Raising Exhaust - Fuel Economy, Hypermiling, EcoModding News and Forum

99LeCouch · 10-12-2009, 09:27 PM

As do many Buicks, Oldsmobiles and Pontiacs of my car's generation, the exhaust on my car hangs quite low now since the OEM rubber insulators have stretched to comedic parodies of their pristine selves.

And being that they are at the rearmost point of the exhaust, a little stretch there translates into a lot of drop. So I'm getting some new insulators to raise the exhaust and tuck it up underneath the car like it left the factory. A bonus is additional ground clearance.

I wonder how much aero gain I'll get from restoring the factory exhaust drop. The underside of my car is pretty smooth except for the exhaust hanging down. Likely not much, but dragging lengths of 2.5" pipe in the air underneath the car can't be good.

Johnny Mullet · 10-12-2009, 10:15 PM

That is a very common issue with those and other GM cars. The new insulators will make a huge difference. It may save you a little as far as drag goes, but the real savings in that repair come from not having to fix your exhaust after driving over something that catches it.

99LeCouch · 10-12-2009, 10:56 PM

That too. It's always the case that I'm being prescient in replacing these. Guaranteed I'll need to straddle something tall shortly after replacing the insulators.

99LeCouch · 10-14-2009, 10:07 AM

Got it done. The new insulators are about 3/4" shorter than the old ones. The tailpipe fits nicely into the cutout in the bumper now instead of hanging down very low as it did previously.

Looking underneath the car, instead of seeing most of the exhaust all that's visible is the reinforcing bar welded across one of the larger bends. I'm waiting to see what effects this will have. Not much likely, but every bit helps!

lunarhighway · 10-14-2009, 10:31 AM

one of the things you see on newer cars is shaped flat muflers wich basically act as an undertray. however i can imagine a standard muffler causing some drag is it hangs to low

99LeCouch · 10-14-2009, 10:44 AM

My car's muffler is mounted sideways across the width of the trunk. Raising it will help with the undertray effect, as you put it. And getting the exhaust closer in to the car's body can only help with reducing the turbulent air underneath. I think.

QuickLTD · 10-14-2009, 01:12 PM

For reference

99LeCouch · 10-14-2009, 09:57 PM

Your insulators look about normal. Mine were all stretched out and deformed in comparison.

I'll get some good data this week commuting 150 miles/day 2 days a week. Especially now that my ScanGauge is back on the ball after a 6-gallon fill distorted the numbers.

2000mc · 10-14-2009, 10:40 PM

this might be a different issue, but i figure it cant hurt to chime in...

usually the problem i see on older gm C and H bodies is the section of exhaust just in front of and around the gas tank seems to hang unusually low, and there is a big gap between it and the body. even holding up the tailpipe as far as you can, there is still a big gap. if you have this issue the best way to fix it is heating a section of the exhaust ahead of that area with a torch until it is cherry red, then bending the exhaust up to where you want it to be.

99LeCouch · 10-14-2009, 10:55 PM

Raising the muffler 3/4" seems to have solved that for me. That loop you describe was low on my car. Now it's not visible looking underneath the car.

Next is replacing the rubber O-rings holding the catalytic converter up. That will keep the exhaust from shifting as much, wearing the rear insulators less.