To put things in perspective, we shot our Summit non-touch thermometer at our stove. At the No. 2 setting, the center of the element is 181 degrees, or 1 degree hotter than the floor of our M-715 before any cooling steps were taken.
We've got this M-715 with a tall-deck Chevy big-block, custom-built fenderwell, exit headers, side pipes, and a sheetmetal interior. The floor is sheetmetal, the dash, door panels, and rear wall of the cab are also all sheetmetal. Since it is an M-series Jeep, this probably doesn't come as a surprise.
Don't get us wrong, we didn't intend to wheel this truck, but you know how that works out. So we planned for it by tucking the exhaust up as tight as we could. That's all well and good, but the problem is that a 2 1/2-inch exhaust with long tube headers built with 1 7/8-inch primary tubes and 40-series Flowmaster mufflers makes a lot of heat. When that whole mess is 2 inches or less from the sheetmetal floor, that makes for a very hot cabin.
To put it in perspective, in 30-degree weather we can take the truck out, and roll the windows down without the heater going and still drive comfortably in shorts and a T-shirt. To put it mildly, the inside of this truck is HOT (maybe we should have gone for 3 inches of clearance on the exhaust).
After some research, we decided that an application of Dynamat Xtreme applied to the interior would help with heat, and coupled with DEI's Floor and Tunnel Shield on the exterior of the M-175 near the exhaust, it would almost make our ride feel air-conditioned. We didn't have any carpet, so we opted to put Herculiner bed liner down on top of the Dynamat for that finished look. | 
Since we were adding all these products, we decided we needed some way to measure the loss of heat. We used Summit Racing's infrared thermometer, with an interior/exterior thermometer from our local home building supply store and a decibel meter to measure any possible decrease in volume from the Dynamat. |
If all of that wasn't enough to excite you, we then went ahead and reapplied Herculiner to the inside of the truck for an easy, hose-clean finish that didn't blind us at noon like the aluminum backing on the Dynamat would've. | |
As we are writing this, summer is fast approaching, along with a possible 3,000-mile trip in this truck, and we just knew that the interior temperatures in the great American Southwest would be murder. Like the true Jeep people we are, we set out to cure our problems.
Look at the pictures and captions to get the idea of the path we followed, but the real useful information is in the table at the end of the story. Look at how the surface temperature of the floor affects the ambient temperature in the truck. Note for all testing, the sun was at its highest, and we had only the driver-side window of the truck open.
The Numbers
To be perfectly honest, we were amazed at both our measurements and our results. We started with a whopping 180 degrees on the floor of the passenger side, and by the end, had it down to 104 degrees in the hottest spot on the floor. Also, as a nice bonus, we were able to cut 6.5 decibels out of the cab, making for a less ear-shattering ride. We used a non-contact thermometer from Summit Racing to test the high and low temperature of the floor, as well as the temperature at the gas pedal where the driver's foot is the most. We used an indoor/outdoor thermometer for the ambient temperatures, and used a decibel meter for noise levels because that is what Dynamat is largely marketed for.