The Ultimate Qmp Car
Originally Posted by MIGHTYMOUSE
i would have thought warbird would have been sent a replacement like mine.. him and rob such good buddies and all.
i hear ya. cant wait to get things sorted out. any help from you guys would be great
Originally Posted by squirrel masta
kaos,that drop problem is due to a lot of backpresure from that kit do the double valve springs and i bet that will help a lot,also does it seem to drop around 4300 rpm
Are are you saying he should do double valvesprings to help him?
I'm confused, also, what's the reasoning of going with doubles vs CC 918s?
lets say you are only running 10psi but your pressure ratio is 3:1 (generally bad)
that means he has 30psi of exhaust pressure and it is forcing on a valve that is 1.5" diameter
through area= 3.14* r^2 = 3.14* (.75)^2= valve area of 1.76 square inches
1.76 square inches * 30 pounds per square inch = 52.9 psi of force against the valvespring.
this is what i believe is generally correct as to why valvespings are MORE important in boosted apps.
same calculation can be done for the intake valve
if you have a valvespring that normally closes at 300psi.. taking 50 of that away is .... bad.
imagine 75 or 100psi backpressure.
that means he has 30psi of exhaust pressure and it is forcing on a valve that is 1.5" diameter
through area= 3.14* r^2 = 3.14* (.75)^2= valve area of 1.76 square inches
1.76 square inches * 30 pounds per square inch = 52.9 psi of force against the valvespring.
this is what i believe is generally correct as to why valvespings are MORE important in boosted apps.
same calculation can be done for the intake valve
if you have a valvespring that normally closes at 300psi.. taking 50 of that away is .... bad.
imagine 75 or 100psi backpressure.
i ran comp 941's and they were showing trouble at the 530rwhp level on my qmp 63mm
i still run the same set of comp 941's today with the new system AND a .600 liftcam vs a stock cam
i still run the same set of comp 941's today with the new system AND a .600 liftcam vs a stock cam
Now this thread is getting a little interesting.
I know very little on the subject of how valve springs and boost relate, but some folks say to increase the spring pressure for boosted applications but I have not found a formula or anything.
MMouse, what are the installed heighth of your 941's and what is the open/closed?
I know very little on the subject of how valve springs and boost relate, but some folks say to increase the spring pressure for boosted applications but I have not found a formula or anything.
MMouse, what are the installed heighth of your 941's and what is the open/closed?
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Verdad Gallardo I think 918's in general are good to 6500, that's what I recall.
You can reshim the springs (ie. change the installed heighth) to increase the spring pressure but you need to know what they are rated up to.
You can reshim the springs (ie. change the installed heighth) to increase the spring pressure but you need to know what they are rated up to.
i have never done it myself but was told you could use any normal boost gauge and a nice length of line so the heat won't get to it, and mount it in the exhaust before the turbo.
easiest thing is to see how it does on the dyno, and if its bad throw some beefier springs at it.
easiest thing is to see how it does on the dyno, and if its bad throw some beefier springs at it.
TECH Enthusiast
Joined: Nov 2001
Posts: 650
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From: Toronto, Canada
The turbo that KAOS bought from me is the T74 Q-trim. On a stock motor it should work, on my old motor it didn't. I wouldn't push it much harder than it already is.
As I had stated along time ago I put a pressure guage on the cross-over and at 12 psi I was seeing 120 psi of back pressure. Small wonder the motor died. If I had of kept the kit I would have tried the wastegate on the cross-over and or run two gates. The only other option was larger tubing and a redesign of the log.
As I had stated along time ago I put a pressure guage on the cross-over and at 12 psi I was seeing 120 psi of back pressure. Small wonder the motor died. If I had of kept the kit I would have tried the wastegate on the cross-over and or run two gates. The only other option was larger tubing and a redesign of the log.
