zerMATT951

I've actually run it both ways and could not tell any difference, but it does make sense to run with the piston side toward the pressure. I just ended up with it this way b/c of the factory (diaphram) unit orientation.

I'll flip it after I get the engine bak in the car

Paulyy

forge 006 and evo motorsports, both good

lart951

dont you guys remember?


https://rennlist.com/forums/2251030-post73.html

URG8RB8

This is not an accurate statement for all applications. If you are running a highly modifided car or running E85 with high boost pressures, you will need a more stiff (higher spring rate) spring to keep piston sealed under heavy boost. Personally I had to remove the standard Green spring and go to the Yellow unit. I run 21 psi of boost on E85. Please see good link posted by Lart.

CurtP

Boost pressure from the reference line keeps the valve closed during boost conditions. Sometimes there has to be an adjustment to the spring pressure (either shimmed or stiffer spring). I am by no means saying that everyone can run the same spring pressure. But if you're relying on a stiff spring to keep it shut, then your reference line isn't sourcing from the correct location (i.e., ported instead of manifold). You should always run the lightest spring pressure allowed. You are not trying to match the spring rate to the boost pressure.

And if you've read ehall's post, he does NOT recommend running a piston-type recirculating valve in reverse orientation, which to me is saying to run the piston face on the pressure side, not the piston wall. I'm not reading it as reverse orientation to the factory installed position.

URG8RB8

Actually he does not reccomend nor discourage reverse orientation.

We DO NOT recommend installing the piston valves in reverse orientation. (Though it is not necessarily discouraged.)

However, I would always reccomend applying pressure to crown of piston as you have stated.

black944 turbo

Curt p I have the old evo unit, had for about 8 years and have run it the way zermat has it the whole time. I have never heard to run it the other way until now. Please provide a source that says to run it the other way. Btw, mine is all round and no 90 degree nipple. It looks identical to zermts.

To answer the original question the evo unit is great.

CurtP

I posted manufacturer's instructions in post 9. Wiki shows the piston face to the boost side in their diagrams, and most BOVs are made with the piston face to the boost side. Run it any way you want. As long as you never have an issue with your reference line, it'll be ok installed the other way. I'd rather have a margin of safety in case something happens (like forgetting to connect the reference line or the banjo bolt coming loose).

If you understand the purpose and function of a bypass/BOV, then it should make sense as to why the piston face should be oriented against the boost side. The only compelling argument I could see for running it the other way is for aesthetics.

black944 turbo

Got yeah, I will check post number 9.

TurboTommy

Virtually all recirc valves are designed to operate so that they open with the same ease in either direction of installation; the boost pressure from the intercooler pipe acts on the same surface area regardless if it's on the "face" of the valve or it flows in the other way
It is true that one should try to get away with the least spring pressure as possible; it improves the response of the valve and is very beneficial to the turbo. At full throttle there is no correlation between this spring pressure and the amount of boost that you're running. The only potential downside to a spring that is too weak is that the valve could open a bit during part throttle, slower acceleration.

URG8RB8

Curt P:

Please accept my apology along to any other readers of this thread. At my age I should know better than to make unfounded statements. Amazing what you can learn with a little reading and not believing everything you are told. My statement about elevated boost pressures is totally incorrect. I was given this information directly from technical line at Forge when installing my BOV, but I now realize it is totally incorrect. Spring pressure has absolutely nothing to do with boost pressure and everything to do with manifold vacuum and should be matched correspondingly to your particular manifold vacuum level at idle. (How to determine this exactly appears to be left out of the how to documents, however I found some good information on the Tial site) Furthermore, you want just enough spring pressure to hold the piston shut under full/maximum vacuum, which corresponds to your light spring statement. Please take a look at the link below for one of the best write ups I was able to find on the installation and functionality of a BOV. At least for their BOV's orientation is quite critical, and I still belive pre-throttle turbo boost pressure should be applied piston seal side and not to the skirt area, as this area is exposed to both boost and vacuum depending on throttle postion.

http://www.gfb.com.au/faqs/blow-off-valves

This is one paragraph out of the large document above, which pretty much sums it up:

How do I adjust the spring pressure to suit different boost levels?

You don't need to! At full throttle there is equal boost pressure on both sides of the piston, so it doesn't matter what boost level you are running, the pressure balances itself out. It then requires very little spring pressure to stay shut. The spring adjustment is used to match the VACUUM signal of the car. The idea is to adjust the valve so that the piston remains just closed at idle. This way, when you lift off the pedal, the spring will be neutralized so that the boost is free to push the piston open.

Information from Tial about how to match spring rate with manifold vacuum:

http://www.tialmedia.com/documents/BOVspc.png

Most likely only applies to Tial though.

Rick

I've got an Evo unit on my bench...as put on the car but removed after one weekend due to PCA club racing rules. I'll ship for $40 in the Continental US if anyone is interested.

Cheers,

Rick

CurtP

No worries, and my apologies if I came off sounding like an arrogant *****. I've been trying to not come off sounding like a KIA (know-it-all) but I haven't been doing a very good job as of late.

I used to run my bypass valve oriented the other way until a friend of mine, who is very knowledgeable about turbo systems, pointed it out to me. Of course, I had to prove him wrong. If nothing else, I learned quite a bit. I also lost all respect for Forge and no longer run their bypass valve or recommend them. Not saying they don't make a good product, but they're one of the proprietors of misinformation.

URG8RB8

Very glad you made me curious enough to do some research. I will now have to go back to the original spring, at least determine witch one goes with my vacuum at idle. Did you take a peak at the GFP write up? I think it is quite good and covers all angles.

CurtP

Yes, thanks for the link. My only complaint is they say bumping up the spring pressure to achieve the fluttering sound doesn't hurt anything - I disagree.