3" exhaust + mitsu turbo = overboost?

[My96z]

I am running my van at 12PSI via a dawes boost controller and mitsu turbo. I am going to upgrade the exhaust to a 3" with ultraflow muffler. I am wondering if everytime I get into it will I hit over boost?

I think I heard awhile back that a 3" on a mitsu will hit overboost. If this is true can I just back off on the boost controller to fix this?

Thanks,
Jeff

[BuRn__]

with a mitsu, id just stick with a 2.5. ud most likely be hitting overboost everytime with a 3"

[My96z]

**** that really sucks, I only want to buy a exhaust one time.

[iTurbo]

Either way, a 2.5 T1 with a Mitsu turbo 2.5" or 3" exhaust will have boost creep issues. I route full manifold pressure to the wastegate can on my Mitsu turbo 2.5 T1 Shadow and it will hit 5 psi instantly, and then creep all the way to cut out. I would upgrade the turbo first. If you do open the exhaust first, you may have to control the boost as described above to avoid cutout.

[turbulence]

I've got a 90 voyager with 3 inch exhaust with mitsu and with the waste gate shimmed it will climb past cutout in a heartbeat up to 19 lbs and then settle to 17 at higher rpms, not that that bothers me :big grin:

In my previous van I had 2.5 inch exhaust and it creep wasn't as much of an issue. If you want to do the exhaust once is there a way of corking it to add back pressure until such a time where you need the 3 inch? put a short 2.5 or 2.25 section in it maybe? Or more restrictive muffler? add a cat?

[Timmay2]

If you have it graingered between the turbo nipple on the air outlet and the wastegate it shouldnt.. i have a mitsu with 3" starting about 4" from the turbo back, hollowed cat and dynomax strait thru...

dont grainger it between the intake and the wastgate or you will have that problem.. i had fluctuations and creep quite often off the intake..

[My96z]

Quote:

Originally posted by Timmay2 If you have it graingered between the turbo nipple on the air outlet and the wastegate it shouldnt.. i have a mitsu with 3" starting about 4" from the turbo back, hollowed cat and dynomax strait thru...

Thats how I have it set up right now. I wanted to upgrade the exhaust as its the 1st thing to do but this issue came up.

Thanks,
Jeff

[turbulence]

Quote:

Originally posted by Timmay2 If you have it graingered between the turbo nipple on the air outlet and the wastegate it shouldnt.. i have a mitsu with 3" starting about 4" from the turbo back, hollowed cat and dynomax strait thru... dont grainger it between the intake and the wastgate or you will have that problem.. i had fluctuations and creep quite often off the intake..

That is how I have mine set up and it creeps. Keep in mind it also depends greatly on ambient temperatures. If it is 90 degrees I dont get creep. 40 and lower, most definately. -30, hang on to your hat!

[Stevien1]

Replace the restrictor in the G-valve circuit with a brass "fish tank valve". You'll should be able to counteract the spike with it by dialing the orfice size.

[Turbolag87]

i have 2.2 with a mitsu with 2.5' exhaust and i dont get any creep at all. I use the brass fish valves, but i use 4 of them on the same line and it works perfect. boost is steady at 11psi. Soon to go up : )

Danny

[TurboShadowES]

ive got a DIY boost control, and a mitsu, along with a home made side exit exaust... a cat but no muffler 2/4. it creeps like crazy...

[lametec]

Boost creep is not affected by boost control. It doesn't matter if you have a g-valve, a $500 electronic unit or a handful of bleed valves.

Boost creep occurs when the wastegate passage doesn't flow enough. The wastegate is wide open, and when the passage is "saturated", he turbine starts spinning faster and faster. This is boost creep.

All boost controllers can do is control when the wastegate opens or closes, and since boost creep occurs when the wastegate is already wide open, there's not a thing they can do to tame it.

[BuRn__]

Quote:

Originally posted by lametec and since boost creep occurs when the wastegate is already wide open, there's not a thing they can do to tame it.

that really cleared up my questions about boost creep. i didnt know that it happened even though the wastegate was wide open

[turbulence]

As I said earlier in this thread, the only way to control boost creep is to restrict the exhaust in some fashion. I know one guy who had boost creep with a 2.2 vnt and 2.5 in exhaust. He solved it I believe by putting a slightly smaller section on the end of his tail pipe.

Or as good old Gus used to say, enjoy it! add extra fuel and put in a cut out raiser.:big grin:

[iTurbo]

I route full pressure to the wastegate can. It still creeps of course, but at least I can avoid the overboost cutout. The best way to cure it is get a TII turbocharger.