johns01ta

We just got back from the dyno with my buddies new 408 stroker and are trying to figure out what is going on at 5600 RPM? If this dip did not happen we where well on our way to 490+ HP. I attached a dyno graph with two runs on it. This is with 28 deg of timing and 0 KR. This dip happened no matter where the AFR was rich or lean. This is what is done to the drive line.

This was dyno'd on pump gas
ls6 intake ported T/B
SLP 1 3/4 headers (no cats) In to Y-Pipe and a Dynomax bullet and dumping before the axel.
ARP under drive pulley
12 bolt rear w 4.10s
6-speed trans
30 degrees timing
12.7 – 13.0 a/f ratio
11.5 to1 compression
APE stage III race heads
APE COMP Cam 614/619-236/240 LSA114(I don’t have the cam card in front of me)
Comp Shaft Rockers
Bottom end is callies and diamond pistons

Any ideas.

Ravenous T\A

iTrader: (12)

What kind of lifters??? and valve springs???

johns01ta

Comp R lifters with 5-10 thousands of preload. Comp 978s

goober35

iTrader: (1)

That is some good power. But the graph looks way off. Just a straight line and them it levels off kinda like the T-Rex cam. But yours does some odd ****. It goes down and then shoots up again. Dont think this is the case but you might have maxed that cam out. I dont think so but it could be. If it was vavle float it would just drop like a rock.

Those 1 3/4 heads need to be bigger like 1 7/8. That will help in power but will not fix this.

technical

I don't see the fuel system mods...what size injectors?

LSUxBlake

iTrader: (3)

hehe. Welcome to Comp R lifters. I'm having the same problem, several other people have. I am pulling that **** out my motor next weekend.

goober35

iTrader: (1)

Here is the funny think LSUxBlake has the comp R problem I do not. I still dont get this. Some people have the problem. They set the preload and do every thing they can to get them right on the money as they are spected. I did not do any of that. I slapped them in and ran them. Never had a problem. Just tighened the rockers down by hand with out a TQ wrench and that was it. Doen it so many times i guess i know what the rockers need to feel like so they dont back out and case a problem.

johns01ta

its not the fuel system we have updated that and We have 42 pound injectors. also notice the AFR its pretty much right on. Out of 6 pulls the graphs all look the same. the dip happens at the same RPM. you would think if it was the lifters it would vary a little. Blake does your graph look the same?

FASTONE

Did you degree the cam in?I think you possible could have a lifter leakdown problem,do you know what the seat pressure is on those springs?Also open pressure?It may be that at the 5800 dip is where the leakdown starts then at a higher rpm the lifter can't leakdown fast enough to cause a problem and the power goes back up,I'm kinda quessing here.What ratio are the rockers?You might have a exhaust problem as well,I believe 1 7\8 heders would be better for that combo.I would go to an x-pipe with 2 mufflers.Maybe I"m wrong but your timing sounds too high for an ls1.

LSUxBlake

iTrader: (3)

My dyno graph looks IDENTICAL. I can see if Allan (Futral) can send me the graphs tomorrow and I will post them. Allan also told me he's seen it several times before, and Telly had the same thing happened. We spent a whole day trying to fix it, nothing worked. I'm taking the lifters out next weekend.

FASTONE

I just noticed that your AFR goes up a little where the dip is,not that much though???

Country Boy

iTrader: (24)

Adjust the preload a little tighter on the lifters. I had major problems with .005 preload.

johns01ta

ok, we re dynoed today and pulled the exhaust and ran open headersjust to see if their was any change. the only change was we picked up 14hp but the dip was still their. we are taking the car back this week and are going to play with the lash. anyother idaes would be helpfull.

Uthinkso

I think that putting a little more preload on them will take care of your problem. We have had issues with running the suggested preload from Comp.

Thanks

Beast96Z

iTrader: (21)

I'm not sure of the ramp rate of that cam, but maybe Comp 977's would have been better?

johns01ta

APEs web site says 978s....come on there stage III heads. Maybe they have the 977s I will check with APE after we try abjusting the preload if that does not fix the dip problem.

Billiumss

iTrader: (11)

Dumb question but is the COT turned off?

Classic

iTrader: (3)

I don't have a box in front of me, but for all you Comp R lifter people -- I believe the preload is to be set HOT. Most don't do this I'm guessing and that is where a lot of the problems are coming from. What you have there could also be spring surge (or harmonics). Its a characteristic of the valvetrain combination, so if you were to change one thing it might go away -- I.E. change the type of retainer from titanium to steel, or whatever. And for goodness sake get some bigger headers on that thing!

2MuchRiceMakesMeSick

I could be wrong, but does this look like a tuning issue to anyone ?

Country Boy

iTrader: (24)

Not a tuning issue. More of a mechanical issue. I had the suggested .005 preload on the lifters and I had major valvetrain problems. I tightened up the preload and gained 20 HP.