Hey all. My problem is this, my car runs a 11-10-11 boost pattern, but near reline my boost drops from 11 to about 8 psi. Is this normal, or a sign that the turbos could be going south?

 

Swamp: That is pretty normal, you'll see your boost fall off as you approach redline. 2 - 3psi down is probably about right. When I'm running 13.5 psi, I'll see it down to 11 by redline.

BTW: If you REALLY want to see what is going on, get your self a datalogit (Sometimes it is hard to stare at the boost guage while going 100Mph+)! Here is an .xls sheet with Boost v/s RPM graphed from a recent Dyno run I logged.

http://flathat.woodstream.net/RX7/Dy...-datalogit.xls

k

 

What causes this?

I noticed this happens in my car too. Can anything be done to make the boost hold til redline?

 

Even with the boost tappering off toward redline, the hp #'s still continue to grow, just torque drops off.

I think DynoRun #6 on this sheet is the run that corrisponds to the above .xls sheet log.

http://flathat.woodstream.net/RX7/Dy...o-runs-3-6.jpg

I don't know any turbo cars whos boost doesn't tapper off toward redline. I am sure there are things that can be done to reduce the tapper, but probably won't ever eliminate it.

K

 

i don't think mine does, i'll have to pay more attention next time i drive it. i only run 12psi of boost, that may have something to do with it

 

According to Steve's site the boost cycle should be:


rpm psi
3,000 10
4,500 8 (as 2d turbo comes on)
4,500+ 10 (recovers almost immediately)
6,000+ 8 (and holds to redline)


But my lightly modified RX-7 (RB intake duct, K&N Filtercharger, DP) does not. I get 11-9-10 , the 10psi holds past 6k rpm if I keep WOT.

 

Well, this may sound silly, but I was just playing GT3 on the PS2 and my modded out RX-7 starts to loose boost at redline. So, maybe that is just the way it is.

 

So what acatully causes this to happen?

 

less exhaust pressure as your rev's climb beyond 6k, in turn allowing your turbo's to spin down a bit? or maybe just boost pressure leak during extended high psi boosting?

k

 

It is weird, you would think with the higher RPM's that the turbos would spin faster producing more boost, not less. Anybody know?

 

well, i actually watched my boost gauge VERY closely and i guess i do lose about 1psi by around 7k rpm.

why this happens??? don't know, but strictly guessing, the turbos may not be able to flow enough air to give the pressure and volume needed while approaching 8krpm. i'm going to play with my apex boost controller in the next few days and see if i can tune this out.