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Old 08-27-2007, 06:32 PM   #1
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Default The bypass valve and venting to atmosphere.

Well, before I did the install I bought a bypass valve from BEGI, but then of course afterward when going to put this on I realized there really isn't a spot after the AFM that I can route the air back into at least not without getting some custom piping of some sort.

This may seem like a stupid question, but will it mess things up if I connect the thing and just vent it to atmosphere rather than back behind the AFM?
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Old 08-27-2007, 06:43 PM   #2
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You could have issues with idle, since it could leak and allow un-metered air into the engine. You'll also get a rich condition anytime it vents and un-metered air escapes. For some this isn't a problem, for me I found it to make the car buck when lifting slightly. This was not acceptable as it affected drivability so I ended up plumbing it back into the intake. Now I don't have an AFM and no longer worry about it.
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Old 08-27-2007, 07:49 PM   #3
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One bandaid that can be applied when running VTA with an AFM is a one-way check valve on the BOVs exhaust port. This will prevent it from leaking at idle and drawing in unmetered air.
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Old 08-27-2007, 08:35 PM   #4
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I talked with a guy at BEGI and he basically said that the only problem I should encounter is the possibility that it bogs because I lose air and it adds too much fuel when I shift. Otherwise he didn't seem to think losing air at idle was an issue.

What would be a way to plumb the thing back in with the stock Greddy setup? I assume my option would be to add some sort of inlet on the pipe coming from the airbox.
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Old 08-27-2007, 11:56 PM   #5
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Quote:
Originally Posted by Harv View Post
What would be a way to plumb the thing back in with the stock Greddy setup? I assume my option would be to add some sort of inlet on the pipe coming from the airbox.
That's pretty much it. Find an NPT pipe nipple which is sized similarly to the exhaust on your BOV. Then drill and tap the Greddy pipe between the AFM and the turbo inlet and install the nipple.

A couple of folks have even drilled and tapped the AFM itself. There's enough space on the end to do it- useful if your AFM is hanging directly off the turbo.
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Old 08-28-2007, 02:56 PM   #6
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I think if I did it I would probably just do the pipe as if I want to put it back to stock having a hole in the AFM might look bad.

As it is I'm contemplating drilling the pipe and putting some sort of fitting on there. What's the advantage to drilling and tapping over just drilling and welding something on?

For now though is it better to just let the thing blow back (I'm at around 4.5psi with the IC) or should I throw the bypass on and let it vent to atmosphere to avoid that and let it go rich during shifts? When I talked to the guy at BEGI he seemed to think it was better to put it on even with the AFM issue.
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Old 08-28-2007, 03:53 PM   #7
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Anything is better than compressor surge which can shorten the life of your turbo.
You can drill and tap or weld on a fitting. Both are great.
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Old 08-28-2007, 04:48 PM   #8
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Quote:
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What's the advantage to drilling and tapping over just drilling and welding something on?
The fact that I happen to own a number of NPT taps, however I suck very badly at welding aluminum.

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For now though is it better to just let the thing blow back (I'm at around 4.5psi with the IC) or should I throw the bypass on and let it vent to atmosphere to avoid that and let it go rich during shifts? When I talked to the guy at BEGI he seemed to think it was better to put it on even with the AFM issue.
I would tend to agree with The Guy. If you search around here you'll find some threads where people have used inexpensive plumbing check valves with Bosch BOVs to great success.

I personally drove around for several months with a VTA BOV using a check valve (this was before I removed my AFM) and there was really no downside. Anyone with a logging WBO2 sensor will see that the mixture goes way rich during shifts no matter what. Just the way things work.
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Old 08-28-2007, 05:04 PM   #9
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I was using a check valve and had some drivability issues when running VTA. If I was in boost at high RPM and attempted to let off slightly while still keeping in boost I would get serious bucking. Maybe the BOV I used sucked ***, but once I recirculated it everything was fine.
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Old 08-28-2007, 05:34 PM   #10
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Well, I have already bought the anti-surge valve that BEGI sells.

http://www.bellengineering.net/Images/ByPass_Sm.jpg

I think it is a Mitsubishi valve, have to look at it again.

