Any advantage or disadvantages to blocking the heat passage in the intake manifold?

Any advantage or disadvantages to blocking the heat passage in the intake manifold of the 425?

If this is the route to go, what is the preferred way to block them? Just weld them closed, or fill in the whole passage?

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

For a race car ONLY!!!!! The car will hesitate BIG TIME if you block the heat in the manifold. Only block the holes in the manifold that run under the carb.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Dont do it,,,,, the engine will not run as good and gas mileage will go down.... that manifold only runs at 127 deg. on a fully warmed up engine with the passages open and working.... i use a heat shield/adapter plate that I use on my 425 that I made out of 1/2'' cold rolled steel and leave the heat in the manifold.... my car gets 18 mpg on the highway....
Tom T. takes a slightly different approach and puts plugs right under the carb and leaves the lower part of the manifold warm to make the fuel flash into a vapor inside the manifold....
Either way will work good,,, allowing the fuel to flash into a vapor inside the manifold....
Completely blocking all the heat out of the manifold would be a race only/high rpm situation....how do I know?? I tried it and the car did not run good at all and i could not tune it to where it would run good.... when I put the heat back in the intake , all the problems disappeared.... the car ran strong.....

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Greg Gessler's Level3 NH porting for "Street Performance" blocks all exhaust ports in the cylinder head for improved flow performance. No heat getting to that intake manifold, and supposed to be a performance street car.

you could call him and ask how you get a car to run with out heat to intake manifold. Probably has ideas on managing this with his cyl head porting experience.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

I use Tom's approach, but Doc's will work too. With the heat passage holes plugged under the carburetor base I have had no operational problems that relate to the carburetor or engine temperature.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

greg did my heads with block offs, in 50 degree or colder the car runs just like tom and doc said, was breaking up off the line.tried to run the heater hoses under the intake but that did not help.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Just went through it myself - was using heat riser block off intake gaskets, but car would stumble badly off the line.

Restored the heat all the way to the carb, problem solved.

I might experiment with blocking the ports below the carb this spring, I've heard of people blocking the heat at the carb base temporarily with tinfoil.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

I used the same approach, works good!

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

I wonder if there is some sort of heated carb spacer that could cure that problem? Doc, don't some Fords have EGR plates.... could those be made to work as heaters?

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Dont know,,,,, many years ago, ford/holley had a spacer that had engine water running thru it.....but why go that way???? I thought about it, but decided that Buick had the best idea all along.... I just went to the thick steel plate... no fuss no muss.....

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Completely understood. I've read threads where people have blocked them, but never really read into it much more than that. I figured I would ask since ill be cleaning up a manifold soon.

Thanks for the info everyone. I'll stick with Buicks design.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Have run mine blocked for 30 years, 2" primary headers, Cam, dual quads, runs great. but I only drive the car in summer.

Roger

http://www.youtube.com/watch?v=pTCnNNA_02s

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

I may have forgotten to mention one detail that may or may not be important. I do not have a heat riser valve in my exhaust. I have headers instead of manifolds. Don't know if this makes a difference or not.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Some things that many forget is that we don't normally use our vehicles as they were once used, as daily drivers. Most of what we have today are our "Play Toys", which very seldom, if ever go out on cold, snowy, rainy days or whatever. Most are delegated as fair weather driving. Heat under the Carb. is NOT necessary any longer. The heat "Under" the carb. was supposed to keep the throttle blades from getting "Iced". This in NOT nec. any longer. Blocking the exhaust "Under" the carb. has NO effect on fair weather running in most instances as is nec. for a daily driver. The carb. stays a bit cooler so fuel isn't as likely to boil causing rough running, stalling, etc. I haven't used a heat riser in my exhaust for 40+ yrs. to NO appreciable cold, warm performance problems. As stated, blocking the exhaust at the heads causes a myriad of problems associated with drive-ability. To be used almost solely in race applications. With headers it's a play as you go & tuning issue more over than anything else.
Just My Humble Opinion.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

I've ben reading this thread and it has got my curiosity up. I blocked off the two holes in my manifold on my 63 401 and never had any problems. I have a 61 Olds 394 that I converted to a 4 barrel and I blocked off the exhaust ports at the heads to keep the paint from burning off and expected no problems but I have had bad hesitation issues and I am now wondering if this is the cause of it.
Thanks
Pat

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Yes

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Yep,,,,, get the heat back and there is just about a 99.999999999% chance that the problem will disappear.....

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Ok i have had the same problem, I blocked the passages off in the heads it caused a big Hesatation so pulled the intake back of and unpluged them my intake gets so hot it burns off the paint. How do you plug them off at carb.when i pull carb of where do i look to block.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

try to use non ethanol gas, ethanol will cause a lot of problems with idle and off line stumble, ethanol likes more heat too. try the heat block off plates and drill 1/8 inch hole in all 4 plates. you can get the best of both worlds.

 

Re: Any advantage or disadvantages to blocking the heat passage in the intake manifol

Just ordered carburetor gasket and baffle plate for my 425 with Carter AFB carb. I have a few questions before I attempt this repair myself; 1. Will only one baffle plate be required? 2. Is it obvious which direction the gasket and baffle should be oriented? 3. Is this the correct top to bottom order - carb, baffle, gasket, intake manifold and lastly confirmation of torque on 4 carb bolts 10-15 ft-lbs? Any feedback would be greatly appreciated.