In my struggle to determine why my car is a slug,I have about 50 gauges monitering every concievable parameter of my turbo system. Does/has anyone ever checked the pressure in the exhaust system,pre-turbo? I have a fitting welded in the wastegate pipe,and with a 15psi gauge,at 5 lbs boost,it pins it.
From what I have heard,2 to 2-1/2 times boost pressure is acceptable,but of course,I have more.
What do you guys think?
Later,John.

 

I have also used the rule that exhaust manifold rpessure should not exceed 2.5 times the boost pressure.

If the exhaust pressure is higher than that, it's a pretty good indication you need a larger turbo - but of course the balance between low rpm boost vs mid/top end boost is a personal preference.

 

You mentioned the pressure tap was in the wastegate pipe? Is that pre or post wastegate? If its post, the dump tube probably is too small. I'm curious about my setup also. I bought two 0-30 psi gauges for the exhaust manifolds when I strap her down on the engine dyno. I'd assume about 1.5-2x boost pressure for the exhaust. With the full catback, crappy manifolds, and small down-tubes, I'll probably have higher. It'll be interesting!

A.

 

Andrew,the tap is pre wastegate. I talked to the guy that sold me the turbo,he said they look for 1-1 boost/exhaust pressure,and I laughed. Imagine how much power you could make with the exhaust restriction that low!
I did ask him about the a/r of my turbine housing,its 1.3.He said do you think thats big enough?
I think i have a leak in my intake plumbing somewhere,possibly the throttle body hat or throttle blades,before I put this dominator throttle body on,I used a Ford mono blade[75mm]and when I got out of the throttle,the blowoff valve was singing like a bird.Now with the 4 hole,it just tweets one time,as if the air is escaping somewhere else.
By the way,I have 10psi right out of the turbo,8psi after the intercooler,and 27 psi exhaust pressure.This is with a blockoff plate where the wastegate used to be!
Let me know what you think.John Bonasera.

 

John,
Thanks for posting some numbers I was always curious. The 1.3 AR is huge. I've got .58 AR's, but that's on a twin. If you had that much of an air leak, you should be able to easily feel it. It'll blow your hand off! I've had times where the intake got blown off the throttlebody since my billet BOV is too small for my application, and the air just at idle out of the turbos is incredible. I have the wastegates set at 7psi currently, and see full boost at 2000 rpms. I imagine that I could use larger ones in the future, but that will wait till later. Is the shaft on the 4 hole TB sealed well? A 2 psi drop through all your plumbing isn't too bad. How large is the IC?

Andris

 

Andris, how about the IAC valve leaking? I have one of the Kinsler remote valves,[it looks like a cylinder that the iac screws into,and on the other end its screwed into the manifold]vented to the atmosphere,is it possible since the DFI has stall saver,the boost is leaking out of the valve?
I just got out of the garage,I took the remote housing off,tapped the 4 bleed holes and plugged all but one,and the one I ran a #6 braided hose into the hat.This way,if it is open on boost,it will just loop back into the motor.If nothing else,at least I wont hear the iac leaking at warmup!
I pressurized the entire intake plumbing with shop air,and that is fine,it holds 20psi.
The intercooler is 29"/20"/3". I ordered the core from griffin,and welded sheet aluminum tanks that I made up myself,it has 3" inlet and outlet,cross-flow core,and I put it in the bumper,where that plastic crash deadener was.
My turbo doesnt move air at idle,the blades spin,but if you hold your hand on the inlet,it stops.As far as hearing it leak,I always hear a whooshing sound when I jump on it,my dumb *** just thought thats what turbo's do! Hopefully that huge whoosh was the iac valve leaking boost,and I can hook my wastegate back up again. I'll let you know tomorrow,if it doesnt rain.
Thanks again for all your help,John Bonasera.

 

John,

What size was the intercooler core before you welded on the tanks?

I went with a Spearco 2-182 air/air core that measures 3.5" x 15.6" x 20.0 ", rated at 1500cfm @ 1.5 psi pressure drop. It's Spearco's largest air/air core and what they recommended.

How much hp are you making? You IC is huge, basically the size of a radiator.

 

Well,it was the iac leaking boost. I drove it to work this morning,made a detour to the sleepy side of town,and with no wastegate,it made 28psi!!!!!!!
Man am I glad that is over.
Monty,those measurements are without the tanks,it is big,but I had it in a 64 Nova before,and there was tons of room for it.It is the same size as my radiator,except with the tanks its about 4" wider,I had to do some trimming to get it in the T/A.
I have 2psi loss through it,what I consider to be good.
As far as hp,I couldn't tell you honestly,but I will tell you this,at 10psi boost,shifting to high gear at about 70mph,it lights my 295/50/15s like its in the snow!
Later,and thanks for everybodys help,this board is great.
John Bonasera.

 

Hey John, your car sounds wicked! If your ever planning to be in south jersey, lemme know, Id like to see this thing!