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Exhaust upgrades - Depending on what’s on your vehicle currently, you can sometimes achieve sizeable fuel economy increases by switching out the exhaust. Low-restriction mufflers, cat-back exhaust systems with mandrel bent pipes, and long-tube headers can all be effective. Your gains might range from 1% to 10%. If you have a very inefficient factory manifold, you might also see a nice improvement from installing shorty headers.
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I think they did this to appease advertisers.
When my friend gutted the converter and put on long tube headers on his 2.7L manual taco he noticed no change in MPGs that he could attribute to those changes. The cast manifold was cracked and his catalyst material was rattling around inside the converter, both cause you to fail Virginia state vehicle inspection. The header was substantially cheaper than even a used cast iron manifold.
Before I chopped and redid the exhaust in my non-turbo diesel I measured the back pressure and found that the exhaust back pressure was very low, almost non existent under almost all operating conditions so I put off doing the exhaust for like 3 years.
Then when I chopped the exhaust, there was no change in fuel economy. Surprise, surprise.
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1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
1989 firebird mostly stock. Aside from the 6-speed manual trans, corvette gen 5 front brakes, 1LE drive shaft, 4th Gen disc brake fbody rear end.
2011 leaf SL, white, portable 240v CHAdeMO, trailer hitch, new batt as of 2014.
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