The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post

piecesparts · 01-07-2016, 03:43 PM

Let me tell you a story about a truck.

I put together my 84 SWB GMC a long time ago and like you I put on a set of long tube headers and wanted to go dual exhaust. I had installed a 383 stroker engine and wanted to do the exhaust right. I called several sources, being Flowmaster and Magnaflow. The feedback that I got was interesting. They both gave reasons for NOT going to a 3" exhaust, which fit into what size engine and what type of driving that I was going to be doing. (383 stroker engine, 700 R4 tranny, 3.73 gears, and highway driving) The 3" piping would be great, IF I was going to be running a large bore engine (big block) and was going to have a lot RPMs involved. Otherwise the use of 3" piping was detrimental to efficient operation of your engine. You want several things to happen when you have an exhaust system connected to an engine. First, you want the exhaust to work with your engine and not against it. That means the exhaust gases need to be removed, so as not to restrict the removal of gases from the cylinders. So, if your exhasut piping is too large, then the gases get "Lazy" and will not create a vacuum effect to pull the cylinders clean, so that a fresh charge of fuel laden air will enter the cylinder. If they are the right size, then the gases will shrink as they cool and this will cause a vacuum on the cylinders and sweep them clear. If the piping is too small, then the gasses still cool, but cannot be removed efficiently.

You will want a 2 1/2" exhaust system for your truck, if you run duals and the choice of muffler is up to you, but I finally settled on Magnaflow mufflers after having several Flowmaster muffler failures in the following years after the build. I have found that the Magnaflows give a low rumble while drivng slow and a loud respnse under heavy throttle. If you run a single exhaust, then a 3" pipe will work for that setup.

My 84 truck is still on the road, with another engine in it and it is no slouch in a run and I can pull down some decent gas mileage with the setup that I have.

01-07-2016, 03:43 PM	#10
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: Muffler/Exhaust Questions Let me tell you a story about a truck. I put together my 84 SWB GMC a long time ago and like you I put on a set of long tube headers and wanted to go dual exhaust. I had installed a 383 stroker engine and wanted to do the exhaust right. I called several sources, being Flowmaster and Magnaflow. The feedback that I got was interesting. They both gave reasons for NOT going to a 3" exhaust, which fit into what size engine and what type of driving that I was going to be doing. (383 stroker engine, 700 R4 tranny, 3.73 gears, and highway driving) The 3" piping would be great, IF I was going to be running a large bore engine (big block) and was going to have a lot RPMs involved. Otherwise the use of 3" piping was detrimental to efficient operation of your engine. You want several things to happen when you have an exhaust system connected to an engine. First, you want the exhaust to work with your engine and not against it. That means the exhaust gases need to be removed, so as not to restrict the removal of gases from the cylinders. So, if your exhasut piping is too large, then the gases get "Lazy" and will not create a vacuum effect to pull the cylinders clean, so that a fresh charge of fuel laden air will enter the cylinder. If they are the right size, then the gases will shrink as they cool and this will cause a vacuum on the cylinders and sweep them clear. If the piping is too small, then the gasses still cool, but cannot be removed efficiently. You will want a 2 1/2" exhaust system for your truck, if you run duals and the choice of muffler is up to you, but I finally settled on Magnaflow mufflers after having several Flowmaster muffler failures in the following years after the build. I have found that the Magnaflows give a low rumble while drivng slow and a loud respnse under heavy throttle. If you run a single exhaust, then a 3" pipe will work for that setup. My 84 truck is still on the road, with another engine in it and it is no slouch in a run and I can pull down some decent gas mileage with the setup that I have. __________________ Frank