heat riser block off

[Jeff M.]

If i block off the heat riser ports on a 69 427/390hp intake, will the stock intake manifold mounted choke no longer heat up and open the choke. Joe has suggested that i block off the carb passages at the front of the carb(done). Will this alone keep the heat off of the carb or should i block off the heat riser also?

[Gene M.]

Re: heat riser block off

Jeff, If you block off the intake heat ports to the manifold, you may be driving a excessive amount of time till the choke comes off (real rich condition). I like Joe's suggestion to just shut down the ports at the carb base.

[Patrick H.]

Re: heat riser block off

Jeff,


I've heard of two "fixes":


One, to use the plates that come with your intake gaskets as block offs. As Gene mentions, as they are smaller than the stock holes, it will take longer for the choke to warm up and come off. I am actually trying this on Dad's 72, as it is only a fair weather car. When I get it running later this Spring, I could update you. Or, come to the MI

[Patrick H.]

Re: heat riser block off

Jeff,


I've heard of two "fixes":


One, to use the plates that come with your intake gaskets as block offs. As Gene mentions, as they are smaller than the stock holes, it will take longer for the choke to warm up and come off. I am actually trying this on Dad's 72, as it is only a fair weather car. When I get it running later this Spring, I could update you. Or, come to the MI chapter tech session on March 19th.


Two, and I've only read this, not tried it, is to place aluminum foil, balled up, in the exhaust crossover passage. Your heat could still get to the choke, but you don't get full-time crossover due to the restriction. Again, I have no idea if it works, just read it somewhere in a Corvette magazine. Maybe someone has tried it.


Overall, I think Joe's approach is best, if you don't want to use the small plates with you intake gasket. You could always make the holes in the plates slightly larger than they are when you get them, to allow more exhaust than otherwise, but still less than if they were fully open.


Good luck,


Patrick

[Alex Gilmour]

Re: heat riser block off

Jeff,


I recommend Joe's response, that is what I did last year...I blocked off the exhaust ports on my 66 327/300 at the base of the carb, mainly to protect the (EXPENSIVE) Replacement Holley from warpage. Basically, I tapped the manifold for 2 allen head pipe plugs and then installed only the stock gaskets. and discarded the metal plate. Haven't noticed any degradation of choke performance.


Alex


'66 A/C Coupe NCRS #22298