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When the car becomes strictly a thru the mufflers track car or goes forced induction. I don't see a need for 3" on a normally aspirated street driven car.
When the car becomes strictly a thru the mufflers track car or goes forced induction. I don't see a need for 3" on a normally aspirated street driven car.
X2, 2.5" is suitable for most applications upwards of 500 hp.
I have to disagree to an extent . My 350 olds realllllly gets choked up by the 2.5. like 2 tenths roughly 20 HP. People make claims that you will loose bottom end tq and all that BS. Go with a 3 inch it will not hurt a think. Opening up my headers makes a big difference all around in performance. You won't kill anything performance wise with a 3 inch atleast not anything you can feel. Even back when th car was a high 13 sec car open headers vs. through the mufflers open headers was faster. So my theory is the 3 inch leaves room for future mods and won't kill anything
One thought is to just run 3" to the mufflers and 2.5" tailpipes. The larger pipes provide the most benefit before the mufflers where heat and velocities are high. Even the Hemi Mopars had 2 1/2" primary and 2 1/4" after the mufflers.
What mufflers are you running Bruce? How loud is it inside? Who cares about the outside noise level😉. A 3" system won't hurt anything other than being louder. I will probably need to add resonators or sound deadening with 2.5" system on the 70 with Aerochamber mufflers. It sounded great under my 88 with super padded Brougham interior. Under my 70S, not so much but good outside.
X2 if you want lower ET's but if you are just cruising 2.5.
Dumps before axle saves weight but you gas yourself in traffic even with a well sealed car.
Note the ladies don't like dumps.
The problem with the current set up for me atleast is my AFR changes by almost one point with the exhaust. So my AFR of 13.0/. 12.5 becomes 12.0 11.5 at idle . Cleans up well cruising but low speed driving it's fat like stop n go city driving. At the track with open headers it's right where i need it to be . Just fwiw.
One thought is to just run 3" to the mufflers and 2.5" tailpipes. The larger pipes provide the most benefit before the mufflers where heat and velocities are high. Even the Hemi Mopars had 2 1/2" primary and 2 1/4" after the mufflers.
I wouldn't use 2 1/2 on any 455 mine is 3 inch to rear axle. I also have race dumps but uncapped was not much difference so I leave it capped on my 1970 442.
I have a 69 cutlass conv. I'm installing a 455. I would like to add 3in SS exhaust to the headers. Strait out back thru the 442 bumper cutouts. Trying to find company that sells kits. Chatt
What mufflers are you running Bruce? How loud is it inside? Who cares about the outside noise level😉. A 3" system won't hurt anything other than being louder. I will probably need to add resonators or sound deadening with 2.5" system on the 70 with Aerochamber mufflers. It sounded great under my 88 with super padded Brougham interior. Under my 70S, not so much but good outside.
Originally Posted by Chatt
I have a 69 cutlass conv. I'm installing a 455. I would like to add 3in SS exhaust to the headers. Strait out back thru the 442 bumper cutouts. Trying to find company that sells kits. Chatt
I have a 3" Pypes kit with Race Pro mufflers. They're straight through like Magnaflow and Borla. I modified the tailpipes to dump behind the wheel instead of straight back.
I was leaning toward 2.5 with some cutouts for track time. 3 seems a bit much to me.
Pypes makes that easy for you. They have an "X-Change" x-pipe system with cutouts built in. You can order it with one of 3 different Pypes mufflers, or without so you can use the muffler of your choice. Pypes X-Change system
Cut, fitted, sectioned ready to hang ( socket and ball jointed ) 3" SS H pipe out the rear turned down ends. Flow master with Mondello SS headers # HD - 57P 1.5" tubes / 3" collector, good shape no dents $500.00 + ride Gurnee IL
While not a exact apple to apple comparison, Ill share my experiences with exhaust.
At the end of a day at the track, I was loading the car onto the trailer. I heard a noise coming from under the car. My first thought was engine noise, it was a strange metallic rattling sound. After a bunch of investigation, turns out a couple of the baffles in the Flowmaster mufflers had broken loose. Im not sure if it was echoing off the deck of the trailer, but my first thought was bottom end trouble in the engine.
Many years ago, back when I had disposable income and could afford the time to race every weekend. I decided to run the car the following weekend open headers. While the car did run a little quicker, Im guessing the majority of the gain was from the loss of 70-80 pounds of head pipes, mufflers, and tailpipes. If I remember correctly, it was worth about a tenth. To me, the added hassle of uncorking the headers wasnt worth it, and I dont care for the noise.
This was long before AFR tools were available, maybe if I was willing to play around with tuning I could have improved more. I guess Im a minority, I dont really want to work on the car at the track, I go to have a good time and relax. Other than swapping tires, thats about as much work as I hope to do.
I dont think too much exhaust hurts nearly as much as being too small. I remember reading in the old Flowmaster catalogs that 250hp per engine bank is about the point where going from 2.5 to 3 inch pipe was beneficial. Maybe things have changed.
Cut, fitted, sectioned ready to hang ( socket and ball jointed ) 3" SS H pipe out the rear turned down ends. Flow master with Mondello SS headers # HD - 57P 1.5" tubes / 3" collector, good shape no dents $500.00 + ride Gurnee IL
