Black LS1 T/A

You guys tickle me when you bring out the "pressure" vs "flow" hammer.

If I put a blower on a stock 346 and make 10 PSI and 500 RWHP, or I put a set of great flowing heads (which may have affected static compression) and cam on an even bigger motor, but only apply 3 or 4 PSI of boost... no matter what your theories are, the first circumstance can take 320 RWHP to 520 while the 2nd can take 420 RWHP to 500.

It happens.

White_Hawk

iTrader: (3)

80 rwhp is an awful lot to make up with a pulley. I usually figure 10 hp for boost and 15 if it's intercooled. That would mean you need 6-8 psi to make up that horsepower. I just took my blower off my car, and it went from 425 to 360 - almost exactly 10 hp/psi (non-intercooled powerdyne).

What I am saying is, there is something else that is causeing your horsepower drop. But that's just my opinion. I'd do a compression test/leakdown to see if everything is OK in there.

-Geoff

Black LS1 T/A

Mine went from 296 RWHP to 486 RWHP with 10 PSI of boost and headers. That's twice the hp/PSI you experienced. I think different setups are going to net different gains.

He may have some problem other than the heads... who knows? But, my conjecture still stands (for me )... if a set of heads make you lose enough boost, the heads may not make up the power. Key word is "may".

ChrisB

Boost doesn't make power - it's airflow that makes power.

With a fixed pulley setup you are flowing the *same* CFM. If the compressor doesn't have to compress it as much that should *increase* your effeciency, not decrease it.

It's not a question of "loosing" boost - all the air is still there, you are just flowing it through in a less restricted fashion.

White_Hawk

iTrader: (3)

Let's see, that's 190 horsepower, so if you figure the headers are worth 30 hp onto your base setup, then 10 psi intercooled boost @ 15 hp/psi = 150 hp from boost, then I would say my numbers were pretty close. That's just a rough estimate though, for a pump gas car, but I think it can get you in the ballpark. Start throwing in C16 and stuff like that and yea, it would probably stop being as accurate, but that is a subject for a whole 'nother post.

All I am saying is that there is something wrong other than 2 psi of boost missing. I understand that airflow means everything, I am not trying to start an argument on that. But, you can use my numbers to ballpark horsepower from boost. So if you are missing 2 psi and 80 hp, there is probably something else going on. That's all I am saying here.

-Geoff

MIGHTYMOUSE

iTrader: (59)

put the old heads back on -100hp is not something i would pay money for. i say 100 not 80 because the increase in efficiency (you should have) netted would be worth @ 20

why were the heads pulled? was the motor hurt before? same dyno? same conditions? same valvesprings as mentioned?

lastly your timing and fueling set up *should* have remained virtually unchanged..same air in the cylinders so same fuel and spark needed.. you say the timing is back up to where it was.. where is the a/f vs. where it was before (put it all back )

1dirtyZ

iTrader: (1)

the dyno used is the same.
the heads where changed because the "old" heads only had exhaust port porting and slight intake port touch up. the new heads have the same exhaust job but have an extensive intake port job too.

the valve springs where changed from 918's to 978 or 987 ( which ever one had the higher pressure #'s)

timing remained the same , the air/fule had to be tweaked cause the injectors on the car now are bigger (old ones where maxed out), the A/F is set btw. 11.5 and 12:1 now.

1dirtyZ

iTrader: (1)

ok , so i had time todat to take a compression check reading for some of the cylinders on the car ( just had time to do a few ) and the numbers from 1,3and 5 are all 150.

i just find it strange that a motor like that would get such low numbers, i know that stock ls1's are in the 200~220 range, but a 6.0 with around 9.8 compression short block ( with ls1 heads) should be in the 170~180 range, right?

White_Hawk

iTrader: (3)

Usually you use compression to tell if you have a difference from cylinder to cylinder. My Grand national was at about 150 in each cylinder and it was at 8:1. Maybe your compression is lower than you thought. If so, then you could probably run 4-5 more pounds of boost and get back that 80 hp.

-Geoff

Pro Stock John

iTrader: (34)

I think you have to come up with a rational list of things to check...

I was told that full point of compression is worth 3% more power. Even if you went down two full points that's not going to explain the loss right?

Are you sure the belt is not slipping?

ARe you sure your blower is not messed up?

MYTURBOT/A

thats kinda funny, I did a compression test on my car wich is 9.1:1 comp and got 105psi +/- 1psi on all cylinders and detroit speedworks said that was about right for a 9:1 comp motor.

1dirtyZ

iTrader: (1)

i'm sure there isn't any slippage, the dyno had a boost hookup and on the graph it was showing a linear increase in boost with no spikes or dips.

how can i tell if the blower is messed up? it spins normally when out of the car and all the blades seem fine.

the compression on that motor is supposed to be 9.8:1 with ls1 heads, so i'm guessing with 6.0 heads it's more like 9.4 maybe ( not sure so if some one knows how much compression 6.0 heads drop please tell me)


you guys have my confused now, 150 psi = 8:1 and 105 psi = 9:1??????

prostockjohn, by "point" do you mean a change from 10:1 to 9:1 or a change from 9:1 to 9.1:1?? ( i'm guessing you mean 10:1 to 9:1)

Pro Stock John

iTrader: (34)

Going from 10:1 to say 9:1.

6.0 heads (I have a set of them) are around 70cc's so they are a modest drop in compression over stock 67cc LS1 heads. Maybe you went from 10:1 to 9.5:1.

White_Hawk

iTrader: (3)

I'm sorry, what I said was really confusing. You are supposed to use compression to see if you have a head gasket or ring problem. If all the numbers are the same from cylinder to cylinder then you are OK, there is no direct correlation between CR and psi in a compression test, they are mostly cam dependant. MYTURBOTA, are you running a cam on 112 or 114? That would account for lower psi in your test. Sorry to confuse, I was just saying that maybe you had a lower CR than you thought. 1dirtyZ, do you still have the stock cam?

-Geoff

JimmyKash

with my old blower setup.....even when i had a slipping belt the boost would still climb linearly it just wouldn't keep climbing when it should've

A belt is a cheap/quick enough thing to do just to check.

Not to be a dick but FI is tedious and these are the things you have to go through when you really start doing a powerful FI motor. I've been through it, friend have been through it and it sucks. But its ALL worth the trouble when its running right, just dont give up

Start making a checklist of things that "could" be wrong and go through them one by one and tell us as well.

Hopefully we can help you find your horsepower again.

MYTURBOT/A

WHITE HAWK i`m still on the stock cam with forged 9.1:1 pistons.

Black LS1 T/A

PSJ... only 3% per full point?

Wow. Off a 500 HP motor, that's only dropping to 485 HP. If an NA motor were 10:1 and you dropped all the way back to 8:1 it would only lose 30 HP.

Why would people quibble over whether they should cut back to 9.5:1, 9.0:1 8.5:1, etc., if you lose only 6% power by dropping all the way back to 8.0:1 Static CR? It's seems it would be no question, with the ability to run less octane and crank the boost so much higher.

MelloYellow

Maybe it was 4%, but that number is close to the normal rule of thumb. Not to many people drop a motor more than 1-1.5 pt from original c/r.

JimmyKash

the torque and throttle response are two main reasons besides others

1dirtyZ

iTrader: (1)

i was just reading another post in the internal section about valve springs and i thought of something.
could the valve springs be too stiff for the lifters?

could the lifters be collapsing under pressure? the car does have 1.8 rockers and the cam's lift is .600

the valve springs are 987's or 978's , i'm not sure but i'll ask.