Technical Exhaust

I just finished mechanically building my 1947 Lincoln club coupe taildragger. Just had the exhaust installed straight pipe to rear bumper they used 1 3/4 tubbing due to arch to get it over the rear end no space because I kicked up the frame and 4 linked it with bags. My engine is sbc 350. I have excessive heat in the cab on this build and wondering if anyone has ran that small of tubbing for exhaust on a sbc. I insulated the fire wall and floor but my cab gets hot inside even with no side glass yet. I'm wondering if the exhaust isnt flowing fast enough and restricting the engine and my pipes are getting too hot and keeping my headers hotter than the should because my engine bay feels hotter than usual. I did everything advanced my timing tuned my carb and engine runs good perfect it idle at 800 rpms with temp at 190 to 200. I'm clueless and feel that now that it has full exhaust I notice the heat. I drove it to test it around in the beginning with make shift exhaust to test and get me to the muffler shop it dumped right under the diver floor board and never noticed the cab get hot but I never drove the car more than a few miles or 10 minute drive untill I got full exhaust now I noticed my cab getting hot. I'm thinking of putting an h in the pipes might help or just run bigger tubing and dump the exhaust before my rear tires. Any suggestions will help, thanks for reading.

 

Do you have the vacuum advance hooked up it will cooled exhaust gas temperatures

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Yes vacuum advance is hooked up

 

Depending on how built that 350 is, the 1 3/4 tubing is more than likely restricting your peak horsepower, but probably is not responsible for your heat problem. How complete is the interior? Does the inside of the firewall get hot? Are all the holes plugged? Without side glass, my guess is you are drawing underhood hot air through the cab in some way or the other.

Pictures would be helpfull.

FYI. A smaller diameter exhaust pipe will cause the exhaust gases to flow faster through the tube. But the dirty little secret is the heat transfer rate does not change much due the velocity of the gas. The surface area of the pipe will have a much greater effect.

 

There are two separate issues here:
Exhaust diameter & cabin heat.

1.75" duals are small but probably ok for a stock 350. An H pipe would help smooth the flow.

Regarding heat; how close is the exhaust to the floorboards? Less than about an inch?

How much insulation do you have on the floorboards? Any carpet?

 

The heat corpuscles* in the exhaust are the same no matter what the pipe diameter is or how fast the flow. But the outer skin of a larger pipe will radiate more heat than a smaller pipe.
*That's science talk.
An H-pipe will only mellow the exhaust somewhat and probably smooth out the "rap" into more of a "rip". An H is not a bandaid for heat.
Getting the pipes outside the frame so they burn your leg exiting instead of burning your butt all the time is an option for ya.

 

Bone stock 1972 350 from a k-5 blazer, exhaust is 1 1/2 away from floorboards and ran through stock holes in x member. No interior just insulation.

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This during your recent heat wave?
I would think 1-3/4" times two would be adequate (just) for a stock 350.
Using the rule of thumb 1" per 100 ci;
(350/2)/100=1.75

 

You have that big V-8 under stuffed under that hood with NO ventilation..

You have those little toy electric fans...There is no way they can cool the engine compartment. Those old cars were designed to have constant air flow under the hood and not a few hundred cfm either.. You need to put a clutch fan on... They flow 9000 cfm at 2000 rpm.
I would also just use the transmission cooler that's in the radiator, they also warm the transmission fliud when the car is cold.. That way you can get rid of that extra radiator.
I would look for things that you don't need under the hood. Anything thats under there holds heat. Do not put insulation under the hood.

Make sure your running a 160 thermostat...

 

It sure looks cool though

 

Cars in the 50’s Fords for sure had heat deflector mounted to the floorboards over the mufflers to almost eliminate a hot floor. Since you have no mufflers I would do the same thing 1/2” away from the pipe and 1/2” away from the floor. Get some 2-1/2” exhaust pipe and split on a band saw. Weld 5/16” nuts near each end and attach them to the floor boards now since you have not finished the interior; stop at the back seat As it cools down a lot by then anyway. Being real low doesn’t help but you can get by it. Have you checked the temp with an electronic thermometer?
Look at any stock exhaust Harley Softtail. You could do it that way to with hose clamps.
Last if you want to spend the $$$ have them coated inside and out At least to the back seat area. Lowered temp by 200•.... good luck.

 

Might sound dumb, but are you sure the heat inside the car is radiating up from the floor, and not a result of the sun beating down on your black roof and no glass? Got any insulation in the roof?

The inside temp dropped almost 20 degrees when I added insulation to the roof and installed glass in my coupe. Gene