Tail pipe question! Building a 55 Buick that I put a truck arm rear suspension in, and clearance around the axle /shocks / panhard bar is tight. 300HP engine so not big power. I have mid length headers to 2 1/2" pipes to cherry bomb turbos, but the only way to continue the system with 2 1/2" pipes would be to exit before the rear wheel on both sides, and I would really rather get pipes to the rear bumper. I think 2 1/4" tails would not be a big deal, but not even sure I can make that work. Would 2" tails be a huge hit on HP, or does it not really matter past the mufflers?
The bonus of having tailpipes, should outweigh the slight performance loss. btw I have a full 2 1/2" exhaust system on my 700ish hp blown 427....I take the pipes off for racing, but in street driving, it has plenty of power. Since you're starting with less than half the power, you should be able to get away with a smaller tail pipe, eh?
As exhaust cools it takes less physical volume so tailpipes can be a smaller diameter than before the mufflers with no power loss. Now how much smaller?
Unless they've been enlarged, that 1955 Buick has like 1 3/8" exhaust valves. I doubt that you would ever notice the difference.
As the others have said, but also, at what RPM? WOT or driving around town RPM? Just do it, you'll be fine.
According to the following chart, 2 1/4 exhaust would be more than adequate. https://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/
These guys are right, you would never know the difference. I would even be willing to bet a box of doughnuts that it would be difficult to see a noticeable difference produced on a chassis dyno given back to back runs, nothing outside of the range of acceptable measurement error anyways. That said, the engineer in me likes to think about an actual answer to this sort of question. So for arguments sake, lets say that the 2" pipes creates an extra 1 psi of back pressure as seen at the piston over the duration of the exhaust stroke. Being a V8, that means 2 cylinders are always seeing this increase in pressure at any given moment. 1 psi on a 4" bore = 12.5 lbf of additional force the engine must overcome per cylinder to push the gases out. On a 3.5" stroke, that will require 3.6 ft-lbs of torque to overcome. Multiply that by the 2 cylinders always undergoing the exhaust stroke, and you have 7.2 ft-lbs of additional parasitic drag. At 5250 RPMS, = 7.2 hp lost, at 2500 rpms, 3.4 hp. I doubt you would see a full 1 psi increase in back pressure, but it sure would be fun to measure it and find out.
i was gonna run my 2 1/4 inch exhaust without mufflers and end it with 1 3/4 turn outs in front of the rear wheels..AKA Mopar sneaker exhaust....reason...back pressure ...low end torque...
Hahaha!! I was just pondering this the other day, I have 2.5" Corvette manifolds on a mildly built tripower 283 but have the 2" exhaust off another heap and was considering just using it since I already have it. Eventually maybe I'll redo it if I stuff the 12:1 327 with the ported 492s in it... I had read this as well and it makes lots of sense.
If you want a “soundalike” go by a big block Chevelle which I don’t think you are looking for with a 55 Buick with any engine transplant. I gave up on noisey street cars log ago and could not be happier..That chart fits my 225 horse engine perfect.
An old round track guy I knew said after a fresh build, they would spray paint the exhaust. Then run it on the track. Cut the exhaust just past where the paint burnt. He said anything after that was waste. I don’t know. Cool story anyway.
More than a couple of dyno runs before-and-after large dents were hammered into header tubes (preceding the collectors!) closing 3/8 of the tubes' diameters (2 tubes, left side for clearance) NO H.P. was lost. I was surprised...but saw it done in yet another instance, both were Chevy engines, one a 402" SBC and the other a 472" BBC. So...2" tailpipes aren't going to 'neck down' any notable H.P.!
I went down to 2.25 on an OT carbureted vehicle and it actually increased my torque. I could chirp the tires in 2nd gear after doing the little smaller pipes which I never could do with the larger pipes. Same muffler, header and everything on the motor. Only change was the smaller diameter pipes after the muffler.
That's exactly what I have done on my OT Plymouth, I use collector extensions and cut them using that technique. It tunes the header to the motor output.
My 500 caddy came with 2.5. runs great. About to build a stainless y pipe and run the single 2,5 out before the rear tire.(need the y pipe to run on the opposite side to clear the tank) Why the single? The 500 will never run in the rpm range where a dual exhaust is needed.
There are places that sell oval exhaust tubes and bends for clearance solving. Next can argue if traditional..
I built these two cars with identical tuned engine, transmission, and rear axle. Both with cast manifolds, one with a full 2 1/2" system and one with a 2 1/2" Y into 2 1/2" single. Both ran great but the dual exhaust car was amazingly quicker from a standing start as well as from a roll. I dont think there was enough of a weight difference to allow for the seat of the pants difference. Myself I would not put a single exhaust on a cad 500, but that is your call.
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