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ggunder

Exhaust Heat in Trunk

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Wow, I was loading some groceries in my '72 Z and the trunk floor on the exhaust side was over 130 degrees F! The previous owner said it was always hot back there, but is this normal? Maybe I am missing a heat sheild or something. I dropped the exhaust system to install a new transmission and did not see anything notable. Thanks for your input!

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No heat shields in that area, just the open cavity between the fender and the spare tire well. Is it possible you have an exhaust leak in the area that is pumping exhaust heat directly at the underside of the body?

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You mean on the floor behind the driver's seat? Anyway I noticed the heat under the mat on the driver side in front - got some insulating material with foil on both sides, at PEP Boys, cut it to fit under the seat and under the floor mat, seem to make a difference - can't feel the heat there anymore. Maybe I should remove it in the winter unless I get the heater working - it would only take a minute. The stuff comes in a roll about $20, enough for five Datsuns.

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Here is an update on the situation. I installed a 2.5" diameter MSA exhaust system (stock exhaust manifold) with the supplied Super Turbo Muffler. That eliminated the exhaust leak just upstream from the old muffler. The muffler is installed with the center pipe as the inlet and the offset pipe as the outlet. It really tucks up into the space provided nicely, you can't see the muffler at all looking at the back of the car. The final outlet pipe nearly touches the sheet metal, it is really close. Unfortunately the temperature on the interior of the car right back in the corner is now as much as 168 degrees F! I suppose I could reverse the muffler (offset pipe as inlet and center pipe as outlet), but that would seem to make the outlet way too low below the rear sheet metal. All this work and not only is the heat problem probably worse, but the car is way too loud! Any thoughts?

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I seem to recall a heat shield on my 76 280Z between the muffler and the spare tire well. Maybe Nissan realized things get hot back there.

I would suggest getting some insulating material to put between the muffler and body metal but you said it's too loud. Seems like a different muffler with better fit would be in order. Two birds...

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My 2.5 exhaust from MSA is reversed from yours, offset in and center hole for tailpipe. It's tilted towards the gas tank and almost touches it but doesn't get too hot. I worried about that at first and was constantly checking it, didn't want all my work exploding. It's on a 280 though and the tanks are different but you might look and see a way to flip it. When I did mine a lot of people did it the same way, I asked because it could've gone either way. Here's a resonator I was going to get but I like loud. http://www.summitracing.com/parts/WLK-24215/

Read post #10 from Arne, he's the reason I put mine on that way.

http://www.classiczcars.com/forums/exhaust-s30/32026-msa-muffler.html

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Edited by siteunseen

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I checked the Dynomax website and the 17733 model is reversible with regard to inlet and outlet. Most of their mufflers are reversible with the exception of those with one inlet and two outlets. So the issue is fit and heat only at this point. Here is a picture of the install with a center inlet and offset outlet. I like the fit, but not the heat.

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Some options:

1. Reverse the muffler and see how it looks and if it reduces the heat. This will only require a new rear hanger since it had to trim the one provided in the kit.

2. Have a muffler shop bend the pipe before the muffler to drop it an inch or so. This would still look fine and may reduce the heat.

3. Shop for a new muffler.

4. Install heat shielding on the car or strap it directly to muffler (Thermo-Tec heat shield).

Thanks for listening!

post-25140-14150826491488_thumb.jpg

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I've got the same system and install method, haven't noticed any heat problems (maybe I'm not looking hard enough ;) ). It looks like you have all of it pulled up pretty tight against the body, thus your clearance comment. Work with the hangers to drop the muffler a bit - this will give better clearance around the valance and possibly improve air circulation.

And... yes it is a noisy muffler. Many have added a 2" glass-pak upstream.

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post-22303-14150826493628_thumb.jpg

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Is it possible that the exhaust heat is caused by something else? wrong mixture or improper timing? Just thinking out loud...

Charles

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post-25140-14150826628964_thumb.jpgJust to follow up, I took the car to a muffler shop and they adjusted the exhaust hangers to lower the system a bit. They did not get it quite right though because the exhaust tip was lower, but was not centered where it should be. The next day I loosened the hangers and the clamp on the inlet to the muffler so I could rotate it a little. Since it has the inlet a the center and the offset at the outlet, a little rotation centered the outlet on the opening in the sheet metal. Now all is well, except maybe too loud. I still think it is too hot back there, but I need to take some additional readings.

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When a local shop made and installed my 2 1/4' pipe and muffler I brought a can of white heat-cure exhaust paint, and a can of prep spray, they painted it after fabricating it, before they installed it. Black (non-insulating type) lets heat in or out, white keeps it in or out. Polished chrome or other shiny metal finish would be better than white.

I painted it mostly to prevent rust. The color probably makes only about 5-10% difference with heat emission.

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