2.5 T1 exhaust modification questions

[glhs399]

I was wondering how much you can modify the stock exhaust on a 89 2.5 T1 van with a stock mitsu without having boost creep. I was planning on taking off the cat tonight and possibly the muffler, I just want to avoid getting boost creep then hitting cutout.

[cordes]

I wouldn't take both off at once. I would probably do the cat and then perhaps the muffler. With 3" exhaust from the end of the DP back, not cat and straight through muffler I would creep to cutout in my shadow. There are others who have not had the same issues though.

[glhs399]

I think I do that, I try taking the cat out tonight and see how that goes.

[HarderFaster]

When I installed 3" exhaust from the downpipe back, with a high flow cat and magnaflow straight thru muffler, I expected my Mitsu to creep, but it's still rock solid (set at 12 psi with MBC until the intercooler gets installed). Maybe the 2 1/2" swingvalve and downpipe are keeping it stable. (Garrett TII is in hand, waiting on the TU 3" swingvalves to be made).

Randy

[Tony Hanna]

It seems like it's a toss up as to whether or not it'll creep.
My advice would be to go ahead and do a full 3" with a hi-flow or no cat, and the performance muffler of your choice. If it creeps, then simply make a restriction you can slide into the end of the tail pipe and secure with a self tapping screw. That will stop the creep and when you upgrade your turbo, you can pull out the restriction and you're ready to go.

[turbovanman²]

I think it largely depends on the MBC. I did a Daytona, 2.5 inch mandrel with a hi flow cat and Borla muffler. Using a Dawes, it crept badly, 4-5 psi, used a Turbosmart and it only crept 1-2 psi.

[IROCNOROLL]

I think it largely depends on the MBC. I did a Daytona, 2.5 inch mandrel with a hi flow cat and Borla muffler. Using a Dawes, it crept badly, 4-5 psi, used a Turbosmart and it only crept 1-2 psi.

I would agree. If you want to try it, leave the stock ecu controlled WG solenoid in control and do the exhaust mods. If all is stable then start dialing in a MBC to get to the target boost levels. We fab our own MBC and don't seem to have as many spike or creep problems some others here complain about. We set ours up as a normally closed valve, and boost pressure
unseats the ball and transfers the boost signal to the WG. One thing we have seen is the sizing of the vent hole in the MBC seems to make a difference in the accuracy and speed of the control. And running either the oem restrictor or a reasonable copy of it on the supply line to the MBC. It allows the pressure transfer, but controls the volume of air movement thru the controller system to the WG Can. It seems to allow a finer boost control without the possibly too rapid on and off WG control cycling that a larger unrestricted line seems to cause. FWIW.

[glhs399]

I removed the cat and no creep to be found. Next to go is the muffler. Thanks for the input.