32k hard miles stock twin t25 turbo lotus esprit no bov,

19k on stock single t3 and another 10k with 60-1 turbo upgrade on older esprit no bov,

the turbos r not even 360* bearings they r old style and no problems,
they spool the same with great responce between shifts

on the 60-1 the car makes more swoosh noise between shifts from the turbo then my fd
with 50mm tial

I haven't tracked it or dragged it because I need new tires to do that and at this point I need new wheels to accomodate a bigger setup. I have done some 2 lane backroads driving (think Deal's Gap but more tame), I've done a lot of round town and some highway stuff.

xcept the 60-1 is 360*
by hard miles I mean

http://www.youtube.com/user/mammamia.../7/AuuV7hdu2A4

http://www.youtube.com/user/mammamia.../9/d06tJJJrfVg

http://www.youtube.com/user/mammamia...10/fFpMFfpvLQg

I thought I was being clever by tapping the ACV blockoff plate on my 2nd gen as a source for my BOV, but I made a mistake.

There are three areas on the 2nd gen turbo ACV flange, which is located on the side of the LIM. The bottom left of the blockoff plate would go is where the ACV supplies secondary air to a passage for the split air pipe to the cat. The bottom right supplies air through another passage in the LIM to the exhaust ports (port air). On the top left of the 2nd gen ACV flange there are several small holes that lead directly into the LIM runners and can serve as a vacuum source. This is for the anti afterburn valve. The anti afterburn valve supplies secondary air to the intake manifold when the throttle closes in order to prevent backfire (FD's do not have this, the ISC valve does this function instead).

Well basically I tapped into the port air passageway in the LIM because I didn't know what I was doing. My manifold vacuum source was... the exhaust ports :wallbash:

To add more to the conversation.

Customer car


RX7 GEN 1 13B Turbo GT3582R 28psi of boost just over 70 laps at a circuit track at full power.

No blow off valve. Turbo has already seen 10-15 000kms o use previously and another track day before that too.

Turbo is in excellent condition.

So what exactly is the advantage of running without a BOV ignoring the possibility of a leak? I'm curious now lol.

thewird

delete

rx72c feels there is some kind of improvement from not running a BOV. From my experience I don't think it makes much of a difference either way. That's the whole point I've been trying to make... do some google searches on blowoff valves and you'll inevitably see somebody on some car forum panicking about "compressor surge" from a blowoff valve not opening. I can tell you that the experience of no blowoff valve has been... underwhelming. The car drives the same, although it sounds a little different.

To the arguments about a loss of response I say: once the throttle's shut, the turbo is going to have to be spun back up to speed no matter what. With the throttle plate closed, there's only going to be a trickle of exhaust gas flowing to the turbine wheel. And that's not going to cut it:

https://www.rx7club.com/attachment.p...1&d=1264821349

That's a T3 35R turbine map. It's kind of hard to get 15 or 20 lb/min of flow through a turbine wheel with the throttle shut. It's like trying to turn a sizeable water wheel with a garden hose: there may be some movement of the wheel, but it's not going to accomplish anything because there's not enough flow.

I'm not suggesting we should all throw our blowoff valves in the trash. If you like your blowoff valve, keep it as long as it's not giving you any trouble. Just don't think of it as some kind of a performance mod. Get an automatic transmission if you want to keep boost between shifts.

I always thought of a BOV as a device to prolong the life of your turbo and nothing else. Reason why I have it between the turbo and the intercooler as opposed to just before the throttle body to "keep the turbo spooled". I think the performance aspect came from the companies that sell the BOV's :P

thewird

For arguments sake; On a diesel it when you let off throttle it takes well over a second to loose manifold pressure, I would say thats an accurate idea of spool down time on a T4 turbo. So the argument that because you loose most of the exhaust flow across the turbine and loose all your boost doesnt really add up because left on its own the turbo will take time to spool down.

This too is my reasoning. Especially with today's dual BB turbo's. This thread is very interesting. I am working on my single build & this information definitely caught my eye.

I would like to hear from more info from experienced builders.

Great stuff guys...

This is true, but on a throttled gas engine you still have air slowing the compressor wheel down whether you have a blowoff valve or not. A blowoff valve relieves pressure but it can't possibly release all the extra air in the intake tract that is slowing down the compressor wheel after the throttle shuts.

