Let's talk "BYPASS" valves
 

I've been running the same plastic OEM Bosch Bypass Valve since I started this turbo thing. I've been reading lately that most of them leak to a certain extent in vaccum and after a certain age, most of them leak a little to moderately in boost.

I think it's time to upgrade. My valve is plumbed into a 1" T-coupler just below the throttle body as standard, so the replacement must also have a 1" inlet. I've looked at Forge, Perrin,VF-Eng, FM's, BEGi's, and a few other pieces I've come across in google searches.

I'm pretty sure I want it to be an all-metal body and I don't want to spend my ass on it. It will also stay recirculated to the intake tract (for stealth) even though I run MS.

OPINIONS, SUGGESTIONS, EXPERIENCE.

This is what I'm looking at:
http://cgi.ebay.com/ebaymotors/Bosch...spagenameZWDVW

I currently run a forge diverter valve (all metal) - its closed at idle, and comes with 3 different tension springs (for 0-10PSI, 12-17PSI, and 17-25PSI)

Have not had a problem yet, as I have a mostly stock MSM I am still using the lowest spring, and its running fine - not audible with the stock MSM intake (lol maze) but I have heard its audible with other aftermarket intakes that use all-aluminum intake piping.

Cheap-o 3rd world produced Ebay valves can be good, or they can be garbage. Problems to look for are piston to valve tolerance, spring metallurgy and heat treating, o-ring material, lubrication type, air-tightedness (made that last word up but it gets the point across).

Most Bosch replacement valves on Ebay are copies of our valves (Forge), we change the appearance of our valves every few years to prevent confusion, even still we get many attempted warranty claims from people with knock-off valves. Usually I give a substantial discount towards one of our products when this happens.

Here are some examples of the potential negative effects of the above:

Piston to valve clearance can lead to a seized valve or excessive wear, which in turn can send little bits of metal into your engine or turbo and can create a leak (see below).

Crappy springs can break (metal into you into engine or turbo) or fatige over time. Usually this is gradual enough that you don't realize it. This can kill boost response and raise shaft speed on the turbo.

I've had people call me wanting to warranty knock-offs that used o-rings that weren't oil safe. In some cases the o-ring fell apart and it was obvious that there was a problem, boost response went to hell, valve fluttered like mad, and, when disassembled, the piston was beat to hell. Others the o-ring simply wore down in size so it didn't seal that well, in these cases its a more gradual failure. Boost reducing over time, that sort of thing.

I've seen lubricants bake into something akin to clay, others eat the o-rings in the valve, both of these are problems that can kill the internals of the valve, slow turbo response, raise shaft speeds, cause flutter, send metal particles in to the engine and or turbo etc.

Valves not sealing no matter what. Well, I can't say enough bad things about an air control device that leaks so much that it can't regulate airflow properly. Spool goes to shit, shaft speeds go through the roof, drive-ability suffers, compressor surge is likely.

On a completely stock, low mile WRX we've seen ~10 whp and ~15 wtq from swapping in one of our valves. All on the low end before peak boost. This indicates a valve being too lightly sprung and blowing open on boost onset.

On the Mazda 2.3 turbos most customers report gaining about 2-5 psi with our valves, much faster response, and improved drive-ability. This indicates a valve being such a piece of crap that it never seal entirely.

If you want a Forge, lemme know and I'll give you a deal.

the Greddy Type R can be recirculated. the outlet is 2" :)

http://gallery.y8s.com/d/423-3/bigbov.jpg

A direct and fairly cheap replacement for your Bosch valve would be the Bosch PN 0-280-142-108, used on Porsche turbo engines. The porsche part number for this valve is 993.110.337.50. I've read that this one is considerably better than the VW/Audi part most people use.

Is this the Bosch bypass valve that's known to leak? (pic from BEGi site)
http://www.bellengineering.net/image...ze/ByP--------

forge

I think that's a 34mm valve, I'm assuming from an EVO or 2nd Gen Eclipse. If it is they incorporate a channel in the body of the valve that connects the chamber above the diaphragm to the one below it, this acts as an air-brake of sorts to slow response. This helps increase how smoothly the valve operates but can increase lag under transient throttle conditions.

Pat, thanks for the awesome writeup. I think Forge would be the way to go, but even with a hookup, I think it's still be about twice what I want to pay. But I hear you loud and clear and will keep it in mind.

Kenzo, the BEGi piece looks to be an upgrade of what I have currently. The one BEGi sells looks like an all-metal direct replacement like the ones you find on DSM's. If you search for BOSCH BYPASS on ebay, you'll see 50 of them, usually from Audi/VW/Saab's... and they are all plastic and used and run about $30. I believe mine was from a Saab 9-series.

I've got a line on an all-metal DSM valve that I'm gonna try first. I'm gonna do some boost logging directly before and after I install it for some definitive evidence. We'll see where I go from there. I'm also familiar with "crushing" and might try that to see if there's a difference.

My favorite looking valve is this one from Forge. It's not an option for me now, but I love the round profile... would look great in my engine bay... probably look into it for my '99 build.
http://www.forgemotorsport.com/conte...uct=FMDV001GTI

1g DSM bovs will be more then you will ever need and can be had for 35-40 bucks. If I remember from my DSM days it was rated to 20+. Crushed the 1g will hold to like god awful PSI (think 30+).

DSM valves are 34mm, so you may need to use some adapters. That will need to be factored into the price.

If you don't mind a minor scratch, I can sell you a rebuilt valve for $50.00. It is a black version of the valve that the Ebay link you posted knocked off.

You know what, you give me some before and after logs and I'll give the damn thing to you.

Awesome offer. Tell you what... since I think I'll have the DSM valve inbound shortly, I'll pay you for the scratched valve and post logs of all of them compared against each other. PM me your Paypal and I'll get you money today.

Stock plastic BOSCH
OEM DSM
Nice Forge piece

Just blow if off...sounds KOOL!

This is what I'm running:

Apex Piston BOV

http://www.hopupracing.com/arabloffva.html

Found mine used for $50

^Yah, and I can hear yours all the way up at the base.

PS: Anything happening this weekend? Where's my favorite tatt'd up stripper?