I had made the radiator mod and also wanted to try a 4 inch exhaust and new muffler. I did not want to change the exhaust before I could test the results of the first mod so I built up the muffler/tailpipe assembly and put it on the roof. Before I headed back home from Wendover NV, I took off the old muffler and tailpipe and put on the new 4 inch Magnaflow 24 inch muffler and 4 inch tailpipe. I amd going to change the head pipe from the turbo to the muffler to 4 inch (it is 3 inch now) but that will come later.

I noticed very little change in performance although I did notice a slight improvement in fuel mileage and slightly lower EGT readings. To early to tell or confirm as I need more runs to measure. Off line performance is still dismal, but with each change it gets a little better.

Ed,
Am I correct that the outlet from the existing muffler, the short tail pipe and the tail pipe tip are 3.5" in diameter? I need to replace just the 12" long tip on mine and did a visual measurement with a tape measure and it seems to be that size. I have not pulled it off yet, but maybe you already know the answer.....
I asked a muffler shop guy I know if changing the pipe from the back of the muffler (3.5" to 4" enlarger) to the exhaust tip to 4" would help with dissipating heat and he advised that unless I was going to at least change the muffler also, I would be wasting my time and money. So, I am interested in future updates if your exhaust experiment helped any in dissipating heat from the motor.

Hi B&K:

On mine the outlet pipe was already 4 inch, but the inlet was only 3 inch!

Changing just the pipe would not reduce any heat into the engine bay.

What I did was to fabricate a plate of metal and attached it to the frame rail so that the air would be channeled straight back (more or less) and keep it from getting into the engine bay, did that a while ago when I changed out the old muffler to a 3 inch straight thru.





I now have a 4 inch straight thru Magnaflow muffler and shortly I will have the 4 inch pipe built from the turbo to the muffler.

Ed,
I like the idea of the heat shield. Anything that will help keep the engine bay cooler is a plus. I have also been following your workmanship with the fans. Could be a winter project for me, as I am trying everything I can to cool the engine down. Since I replaced the water pump last month it seems to be running cooler but I don't have enough trips on it to verify that. I am already going to pull the radiator and have it cleaned and checked next. I already did the fan forced trans cooler.
I did get under the coach and tried to pull off the exhaust tip, which I believe to be original. Needless to say, I couldn't get it off after being in place all these years but did get the clamp off and verified that it is a 3" exhaust. That is good, because my local muffler guy can help me. But, I think a 4" exhaust system would help even more. Another winter project???

I may have had a bigger outlet on my muffler as the engine is 230 HP, the inlet is in fact 3 inch. As I mentioned I am going to fab up a 4 inch SS inlet pipe after things quiet down the summer.