derekd7987

So some of you might have read about my situation before, but long story short I built a 408 for all motor to maybe add a little spray later on. It didn't make what I wanted on motor and I found a good deal on an A&A kit and decided to go the blower route.

Main info on engine is LQ9 block. Forged crank, rods and flat top Weisco pistons. GMPP LS3 CNC heads (68cc) with BTR springs. Stock LS3 intake and cam is a 238/254 .625/.610 114+3

Compression is around 11.2 or 11.3:1 and I run on 93 pump and added meth with the blower (V3 Si). On a 3.8 pulley its only making 5 lbs of boost and the car put down 608/561. I assume the cam is what is killing the boost as I'd think I'm blowing most of it out of the exhaust with all the overlap.

Changing the cam is not really an option right now so I can pulley down to a 3.4 and that should put me around 9 lbs of boost.

Is this too much for my compression on 93 and 100% meth or my thought was I could maybe pull the heads and have them ported and go bigger on the CC to drop the compression some to be a little safer?

I'd really like to get the car to or very close to the 700wrhp mark so any advice or input from you experienced guys would be awesome. This is my first forced induction car so I have a lot to learn...

derekd7987

anybody? 9 lbs on my current setup...or too risky?

Turpid porpoise

You're willing to pull and port the heads but not change the cam? I'd think a blower friendly cam is the way to go.

derekd7987

If I change the cam right now, that still doesn't help me with the compression, so all that would really do is allow me to run that 9ish lbs of boost with not such a small pulley.

The reason for doing the heads would be to go bigger on the cc and hopefully get the compression down to maybe 10.5 - 10.7:1. I would feel a lot better about running 9 lbs at that compression than what I am at now.

Then if I wanted to up the boost some from 9 lbs later on, then I could look into changing the cam or bigger headunit, etc.

This is just my thinking, but like I said I have a lot to learn so all input and opinions are welcome.

Turpid porpoise

I wasn't trying to criticize, just trying to understand where you are coming from and where you're going with your plans. I'm no expert by any means but I'm all for generating some constructive conversation.

Rather than machining the heads couldn't you run thicker head gaskets to drop the compression a bit? Increasing the CC size would also do the trick but head gaskets are cheaper and easier to get done.

Who is tuning it for you? Did they have any input? IMO if your tune is meth dependent then you have to much compression.

HardcoreABN

with a supercharger and meth, your compression isn't an issue.

derekd7987

Nah man I didn't take it that way. I appreciate your input and that's what I want is people's input which is why I posted on here.

I'd have to look at the build sheet on my engine but I'm pretty sure I'm running stock thickness gaskets. I know they make thinner gaskets but I don't know if they make thicker than stock gaskets. Gives me something to research. Right now it is not meth dependent but I'm sure it will be at 9 lbs.

Thanks for the input

derekd7987

So your saying at the 11.3:1 you think 9 lbs isn't an issue?

I'm just guessing it would be meth dependent for sure, even if the timing was low like 10-12 degrees?

Dragonvette

I am currently running 9psi at 11-1. With no problems with 93 and a progressive meth system. Last time it was dynoed it made 694 and I have since went to a smaller pulley. No problems

Dragonvette

My tuner has told me that he doesn't think it is a problem to drop another pulley size just no need to size I am not holding the power right now. I have a 3.8 now but had a 4 before when it made 698, it is a 383 though

neverstop

compression is not an issue at that level imo but that comes down to the quality of your tuner. there are lots of guys with higher compression and way more boost and 2x your whp who run fine. heck, a lot of the EVO guys run 40-50psi on 10.5:1 compression. Tons of guys making 650+whp on stock ls7. Don't worry about static compression. The cam is what determines the dynamic compression anyway.

porting your stock heads is a waste of time imo. If you must pull the heads get some thicker deck aftermarket castings so you don't have to do it twice later on if you push the power higher.

derekd7987

Thank you sir

Dragonvette

Here is the dyno, I am not sure how much it is making now but my tuner is better for sure

derekd7987

Oh ok. So do I need to calculate the dynamic compression you think or you just think at only 9 or 10 lbs I should be good either way with meth and a good tune?

robert miller

You will be good just with the meth have tuner to use it for cooling runners down and not for the big ## just for safety with the meth.

Blower cam and good set of spring on the heads.

ajrothm

I don't think the cam is the problem honestly. Sure it's not ideal but....it's not holding you back. On the contrary, that cam bleeding off some cylinder pressure may actually help you keep it alive with more boost. If you put a smaller/tighter cam in it, cylinder pressure is gonna come UP...this could potentially make it detonate more when you add boost.

I agree your HP is way down, I think I'd do a check up on the motor's health (compression and leak down test)... If that's all good, I'd check the tune and make sure it's correct.. If everything seems in line, I would then pulley the blower down, re-tune and read the plugs.

I think with dual nozzle meth, straight M1, a correct tune, 9-10 psi will be fine on 93/meth, as long as you don't get crazy with the timing.

You should make 700rwhp pretty easy I'd think.


FWIW, stock LS3s make 10.7-1 comp and lots of people put 9-10 psi through them and make 650-700rwhp..

Also lots of "centrifugal blower cams" have some overlap. Some have a lot..

derekd7987

The engine only has about 800 miles on it if that and was built and installed by Tick Performance. On motor it made like 469/43x which I thought was low. Tick said they did a compression test and also a leak down test I believe and it was fine. They said it also makes the same numbers when dynoed multiple times back to back and said it was healthy.

You think the all motor numbers (469/43x) were way low or the numbers now on boost (608/561) are way low, or both? It's on a 3.8 pulley now making 5lbs of boost.

I trust the tuner completely and he tunes alot of big power cars around here and have never heard of anybody having a problem with him or his tunes.

Thanks for the input.

SBCGENII

NA numbers don't sound crazy low. If you had a before and after on the same dyno that would be better. It's more important that the car runs good and you are happy with it then to worry about dyno numbers.

derekd7987

Yea its easy to get caught up on the numbers. Unfortunately I'm one of those that probably won't ever be happy. lol

On motor it was dynoed at Tick's and again at JR Racing. After the blower it was dynoed at Hawks. Here are the graphs:

1.) 408 at JR Racing





2.) After blower at Hawks (Unfortunately I don't have the file yet, but only this pic he sent me)

ajrothm

Well... assuming it was the same dyno, using the same correction factors for both the 469 NA pulls and the 608 boost pulls, that is 139 rwhp gain for 5 psi, that's really pretty good.. Almost 28 rwhp per 1 psi of boost.

All in all, I guess your numbers are not that bad. I would have expected a good bit more NA also but.... There is so many variables that affect everything.

Throw a 3.4 pulley on it, put dual M15 nozzles on it and sneak up on the tune, stay very conservative on the timing....and see what it does...

At 9 psi, I could see it making 650-700rwhp.. That's perfect for a street car.


***EDIT***

Just saw it was different dynos so.... no telling..

just pulley it down, retune and go...