1969 l36 390hp 427 heat riser question

[Brad H.]

I want to block my heat riser off to the carburetor completely. I'm pretty sure I have read about this before here but I couldn't find the answer to my question. Here goes: Under the Q-jet within the stock aluminum manifold as you know there are two vertical channels which essentially route hot air off the exhaust thru a little channel right under the front of the carburetor. Typically a thin stainless shield is used to cover the entire carburetor base from this heat. It does allow some heat to transfer to the carb though. The carb base gasket goes on over the stainless shield. What I would like to do is plug both the vertical holes under the carb. I believe these holes/channels are completely enclosed in the intake manifold. In other words, if I tap the holes for pipe plugs, will the metal cut by the tap that falls down in there be contained or can it get in to the engine? I would use rolled up masking tape pushed down in the holes which will get most if not all of the debris, but I don't want to take any chances if there is any possibility of the metal getting out of the intake and into the engine.
Sorry for the long dissertation, but I wanted to more thoroughly explain what I hope to do. I am having some issues with hot starts and Cliff Ruggles suggested doing this to help with ethanol fuel boiling problems.

While I'm at it here's one more. Is there a way to block the hot coolant flow under the carburetor other than using intake gaskets not relieved for the coolant passages? If the heater is not desired, could the upper 5/8" nipple coming off the intake manifold and going to the heater core be plugged? Pardon my ignorance but how does the coolant flow to the heater core? Is it from the intake to the core and core to the header tank or the other way around?
Thanks a second time!
Thanks for your thoughts,
Brad

[Domenic T.]

Re: 1969 l36 390hp 427 heat riser question

Brad,
I'll take a stab at this. The holes you are talking about should have exhaust only going thru them and if anything from you using a tap gets in there it should find it's way out the exhaust pipe.
The SS plug is best.
I have never seen coolant under the carb on a chevy. The coolant to the heater should come from the intake and the water pump sucks it out.

DOM

[Ken A.]

Re: 1969 l36 390hp 427 heat riser question

Here's the way to do it:
Get some heavy grease and put about a half inch in each hole in the intake.
Tap each hole & then, using a good shop vac, suck out the grease & chips.

[Timothy B.]

Re: 1969 l36 390hp 427 heat riser question

Here's the way to do it:
Get some heavy grease and put about a half inch in each hole in the intake.
Tap each hole & then, using a good shop vac, suck out the grease & chips.

Or, go get some cup plugs at a machine shop and tap them in. To keep the exhaust heat down in the plenum wire the heat riser valve open. The cast iron manifold needs a little heat and enough will radiate up with the valve wired open.

Also, Check the gasket arrangement, on my 67 300hp engine it's manifold, gasket then stainless shield just under the carburetor.

[Ken A.]

Re: 1969 l36 390hp 427 heat riser question

Cup plugs are OK, but they can fall thru. For the heat riser, just remove the flapper and weld a bead on the inside of the rod ends to keep it from falling out. Then it will pass judging and no one will be the wiser.

[Brad H.]

Re: 1969 l36 390hp 427 heat riser question

Thanks guys,
I should have mentioned that the heat riser valve is held open all the time. On the coolant thing, I didn't write that well. What I was after though is what Dominic answered. Does anyone think that plugging the nipple out of the intake would cause any problem other than obviously shutting down the heater. I keep having this nagging weep of coolant from the core and frankly I just never use the heater so I would prefer to plug it if possible. This engine has the remote header tank so that is the part I was unsure of.
Thanks a million!
Brad

[John H.]

Re: 1969 l36 390hp 427 heat riser question

Thanks guys,
I should have mentioned that the heat riser valve is held open all the time. On the coolant thing, I didn't write that well. What I was after though is what Dominic answered. Does anyone think that plugging the nipple out of the intake would cause any problem other than obviously shutting down the heater. I keep having this nagging weep of coolant from the core and frankly I just never use the heater so I would prefer to plug it if possible. This engine has the remote header tank so that is the part I was unsure of.
Thanks a million!
Brad

Brad -

The C48 Less Heater option available through '67 used a plug at that intake location, and a cap on the rear leg of the "tee" on the expansion tank.

[John H.]

Re: 1969 l36 390hp 427 heat riser question

For the heat riser, just remove the flapper and weld a bead on the inside of the rod ends to keep it from falling out. Then it will pass judging and no one will be the wiser.

Ken -

That will get a deduction in the Operations section (lack of reduced flow on the R.H. side exhaust pipe from cold start) in Flight Judging, and will fail a P.V. for the same reason.

[Timothy B.]

Re: 1969 l36 390hp 427 heat riser question

Thanks guys,
I should have mentioned that the heat riser valve is held open all the time. On the coolant thing, I didn't write that well. What I was after though is what Dominic answered. Does anyone think that plugging the nipple out of the intake would cause any problem other than obviously shutting down the heater. I keep having this nagging weep of coolant from the core and frankly I just never use the heater so I would prefer to plug it if possible. This engine has the remote header tank so that is the part I was unsure of.
Thanks a million!
Brad

The heater circuit allows the water pump to circulate fluid from the top of the engine through the heater core back to the water pump impeller into the block. If you plug the tee like the heater delete engines so the coolant will circulate out the top of the engine through the tee and back to the impeller to the block it will be fine.

[Joe R.]

Re: 1969 l36 390hp 427 heat riser question

Ken,

That's one way to do it. I don't have the GM part number handy, but I believe there is a spacer that can be used as well.

Joe

[William F.]

Re: 1969 l36 390hp 427 heat riser question

Also fill the recesses in the tap with grease to catch the chips. Go a little at a time , back out tap, wipe off chips, grease tap and cut a few more threads. Don't have to cut threads all the way to bottom of holes, just enough to get plugs screwed in securely.

[Joe L.]

Re: 1969 l36 390hp 427 heat riser question

Ken,

That's one way to do it. I don't have the GM part number handy, but I believe there is a spacer that can be used as well.

Joe

Joe-------


The exhaust spacers used in place of a heat riser valve for FI and certain other applications are long since GM-discontinued. However, they are available in reproduction.

[Brad H.]

Re: 1969 l36 390hp 427 heat riser question

Thanks Everyone, I appreciate it.
Brad

[Brad H.]

Re: 1969 l36 390hp 427 heat riser question

John,
With the intake location plugged and the aft leg of the expansion tank plugged, how would coolant still be able to circulate correctly through the engine? I may have misunderstood how the heater delete is plumbed.
I appreciate any insight you may have John.
Thanks,
Brad

[Timothy B.]

Re: 1969 l36 390hp 427 heat riser question

Brad, And my post may have been not accurate when describing the heater delete. Take a look in the AIM under the heater delete and the question may be answered.