My set up involves a 50 trim T3 turbo on a D15B vtec engine. Can't find any bad intercooler piping leaks.....now for the nonsense.

My turbo reaches full boost by 3k RPMS....reaches a steady 8 lbs. However, by the time it reaches 6 - 7k rpms...it drops down to ~ 4.5 - 5 lbs of boost. I can't find any leaks, however, i do have a lousy downpipe. It goes from 2.5 - ~ 1.75 (long story).

What could be the cause of me loosing so much boost by redline? it pulls nice for a little bit, then drops in boost rather dramatically. Any tips? Thanx.

- optimus

 

the downpipe

 

I'm not trying to doubt you or anything, but out of honest curiosity, why would it be the downpipe? Is the restriction causing the turbo to slow down or something?

 

bump!

 

yea, as the car revs higher, more exhaust gases are being forced out... turbos work the principle of pressure differential... more pressure before the turbo, less after. in the higher rev ranges, the backpressure from the small exhaust is nearing that of the exhaust manifold, causing boost to drop off.

upgrade the dp and youll find quicker spool and full boost till the rev limit

 

you are the man

 

i know, lol.

now only if someone on this board knew anything about holset turbos

 

thats what i had happening on my old setup when i was running a stock cat. once i switched to a 2.5 test pipe it held boost fine until redline...problem solved. then i threw a whole new setup on the car