Boosting Problems

[UPSIDE-DOWN-FACE]

heres the setup-
'90 2.5 t-1 mitsu auto
srt intercooler
side exit, no cat exaust


i just did the vac lines after having problems with leaks. i made a custom vac block and shorten the vac lines up as much as possible. i have g-valve b/c going to the w/g from the vac block. only about 10" long. im sure theres no leaks. heres the problem... with the g-valve set as low as possible it will still go to about 12-14psi. so i put just a straight pice of vac line on the w/g to the vac block and ran it that way. same thing it boosts way up. i cant seem to get control of my boost. what could be my problem?

thanks for any help.
kyle

[Capt'n Dave]

are you sure the guage is reading right? tryu a after market guage to see what you got. have you taken the controller apart? maybe the spring is in wrong,just throwing a few ideals at you, 12 to 14 PSI boost is pretty good for a t1 Turbo set up....you aren't getting over- boost are you? let us know what you find out! Good Luck with it.if it came from some one else,they may have changed out the springs or added spacers to increase their boost.

[UPSIDE-DOWN-FACE]

its an auto-meter guage and it is reading right. it could be the grainger but then why would it do the same without it? when i went full throttle it went to 11-12psi, held till about 4500 rpms then overboosted and i let off. does the spring have to be in a certin way?

[deuce dodge]

sounds like an awesome set up....

deuce

[Aries_Turbo]

its the catless, short, free flowing exhaust. the stock wastegate cant bypass enough with that tiny turbo to keep it under control even with the hose from the manifold to the wastegate can and the arm tension loose.

i think also the mitsu can has less travel than the T2 can but im not sure.

I have a feeling that you could wire the wastegate open and still hit cutout in the upper gears.

Brian

[bill2]

You could try disconnecting the wastegate arm to the swingvalve flapper, and see if the boost is still to high. If it's still too high then your easier fixes are either restricting your exhaust, or running more boost. If it is closer to the levels you'd like to run, you could try to find an older mitsu can with less spring tension on the wastegate arm, or you could take your can apart and weaken the spring yourself.

[whistlin']

Maybe the diaphram in your wastegate canister is leaking, not allowing the wastegate to open all the way. If you have air pressure handy, you can run pressure to the can and see if it's opening.
My big can on my garrett is so tight, I can hit 17 psi with straight manifold pressure to the wastegate.

[Aries_Turbo]

the problem really is going to end up being the exhaust. most folks that open up the exhaust with a mitsu have boost control issues with a stock 2-bar computer that still has cutout. the turbo usually wants to scream instantly to 18psi.

just get a cal or a socketed ecu, +40's and a 3-bar map and run one of robs 3-bar 90-91 cals. theres a solution

Brian

[UPSIDE-DOWN-FACE]

im hooking up a boost cutout this week end. then see where the boost goes. and mabey get some control. thanks for the help guys.

[Aries_Turbo]

dont remove cutout without some extra fuel.... extra inj, +20's or something

Brian

[UPSIDE-DOWN-FACE]

i know. ill be watching my a/f/ guage very closely.

[whistlin']

the problem really is going to end up being the exhaust. most folks that open up the exhaust with a mitsu have boost control issues with a stock 2-bar computer that still has cutout.

Yes, there will be some creep, but he shouldn't be going that high with the manifold pressure straight to the wastegate.

[TurboII]

ill put my money on exhaust dude, I have a 3 side exhaust as well with know muffler and a catco cat and i get boost cutoff on my mistu all the time when the weather is just below warm. I have a turboxs boost controller and she hasnt done it in a while. but ill say 3" exhaust. mistu are know for spooling out of control with a 3" exhaust.

[whistlin']

I'm just saying he should make sure everything is functioning properly before blaming the exhaust. When I went to a 3" side exit I switched to a garrett at the same time so I can't say from personal experience what the problem is. I have had a free flowing 2.5" on a mitsu, and with the arm disconnected could barely get 7 psi at 6k.

[Aries_Turbo]

maybe with the arm off with the 2.5" it would be ok especially in the lower gears, high speed, higher gears i dunno. with the wastegate arm on its going to darn near always hit cutout. I know that the mitsu can has less travel than the t2. i wonder if swapping cans so the puck opens farther would help. when i get my GTC on the road, ill do some tests.

Brian

[TurboII]

I know what you mean, but I had my 3" exhaust for about 2 months and its spools out of control sometimes depending on the weather. If its really cold I don't even bother opening it up cause boost cutoff kicks in Thank God for boost cutoff or else I will have know more engine LMAO. But all IM saying is mistu tend to spool out of control when theirs know back pressure especially when you have know muffler or cat. The turbo is just doing its job on spooling cant blame that.

[Aries_Turbo]

I dont disagree. i was more responding to whistlin' as its been a known issue for quite a while that the mitsu goes out of control with little to no backpressure. I remember hearing some hints that originally came from Gus to peen the end of the tailpipe over to keep the mitsu under control lol.

Brian

[UPSIDE-DOWN-FACE]

is there no way to controll it? is my grainger useless? it has a glasspack muffler on it. do i need somthing more restrictive? that sucks! i just got this exaust done.

[TurboII]

I used a turboXS boost controller and im fine and i have no muffler with a high flow catco cat on it.

[contraption22]

Is there a nipple on the compressor housing in the turbo? If there is, use it for boost control. It will react faster, and maybe slow the spool some. Also, if there is any pressure drop across the intercooler, it will work to your advantage in this case, in that there is usually more pressure before the intercooler than after.