Think of it this way. Boost dropping off isn't necessarily a bad thing. The turbo is more than likely pushing out the same amount of air. It's just that the engine is gulping a lot more than before because of higher rpms and the third intake transition.

Before the third transition, the engine isn't taking in as much air, so the air that the turbo is pushing out is backing up in the intake manifold (the computer reads as more boost though). Once it goes past the transition, the engine takes in more. Also this is good because the compressor is having to work less to push the same amount of air, reducing the amount of heat it dumps into the air. It's kind of a win-win.

Now I don't know if this is the case with the Greddy kit... But it makes sense to me...

 

The custom kit by Ozzy holds boost pretty well. Jeff claims his holds boost. The Bullseye upgraded turbo can supposidly hold boost, and I believe, although I'm not sure on this one, that the SFR turbo holds boost.

 

Hey rkostolni, just checked out SFR dyno, Power falls off after 7100rpm's I assume the boost is falling also... You say: "ozzy's holds boost pretty well" What's pretty well, either it holds boost or it dosen't..

I'am not being a (smart ***) just trying to see if it is true that nobody is holding steady boost after 7200RPM's.... for an RX8...

 

I don't think the power falling off is indicating the boost is falling off. You might want to call them and see. If I remember correctly, Ozzy's was running like 13psi, it does dip down some, but he is still able to hold 9+psi to redline.

 

From my experiments, the boost seems to fall-off due to the increased exhaust gas pressure cracking the wastegate when the tertiary runners open. Adjusting the wastegate let me hold about 2.5-3 psi more at redline. I go from 10psi to about 7.5-8psi.

 

Sounds like a good idea MadDog, I'll try it. Actually I remember Benny telling me to losen the adjustment at the beginning of my install last year because I had too much boost ..So I'll try tightening the adjustment to the orginal setting, then go from there.. I always have a record of what I've done before... Thanks..

 

Hey Rotarygod, on the (3rotor thread) you say the Renesis intake is much bigger than the 13B, where did you get this info or where can I see this info... If that's true can that be why boost falls off on the Renesis FI, because the turbos are not big enough to handle the massive intake size... I wonder if twin seq. turbos would help that or just a bigger Turbo, Hey what do you experts think...I
was still thinking of getting the Acosta Intake but I don't know now...

 

Let's see if I can help you guys. It wouldn't make a difference if the intake manifold were as big as a fuel dragster. When it is full, that's it. If the engine is so big that it sucks more air out then the turbo puts in then pressure will go down.
If the turbo puts out more air then the engine takes at X pressure then the waste gate opens.

Now in the instant case I believe that some have gotten pressure up top with these kits. However if you are going way out of the efficient operating range you will gain nothing but trouble. There may not be anything to gain going away from the original design point. Some engineer matched that blower to where he was aiming with his design. If you guys think you are smarter then he is, then by all means modify the **** out of it.

You might look to see it the TB is closing off from some input it is getting. Not sure that works that way, you might want to ask MM.

 

Too bad someone like Greddy, SFR, Mazsport,RP,Pettit etc, don't have the time or interest to buy a Renesis Motor so they can work on it in a dyno room and really see what's going on , on this motor.. I would believe it would be so much easier to see what,where and why we are having problems with boost falling off.

This way we can see if it's the Intake, Intake Ports, The Exhaust, the Exhaust ports, The Turbo or whatever.... that way we would know what to fix and what to spend our money on. Ah well someone will figure it out eventually...