The guy at BEGI didn't seem to think that leaking at idle would be an issue, but before I put it on I think I will try altering the intake piping to route the air back in. Right now the car is running well except for the compressor surge during shifts. Also, the danged inlet on the valve is a lot larger than the outlet coming off the IC pipe that goes into the intake manifold. Gonna have to find some way to mate things up.

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The fact that I happen to own a number of NPT taps, however I suck very badly at welding aluminum.
Would JB Weld be a bad choice in this situation?
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Old 08-28-2007, 05:38 PM   #11
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JW Weld will work fine. Scuff your parts good to get good adhesion. There is a better epoxy that 3M makes as well. It just won't be pretty.
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Old 08-28-2007, 05:56 PM   #12
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Quote:
Originally Posted by cjernigan View Post
JW Weld will work fine. Scuff your parts good to get good adhesion. There is a better epoxy that 3M makes as well. It just won't be pretty.
Yeah, I don't really want it to look like ***. If my buddy can't help me with the welding maybe I'll look into finding a local shop to do it.
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Old 08-28-2007, 05:58 PM   #13
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Quote:
Originally Posted by Harv View Post
Well, I have already bought the anti-surge valve that BEGI sells.

http://www.bellengineering.net/Images/ByPass_Sm.jpg

I think it is a Mitsubishi valve, have to look at it again.

The guy at BEGI didn't seem to think that leaking at idle would be an issue, but before I put it on I think I will try altering the intake piping to route the air back in. Right now the car is running well except for the compressor surge during shifts. Also, the danged inlet on the valve is a lot larger than the outlet coming off the IC pipe that goes into the intake manifold. Gonna have to find some way to mate things up.


Would JB Weld be a bad choice in this situation?
fwiw, bosch makes mitsu's bypass valves
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Old 08-28-2007, 06:00 PM   #14
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The drill, tap, fitting and hose to do this shouldn't cost you more than $25 and you should be able to get all those things local tomorrow.

Or harborfreight.com is your friend.
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Old 08-28-2007, 06:00 PM   #15
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I used jb weld on my radiator overflow fitting and it looks pretty good. but that was already threaded and was just resealing it.
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Old 08-28-2007, 06:05 PM   #16
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Quote:
Originally Posted by cjernigan View Post
The drill, tap, fitting and hose to do this shouldn't cost you more than $25 and you should be able to get all those things local tomorrow.

Or harborfreight.com is your friend.
Who sells fittings that would work? Home Depot? Am I looking in the plumbing section?

Drill bit I might have. I actually need to measure the outlet from the valve to get an idea of the size hose I need.

I have a tap kit, but it is one of those ones they sell at Autozone so the biggest it has is about a 1/2" NPT I think.
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Old 08-28-2007, 06:19 PM   #17
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1/2" NPT should work fine. You can get a brass fitting at home depot or a steel one at autozone in the fuel section or something like that. Tell them you need a hose 1/2" NPT hose fitting.
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Old 08-28-2007, 06:30 PM   #18
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I used a metal threaded pipe coupler from HD cut in half for my BOV routing, as well as for the idle valve hose. I think it was about $1. Drilled into the IC hose, tapped, screwed in, and got a nice seal with some JB Weld, smoothed it out, and sprayed it black. Doesn't look half bad, and is fully functional.
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Old 08-29-2007, 10:48 AM   #19
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Quote:
Originally Posted by cjernigan View Post
1/2" NPT should work fine. You can get a brass fitting at home depot or a steel one at autozone in the fuel section or something like that. Tell them you need a hose 1/2" NPT hose fitting.
The jackasses at my local Home Depot don't have any clue about that stuff. It's pretty sad overall.
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Old 08-29-2007, 11:31 AM   #20
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When you drill into your charge pipe, install the brass fitting, and seal it up good with JBweld... then dremel out the threads in the inside to the pipe is smooth. One of the heavyduty Dremel cutting wheels goes through brass like freakin' butter.

Here's how bad VTA was on my 1.6:
https://www.miataturbo.net/diy-turbo-discussion-14/freeway-speeds-vta-02clamp-6149/

Here's how happy I was recirc:
https://www.miataturbo.net/diy-turbo-discussion-14/recirculated-today-awesome-8069/
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