Do I need a different blow off valve?
 

Just bought a 94 DIY turbo miata with a Borg warner efr 6258 (http://www.full-race.com/store/turbo...258-turbo.html) setup running 12 psi. The tuning seems to have been done very well, but I'm getting a pretty bad "chuffing" noise even when the bpv activates at higher boost pressures. I'm nearly certain that the noise is the compressor seeing the back pressure from the closed throttle plate like it's not _supposed_ to see. This also makes transitions between gears difficult because it immediately kills my turbo momentum and I have to respool.

The bov (actually I believe it's technically a bpv) is a flying miata unit that he bought used some time back. It has a little filter on it and I think instead of just using a proper bov he just venting a bpv to atmosphere.

FYI, additional details about the car can be found in my meet and greet thread. https://www.miataturbo.net/meet-greet-40/miata-noob-saying-hi-59080/

Any suggestions? I'm going to start by lowering the boost to 10 psi because I don't like what it's doing. I've heard the same noise on turbo cars with no bov or bpv, so I'm sure it can't be good.

Why aren't you using the built in bov
On the efr?

Well the po never set it up that way, but he did mention it as an option when I questioned him about what the block off plate on the compressor housing was. He gave me the associated parts to set it up, but as I've never seen a setup like it before, I wasn't comfortable just setting it up without more info. Would it be superior to the bpv that's on there now, you think?

It's the setup that Borg warner created to solve the exact problem you're talking about on race cars. It's supposed to be amazing, but no Miata people have reported on it yet.

Gotcha. I just installed the built in bov today, but now I'm having problems with an exhaust leak that I can't pinpoint, so I haven't gotten a chance to test it out yet. Will report back when I try the new setup.

If it doesn't work as I hope, would I be better served with a beefy bov as opposed to the old bpv that I previously used?

The internal BOV on the EFR is used for nearly all their models and works for 30~psi or whatever the turbo is rated for.

It's a very good unit according to Geoff @ Full Race.

Those 'on turbo' BOVs have been around for a long time. The version the EFR turbo uses is the same as that run on Vauxhall/Opel engine in Europe. They have excellent repsonse, however they do fail regularly - the rubber diaphragm splits. Talk to Forge Motorsport about the FMDVK04D valve which is a bolt up replacement with an aluminium piston www.forgemotorsport.com (its not listed on their US website as its a part made for Europe only)
I should point out that i work for Forge so am biased, and that there are other aftermarket options available e.g. EVOMS.

Thanks for the tip!

I did install the built in unit the other day and the response is amazing. It's lightning fast and I experience none of the issue that I was getting before. I may sell the FM BPV and see if I can put the money toward an aftermarket built in solution like the one lloydie mentioned.

Here it is on the Forge UK wesbite in case anyone searches in the future:

http://www.forgemotorsport.co.uk/con...oduct=FMDVK04D

If anything users have reported improved response over and above the OEM valve.

The product page says its good for stock or mildly tuned engines. Can you tell me what max boost pressure this rated for?

Its good for mildly tuned engines as shipped - the springs are interchangable. But Forge can supply springs that will support 25psi static (i.e. with boost only acting on one side, which isnt how it works in the car) which would be 35~40psi on the car, with boost acting on the top port too. I cant say an exact figure as we've never shipped one of these springs!

Confused as BOV springs are rated by vacuum, not boost...