear. What do you guys think?

 

is your car stock or do you have the mods in your sig?

 

If the car is stock, the stock redline gives the optimal shift point. I've done the math and charted it out in Excel. I was surprised that it lined up almost perfect.

Once you do all the bolt-ons, the redline should move to about 6000-6200 rpm. For me, it's 6100 rpm with headers, catback, CAI, 1.6 RR's and a tune.

Once you put in a cam, most of the time the optimal shift point is beyond what the valvetrain/bottom end can handle, so you shift at ther RPM that your valvetrain can stay alive.

Dan

 

Howabout the A4 shift points? I believe the shift are at 5700 rpm... are these the optimal RPM for a stock car? Does this shift with boltons? is it bad for the tranny to shift at higher rpm?

 

i ran my to 6700 with cam/heads/nitrous. i never had a issue.

 

Mine is a bolt on motor right now, m6, longtubes,52mmtb with air foil,hypertech tuning,ramair,160stat,tbbypass,magnaflow catback,etc. It keeps pulling pretty hard after 5800, 6200 seems like a good shift point with out hitting the rev limiter.

 

From what Ive been told stock Main bearing begin to chew them selves up after 6200rpms

 

My stock bottom only lasted a few hundred miles w/ high rpm shifts (well over 6500) before the retainer bent and spun a lifter. No need to spin anywhere near that high with a stock h/c. Hindsight I probably wouldve been ok with link bars

 

Bearings eating themselves up at 6200? That sounds like an urban legend, the LT4 uses the same bearing, and the rev limiter kicks in at 6400

 

The bottom end will go pretty much as high as you want it to. It's control of the valves that is the rpm issue.

 

safest? Stock limits.

There are those of us that turn them higher but you are taking a chance. I have been turning mine as high as 7k for the last 2 years with no problems, but your results may vary.

 

I don't see why you want to turn it past 5,800 since it slows down if you shift above that point. With some setups, you might go a little higher on the track to avoide an upshift, but in general, the factory limiter at 5,800 is in the right place.

As far as what is "safe", that's always a relative term. Loads go up as the square of rpm. The higher you rev it, the sonner stuff will break. I bet the limiting factor on a completely stock motor is valve float. The springs are pretty wimpy and the valves relatively heavy. Interesting that the LT4 has better valve springs and associated parts as well as lighter valves.

Rich

 

I dont have track times or a dyno run to prove it, but the way it feels to me is the car is faster shifting at 6200rpm, it does not stop pulling at 5800, and it doesnt have valve float at 6200. I have Proscan software with the built in Dyno, i am going to make some 2nd and 3rd gears pulls, with the rev limiter set on 5800, shifting at 5700, and some pulls with the rev limiter on 6300, shifting at 6200. I will get back to you guys later this week with the results.

 

I hope thats a joke with the dyno based off software. And by 5800 the power is already dropping off pretty hard, at 6200 it will be way down, its all in your head that it is still pulling harder up there.

 

from what i've heard/read/seen the stock powdered rods start to stretch above 5900 or so. and the stock LT1 cam has already fallen off well before that point. we also saw a roadraced LT1 TA running at roebling a few years ago that he said he was running 6500rpm on a stock bottom end and he blew his motor sky high in the carousel turn and left a nice plume of smoke all the way into the pits.

so, on that note, i wouldn't run it above 6000 with the stock bottom end or without some sort of rocker stud brace