SC bumper surface hot
 

A friend and I were tinkering on his ‘82 SC Sunday. I have an ‘81. He arrived at my garage after driving about 5 miles and we open his engine deck lid. As we were looking things over, I touched the horizontal top painted piece of the bumper, in between the overriders, and the surface was painfully hot.
Obviously there is muffler under the bumper, but holy smokes, you couldn’t keep a finger on the surface.
He bought his almost all original SC in October and I bought mine in March so we’re both new to the 911 world.
I drove mine to several places today and after each stop, I touched my surface and it was warm, but not uncomfortably hot. I had my bumper off a few weeks back to polish the paint and don’t believe there was some kind of obvious insulation.

Any thoughts why his stock exhaust is creating so much heat under the bumper? Too lean thus too hot exhaust?

Charles in Dallas

That is interesting. IF you are speculating the engine is hotter and that is causing the exhaust to be hotter is there any comparison made between the both off you on operating oil temps? Not sure if there would be a correlation but I am curious about it. My '79 bumper certainly gets hot but I would not classify it as painfully hot.

Charles,

Using an infrared thermometer, I'd suggest comparing your temps with your friend's car and if there is a significant difference, start checking things on his engine.

Your friend's engine MAY be running too lean, incorrect ignition timing. or a partially plugged cat.

My friend's car drove wonderfully, however, his O2 system is disconnected, thus under full throttle, he could be missing out on some extra enrichness.
We'll be back together tinkering in the next few weeks and I'll see if i can gather some more data, check timing, shoot some temps, etc.

Thanks!

When my SC was not tuned correctly after an engine swap the bumper was hot enough to fry eggs. After the mixture was sorted out, it was warm to the touch.

CAR
 

check the timing

More on bumper hot
 

Sorry for the delay, but a couple of weeks back we ran a smoke generation machine into the intake system of friend's '82 SC, the car with the too hot to touch bumper. We used the pop off valve as our input location and quite quickly we had smoke wafting out from under the air box on the right hand side. Obvious signs of a cracked air box, plus the middle screw on his airbox is loose, another sign.
In addition, we had smoke coming out on the back of the butterfly assembly and an old vacuum hose was cracked, almost broken in half. We replaced the vacuum hose which helped the bumper temperature and brought the idle down a little, and so he could drive home.
He'll be replacing the air box soon.

did you take pics of your smoke machine set up ? that would be cool to see.. did you have to pressurize it some where to force it out the crack ? or did it just drift out on its own ?

I agree, plugged cat will do it every time.

The smoke machine has a regulator which reduces air pressure to 3-4 psi, so it gently blows into the intake system. One has to block off the air flow meter flap area with a cloth or something to slow down the smoke there. It takes less than a minute of pumping smoke into the system for smoke to start appearing at any leak or opening. Two short videos, one showing the leaking house behind the idle adjustment screw and the other showing smoke coming out under the air box on the right hand side. No photos, sorry.

My CIS air intake box is split too
 

With the warmer weather, I thought I’d check the mixture on my 81 SC. As I placed a little downward pressure on the air filter lid to release the straps, the idle speed changed. That’s not a good sign. So I pulled out my smoke generation machine and sure enough, I have a split in my air box. A couple of months back as I was trying to get my rebuilt WUR calibrated, the engine was back firing quite a bit. I saw the pop off valve working, but clearly just because one has the valve, it is not 100% protection. (I had previously tested my system with smoke and had no leaks)
So in the last couple of days, I pulled the engine/tranny out to work on the CIS system.
There is discussion whether to pull the engine or to replace the air box without dropping the engine. I studied both methods and decided the easier, less strain on the back, etc., was to drop the engine out. I read in the Bentley Manual and in the 101 Project book to get an overall feel of what will need to be done. It took me two hours to perform the under the engine tasks, not counting I drained the oil a previous night and gave it lots of time to run out.
This afternoon I spent about an hour and half performing the top side disconnections.
I had the rear of the car very high on jack stands. I used a furniture dolly with 2x4’s to put the weight of the assembly on either side of the sump drain. The dolly was already over my floor jack so as I lowered the engine down it would come to rest on the 2x4s, on the dollt, and I could just pull the floor jack out.
I had the floor jack supporting the engine/tranny on a block of wood on the case, between the sump cover and flywheel. That seemed to be a remarkable balancing point.
I had to remove the rear bumper, but not the wiring, and just held the bumper up out of the way while my wife pulled the engine out.

With the engine on the dolly, I’ll hook up the smoke machine and see if I can get a good video of the leak.

photos:

https://cimg8.ibsrv.net/gimg/rennlis...e24065932.jpeg
https://cimg2.ibsrv.net/gimg/rennlis...5b3669817.jpeg
https://cimg3.ibsrv.net/gimg/rennlis...1286cb9a2.jpeg
https://cimg4.ibsrv.net/gimg/rennlis...c046ff3ea.jpeg
https://cimg6.ibsrv.net/gimg/rennlis...e883d9430.jpeg
https://cimg8.ibsrv.net/gimg/rennlis...085714d25.jpeg
https://cimg9.ibsrv.net/gimg/rennlis...8f8d84de9.jpeg

Here is a link to a video I made using my smoke machine verifying my split air box.
I’m also starting a new thread opening with this video and discussion of other items to attend to while the engine is out.
The new thread will be titled, “Smoke Machine Verifying Cracked Air Box”

great video. Thanks for posting and showing how that works.