Exhaust heat abatement on mid year

[John L.]

I have a factory air powerglide coupe that I drive. Have original A-6 compressor rebuilt and blowing 40 -degree air. Couldn't ask for any better! However., excessive exhaust heat warms the cockpit up beyond the air conditioners ability to cool it. With a heat laser, I am getting 100 degree+ temps all over the top of the lower console including the carpeted sides.

The exhausts have small factory heat shields and tranny tunnel has a small piece of insulation. I would like to greatly enhance the heat abatement and was curious of experiences you all have had. Not concerned about judging points. Have finished all that. Want to drive in best conditions possible staying cool! Ideas? Thank you!

[Gene M.]

Re: Exhaust heat abatement on mid year

John,
Your profile says 64 coupe. That would have 2" pipes with base engine and also with automatic tranny. Others will have 2 1/2" exhaust. My 65 has 2" stainless pipes with thick wall .060 tubing and stainless heat shields. I removed the plate in the heat riser. Also there is a full stock tranny insulation in the tunnel. Heat transfered to the interior is almost non existent. My thought is the stainless holds the heat better causing the exhaust to flow faster.

[William C.]

Re: Exhaust heat abatement on mid year

Some questions, how hot does the PG get? Does it have the proper cooler attached and flowing freely? Add all the insulation you have room for around the upper trans area between the trans and the body. I had one of those some years ago and it stayed cool on pretty hot days here in Ohio summer (high 90's) I'd be trying to get the trans temp down for starters. What is the status of the torque converter in the trans? Slippage there generates lots of heat.

[John L.]

Re: Exhaust heat abatement on mid year

Bill, as far as I know the transmission cooler is working. It appears this is exhaust heat running from the pipes close to transmission tunnel and we will look your suggestion of insulating everything the best we can around the tunnel. We are also adding two more exhaust deflectors.... Not factory of course but could help.The 64 had very short ones.

We are going to try and custom fit two more around that area to try for better heat deflection. Any recommendations on insulation to use that might be better than the stock piece we have? I had heard of a product called Dynomat that is a reflecting foil metal material with a thick rubberized sticky side the Hot Rod guys use but, but seems like if we put that up inside the tunnel we may never get it off. We are trying to do things that don't significantly alter the car and can easily be removed. Not sure that's it. Recommendations? Tks!

[Wayne W.]

Re: Exhaust heat abatement on mid year

There is something else going on there if it wont cool a coupe and the output is 40 deg.

Later models had a thick foam collar between the tunnel and the transmission. To me, that is one of the most beneficial mods at speed. It keeps the engine air from coming back through the tunnel.

[Gary C.]

Re: Exhaust heat abatement on mid year

John,

Great article in the Restorer about installing HushMat in a C2 in 2010-12. Sorry don't recall the exact issue.

I did a road test comparison in 2008 with the different under carpet insulations. HushMat had by far the best heat reducing properties and was the thinnest.

Gary
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[Jim T.]

Re: Exhaust heat abatement on mid year

I had a 1964 convertible with factory air in 1968-1969. Don't remember having the heat problem you are having. Side exhaust would move your exhaust pipes away from the transmission tunnel I did not have them on my 1964.

[Jim S.]

Re: Exhaust heat abatement on mid year

There is something else going on there if it wont cool a coupe and the output is 40 deg.

Later models had a thick foam collar between the tunnel and the transmission. To me, that is one of the most beneficial mods at speed. It keeps the engine air from coming back through the tunnel.

Here is the item Wayne is speaking about https://www.paragoncorvette.com/p-35...am-collar.aspx

[Duke W.]

Re: Exhaust heat abatement on mid year

I am getting 100 degree+ temps all over the top of the lower console including the carpeted sides.

That doesn't sound normal. Get some IR gun readings of the exhaust manifolds after you've been out for a drive and then a few minutes of idling in Drive. Hold the IR gun close to the manifold to get accurate readings.

What range of coolant temperatures are you seeing on the cockpit temp gage in hot weather driving around town? How does the gage temperature compare with IR gun readings of the thermostat housing, upper radiator hose and, radiator inlet?

What is the manifold vacuum reading ("Hg @ RPM) idling in Drive with the compressor engaged?

