Where do you guys hook up your blow off valve signal? Before or after the carb/TB? I'm using a turbo xs rfl with the signal hooked up to my manifold. I noticed today that when I put my hand over the valve at idle it was getting sucked in. It seems that my valve is leaking at idle causing my stumble when I stab the throttle. I disconnected the signal from the valve and plugged it and the stumble went away. Any thoughts?

Thanks, Ed

 

I believe they are just supposed to be hooked up to manifold vacuum. Nothing real special.

 

Thats what I thought but I figured I would post it here and get some input.

Thanks, Ed

 

The signal must be plumbed to the manifold vacuum,below the throttles.
BOVs are a pain sometimes.They tend to open under vacuum,but theres vacuum in the manifold anytime the engine is running and the turbo isnt boosting.So that means the BOV is often open and passing unfiltered air into the engine....or F-ing up the mixture if you run metered air fuel injection.
You try to adjust them to get the diaphram stiff enough to not hang open at idle,but no so stiff that they dont open when you shift.Its usually a pain to get right.Thats why the good quality units respond to changes in signal,not just vacuum in general.That way they dont hang open at idle,but they respond quickly when you shift and let off the throttle.Blitz,HKS SS...ect.
For my application,I just plumbed my Blitz BOV back into the turbo inlet like the stock TII bypass valve.That way when/if it hangs open under vacuum,the air will be drawn from the clean side of the air filter,and any bleed air will be after the AFM,so my mixture will be correct.
Whats your application?....stock EFI,standalone,carb,blow through?

 

Steve, this is on a blowthrough set up. I opened up the valve there are no shims in there just spring pressure. I'm going to try some shims and I'll let you know what happens. I cant believe all this time I thought it was a jetting and or timing issue? Thats why it has not seen the road yet.

Thanks, Ed

 

Well,if the BOV is mounted between the turbo and the carb,it should have absolutely no effect on the carb mixture.Anything before the carb, is just air.....the carb doesnt care if the air goes directly into it,or if the air passed through a hundred feet of pipe first....,its just feed air.
After the venturies and throttle plates is when air leaks will mess up a carb's mixture because the engine will suck air through the leak,which will reduce the air passing through the carb's working parts.

The only time an air leak before the carb is a problem,is when the turbo is boosting.Then,a portion of the pressurized air will leak out of the system,instead of making it down the carb's throat.Even then,its not going to change the mixture,youll just see less manifold boost and less power. At idle and under vacuum running,there should be not issues.
On a metered air EFI system,you will have mixture isues because the AFM has measured all the air going into and out of the turbo,so if it doesnt all make it into the engine,youll have problems.

 

DUDE what did I tell you yesterday. It's supposed to do that. don't worry about that. Thats why when you buy a Blitz BOV they come with a air filter. A real BOV or pop off valve usually has a really stiff spring and will only open with large changes in vaccume. But one like mine a Greddy Type S is really a recirculator valve that can just be blown off into the atmosphere, or recirculated into the intake streem pre turbo. It's not your problem. It's not a vaccume leak. The vaccume is pulling on a sealed diaphram and opening the valve.

 

Correct.
In fact,my first BOV was a Greddy type S and it did the same thing.Bugged the hell out of me because it didnt have a filter.I ended up getting the Blitz and first running with the filter,then plumbed it back into the TID to keep the ECU happy.

If you get a filter on the BOV,you wont have to worry about dirt ingestion.

 

Okay guys the blow off valve is not the problem as you guys stated. I yanked it off the car completely and it still did the same thing. Problem was COUGH poor tuning on my part COUGH! I had my idle mixture screws leaned out all the way to try and get a nice idle. Stupid me must of forgot that my motor is ported (lumpy idle). I turned the screws 3 turns out and the poping went away. Gotta do more tuning.

Thanks, Ed

 

Lumpy idle, my half bp shakes the entire car, and I'm concidering going with solid mounts. If it wasn't for the exhaust noise, I could get rocked to sleep, waiting at a stop light.