I'd like to get everyone's thoughts on whether or not a Pypes GM A-Body 3" X-Pipe exhaust with 2.5" tailpipes is something you'd be interested in. The system would be a 3" header-back system with 3" mufflers reduced to a 2.5" outlet and 2.5" tailpipes. It's designed for engines in the 600-750HP range without reducing performance, while providing lower sound levels and easier fitment. They are currently available for Mustang, Duster, Nova, & Impala, but not the GM A-Body. I've included a link to the Impala system so that you can read the Pypes description of the system. I think people would be interested, but the question is.... what do YOU think? https://classicmusclecarexhaust.com/c/quick-search/general-motors/b-body/pypes
Very common thing to do on the BBF side, especially in Mustangs as you stated to help mellow the noise in the smaller cars. I'd think it'd be a good idea for the A-bodys (I don't own one) to make hooking up to the N25 tips easier.
The exhaust gas also takes up less volume, the lower temperature it has, and speciel after a X or H crossover, which makes up for smaller diameter pipes..
As far as the N25 tips go, I'd love to say that the system Pypes developed for the 68-72 442 and 70-71 GTO would fit the N25, but I'm not really sure and neither is Pypes (I've asked them). N25 looks to be another inch or so higher than the 442 bumper cutout, but at least it's a lot closer than a standard Pypes/Flowmaster/Magnaflow system. Perhaps the tailpipe can be lifted enough to meet the bumper cutout without the over-the-axle part hitting anything. Only way to tell at this point is for someone to actually try it. And then there's the matter of 2.5" tips being available.
I'm with you. My point was that it's a lot easier for most shops even if they have to do some custom work to bend and make 2.5" tailpipes go where they want it then to do 3" pipe, plus reducing the 2.5" down is easier then 3" when you do get to the tips. Lots of smaller shops can't bend 3" at all.
I don't know what it's like near you, but it's nearly impossible to find a shop that bends pipe at all, let alone mandrel bent pipe. Your average shop only compression bends, which leads to decreased diameter at the bends. I recently had the opportunity to measure the bend on an original 2" Olds W-30 tailpipe- it was 1-3/4" I.D. over the axle. Point is, if a shop bends tailpipes for you, make sure it's mandrel bent
We've still got 4 or 5 custom exhaust shops here in town, luckily. Oddly the Midas shop here is the best for custom one off exhaust. My (very dirty underneath) F100 was a complete custom job with 2.5" pipes having to route both to the passenger side, under my custom rear sway bar, over the rear diff but under my fabricated panhard bar (that was cool figuring that out), and then one out each side. Last pic you can see the sway bar, rear diff, and panhard. Wish everyone had the benders for doing mandrel, but 99% of shops can't afford the tooling. One here in town switched over, but I heard it was the tune of $120k, and now a system from them is almost doubled in price. Their old standard bender and dies sold for something like 20k. I've done custom exhaust myself, and dang near owned my own shop. Dyno results on anything under 700 hp with a 3" system you might lose 5-10 hp if done right on a standard bender vs mandrel. Ask me how I know.
If you have 2 1/2" tail pipes then even with 3" front pipes it flows the same. You won't gain anything but weight. If you believe differently then feel free to provide proof. I know at about 450HP full 3" exhaust flows like open headers. There is no time difference at the track.
Couple friends of mine (father and son) here in town have some pretty serious Chevys. One is a '69 Camaro 427 nitrous engine that runs 9.9s, the other is an 8 second 2500 lb. '64 Nova with a 515, both run through the mufflers. The Nova owner father has a chassis dyno, and made the exhausts for both of them on a regular pipe bender first. Both using Magnaflow 3" bullets. When the whole mandrel bent exhaust became a "necessity" to serious performance cars, they spent the money and bought sections of straights and bends. Copied their original exhaust but this time with the mandrel bends. When they put them on the dyno (I was there), the Camaro made something like 3 hp more, the Nova was 12 more if I remember correctly. Camaro still runs 9.9s and the Nova turns the same 8 second passes before and after the change.
General rule of thumb is that most engines don't start to see the benefits of a 3" system until about 500-550hp, and that's at the track. Street driven cars in the 600-750hp range can benefit from a 3" system and 2.5" tailpipes as exhaust gasses have cooled by about half and are less dense. This keeps gas velocity up without adding restriction, which helps keep up low end torque. I'm looking at the list of cars that you own. Was that your '73 GS350 in HMM at the Pure Stock Drags? If so, that's a beautiful GS. Even back when they weren't cool, I always loved the Colonnade cars, especially the GS and 442.
Yes that is my 73. Thanks. It went from 2" single exhaust to 2 1/2" mandrel bent and didn't gain anything. LOL but it sounds better. Not much pipes can do with 140 hp. I've often thought it would be good to use bigger muffler inlet/outlet than the pipe size. Due to the fact most traditional type (non welded) mufflers tend to have necked down internal tubes. Makes sense to use 3" back to a 3" muffler but you will give up a little with 2 1/2" tailpipes. Not really a worry with less than 500ish HP. Changing my 70 Chevelle from 2 1/2" to 3" was worth .25 seconds. With the 3" there is no gain over open headers so I no longer have to crawl under it to disconnect them.
I ran a 3" to 2-1/2" system for many many years and it was great. And it is NOT true that the smallest diameter pipe in the system makes the entire system essentially that same size. The total pressure drop in a system is the sum of all the pressure drops throughout the system. And those pressure drops are a combination of density, viscosity, Reynolds number, etc... But I also have to say that the toughest thing for me was always finding a muffler that was: - Quiet - High-flowing - Durable Not everyone likes a whisper-quiet car like me, but that was the sleeper effect I wanted. Even the quietest muffler I could find, while quiet by most standards, was still a bit too loud for my preference. -Bob C.
While perhaps not true scientifically, in practice the difference would not be measurable. If you have any data, please share with the class. I use Dyno max long case and feel they are very quiet. About as quiet as a muffler can be. Also muffling sound is a byproduct of restricting flow. You can't have maximum flow and minimum sound together. Not without sound cancelling technology. For examples look at a Hellcat which has bypass valves for full throttle, max output. Look at an AMA supercross bike. If they could make the power needed to be competitive at lower db they would.
OK, nothing scientific and nothing power based in my response, I went with 3 inch for the sound. I have the Pypes SS system with an x pipe on a pretty stock 462. The tail pipes had fitment issues which required multiple installations for marking interference points followed by heat and beat sessions. The exhaust system hangs quit low so you have to be careful where you drive. If I am capable I will post a short video clip of the car idling, I like the hollow throaty sound. Jim
