Stock Boost levels for 1992 Five-Speed?

[rampant150]

1992 Dodge Spirit ES
2.5L turbo, five-speed manual
All stock

I have started the process of tuning my spirit and have just put my boost gauge in. My question is: What are the factory boost levels, and how are they controlled? My car holds about 9# up to 3500rpms and above that it surges back and forth from 9 to 15#s (sticky wastegate or solenoid?)

[BadAssPerformance]

Stock on a T-I should be ~9psi

Controlled by computer using solenoid and MAP reference.

To start, check for cracked/leaky vacuum lines. Has the exhaust been opened up or cat removed? That can induce higher boost as well.

[rampant150]

The cat is gone but the rest is the tiny factory piping. It will be upgraded to 3" soon. It still has all the crappy plastic vacuum lines so I wouldn't be surprised if there was an issue there. A redo will be in order. Being a 92 does it have the ability to change the boost with the rpm level? Or should it be 9# no matter what?

[ShelGame]

The cat is gone but the rest is the tiny factory piping. It will be upgraded to 3" soon. It still has all the crappy plastic vacuum lines so I wouldn't be surprised if there was an issue there. A redo will be in order. Being a 92 does it have the ability to change the boost with the rpm level? Or should it be 9# no matter what?

The boost changes with RPM, coolant temp, Speed, time, etc. I believe that the peak boost is actually 11psi on the 2.5 T1. But, it's only for like 2 sec before it drops to 9psi.

[zin]

The boost wouldn't be fluctuating quickly as the OP seems to be indicating if it was under control... As such, I'd put my money on leaks in the plastic lines between the MAP and vacuum source and/or to the actuator on the turbo, either could cause the wacky boost by alternately holding then leaking boost pressure.

Mike

[rampant150]

It does fluctuate rather quickly, but only over 3500rpm or so which I thought was odd. Under that engine speed it holds 9 psi solid.

[Vigo]

This is not helpful to your current issue but be aware that if you bolt on a 3" exhaust you probably wont be able to control boost at higher rpms and will be 'creeping to cutout'. Fixing that requires porting the wastegate orifice on the turbine housing, which means taking the turbo off the car.

If you dont want to run into that issue i would just go with a 2.5" exhaust, and if it creeps you can just put a more restrictive muffler on it or add another muffler. A 2.5" system can easily flow enough to make more hp than the mitsu turbo can!

[rampant150]

The 3" will be going on because that's what I have to swap in - along with my good 2.5 running forged pistons and a garrett turbo. But this is all in the future as I want to run this high miler stock engine as long and as safe as I can until it pops the cork.

[ShelGame]

You can control the boost on a Mitsu using the factory boost control to a decent boost level. I run 20psi without a ported WG hole. My exhaust is a total of about 2' long after the turbo. 2.5" opening to 4" just past the k-frame.

It will work, but you will have to tune the duty cycle...

[Vigo]

How is a solenoid able to do anything beyond putting full manifold pressure to the WG can? Because that's what an MBC does and my mitsu + 3" car still creeps. Even if i turn the boost controller down until it's basically wide open, the boost will start at ~7 and after 3500-4000 or so will climb to cutout.

[ShelGame]

How is a solenoid able to do anything beyond putting full manifold pressure to the WG can? Because that's what an MBC does and my mitsu + 3" car still creeps. Even if i turn the boost controller down until it's basically wide open, the boost will start at ~7 and after 3500-4000 or so will climb to cutout.

Not sure. It could be in my car that I have the Mitsu maxxed out (I assume so anyway).

[Vigo]

You might be right. Either way, if the OP puts on a bigger turbo at the same time as the 3" exhaust it will probably avoid the issue entirely..

[GLHS60]

Rob, can you hold say 10 psi with your Mitsu and open exhaust?? I've never been able to with any Mitsu's with free flowing exhaust as they always creep to overboost pretty fast. I've had to put a restriction on the tail pipe a few times.

Thanks
Randy

[ShelGame]

Rob, can you hold say 10 psi with your Mitsu and open exhaust?? I've never been able to with any Mitsu's with free flowing exhaust as they always creep to overboost pretty fast. I've had to put a restriction on the tail pipe a few times.

Thanks
Randy

Never tried 10psi; but I've turned it down to 16psi and it still worked. I've run from 16-21 and the boost control works. I did do quite a bit of re-tuning to the WG duty cycle table. Mostly just the slope. It's still a straight line.

[GLHS60]

Well that explains it for me as I was thinking of engines running stock computers so 16 is a bit over their limit.

Thanks
Randy