Newbie question anyone use a BOV?

[matty74]

Just wondering if anyone uses a Blow off valve on their 911 turbo's?

do we need them and is it a good idea to have one?

Matt

[matty74]

any pics? what type should I get for a single turbo, KKK 7200, running .8 bar, efi on a 3.6, what kinda $$ should I spend?

Matt

[turbobrat930]

Correct me if I am wrong, but isn't a BOV on a CIS car a bad thing?? You are venting metered air.... In an EFi car, it is not bad as you have the O2 sensor, and the MAP sensor to keep the A/R ratios in check. I would think venting the air after the metering plate would cause a pig rich condition....... Or are we talking such little air that it makes no difference?

A CIS car has a recirculating valve as stock equipment..... which does the same job as a BOV, but it reintroduces the metered air back into the flow instead of venting to atmosphere.....

[turbobrat930]

Originally Posted by Shadetree930

May be a semantics issue ..... but anyway, you do want some way to relieve excess boost pressure ...

Blowoff valve - Wikipedia, the free encyclopedia

I agree, compressor surge is a bad thing...... but the 930 does this in stock form, and vents the metered air back in before the turbo...so the air is still metered.

[mark houghton]

Originally Posted by turbobrat930

I agree, compressor surge is a bad thing...... but the 930 does this in stock form, and vents the metered air back in before the turbo...so the air is still metered.

You are correct. Venting that already metered air to atmosphere in a CIS fueled system will cause pig rich conditions when shifting. With EFI, not an issue.

With that said, many of us are using the updated BOV's in place of the recirculation valve that comes stock with CIS 930's, but we're still plumbing the boost air charge back to the front of the turbo so as not to generate the pig richies.

[pkracer21j]

I vent to atmosphere on CIS, I've been doing so since 2002. so you get a little more flamage, and some excess fuel to cool off the heads. meh, not bad things if you ask me.

[jwasbury]

^^^Ahh. The "secret" of Pete's decel flames finally revealed!

[turbobrat930]

Ahhh, ok, I guess it is not that big of an issue then.... Coo, well BOV away then!! LOL

[matty74]

Originally Posted by jwasbury

^^^Ahh. The "secret" of Pete's decel flames finally revealed!

whats the trick to getting decel flames on EFI?

[smurfbus]

add fuel on decel or just vent your BOV to atmo and maybe retard the timing too on decel. Have an extra rear valence/bumper as a spare.

[krasuskyp]

Originally Posted by pkracer21j

I vent to atmosphere on CIS, I've been doing so since 2002. so you get a little more flamage, and some excess fuel to cool off the heads. meh, not bad things if you ask me.

^troof^

and the sounds added to his already fantabular repetoir of audible awesomeness are to addictively *behold*!!!

schweeetahhh!!!

8-)

There certainly is _A_LOT_ goin on back thar... good thing

cause

there most certainly isn't much going on

UP thar (driver's seat, upstairs)

of course I mean... when I was havin at it... yeah that's it

heh heh heh

[gsmith660]

I think I am going to use this one

[911st]

Matt,

A K27-7200 on a 3.6 with C2 cams or better and EFI is not a good fit and may not even be able to hold .8 bar to red line. You are talking about a motor that has 450hp+ potential and putting a sub 400hp turbo on it. It can support up to a max in some cases to 425hp but not efficiently.

To get flames you need fuel. CIS keeps sending fuel on overrun but EFI mostly dose not. You would have to program in fuel on overrun as noted above.

Venting to atmosphere with EFI probably will not do any thing unless you are doing a blow through system and put the BOV after the AFM / MAF.

Mostly making this a goal is not a sign of a good EFI build, will not add any HP, and make for early turbo ware.

There is an anti lag strategy that plays with timing and sends fuel to the turbo and turns it into a turbine bit that eats turbos.

[matty74]

911st - your talking sence and i apprciate the advice, I was going to use the 7200 because I had one available, I may as well bite the bullet and get a K27 HF thats what Brian recommended.

[smurfbus]

Originally Posted by 911st

CIS keeps sending fuel on overrun but EFI mostly dose not.

Air metering is the key here even with EFI.

[911st]

Yes but it depends.

Where is the BOV. If it is a C2 style blow through conversion the BOV is usually before the AFM and no effect.

If it is a 993 based conversion it should be converted to a suck through to protect the MAS wire. So the BOV should be after the metering function. However, these cars have TPS, when the TPS signal's low throttle angle at an elevated RPM fuel it usually cuts back fuel based on the cell value.

With a stand alone EFI, most turbo's are MAP sensing after the throttle body so the BOV is not going to be able to be located where it can effect AFR's. However, fuel can be programed where ever or how ever you want it.

On an MFI or CIS car the popping and flames are kind of part of the ambiance. Doing this on an EFI car for the effect is as the potential expense of premature turbo ware.

[pkracer21j]

Turbos are wear items.

[Cobalt]