Controlling boost spikes (ProfecB)
 

Hi !

I was just wondering if I will be able to control the boost spikes at 4.5k RPM when I add the DP to my Rex. Problem is that previous owner already replaced the main cat with straight pipe and left the pre-cat on. I think I want to remove the stock DP, but fear that I won't be able to control toe boost spike when 2nd turbo kicks in. I will be limiting the boost with ProfecB, so I'd like to get some input from owners of the unit.

Thanks !

remove the restrictor pill from the wastegate line....and install a more restrictive restrictor in the prespool line...this should tame it down....

you'll find that the problem with the midpipe is the wastegate hole is not large enough to let all that excess air out. the profec will work fine, and open the WG, but the WG is too small to hold down 10 psi. i'd do 2 things:
1. search on "porting wastegate". (to learn more)
2. sell the midpipe, get a downpipe, and get a highflow cat. the downpipe is much more important than the midpipe

Profec B
 

I don't see any need in modifying the wastegate. Try reading this thread. I have perfect control of boost using this method without the need to modify the wastegate.

https://www.rx7club.com/forum/showth...hreadid=105959

MCF

Re: Profec B
 

That depends if you are controlling boost "spikes" or "creep".

If creep is the problem, then a boost controller or pill won't do anything and you'll have to look into silver93's suggestions. However if it's just boost spikes, then that can be controlled via boost controller and/or pills.

Profec B
 

With all due respect Mahjik, creep was precisely the problem that I had - and this set up completely eliminated it. I don't understand why, only that the PCA must have been the cuplrit (not the wastegate), because that is the major change when t-ing the two off.

Re: Profec B
 

Then what you had wasn't boost creep. Boost creep is when the wastegate is being overrun. It's already at 100% and that is still not enough. A boost controller can't help. In those cases, restriction needs to be added to the exhaust or the wastegate needs to be ported.

You should take a read through this thread:

https://www.rx7club.com/forum/showth...threadid=26389

Anyway, if your boost is under control, that's a good thing.

Makes sense... I'll bet there are tons of guys who have ported their wastegates that didn't need to.

When I had a mp, dp, catback I did not get boost creep or spikes using the Profec B. I was solid at 13, 14 psi on my high boost.

I would lose the mp and get the dp. Look into Silver93's suggestions.

Take care who you listen to.

I know of many modded Rx7's (full intake and exhaust and ECU) that required the wastegate to be ported to control creep; Profec B ... manual bleeder ... AVCR ... sequential or non-seq ... didn't matter. It's a flow issue, too much exhaust flow aka horsepower and boost creep results. Do a fourth gear pull in a 350 rwhp 7 with a non-ported wastegate and you get about 16+ psi above 6500rpm. Port the wastegate and this can be as low as 12 to 14 psi. YMMV

I will then just install a hi-flow cat (around $180). Thanks !