This is a question directed towards people who have the stock twins but a open exhaust (IE: no cat) I have a hi-flow cat now and was curious to see what kind of boost patterns you get with a open exhaust (so that I can simplify my engine bay and remove a lot of emissions systems.)

Thanks

I've ported my stock w/g and have a 10-11-10 pattern with a mostly open exhaust(somewhat trashed hi-flow).

 

Anybody? I see quite a few views...

 

The first day I got my mid-pipe and replaced my high-flow cat, I got crazy boost spikes. I had an autometer boost gauge and I'm not lying, sometimes it would peg the 20psi mark at the end of the gauge. If I were you, I'd make sure you have a better fuel management system, along with a boost controller to help prevent this. IE: power FC, bigger secondary injectors, profec B, and if you don't already have it, I'd also upgrade the intercooler.

Honestly, I didn't really like the midpipe. To run it I knew I had to drop a good amount of money in the fuel management and tuning. So after figuring in all of that, I would always run my high flow cat. Not only was it more reliable with it on, but I would run a solid 12psi with no spikes. It was plenty fast and it would pass smog.

 

Yeah I don't have smog and I have a profec b2. Did you port your w/g?

 

Nope, sure didn't.

 

When ambient temps are above ~65, my boost pattern is 10-8-10 throughout the rev band using my Profec B Type S to control it. Even with the Profec, the transition is difficult to tune and it fluctuates up/down 2-3 times during the transition.

When temps are cooler (especially winter), the transition fluctuation occurs more often and I creep badly after 5500 RPM.

Air flow mods are: Greddy intake + FMIC, down pipe, resonated mid pipe, rb cat back.

 

^ You were seeing boost creep, not spikes. The only solutions for creep are to port the waste gate or add restriction to the exhaust. A boost controller won't help.

 

Boost creep, spikes, whatever... All I know is I was going 65mph on the highway and when I downshifted into 3rd gear and floored it, it hit 20psi on the gauge and my car lost traction on the highway and went sideways.

 

perfect 10-8-10. 13-11-13. with my profec b spec II, and ported wastegate sometimes the boost actually trails off and I have to increase the gain

 

well, i guess I should of ported my wastegate and I would of been ok.

 

I don't have ported a wastegate, full exhaust, profec2 and low setting pattern of 11.5-9-11.5 and high setting of 14-12-14.

 

Weird. I was hitting 10-12-10 with my Profec B2 on a stock port with a hi-flow cat! I guess I should hook my BC up and see what I get on the ported w/g.