It could be somethilng as simple as a problem with the spark advance map, which is usually an easy and inexpensive fix. Check and also report the data stamped on the VAC bracket and check it for conformance with specs, but the OE '64 VAC on 250/300 HP engines had issues. There was a TSB issued, which has been posted here in the past.

Duke

[Leif A.]

Re: Exhaust heat abatement on mid year

That doesn't sound normal. Get some IR gun readings of the exhaust manifolds after you've been out for a drive and then a few minutes of idling in Drive. Hold the IR gun close to the manifold to get accurate readings.

What range of coolant temperatures are you seeing on the cockpit temp gage in hot weather driving around town? How does the gage temperature compare with IR gun readings of the thermostat housing, upper radiator hose and, radiator inlet?

What is the manifold vacuum reading ("Hg @ RPM) idling in Drive with the compressor engaged?

It could be somethilng as simple as a problem with the spark advance map, which is usually an easy and inexpensive fix. Check and also report the data stamped on the VAC bracket and check it for conformance with specs, but the OE '64 VAC on 250/300 HP engines had issues. There was a TSB issued, which has been posted here in the past.

Duke

Duke,

You state to check the vac canister for conformance within specs. Can this be done with the vac canister still hooked up to the distributor? Is it as simple as pulling the vacuum line from the carb and hooking in the Mityvac and lifting the distributor cap and watching when the plunger on the cannister starts to move and when it reaches final pull? What "Hg are we looking for before it starts to move and when it reaches the end? About to start this whole fine tuning process with my L79 next week and I want as much accurate info at my finger tips as possible. I have read every article here and in the other forum over the last four months, searched the archives and done a ton of research so that I feel as comfortable as possible as I tackle this situation i.e. fine tuning the carb, mapping the spark curve. checking all vac levels, setting timing correctly, etc. My, obvious end result, is to have as smooth a running L79 as possible with as little excessive heat as possible. Being an A/C car and the 100 degree summer heat, I really wan't to dial this in. Thank you and all the other contributors (John H, Tim B, Dennis, Ed J, etc).

Leif

[William C.]

Re: Exhaust heat abatement on mid year

Don't forget to have the distributor curve checked to see if it is still performing to the original specifications.

[Duke W.]

Re: Exhaust heat abatement on mid year

The answer to your first two questions is yes.

Spark advance map specs are in the AMA specs and your service manual.

Download my 2012 National Convention presentation and thoroughly read it, so you can start with a basic understanding of the issues.

In December 2012 I started a thread on rebuilding/blueprinting a L-79 distributor, and I set it up as recommended in the above presentation. It should be easy to find. I don't start too many threads.

After a brief test drive to check for performance and detonation (none detected) I was very happy with the results and so was the owner.

Since your L-79 has A/C, you need to check manifold vacuum at idle speed when the compressor is engaged and apply the Two-Inch Rule. You may find that you should stick with the OE 8" VAC instead of installing a 12" VAC that I recommend for non A/C L-79s assuming they show evidence of the correct OE cam, which is indicated by 14-15" Hg @ 750 RPM idle speed in neutral. Since the compressor places a signficant load on the engine at idle, manifold vacuum at the same engine speed will be lower when the compressor is engaged.

Duke

[Leif A.]

Re: Exhaust heat abatement on mid year

Thanks, Duke. I have read your article several times, printed a copy and will re-read again before starting on my "journey" I have bought a new B26 & B28 vac canister just in case I need them. Can't hurt to have them on the shelf anyways. I think this is the first time I have seen mention of turning on the A/C when checking idle vac...certainly good to know and logical. I'm actually looking forward to doing all this and taking copious notes to pass on to all who have helped and, hopefully, solve my overheating and slight stumble issues.

[Dennis O.]

Re: Exhaust heat abatement on mid year

My car isn't air-conditioned, but I did experience a hot cabin. I just installed sidepipes. Problem solved.

[Gary C.]

Re: Exhaust heat abatement on mid year

Years ago I used Thermo-Tec exhaust wrap and it was successful in reducing exhaust pipe heat on a C2 floor. Suspect there should newer and better products available today.

Gary
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