Turbo Downpipes (ricer question kind of, need Turbo guys, HELP)

[sled_dog]

I have an 03 Mitsubishi Evo VIII on my lift right now. It has a p0300 code(random misfire). You can feel a slight miss at idle. Anyway, I road tested it and watched the factory boost gauge. It read 1.5kg/cm2, that comes out to about 21.4psi.... thats almost 5 pounds more than it is suppossed to be pushing. I can't find ANY boost controller(manual or electrical), and I've been over the car over and over. I have a call to the customer to see what all he has done to the car. All I see is an aftermarket blow off valve, 3" downpipe, high flow cat, and a full 3" exhaust. It runs fine when you lay into it. The tailpipe and rear bumper are black though. Plugs didn't look rich however(one side was white/lean, other looked decently normal).

So anyway, I can't see it being possible, but could a full 3" exhaust turbo-back cause a 5psi increase in boost?? Stock exhaust is something like 2 or 2.25 back to the cat then 2.5 out. I'm trying to avoid calling Mitsubishi technical hotline, because I don't want to screw this guys warranty. If I call and say he has the upgrades I see, hes screwed. And as someone who would like to own/mod one of these cars, I don't want to **** anyone over on one.

 

[83ZZ502_Jimmy]

Speaking from Diesel experience..

Is there a wastegate with a hose attached to it? Is the turbo a VVT? (variable vane turbine) I know that vane position can be changed via software to open differently.

Just a thought.

I am 99.9% sure a larger exhaust from the turbo back will not create more boost. There is only a few things that will increase boost, ie: more fuel, wastegate set differently, etc.

John

 

[sniperd]

if it runs fine at WOT then why are you questioning if too much boost is causing a problem?

its screwing up at idle (no boost)

 

[sled_dog]

I know but I was looking for any strange reasoning for what was happening. Found the reason. The guy called back and informed us it has an aftermarket Piggyback ECU. Doh.

They don't have VVT, but it does have an electronic solenoid that actuates the wasgate(by means of boost/vacuum). The piggyback must be keeping that solenoid from working till much higher boost.

 

[SchnorrCS]

I'd guess it's been reflashed.
I personally am a Subaru guy, but I'll take a whack at it....

Call the guy, see if it's been flashed (Software Rewrite). Chances are it has. A 5psi difference would cause those plugs to look super duper lean if the car's not supporting the boost with fuel.

As far as that CEL...could be a crappy coil. That one has coil on plug or some variation, right?

 

[k5blazin]

A larger exhaust will cause a boost increase... It happened on my nissan when i put a 3 in turbo back on it... stock boost is 7 PSI and it went to 9-10 PSI when the turbo back was on..

BTW I have a Megan racing turbo outlet, Blitz Stainless Downpipe, Test pipe, and a 80mm catback from GP sports.

 

[SchnorrCS]

Good point....I wasn't thinking. It can cause a little increase. Usually called boost creep. In smaller turbos, the wastegate outlet in by the turbo ouotlet and kinda looks like a door. With a larger exhaust, more specifically, going from a flange style downpipe to more of a divoriced wastegate or bell mouth downpipe, it will cause creep, sometimes. The creep usually is more of a spike that isn't really a constant thing. Does the gauge hold peak boost or does it hit the peak for a min or two and then drop?

 

[k5blazin]

Yea i have a little problem with boost creep and spiking due to my internal wastegate.. but nothing big.... It will usually spike a good 20 psi before settling down to 17-18 psi... Im def. gonna go external gate on my next set-up if i go bigger. Half of my problem was that i had a ****ty homemade manual boost controller... now that i switched to a good Hallman most of the boost problems go away...