Is a TBI intake true dual plane or is there a crossover?

[RichLo]

Ok, long title aside. I've recently been having problems with one of my injector plugs popping loose going over potholes.

I know what the problem is and how to fix it but since it runs decent when this happens I'm wondering if anybody knows if each injector supplies only 4 cylinders or if there is a crossover in the stock manifold at all?

The curiosity in me began two weeks ago when it first happened and I was able to limp home (about 2 miles) easily and found the problem after getting home. The coolant temp didn't move, the engine ran regular but weak, literally like a 4-banger but with extra drag. I was still able to get up to 55mph with a 5 speed.

So now, I've started wondering if the manifold is actually separated between injectors, if I could do an 'on command' cylinder de-activation like newer trucks to save gas when cruising?

Also, before anybody asks, I already have another engine in my garage to swap in and this is not a daily driver.

However, I also don't want to be stranded somewhere because I lean-melted a piston.

If it is a truely separated intake, I would like to try adding a switch to each injector plug and experiment a bit.

 

[Supercharged111]

I believe left injector feeds right bank and vice versa but don't quote me.

 

[DerekTheGreat]

I've always wondered about that too, but I'm sorry I can't add any information. I never thought about unplugging an injector though.

I'm not an engineer but I thought if one wanted to deactivate cylinders they also needed to deactivate the valves? Something to do with balancing & harshness related to a non firing cylinder & such if I remember right. Did you plan on retrofitting something to do that?

 

[Wade]

Here is an 89 TBI manifold.

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There is a crossover about 1/2" wide.

it looks like Right side feeds cylinder 3,5,2,8. Left side feeds 1,7,4,6.

 

[Schurkey]

I believe left injector feeds right bank and vice versa but don't quote me.

Sorry...you're quoted.

One carb primary venturi, or one TBI injector will feed the inside two cylinders on one bank, and the outside two cylinders on the other bank. This is standard operating procedure with a dual-plane manifold, since Fido was a pup. Look at the runners of the manifold--it's easy to see which is the upper plane of a dual-plane manifold. You'll see that the upper plane feeds an outside and an inside cylinder ahead of the throttle body. The matching inside and outside cylinders will be less visible behind the throttle body.

You disable one injector, and the O2 sensor will command wildly-rich mixture for the remaining injector due to excess O2 in the exhaust. Doesn't matter which injector you disable, two cylinders on each bank will be affected. (two inner, or two outer depending on which injector)

Fairly typical for there to be some minor interconnection between the two planes of the manifold. It can be built into the manifold, or it can be part of the throttle body base, or base gasket.

 

[DerekTheGreat]

Huh.. You learn something new every day. No wonder they can get away with just one O2 sensor. Any idea why there is some interconnection between the two planes?

 

[Schurkey]

Often the interconnection is part of a vacuum sensing port. They drill a port into a hole connecting both planes in order to get manifold vacuum from the whole engine instead of just half.

A PCV fitting would be installed so the fumes mix fairly evenly into both planes.

Another reason would be to increase the CFM of the throttle body--instead of two throttles/barrels/venturi each working half-time in alternating pulses, they work increasingly full-time as the connection between the planes of the manifold is increased.

 

[someotherguy]

*clears throat*

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Richard

 

[Gramps]

*clears throat*

Richard

So now that your throat is cleared, what’s your point?

 

[someotherguy]

Was there a point? U mad?

Richard