Exhaust Block Off How To

[RustyRatRod]

Yall can make this a how to in the how to section......or not. I don't really care. Just thought I'd share "what I did", so here it is.

Since I have the manifolds off my 170, I got to thinking about exhaust manifold heat in the intake manifold. I live in Georgia, so I don't need manifold heat. I've blocked it off in almost every V8 I've owned, my 75 Ford F250 included.

So it's real simple. Find a piece of scrap metal. It cannot be "too much" thicker than the tin gasket that fits between the intake and exhaust manifolds, because misalignment will occur. I just used a piece of a late model Pontiac Grand Prix fender I had layin around. Who says Pontiacs aren't good for somethin? I hammered it out flat on the vise. Then laid a tin gasket I had for the intake and exhaust manifolds on top and sprayed black spray paint over it like this:

If you look close above, you can see I've already center punched the future holes.

Now over to the drill press, and I drilled out the three holes. So this is what we have now:

Finally, I trimmed it down with my angle grinder. You have one, right? If not, turn in your man card and immediately get rid of any vehicles you have, because you are not a serious car guy, you're just a poser. I will clean up the rough edges and blast and paint it with some high temp VHT. I'll use red high temp RTV to seal it good. It'll probably out last me.

 

[RustyRatRod]

Here it is blasted and painted with VHT FLAME PROOF flat black. It ain't purdy, but it'll do the job.

 

[65 Cuda 340]

Your experience may differ, but a many years ago I blocked the heat riser in my 66 Barracuda when I converted to a two barrel carb. Big mistake - took probably ten miles of driving to warm up enough that I didn't have a BAD off-idle flat spot. I've blocked the heat riser on V8s no problem. Either the carb sitting over the engine lets a V8 carb/intake warm up more quickly, or the V8 has enough surplus of power to sip past any off-idle flat spot, or both, can't say. But that slant was an aggravating car to drive in stop and go traffic until it completely warmed up. I've run a stock heat riser flap on slants ever since. And, when the motor is warm, the flap should be closed and pretty much block the heat anyway.

 

[Mike69cuda]

If you have a v8 with a mechanical choke in the manifold, it will never open if you block off the heat riser ( my experience). If you have an electric choke, no problem.

 

[MOPAROFFICIAL]

Your experience may differ, but a many years ago I blocked the heat riser in my 66 Barracuda when I converted to a two barrel carb. Big mistake - took probably ten miles of driving to warm up enough that I didn't have a BAD off-idle flat spot. I've blocked the heat riser on V8s no problem. Either the carb sitting over the engine lets a V8 carb/intake warm up more quickly, or the V8 has enough surplus of power to sip past any off-idle flat spot, or both, can't say. But that slant was an aggravating car to drive in stop and go traffic until it completely warmed up. I've run a stock heat riser flap on slants ever since. And, when the motor is warm, the flap should be closed and pretty much block the heat anyway.

Tell that to all of us who have run headers on a slant..ain't no thing. 10 miles is pretty exaggerated.

 

[RustyRatRod]

If you have a v8 with a mechanical choke in the manifold, it will never open if you block off the heat riser ( my experience). If you have an electric choke, no problem.

I live in Georgia. What's a choke?

 

[RustyRatRod]

Your experience may differ, but a many years ago I blocked the heat riser in my 66 Barracuda when I converted to a two barrel carb. Big mistake - took probably ten miles of driving to warm up enough that I didn't have a BAD off-idle flat spot. I've blocked the heat riser on V8s no problem. Either the carb sitting over the engine lets a V8 carb/intake warm up more quickly, or the V8 has enough surplus of power to sip past any off-idle flat spot, or both, can't say. But that slant was an aggravating car to drive in stop and go traffic until it completely warmed up. I've run a stock heat riser flap on slants ever since. And, when the motor is warm, the flap should be closed and pretty much block the heat anyway.

Since the best manifold I have already had the flapper removed, I don't really have a choice. It was either run without the block off and run heat to the manifold all the time or block it off. I chose to block it off.

 

[nitro_rat]

I would try to maybe weld a curved baffle to the plate to fit inside where the original went. This will help direct the flow out the exhaust instead of stagnating in the riser area.

Dan will be along shortly to tell us how we're all gonna die without properly functioning heat risers...

 

[MOPAROFFICIAL]

Don't overthink it.
Good ideas sometimes just dont pan out.
Perhaps the volume in that area is a good thing, I really have no testing to know one way or the other. Just a thought.
The curve plate sounds good, could drill -tap the side to go through plate to hold it inside, nik the threads so it never comes off on it's own. Keep it very tight to the wall of the manifold.

 

[nitro_rat]

The dead air without a curved baffle will build up a lot of heat and burn out the flat block off in short order.

Probably no noticeable power difference either way until the flat plate burns out and boils the fuel out of the carb.

 

[RustyRatRod]

I would try to maybe weld a curved baffle to the plate to fit inside where the original went. This will help direct the flow out the exhaust instead of stagnating in the riser area.

Dan will be along shortly to tell us how we're all gonna die without properly functioning heat risers...

I thought about him. But it's funny, everything's just fine when he recommends Dutra Duals all the time.....they have zero provision for manifold heat.

 

[Demonracer]

I live in south Texas, no choke & the exhaust cross over on all of my intakes are blocked off.

 

[MOPAROFFICIAL]

I thought about him. But it's funny, everything's just fine when he recommends Dutra Duals all the time.....they have zero provision for manifold heat.

Exactly

 

[RustyRatRod]

And as far as the factory flapper that's there, if some of yall magically think somehow it completely seals hot air off the bottom of the manifold when it's "closed" I got some acreage on the moon goin real cheap. And as for this piece I made burning through, I think it'll last a good long while, especially since it's almost as thick as the flapper itself. This is a how to. It's not askin opinions. I'm doing it so that's that. lol