Blocking heat riser and effect on choke operation?

[Some Car Guy]

If you run an aluminum intake and block the heat riser, will the choke just stay on longer? Or never pull all the way off?

 

[toolmanmike]

If you run an alumnus intake and block the heat riser, will the choke just stay on longer? Or never pull all the way off?

Possibly. Most aluminum intake installs include a newer carb with electric choke.

 

[pnora]

If you run an alumnus intake and block the heat riser, will the choke just stay on longer? Or never pull all the way off?

For the most part both yes.

 

[Don Frelier]

I would go electric choke.

 

[Some Car Guy]

If I run electric it will stick out more. My car is all stock. I doubt many will notice the painted intake. Not one person has picked up on the extra wire for the petronix. I’m also sticking with the stock avs. This car drives heavy, noticeably more than my others did, so saving the weight would be nice.

 

[Some Car Guy]

I’m afraid if I don’t block it, the intake will warp.

 

[WileE]

I’m afraid if I don’t block it, the intake will warp.

Meaning that all the aluminum intakes we've installed without blocking the heat passage have all warped ?

 

[R413]

It will run like crap with the crossover blocked and a stock carb. It won’t have good throttle response until it gets enough heat into the intake.That intake heat atomizes the fuel.

and the intake will not warp either.

 

[Some Car Guy]

Hmm more Than a few guys have claimed damage from running an aluminum intake without it blocked. Would be nice to skip having a drone. I do remember my last car having a real bad one after blocking the manifold.

 

[Geoff 2]

Compromise. I often use a plate to block the exh xover, but drill a 1/2" hole in the plate to let some heat through.

 

[493 Mike]

I welded 1/4" aluminum plugs in my 6 pack intake. I have been using it for decades this way. I installed a manual choke. The stock choke thermostat adjustment can be loosened up to just close the butterfly and open sooner. You wouldn't block the heat riser passage if you were not looking for more performance/fussier cold operation.
Mike

 

[lewtot184]

I use the felpro gasket with the blocked heat crossover. I drill a hole in the blocked off part of the gasket to allow some heat. Your manifold won't warp from heat.

 

[Darter6]

running an aluminum intake without it blocked.

Never have I heard of that.Ever. The manifold maker would not have provided the cross over if it was true. Do you still have the exhaust heat riser in the exhaust manifold ? Even with it blocked
having the heat riser working will heat the head in the choke well area. Not like stock but it will supply heat .
Also I will ask where your cars weather and what time of year do you drive it ? I doubt that the choke will not open fully after the engine reaches operating temp on a hot summer day. You can check if the choke spring is adjustable,if so you can play with adjustment making it just tight enough to close and function.

 

[lewtot184]

I've done this a couple of times.

 

[Dave6T4]

I blocked the crossover on the stock iron intake on my 1967 R/T with no adverse effects on its drivability. I am using a 750 Eddie with electric choke. One positive result is that the cooler intake does not evaporate the fuel out of the carb as fast as it used to. After a drive, the hot intake used to evaporate the fuel in the carb pretty quickly, making my garage stink like gas for days.

 

[Cranky]

Never ran a choke on my junk and never warped any aluminum intakes.....but don't know how cold it gets in 'Online'.....

 

[WileE]

Hmm more Than a few guys have claimed damage from running an aluminum intake without it blocked. Would be nice to skip having a drone. I do remember my last car having a real bad one after blocking the manifold.

Ok, so that's the first time in 50+ years I've heard of an aluminum manifold warping due to the heat passage.

 

[AR67GTX]

I’m afraid I will be the devils advocate and get slammed here but I just swapped a different (used) L72 aluminum intake on my 427 Corvette and had bad coolant and air leaks and it was due to very uneven gasket surfaces (warped???). I actually have 3, used factory aluminum castings for the engine and after straight edging all three, I found all of them were uneven with the worst areas at the bolt holes and at the heat riser crossover.

The bottom one was the one I installed that leaked and it has never been cut. The one I removed is in the middle and it had been cut and port matched to L88 heads. I ran it for decades but when I installed it I ran a bead of RTV around literally every port on both sides of the gasket so it never leaked. The upper one is an old casting I bought but never installed, never cut and it too is uneven. It appears to me that bolt tension and heat around the crossover - at least on these GM aluminum manifolds does distort them over time. With feeler gages I found gaps On the lightly bolted manifold, of as much as .011” between the gasket and manifold. A straight edge literally rocked across the heat riser on most of these surfaces.

The good news however is it’s relatively easy to fix with a good sanding beam and some 220 SA sandpaper.

I blacked out the gasket surfaces with a large sharpie, and used a almost new 24” machined aluminum level with a 1-1/4” wide base and 220 grit, I block sanded the surfaces with a careful crosshatched pattern until the worst of the black areas were gone and the manifold would sit loose on the gaskets without any place that I could slip a .0001” feeler gage in. I did apply a light smear of RTV on the gasket at the areas that were still showing some black as a precaution, but the areas could not really be detected by straightedge so the gasket would take care of them. A straightedge sat flat now and did not rock across the heat riser passages. It seated fine now and I don’t have any coolant leaks (bad before) and vacuum is holding steady.

Just my experience with a Chevy. But I wouldn’t let that prevent me from running an aluminum manifold. And B-block engines have a simpler intake gasket seating condition without water passages so that even if there is some waviness, they could be easily dressed down before installing.

 

[Some Car Guy]

Ok, so that's the first time in 50+ years I've heard of an aluminum manifold warping due to the heat passage.

I was reading threads in the topic and sure enough it was mentioned. Heard it a few times in thirty years of doing this as a hobby.

 

[Some Car Guy]

Never ran a choke on my junk and never warped any aluminum intakes.....but don't know how cold it gets in 'Online'.....

car isn’t driven when it’s below 50-55 out.