can't get enough boost

[TurboMatt]

Strange problem.
'07 Apex mtn. custom built kit using a impulse header, gt28rs turbo(internal wastegate), custom built intercooler & piping, Hallman pro rx boost controller 3 stacked stock head gaskets & arp studs.

Here's the deal. I live in WI, ie. low elevation. When I run the sled back home or in the U.P. the lowest I can get my boost is 12psi. This is with either the boost controller removed from the line line to the wastegate(ie wastedgate line running str to the boost source) or with the boost controller setup and turned all the way out. 12psi is as low as it goes. I haven't tried to turn it up from there because I run it on pump gas and thats my limit.
When I ride out West, 9000+ft elevation: If I don't change anything from my settings back home sled will make about 6-7 out of the gate. If I put the heavy spring in the Hallman boost controller and crank it all the way down the absolute most I can get out of it is 10-11 psi sometimes, but usually it falls off to 8-9psi. This is with the boost controller cranked all the way in.
Is this normal? Doesn't seem like it to me.
Im my eyes it should make the same about of boost, its just the turbo will be spinning faster to do it.
I have done a boost leak test. It checks out good, no leaks. While doing the test I can verify that the wastegate actuator is working properly. It crack open at about 10-11psi and goes further from there. I have the actuator off the sled right now and test it in my hand, same thing, it seems to operate correctly without leaks.

What gives? Any idea?

 

[08nytromtxa]

leak

check all you vacumm lines and plastic t's in your system. i had the same problem and it was a plastic check valve that would seperate and bleed off most of my air. it is amazing the smallest leak can cause a problem like that.check your boost guage line for cracks etc. and on my wastegate actuator it takes about 30 lbs to come out all the way.

 

[Duke]

Sounds like you need more preload on your wastegate?

 

[08nytromtxa]

preload

it could be that but when i had vac leak i had my preload over half an inch and still would only make the same boost numbers. what do you mean by the lowest it will go is 12 pounds.

 

[Wheel House Motorsports]

if your disconnecting your wastegate line you should be getting huge boost levels. sounds like either an exhaust leak pre turbo or some sort of reference line issue in your plumbing.

 

[TurboMatt]

if your disconnecting your wastegate line you should be getting huge boost levels. sounds like either an exhaust leak pre turbo or some sort of reference line issue in your plumbing.

Sorry, I meant I disconnected my boost controller from the system, ie. ran the line straight from the wastegate actuator to the vac/boost source.

 

[TurboMatt]

check all you vacumm lines and plastic t's in your system. i had the same problem and it was a plastic check valve that would seperate and bleed off most of my air. it is amazing the smallest leak can cause a problem like that.check your boost guage line for cracks etc. and on my wastegate actuator it takes about 30 lbs to come out all the way.

I am going to go back through and do another boost leak test. I'll get some soapy water and check everything thoroughly.

it could be that but when i had vac leak i had my preload over half an inch and still would only make the same boost numbers. what do you mean by the lowest it will go is 12 pounds.

That's what I've experienced with preload as well. Usually doesnt help anything.
What I mean about 12psi being the lowest I can go is: at low elevation,if I have my wastegate actuator hooked straight to the boost source(no boost controller) or if the BC is hooked up and turned all the way down, it's the lowest my boost will go. I.e that's the spring pressure of the wasetgate actuator.

if your disconnecting your wastegate line you should be getting huge boost levels. sounds like either an exhaust leak pre turbo or some sort of reference line issue in your plumbing.

I'll check things over again for an exhaust leak preturbo. I don't think I have one, but I'll check again. I'll also recheck my reference line plumbing.

 

[nytro41]

what size turbo?? my rx1 is the same thing. can only get about 11 pounds. mine is a 2860.

 

[TurboMatt]

what size turbo?? my rx1 is the same thing. can only get about 11 pounds. mine is a 2860.

Its a 2860

 

[BigFish BC]

a 2860 will make 20+lbs boost, so you have a leak make sure its not your blow off valve too lots of guys never check them they can leak & cause the same probs.check header bolt + check header for cracks too.

