Bov
 

i was looking to get some advice on BOV options, i have a twin turbo SBC with a 700r4 trans, i currently have no BOV and if the turbos spool up and take my foot off the gas i get a chatter from the turbos. should i add a bov to help provide relef to the turbos or does it not really matter running a auto trans.

Thanks Joe

I think you need a bov, really hard on the impellers without it. I'm running a single Tial 50mm on mine, not sure if that's enough yet, but it should be.

Jody

Carb'd or EFI, you need them- they are mainly for your safety. The Tial 50mm is a nice piece (I'm using it as well).

As mentioned they are a must have on any forced induction setup. Otherwise you will get compressor surge as you are in a best case scenario or break something on hard decel as a worst case deal.

I use a lot of Forge BOV's and recirculation valves depending on the application. They are billet aluminum and can be setup as a release to atmosphere or reciculate if used behind a MAF sensor. For install they can use either a 1-1.25" nipple to go on a hose, a weld on fitting or there are a couple flanges available.

I am trying to attach a couple pics. Prices are genrally $125-175 shipped in the lower 48. Hope this helps.

Mike Norris

Depends on the amount of boost, volume needing to dumped when the throttle closes, etc, you may be OK not running one... but it's always a good idea to have one. A BOV is pretty cheap insurance for the turbo, so there really isn't a good reason not to run one!

Argument on the flipside though: Buick GN's didn't have a BOV from the factory and the factory turbos could last years and years and well over 100K miles with zero problems. Then again they had an automatic tranny so you're not stacking up the air on every shift as you would with a manual tranny and their intercoolers and total piping volume are rather small so they didn't surge all that badly in stock form if you snapped your foot off the throttle when at WOT.

Cheap insurance
 

your going to want one no matter how little boost you are running. The pressure build up when the throttle blades slam shut will break stuff.

If you dont want the sound, you can run a recirculation valve and dump it back into the intake piping behind the air filter.

Thanks for the information, i have one more question i have a two into one piping off two seperate intercoolers, do i need one BOV on each, the pipes merge at the throttle body. i only have about an inch or so of combined space on the boot/clamp. i have attached a pic.

Thanks Joe

duals
 

i would run a smaller bov on each tube unless your running a lot of boost then i would say due twin tials or turbo smarts.


there is very little area for the preasure to pass from one tube to the other there so i would think it would be very hard on the Tbody unless you ran duals on each pipe


also the cheapo chinese tial copies work just fine and save you about 120 bucks per valve heh

Thats is what i was thinking, i will go with the two BOV right before the merge at the throttle body. Thanks for your ideas.

The other thing you could do is fab a small merge pipe before the TB and mount a single BOV... it'll be a lot cheaper.

Or you could mount it on the intercooler

Marty, he's running twin intercoolers (so he'd still need 2) and by his description I don't think there is any commonality between all the piping until right at the throttle body entrance.

Opps - I missed that post.

bov
 

Thanks Guys, i think i like the crossover tube with one BOV, i could place it on the bottom side of the pipes, it would not be the first thing you see looking at the engine. Also i had some concerns about setting up a dual BOV, how do you get them both to pop at the same time. I would think it would be a pain in the butt to dial them in properly without the car on a dyno.

Thanks Joe

most oem setups do not use blowoff valves.
there are a ton on the market, including some real monsters from ati procharger and vortech.
they're much less critical in a turbo app then a centrifugal blower app as turbo rpm rapidly falls off with throttle while blower boost is tied to rpm.
if you need nay help or advice feel free to contact me at my shop.
hi marty,
what ya been up to?
i'm gonna sell off my syclone soon...it's been parked 3 years now, kinda lost interest.
-mike
rockville speed & custom
estd. 1972
301-279-0070

Most OEM cars use MAF-based PCM's and thus use recirculating blowoffs so metered air is not lost (unlike aftermarket dump to atmosphere setups)... turbo cars from Volvo, Subaru, Mitsubishi, Saab, Audi, VW, etc, all use recirculating type blowoff valves. I can't think of any OEM turbo application that didn't use a blowoff valve of some sort except for mid 80's Buick Grand Nationals and some other 80's stuff. Any 90s and up factory turbo car I have ever worked on or checked out all used a bypass/blowoff valve of some sort.

If the OEM's could save a few bucks and skip the blowoff valve, believe me, the beancounters would axe them... so the engineers have a good reason to put them there.

some of the many many examples of domestics without bov's include the syclone/typhoon, svo mustang, turbo coupe, merkur, all the dodge products using 2.2/2.5's, the 1.8 turbo gm sohc cars, 2nd-gen turbo trans am, 3rd gen turbo trans ams, etc.
not arguing their usefulness, just their necessity on mild turbo applications.
to this day, even on low-boost Vortech/similiar centrifugal blower kits, a BOV is not included.
it is part of higher boost kits and kit upgrades to high-boost.
on maf vehicles, the recirculating bov's create driveability issues when not oem-engineered due to maf backflow.
when i changed my procharged mustang to externally vented double bov's the driveability went from unacceptable to almost oem-like, as an example.
a new company, abaco, has released a brilliant digital maf that can be digitally filtered to ignore backflow, among other neat features.

compressor surge simply isn't a critical issue on small, responsive turbos set for low boost with typical oem short intake tracts.
any serious turbo effort should incorporate them.
any serious centrifugal effort should use as many, as large as possible, units as possible.
lastly, euro cars gravitated toward them because they, regardless of turbo app, reduce lag between part-throttle shifts.
auto trans vehicles don't have this particular issue.