Inconsistent Boost Levels

[Cool Mr Steve]

When I hit boost, my boost spikes to about 16 psi, then falls to about 14 for a while as if that was where it was set, then in higher in the powerband it falls to about 11-12, where it stays until redline. This is pretty annoying, as it feels as though I am running near stock levels. It has been this way ever since I purchased the car, and I have repaired some boost leaks to no avail. My Hallman MBC seems to be hooked up correctly, and I'm not sure if it could be an issue, but my HKS SSQV and boost controller are T-tapped, which I heard before is bad.

 

[allgripnoslip]

welcome to the T-25..... just upgraded to a 14b holds boost to redline, where as my t-25 would hit 16 psi really fast then just at it hit it, it would go down 2-3 psi :thumbdown . advice: try to upgrade your turbo. I got my Install kit for 175 and my 14b for 60. just look around for good deals in the classifieds and on dsmtrader.com

 

[98eclipseRS]

Its just your turbo, the exhaust housing on the t-25 is just too small to flow enough air in the upper rpms so boost drops off. As my t25 was dying a did a couple uhhh "experiments" to see just how well a t25 could possibly hold boost. I set my ebc to 25psi by the time I hit 6500 rpm I was at maybe 11psi. That is over a 50% decrease in boost preasureso turning up the boost on your mbc isn't going to do anything for you. Second going to redline with the t25 is actually going to make you run slower times becauseof the fact that it can't hold boost. You should be shifting by 6500 rpm at the latest, my best time at the track on the t25 was done by shifting at 6200 in everygear. And don't worry about the mbc/bov line being t'd me and the majority of my friends have all had it like that for as long as I can remember and none of us have had any problems.

 

[Quasimondo]

You got yourself a twofer (two problems in one)

Problem 1: Boost spike. The buildup to 16psi before it goes back down to 14psi is your wastegate not opening fast enough when it sees boost. Move your boost source line from being tapped at the BOV vacum line to the nipple at the compressor housing, and do whatever is necessary to shorten up the lines that go to and from your MBC. Long vacum lines = boost spike.

Problem 2: The T25 turbo. They have that problem of falling off at the top end. You're stuck with that problem until you upgrade. A larger downpipe might help, but a good used 14B will be even better.

 

[Cool Mr Steve]

Ok, that sucks, kinda. But it sounds like a lot of people are swapping to the 14b, so I have a couple quick questions about that swap. I would like to run about 16 psi daily driven and 18psi on track days. Is the 14b just as good as, say, a Evo III 16g? Does one spool significantly faster? Will the 14b hold 18psi to redline?

 

[allgripnoslip]

the 14b will work best up to 17 or 18psi, but it cannot be compared to any 16g, especially the evo3 which is capable of 400 whp. as far as spool up, the evo3 will spool up a little slower but it wont be that noticeable and the top end is very good with the evo3.