I'm tuning my neighbor's car. He installed some E-Bay kit with a divided T4 turbo. It's a pretty small turbo.

This is a MAF car with an unknown junkyard 302 that idles smooth. It has an HO firing order.

The thing makes so much pre-throttle body boost at idle I can't idle it down. Even if I pull the BOV totally off just leaving the mounting flange it still pressurizes the inlet side of the throttle body. I don't like where they mounted the BOV, it is about 1-2 foot before the MAF meter and 2-3 ft before the throttle body.

It strikes me odd with the whole BOV removed it still builds up pressure. The turbo is spinning pretty good.

My engines never did that, even with something like a good .96 A/R T4 Precision 76 CEA turbo.

I can't really dump the exhaust side by forcing the gates open. That's not practical and I'm not sure it will work anyway.

I'm thinking the turbo is just totally wrong. I'm thinking that tiny turbo has a turbine that spins it up way too easy, like maybe something for a real small engine. I haven't measured the pressure, but it let's out a big whoosh if I yank the hose off.

It idles 500-600 RPM with the hose pulled, but if I put the hose back on the pipe the idle goes to 3500-4500 RPM! If I pull the BOV totally off it idles at 1500-2000 if I totally close the throttle blade and force the idle air control closed, I can't tune around that.

It runs and drives normal if I either pull the hose off the turbo or intentionally lock it up so it can't spin up. It's like the turbo is boosting at idle, and the only thing I can think of is the turbine is for real low flow. I'm at normal idle timing and 14.5 AFR so I'm not forcing a lot of unnecessary exhaust.

Could this just be a poor turbo selection or poor BOV placement?? Should I move the BOV to the inlet side of the intercooler?

 

put tube back on and start backing out the idle set screw to see if you can bring idle speed down that way. my Vortech blows massive air at idle but still idles normally. MIght also be pushing the plunger in the IAC??

 

The idle screw is all the way out, I guess I can block the IAC and see what happens. The IAC does work normally at atmosphere on the inlet.

I better look and see if he put the IAC on upside down or something. It may be directional sensitive.

 

How small is the turbo?

 

It is absolutely directional sensitive. The connector should be facing the inlet tubing, body facing the intake.

 

I have no idea what it is. EBay stuff. I asked he what it was and he said "CS Racing" so I'm guessing CX racing.

The wastegates leak dome air like crazy and there are two of them. I hope the turbo sample port can keep up. The stems have a lot of clearance and there isn't any other sealing. The dome air just blows right out around the stems with a whoosh.

I'm pretty sure it is blowing the IAC valve open. When I block off the IAC I can set idle with the throttle body stop. It still comes up at idle when I connect the turbo outlet but nearly as bad.

I looked at things and the air moves in a direction that would force the IAC off the seat.

I'm going to flip it around the other way so turbo air pushes it closed. Maybe it is just bad though it works OK with no air out of the turbo.

 

That's how it was, but the air pushes it open near as I can tell.

 

Can you post a photo of the turbo, whatever is written on it might also help.

 

I'll ask him to show me where he ordered it from and exactly what it is supposed to be. He ordered it from his phone.

 

Sounds feasible for the turbo to be that undersized. If the turbo was spec'd to make boost on a little 2.0L @ 2,000rpm, and it's on an engine more than double it's intended size, could be moving enough exhaust volume to make unmanageable compressor charge, even at idle.

In for results.