Who has suffered manifold backfire from too small BOV?

[douglas vincent]

Obviously I am different, but I still hvae a BOV/ABV like the rest of you. However, I have the occasional manifold backfire when I go REAL HIGH into the rpms in third gear and then dont continue into 4th. This tends to blow off the pre-throttle intake somewhere.

Anyone have this problem? I intend to get an atmosperic BOV one of these days.

[vrg3]

Why do you think the blowoff valve is responsible for the backfire?

[douglas vincent]

Cause it only happens when I shift out of gear and let off the throttle at 6k or so AND don't continue to accelerate. ie I close the throttle and have the SC spinning at 12000 rpm and no where for all that compressed air to go except out the little tiny supra ABV. The SC is essentially off at this point but there is the 1/2 second or so its still pressuring against the closed throttle body.

[vrg3]

Hmm. I don't see why that would cause a backfire, though... What would high pressure between the supercharger and the throttle plate do that would result in combustion happening in the intake?

What type of Supra valve are you using?

[douglas vincent]

Well, now that I finally tracked down my bad running problems to the coolant temp sensor, the wagon runs really really well considering its not supposed to be running on boost.

So I think I will leave it as is. If it aint broke, don't fix it. Aside from that pesky occasional backfire, I really don't need to fix anything finally (oh yeah, other than the leaking waterpump).

I will look for a picture of the ABV valve

[douglas vincent]

kind like this one

[vrg3]

Oh... You're using one from a 7M. It's basically the same as an EJ22T's except that it's got a metal housing instead of a plastic one.

See, I don't think your problem has to do with the blowoff valve. I think you're getting spark way too early when you're at high loads. A supercharged engine needs ignition timing to be much less advanced than a naturally aspirated engine.

I think that excessive advance is screwing with things. Like maybe the heat is causing preignition. When you back off the throttle at high RPMs, manifold vacuum shoots up and the charge is no longer being forced into the ports, and so the combustion of preignition manages to sneak back out the intake valve during the intake stroke.

If my conjectures are correct, then these backfires are a symptom of a bigger problem that might need fixing if reliability is desired.

I dunno, what do you think?

[douglas vincent]

It makes sense, I agree. However, until i actually can pull timing, I think I need to remember to just shift into the next gear and let the air escape through the exaust instead of the intake!

[vrg3]

You're my hero, Doug.

Maybe you could sell the Silvia Injectors and MSD FPR and use the money to deal with spark after buying an RRFPR.

Wait -- don't you have a DIS-4? Those don't do boost-dependent retard, but you could at least set up speed-based retard.

[douglas vincent]

The DIS-4 I have is has something extremely weird/broken going on with it and it randomly just dies. So I either need to send it into MSD to get fixed or sell it on EBAY and pick up a DIS-2.

Nah, I think I will keep the bigger injectors AND get a rrfpr and do the bleed off setup like you suggested. Since I am not getting detonation currently, I am going to attempt even more boost somehow (really don't know how easily though). I don't think stressing 270 cc injectors will send enough fuel to cover 12-14 psi.

[vrg3]

You're the boss... I don't think it'd be correct to say your engine's running safely despite the fact that you can't hear detonation yourself, and I also don't think EJ22E injectors would be insufficient for that kind of boost if you used, say, a 6:1 RRFPR, but I'm eager to see what you come up with anyway.

Instead of trading the DIS-4 for a DIS-2, maybe you could look for a J&S Safeguard. As I understand it, these guys can perform both proactive and reactive timing correction, while making you aware of detonation when they detect it.

[douglas vincent]

I actually had a J&S safeguard but never installed it because the J&S guys wouldnt get back to me on how to install it on a 90 ecu.

And I grant you that I may be getting detonation that I can't hear. The detonation that I used to hear on the two broken motors was most definately pre-detonation, the most destructive kind. But if I do toast these pistons, I do have that extra 2.2t block and pistons still. That reminds me, I need to get it back from the machine shop.

[vrg3]

Well, if you'd like a hand figuring it out I'd be glad to give it a try.

Yeah, I'm concerned about inaudible detonation, but I'm also concerned about things like, say, the cause of this backfire.

But, yeah, you can just swap parts when they break.

[douglas vincent]

I think we should start the Doug Vincent Charity Fund. This would purchase me engine management, a larger pulley and a rrfpr. The goal would be 225 whp with stock pistons. HAHAHAHAHAHA.

OK, this is really my dream. Don't laugh at me or I will cry.

[555BCTurbo]

Doug, you are the man, because you are navigating uncharted waters, and whooping ass at it!!!