 

[MRFUSION]

Okay been there on my Nypex project, I wish I could make as low as 12 psi boost. I am running a 2860 on a custom system and with a midmount type header system and the bottle neck is the exhaust housing. See if you are running the .64 or the .86 housing. I had to get the exhaust housing ported with the larger .86 housing just to make 15psi at low boost at 2000ft altitude, boost controller in or out. I was running 19psi at low boost before. You probably dont have a problem, just port your wastegate and use your boost controller to adjust, such a short tube header with good heat will spin that turbo lots. Good luck. Shad

 

[08nytromtxa]

turbo

your turbo should be fine as is your porting... a 2860 will make 20 lbs plus as stated above. maybe not as effiecient but it still will.

 

[TurboMatt]

Gonna work on this tonight.
The thing that REALLY sucks in that I'm in WI so I can work on stuff but I can't just open my garage door and take er for a spin. I'm 1200miles away from where I ride so It makes things difficult obviously.

So here's another theory I have come up with:
At this point I am 90% sure that I don't have a boost leak or an exhaust leak pre-turbo. I do plan on checking it though before I do anything else. Is it possible that I could have too much backpressure in my downpipe and this is not allowing the turbo to spool up like it should? I'm running a tunnel dump exhaust,it's only 12" long, but as I'm looking at it, it could be the problem. The downpipe i'm using is off a Impulse Nytro pump gas kit. It's only a 2 1/4" pipe. I'm using it because it came with the turbo when I bought it. Made things easy. The thing I don't like about it other than the small diameter is the fact that the pipe runs back at an angle towards the back of the sled when it dumps in the tunnel. In theory won't all the air from the track spinning forward be causing a bunch of turbulance and basically be trying to push the exhaust right back into the turbo.
Ideally, I'd think I want the downpipe dumping right down in the space between the front cooler and the track, so the exhaust has somewhere to go. I've never really looked how other tunnel dumps dump. Just a thought, does it seem plausible or an I grasping at straws?

 

[canucklehead]

Our group dumps them all pointing forward.

 

[TurboMatt]

Well fortunately/unfortunately I think I found the problem.
I was WRONG. I have exhaust leak preturbo. It's on the 4 bolt header-to-turbo connnection. One of the studs completely snapped off!!!and one of the other nuts was completely loose. This wouldn't be the biggest problem in the world except Impulse welds the studs in from the back side, so basically the studs need to be drilled out. I don't feel comfortable doing this on the sled so I pulled the header off.(thats why I said unfortunately in my first line, these headers are not easy to get off!!!!!I was hoping for this to be an easy fix).
Another thing:
So I noticed this when I originally put the headers on that the 4 bolt flange on the header isn't completely flat. Its basically convex in both directions. I wasn't sure if it was supposed to be like this for some reason to help make it seal in the middle or, it just warped. I guess I soulda questioned this 8 months ago before I put it on, but the way it convex in both directions it almost seems like it was meant to be like that. EVERY headed/turbo flange that I have ever seem in the past has been flat. Should i mill this flange flat too?

 

[TurboMatt]

Our group dumps them all pointing forward.

Anyone else? Looking for how everyone's tunnel dump enters the tunnel.
How far does it extent into the tunnel? Is there a angle cut at the bottom to help deflect the air moving from the track? How big of pipe are you using?
I'm seriuosly considering redoing by downpipe, gonna be a 3" this time, just want to get it right.

 

[BigFish BC]

3 inch is better if you can & all alpine tunnel dumps angle forward to they go into the tunnel between the track & front cooler if i remember right the go in about 1 1/2-2 inches.as for the flange it should be flat if you dont have a 100% seal you will lose efficiency & the exhaust leak will create allot of heat under the hood & melt things.

 

[ARMac]

A new header/turbo gasket has a pretty thick crush zone-when I replaced mine because nuts loosened up+gasket blew, it wasn't totally flat either. As long as the gasket will seal well when nuts are tight I wouldn't bother milling it.

 

[TurboMatt]

It didn't hold the 1st time I put it one and it was the same way. I don't trust it, I'm having it milled flat.

 

[BigFish BC]

the prob when its not flat is it may be sealed when its cold but when it heats up you will get some movement with the header heating up & cooling down.so if it moves & its already warped then it will not seal.