Is stock muffler THAT restrictive?
 

Ok After the non-sequential conversion my car is running hard as f*ck. Took an SRT-4 yesterday good friend of mine, but dam those things are fast. I was getting a solid 10 psi until 6.5 to 7k then it would drop to drop a bit. It went down to about 7 psi at high rpm. So I would just shift at 7. Now my mods for exhaust are downpipe, gutted cat, and stock muffler. I thought after gutting the cat I should get boost creep?! what gives?

Re: Is stock muffler THAT restrictive?
 

I don't believe the stock piping is 3" so you still won't flow as much as a 3" midpipe (which will help give some backpressure to control the boost).

Well I got massive flame for doing it, that the motor was going to blow and all this BS and the boost controller holds it just fine. Im pretty sure mine was clogged because I was having hard time getting boost up.

But My concern is more with the muffler, because I have a feeling a may be that more than anything.

While aftermarket exhaust do provide better flow, the stock exhaust is not bad. Seems like something is wrong though if your transition is dropping down below 8 PSI.

I had heard a while ago that someone tried the mid pipe/stock muffler combo, then switch to the stock cat/aftermarket catback combo and that he found the latter to be much more free flowing, now this was a long time ago but the principle wouldn't change over time. The exhast tips alone are restictive as hell arent they?

Mahjik im non-seq there no transition. Once they spool they kick me back, yet I can feel and see it die as I get high on the RMP. I guess I'll go RB duel tip as soon as I get the cash for it. Heard the flow is good and the look is near stock.

haha "RB Duel" .... i like that better :wink:

If you are running the stock ecu, the boost will start to drop after 7k rpms. It's programed to do so.

I've heard that the ECU was programmed for the 7k boost drop only on some cars. Maybe yours is just one that does have this programming.

My car was all stock except for a downpipe. The night I removed the stock catback and bolted on the M2 dual I couldn't believe the difference! I don't know of the stockers blow out and clog (mine had rust holes in the casing) but I was not prepared for such a big improvement. Pattern before catback was 10.5-9-spike to 12-10.5 and it went to about 11.5-10-spike to 15-11.5 before I installed a needle valve in the wastegate line to keep boost to no more than 11 psi on cold days. Spikes are no higher than 12 when it's cold out.

Ah, ok. Didn't remember you were non-seq. ;) The stock system typically has enough flow to maintain 8 PSI to redline (hence the normal 10-8-10 and back down to 8 until redline boost pattern most people see).

I think the RB Dual would be a nice mod. As Damon pointed out, you'll feel a little extra on the butt dyno with it. :)

My Fd's exhaust back pressure dropped by 4 PSI (as measured at O2 bung in SS DP) when I replaced the OEM catback with a new one from RX7Store. The difference was quite noticable, even though I still have a partially clogged cat. Boost came up quicker, max boost went up ~ 0.5 PSI, and tansistion was faster.

Interesting, well as soon as I can get an RB Dual tip sounds good, the duel is alright for track as well?