Darren P

iTrader: (1)

my car has been loosing boost on the top end ever since I finished with the Turbo install in September.

My setup is a PTS kit with a Precision T67Q trim turbo w/ .96 exhaust housing and a .70 coldside housing, PTS FMIC, stock engine W/ LS6 valve springs, Exhaust with 3 inch cutout in front of rear axle
It will bleed off around 2 to 3 pounds from 3500 Rpm to 6500 on a steady decline
It did this before the Valve springs and the cutout was installed
what can I look for to fix this problem

I have a E-Boost 2 bost controller, Mitsibushi (sp) by-pass valve, and A turbosmart 38mm wastegate
could someone please help me with this
is the turbo to small,
I have 2 settings on the Boost controller, 1 for 7 PSI and the other is around 8.5
on both settings the waste gate starts to open at 3.5 to 4 pounds
I have the syn. set on 90 on the higher boost setting
can someone please help me

thanks Darren P

ChevyNo1

Does your controller have a balance/sharpness ****? Mine was/is turned too far on the sharp side and it's bleeding off just like yours . . .

Slowhawk

iTrader: (12)

Do you have the vacuum source for the controller coming from the intake? If it's hooked off the Turbo housing,that would make it fall.

smokinHawk

iTrader: (48)

ya the turbo is to small, switch to a T76gts and dont worry about it.

RW99

There's no way that turbo is too small.

Darren, sorry to hear about the problems...

Are you getting any crankcase pressure? Or are you sure that you're losing your boost via the wastegate?

Seems like one of the first things to try would be to take the boost controller out of the picture and run strictly against the ultragate (w/default 7 lb spring) with the "top" port connected only to atmosphere.

If you're still losing boost while on the dyno, are you sure that your clutch isn't slipping?

And I'll throw this in just because it happened to me: my stock bottom end was fine running 400 rwhp N/A. But as we got to final tuning with my PTS setup, it wouldn't hold higher boost levels. There was crankcase pressurization, and a compression test revealed that #7 just wasn't going to hold on for the party. Hello, forged motor. So that's going into my car as we speak. Hopefully back to tuning it next week, I will keep you posted.

Let me know what you find on your setup...

Rich

ESR

iTrader: (7)

It could just be boost spiking and where it settles to is actually what you boost is set for.

RW99

...but the "settling point" should not be below the wastegate spring rating. Right?

Darren P

iTrader: (1)

it is not spiking it is falling off slow and steady

the waste gate has a 7 pound spring in it
it is peaking at around 8.5 PSI and falling off to 5.9 to 5.5 at 6000 RPM

bboyferal

iTrader: (9)

Man, I know you have LS6 valve springs and all, yet it sounds so much like valve float...

Smearin

Doesnt sounds like floating to me since he's only getting up to 6000rpms and the boost is falling..

You sure the Turbo isnt choking out?

bboyferal

iTrader: (9)

Maybe the turbo is NOT too small, though the turbo just might not operate well if you're spinning past 6k rpm???

Forget it... Oooops, I just read now that it starts to bleed off boost starting at 3500 rpm. There has to be something wrong maybe with a line? I changed one of my fans and I lost ALOT of boost... Later I saw a had pinch a line with a tie strap by mistake... Look for stupid things like that maybe?

Boostaholic

iTrader: (4)

Where are your wastegate and boost gauge reference(s) hooked up to?

Smearin

HAve you checked the Wastegate and/or spring? its that or the Boost controller

bboyferal

iTrader: (9)

Valve float can occur below 6k rpm. It usually does...

However, I hadn't read that the power drops off after just 3500 rpm's, Definitely something else... I rushed through reading his post.

Smearin

I have no idea how prone ls6 springs are to float at higher rpm's.. but if he had float at lower rpm's.. that means it would continue up in the rpm range and have the chance of some valve to piston contact..

right..

bboyferal

iTrader: (9)

Correct... AND many have experienced valve float on stock LS1 springs starting at 5k-5500 rpm... not as high as 6k rpm... with no such contact... only a loss of power... right... Valve float is not an over-6k rpm problem. It occurs lower than that often... happened to me.

Of course, though, that is not what is happening here.

Darren P

iTrader: (1)

well I just ran it with no boost referance and it shot to 14 psi
I riconfigured teh boost controller Hook up to the second method told about in the instructions and it made 11 PSI and I could not get it to go lower


the turbo is not to small for sure
it made 14.5 psi like it was nothing

but I am confused now Because Jose said that if I unhooked the boost referance it would only make about 1 pound more than the spring pressure and it has a 7 pound spring
am i missunderstanding this or just stupid

oh well back to Square one

markp03

iTrader: (4)

one this is you are running a 38mm waste gate, I have been told that the 38mm is too small of a WG to run low boost on with our engines....aka the WG can't bleed off enough exhaust to make the 7-8 LBS of boost consistant. there is a good chance you waste gate is just fighting to keep your boost at what you have you controler set at and it can't do it consistantly. if you have the ability try to run a larger WG and see what happens.

If i am way off here guys let me know, but i always thought a 38MM WG was risky and too small if your gunna run low boost on our big engines

Darren P

iTrader: (1)

to the turbine housing

Darren P

iTrader: (1)

who knows what the spring pressures are for a LS6 spring