Oh, and I finally found one OEM source claiming that blowoff valves are to improve longevity. It's in a service highlights style document for the BMW N54 biturbo motor (current 335, 535 etc). Now those are very tiny turbos, I wonder how much of a role that plays? They are twin TD03-10T ...which make the FD twins look like GT42's.

Again I am going to keep driving the car like this just to see what happens (won't get to put miles on it for a few weeks though with the weather and other stuff going on). I basically have the least reliable setup on paper... oil cooled with no BOV. So we'll see if I notice any problems.

Im not going to run a bov neither. I suppose i dont have no real reason besides i just dont feel like buying one. i could care less if the turbo spins backwards upside down whatever way when the throttle is closed.....the throttle is hardly ever closed......

The RE cars don't run them either...can listen to them on YouTube as well. I have run it both ways...as long as you have a shaft with reverse threads, shouldn't really hurt but I have loosened the nut that holds to compressor wheel on if it's not reverse thread by not running a bov on a cheap turbo(s)

But I do like the sound without one alot better :)

Just a quick thought. I don't see a reason to argue, ( Not that anyone is arguing) But woudl it be possible that the BOV isn't a performance modification, But maybe an emmisions control device. How have you guys been doing at the sniff test, ( If your state has that). I'm just curious. Thought in delaware they only do an idle, and high idle test, no dyno. Just a bit of irrelevence to add to the subject. lol.

No plans to run a BOV here either with a GT40R turbo. Everyone knows what sound a BOV makes but does anyone know how much air each will flow? It's funny that it's job is to vent air but that's not their selling point.

I don't run a BOV on my half bridge using a BW S362 ETT. Pulls strong and hard and shaft play still feels the same when I purchased it brand new. I have the anti-surge housing, I don't hear it surge much at all, just whine down quite loud :)

on a MAF sensor based car not having a BOV may confuse the sensor and result in backfiring, rich condition, high HC emissions, etc. That is speculation however.

THEIR IS BETTER RESPONSE BETWEEN GEARS.

NOT SOMETHING I FEEL.

Considering my car has a gt42rs on it every little bit of spool makes a difference.
With a bov my car would need to rebuild boost all over again between gears unless i flat shifted and never came off the throttle.

Now with no bov. THe turbo comes straight on between gears and takes alot longer before it has to respool.

Oh, forgot, we tested, with GPS timing gear (Datron), on a 400bhp+ Pulsar GTIR running a GT30 ball bearing turbo, the acceleration times running without, with a recirc, and with a VTA dump valve.

No and behold, it was fastest with none at all. Not by much, but even companies selling them rarely if ever claim performance benefits anymore as they know it dont happen

Always feels that way on the countless cars ive ran too.

Reason you never see them on modern turbo racers ran by big money works teams is for this very reason- They either do no good at all, OR any good they do do is outweighed by the fact they give more things that can leak and go wrong.
Same reason almost no serious race cars run water cooling on the turbos, in fact a hell of a lot of rally cars that are homologated to run with the stock sized turbo have the water cooling removed for the race cars.

Isn't this kinda like smoking? You can smoke your whole life without much side effects (other than smell and voice), and then one day 40 years later you die of cancer? But then some people smoke and never die of cancer?

I mean physics tell you that the compressed air has to go somewhere, at the end of the day though it may not make a huge difference, but the BOV was invented for a reason if it had no reason then car manufacturers (other than Nissan and the 300zx) wouldn't waste their money putting in BOV or other types of relief valves.

Already pointed out, emission reasons...

like I always say it also depends on your application. You run your car without a blowoff valve and I have to run my car with 2 of them. with only one it was still surging to the point that the compressor wheel nut came of and jammed the wheel to the housing. fixed the turbo. had to get a bigger wheel and cut the housing (special thanks to mike turbo!!!!) added an extra BOV and solved the problem. again Im only running with 27 PSI of boost!!!

I've had a nut come off of a compressor wheel with a BOV that was correctly functioning, and that was with 20psi. I would say the fact that yours came off is indirectly related to the BOV's function or lack there of.

Very interesting. I'll keep mine because it sounds cool.

I'd love to see a comparison with/without datalogged on a turbo tach.

You've got an extra $425 laying around to spend on data, I presume? :)

http://www.034motorsport.com/product...ducts_id=14007