I finally took the plunge and got the exhaust replaced on my 1990 Chevy truck. I went with a simple one-in, one-out magnaflow muffler with a turned down outlet pipe. It sounds great, but the star of the show is the custom Y-pipe I asked my exhaust guy to make. It looks like the one pictured above. I’ll take a picture of the actual exhaust when my garage drops below 98 degrees F.
After reading in numerous places that the stock Y pipe on these trucks is very restrictive, I wanted to see if I could squeeze some performance and efficiency out of getting mine replaced. My exhaust also had holes from rusting throughout it, so it was time. Reading on tbichips.com, you’ll find this:
GM intentionally made that Y pipe restrictive to increase back pressure and most have paid someone to spread a myth that back pressure in the exhaust is GOOD. Its NOT. Air velocity is good not back pressure. The reason for the back pressure was so that the EGR smog system would work better and the increased pressure would build up a lot of heat to keep the o2 sensor hot. A good free flowing exhaust does typically need a 3 wire heated o2 sensor conversion to maintain its temperature. To fix 90% of the exhaust issues, I recommend a Flowmaster Y250300 collector from your favorite vendor and replace that section of Y pipe where the 2 pipes merge. Dramatic improvement over that stock GM design.
Here’s what the stock Y-pipe looks like:
I showed the exhaust guy a picture of that Flowmaster collector/Y-pipe and he said “I can make a pipe like that, just not as pretty”. So I said go for it. And boy is it awesome. The truck feels like it has more torque off the line, seems to have more power on the highway, and my gas mileage increased 17.5% (13.1 mpg to 15.4 mpg).
The whole system rang in at $196. Not cheap, but it was needed and I’ll recoup some of that (or all of it, eventually) with better gas mileage. Thanks to David Jones at Extreme Muffler for building and installing the new exhaust.