Looking for '70 Anti-Backfire Valve Detail

[mdbrandy]

So it's alot like todays Idle Air Control Valve when the throttle shuts right? Primarily for decleration though ??

When you take your foot off the accelerator pedal, and the throttle butterflys slam shut, apparently there is a slug of very rich mixture that will then pass through the combustion chamber without burning. As it exits into the exhaust manifold, the air injection system on the carburated cars shoots fresh, cold air into this rich, hot mixture, and it combusts right there in the exhaust manifold - a backfire. The anti-backfire valve apparently "gulps" a slug of fresh air into the intake manifold to mix with that rich mixture, so it will combust in the combustion chamber, and then not in the exhaust manifold.

At least that's how I now understand it.

[PrOxLaMuS©]

hehe.. thanks I understand that

But when I was researching Anti-Lag systems on turbo rally cars.. they use a idle air control valve, so when the throttle butterfly closes, the idle controle valve opens and lets extra air into the engine..... now as the throttle closes the timing is instantly retarted about 40 degress and that air from the Idle Air Valve mixes with the fuel and ignites while the exhuast valve is open...

the resulting explosion with the exhuast valve open, spools the turbo while the throttle is closed... resulting in anti-lag =)

http://www.valvers.com/downloads/antilag.pdf

[sblake01]

Back in the day, we called them 'gulp valves'.

[frankfou999]

Attention all you 70 and early 71 owners! And the rest of you that enjoy getting into the nitty gritty details.

I have a '70, blt 6/70 and the A-B valve quit doing its thing. This is a show car, so I trying to replace it with as correct of a part as possible. I got a hold of an NOS valve, P/N 14835-25601, which is supposed to be good up to 6/72. However, it doesn't look the same as the one that came off the car. My early 71 has a valve that is identical to the one on the 70 as well.

If you look closely at the picture below, you can see the differences. The one on the left is the one that came off the car. As you can see the input/output nipples are reversed on these 2 versions. The center nipple is also offset on a 45 degree angle on the new one I got.

So, which one do you have on your car? Plese specify the yeatr also.

Thanks,

Marty

The one on the rigth is the same than the one I have on my 12/71 '72. I part out a 8/71 '71 last summer and it's the same. So unless the early '70 has different valve I would think the rigth one is the good part.

[Go240Zags]

I am missing this valve, as well as the air pump. A previous owner had installed webber downdrafts, which are coming out and 70/71 SUs will be going in. Should I find an airpump and anti-backfire (gulp) valve or just leave them off? Will this help with performance, or should I try and mimic what came on the car from the factory? What are your opinions?

[mdbrandy]

I am missing this valve, as well as the air pump. A previous owner had installed webber downdrafts, which are coming out and 70/71 SUs will be going in. Should I find an airpump and anti-backfire (gulp) valve or just leave them off? Will this help with performance, or should I try and mimic what came on the car from the factory? What are your opinions?

The air injection system is part of the emissions control system on the carburated Z's. It injects fresh air into the exhaust manifold to help lower emissions. It is not a performance enhancer, but except for a small drag for running the air pump, it doesn't hurt either. And it does help keep our air clean.

And you need more than just the pump and AB valve. you need an intact air gallery (tubes connected to the exhaust manifold), a check valve into the gallery, a "T" connector and several short hoses, as well as a large hoses from pump to check valve. Oh, and the hose from AB valve to intake manifold. I think that's it. I'm doing this from memory...

So, if you're restoring it, or like clean air, put the system back! But look into what parts you need before you start. Some are NLA new.

My 2 cents.

[Go240Zags]

The air injection system is part of the emissions control system on the carburated Z's. It injects fresh air into the exhaust manifold to help lower emissions. It is not a performance enhancer, but except for a small drag for running the air pump, it doesn't hurt either. And it does help keep our air clean.

And you need more than just the pump and AB valve. you need an intact air gallery (tubes connected to the exhaust manifold), a check valve into the gallery, a "T" connector and several short hoses, as well as a large hoses from pump to check valve. Oh, and the hose from AB valve to intake manifold. I think that's it. I'm doing this from memory...

So, if you're restoring it, or like clean air, put the system back! But look into what parts you need bef

ore you start. Some are NLA new.

My 2 cents.

Thanks, Mark. Looking at my FSM I see I still have the air gallery pipe on my Z as it is now, it appears to be capped off at where the check valve goes. I also have an extra pipe from a parts car. Like you said, I will need the air pump, check valve, A.B. valve, a Tee and some hoses I guess. I've got nothing against clean air just was curious about the need for the air pump, I'd rather have it than not. Just a little worried about coming across the right parts. I'll keep an eye out on eBay I guess, I never thought to look for this stuff at the wreckers because every 240Z I've come across that has the engine intact is missing the carbs and that's as far as I've looked. Want to get back to a semi-original look. Since I don't have the matching #s motor I've decided to put in an L28 F54, flat top pistons, (N90/E31/E88 head) with the SUs mounted on the N36 manifolds with a fairly early Balance Tube missing some of the extra connections of the later ones -- not quite as clean as the "Euro" balance tube, but a little cleaner than the other ones I've seen.

Another question, does the air gallery pipe hook up to the factory headers? If so, and you go to after market headers can you still use it? I need to go back out into the garage and look again.

[Bambikiller240]

Another question, does the air gallery pipe hook up to the factory headers? If so, and you go to after market headers can you still use it? I need to go back out into the garage and look again.

Factory Headers? What are these?

[mdbrandy]

Another question, does the air gallery pipe hook up to the factory headers? If so, and you go to after market headers can you still use it? I need to go back out into the garage and look again.

Factory headers? If you mean the cast iron factory exhaust manifold, then yes. Otherwise, I'm out of my element. My 240Z had headers on it when I got it, and the PO had dispensed with the entire air injection system and exhaust manifold. I have subsequently bought all the parts needed to reinstall it when I get to that time. I actually found an NOS, brand new air gallery on e-bay, and got a new check valve and the big hose from Midwest Z before they disappeared. Anyway, I've seen headers advertised with and without emissions fittings, and I assume 240Z headers with emissions fittings would be for the air injection gallery, but I have no personal experience there.

[Go240Zags]

Sorry, meant factory exhaust manifold not headers.

[Bambikiller240]

Gary:

There are small tubes (located in each runner of the manifold) that stick into the exhaust area of the head. On the outside of the ex. manifold the "Air Galley" screws into each runner. At the forward end of the Air Galley a Check Valve is attached. From there you get into the small hoses, T fitting, A/B valve, etc.

I may have a spare smog pump. PM if you are interested.

[Dreco]

edit oops I thought I was starting my own thread haha