UMI performance rear lower control arms

TheYak

Member
Joined
Jan 31, 2007
Hey guys, having an odd issue with my car. Hit the dyno and we couldn’t get the boost to come up past 15 psi, no matter how the bleeder-style boost controller was adjusted. Still 15psi, no more or less. Found a tiny leak in the header a few days later, can that cause this issue?

I’ll get the header fixed, but seems like there’s something else going on. Thanks for your suggestions...
 

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Lemme guess....Ported waste Gate hole on the exhaust housing ?
Sounds like it may have been opened up too large. This could explain difficulties in building boost.
 
More info:
HD stock style wastegate


Confused here.

Adjustable or "stock non-adjustable" style waste gate controller ?

And/or what 1KWIKSIX said?
 
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Lemme guess....Ported waste Gate hole on the exhaust housing ?
Sounds like it may have been opened up too large. This could explain difficulties in building boost.
Yep you nailed it, I had it machined for the larger RJC puck. I’ll take a look, thanks for pointing that out... I forgot about that.
 
Yep you nailed it, I had it machined for the larger RJC puck. I’ll take a look, thanks for pointing that out... I forgot about that.


There's your problem, most likely.

I did the same thing some years back. RJC sells a plate you can use to help fix the issue. (imagine that?)
 
There's your problem, most likely.

I did the same thing some years back. RJC sells a plate you can use to help fix the issue. (imagine that?)
I’ll check it out, hopefully there’s a way to fix it. Makes sense, because I didn’t believe a small header leak would bleed off so much pressure. Thanks
 
Is this what you’re talking about?
 

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I’ll check it out, hopefully there’s a way to fix it. Makes sense, because I didn’t believe a small header leak would bleed off so much pressure. Thanks
A header leak will mess with the AFR., which will mess with the boost.
What were you seeing, when on the dyno?
 
That makes sense, because we were chasing gremlins. One pull the XFI would add fuel, the next it would take fuel out like crazy. I’m definitely going to repair or replace the header before doing anything else.
Question: How does the AFR affect boost? I thought it was the other way around. Not disagreeing, just trying to understand. Thanks!
 
After the headers are fixed, another option if you bored the hole too big is an external waste gate. That's what I did on my 6765. Now I'm running a brand new combo now with a 6466 for a little faster spool up.
 
I’ll visually check, but leaning towards the header AF ratio theory first. I had the exhaust housing machined my taking it to a CNC shop along with the downpipe for fitment. They left me some material around the puck for a
 
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