408 Not putting down the power
Thread Starter
Staging Lane
Joined: Dec 2003
Posts: 63
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408 Not putting down the power 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.
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.
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.
Those 1 3/4 heads need to be bigger like 1 7/8. That will help in power but will not fix this.
Originally Posted by LSUxBlake
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.
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Thread Starter
Staging Lane
Joined: Dec 2003
Posts: 63
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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?
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TECH Enthusiast
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From: Foley, Alabama-southern Alabama
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. 
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.
Thread Starter
Staging Lane
Joined: Dec 2003
Posts: 63
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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.
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!
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.