JimmyKash

i dont think so dirty.....but you are on the right track. Sometimes valvesprings can be too WEAK and they cant stay closed against the pressure and you'll lose power that way. That is why on many boost motors you need more spring that you normally would n/a for the same type of horsepower. I only have a .515 lift hydraulic FLAT TAPPET cam and i need doulbe springs to keep them closed against the airflow

NoGo

iTrader: (2)

Compression / Power is not linear. The more you reduce the compression, the more power will be lost. The first point may be 3%, the second 5%, the third 9%, the fourth 17%, etc..... you get the picture.

1dirtyZ

iTrader: (1)

jimmykash i hear what you're saying, but how about the lifter itself? can the increased pressure from the double springs and the 1.8 rockers cause the lifter to colapse, thus loosing lift and duration?

1dirtyZ

iTrader: (1)

well the lifter collapsing theory is out , we just dynoed today after swapping the 987's back to 918's and using 20w-50 oil. almost the same graph.

i'm almost out of ideas,i can't explain it.
i guess the only solution is to have him get a bigger bower.

JimmyKash

if the lifters are collapsing it is from a user error. The only reasons to my knowledge why a lifter would collapse is from too much preload and/or RPMS

DaveSchott

iTrader: (5)

Better not to compound the situation with more changes. Find out the root cause, even if you have to return to the prior combo as a starting point. maybe tear down the heads or at least cc them? It'd be interesing to see those heads dyno'd on another proven engine. Good Luck

1dirtyZ

iTrader: (1)

he already sold the old heads, so i don't think putting back on is an option anymore.

the springs were swapped just to try to bring the combo to where it was bfore.

wouldn't a very stiff spring cause the lifter to collapse under load?

02BlackWS6

Not to change the subject but, how good do the 6.0 heads flow over the 5.7heads? I'm getting 6.0 heads but don't know if I should bother having them mildly ported or just leave them stock? What does everyone think?

1dirtyZ

iTrader: (1)

i know that the 6.0 heads are just like the z06 heads only with lower compression.

1dirtyZ

iTrader: (1)

a call to comp cams netted the following, they said to advance the cam timing 4 deg. they think that the car has toomuch exhaust compared to intake.

we'll see how that goes.

MelloYellow

What are your cam specs?

Pro Stock John

iTrader: (34)

That's interesting, I wouldn't think that would help that much for a FI car.

LSs1Power

iTrader: (5)

Intresting thread. I would like to know the solution for this problem.

1dirtyZ

iTrader: (1)

the cam he is using is a comp cams 220/226 .564/.569-114 ( lift is actually .598/.602 with the 1.8 rockers)