81_vette!

Asking about the the tail pipe size (part after the muffler)

I have seen several that were 3" in diameter, and some that look 2" or less.

Does it make any difference at all? (sound wise... or performance?)

I am going to replace the mufflers soon and wondered about this.


** 1977 SB manual with headers and true duals, no cat. **

billsfan

Never go smaller than the diameter of the whole system; why put in a new system and restrict the flow at the end? Larger sizes are mostly for looks and maybe a different sound, but won't hurt anything.

KJL

Go with flow master mufflers. The super 40s flow great and have a nice deep rumble. I have never seen a muffler with a different size exit than entrance. I am intrigue by your question.

PowdercoatBill

It'll change the sound, but that's it. Like the other poster said do not go smaller then the head pipes.

7T1vette

As the hot gases cool running through the exhaust system, the gas volume reduces. So, the most important place to have large openings is in the heads and headers. If the tailpipe/outlet pipes are as large as the openings in the heads, it really won't help any to make them even larger. And, if you reduce exhaust system backpressure too much, other problems occur. The exhaust/outlet pipe size is the least of your concerns.

69427

And what would those be?

MotorHead

To the OP, go with the same size muffler as your exhaust system is, pretty simple stuff unless you have found a muffler that has a different size intake than the output ?

One thing I found out many years ago is some mufflers will have for example a 3in input and 3in output but the pipe in the muffler itself is only 2 or 2 1/2 ", I like to roll a tennis ball through the ones I buy just to be sure

81_vette!

What I have now is a 2.5" exhaust that runs into the muffler, then exits a 2.5" outlet... then the Tailpipe tapers down to 2 1/4".

So I wondered, when I get the new exhaust installed, does it make a difference what size tailpipe you have? Can you go from a 2.5" exhaust/muffler and exit through a 3" tailpipe?

Will this cause any negative issues (with back pressure for instance)?

MotorHead

You can put a 3 inch tailpipe extension on. Could you explain back-pressure and how that effects anything positive or negative ?

*This goes on all my posts: Please report back to those who helped you the final outcome of your initial post

baxsom

From everything I have been able to read about backpressure from sources other than old car people the less backpressure the better. What the common scenerio I have read is that people put on huge exhaust pipes and that causes the exhaust to cool down too much before it exits the rear of the car. That cool gas is denser and requires the engine to work harder to push it out losing hp. The person then puts smaller pipes on and see hp goes up. The perception is that the smaller pipes caused more back pressure and that back pressure caused the hp increase. From what I understand and it seems to be substantiated by fluid dynamics models, the smaller pipes keeps the gases moving, throw in a bend or a curve and it causes the gas to speed up. So in reality it is exhaust speed not pressure that increases the hp. The secret is to get the correct size pipes, too big and the exhaust cools down too much before exit, too small and the gas cant exit fast enough. At least thats how I have read a an actual explanation. This site kinda explains it but who is to say that they are right either.
http://www.uucmotorwerks.com/html_pr...torquemyth.htm
http://www.thumpertalk.com/forum/sho...d.php?t=659727
now cue the engine builder that swears this is all bunk.

69427

I'm just an amateur engine builder, but your stuff above is contrary to my experiences and what I've read in physics and engineering books. The formula for pressure drop in a tube says that the pressure drop increases with the length (I think we would all agree with that), but decreases with the diameter (less wall surface/friction per slice area), and goes up with the speed of the fluid. Makes sense to me.

Regarding the OP's initial question (the pipe size after the mufflers), the length of pipe is so short that unless you use an extraordinarilly small pipe the hp loss should be insignificant.

Go Vette

Don't know the science, but little or no backpressure is good for high horsepower but bad for low-end torque. So good for drag cars where the clutch is engaged at really high RPM but not so good for street cars. Next time your exhaust is apart (or falls off!) try running the car without pipes and mufflers. When you step on the gas, your car will sound badass but you'll have little throttle response and might get smoked by a Prius.

69427

Can you cite a law of physics to support your position?

neilvosko

you can go smaller diameter at tailpipe as exhaust gasses slow and cool by the time they reach the muffler...smaller diameter can increase the velocity of the cooled higher density exhaust gas

http://www.pontiacstreetperformance..../exhaust3.html

http://www.pontiacstreetperformance..../exhaust2.html

http://www.go.jeep-xj.info/HowtoExhuast.htm

gcusmano74

If the engine controls (carb and distributor) have been optimized to work with a relatively restrictive exhaust system, and then you change over to a free flow exhaust, the carb settings and timing may no longer be optimum. So you will have to retune the controls to work most efficently with the new exhaust. Until you do that, the HP/drivability might be somewhat less than the origional system.
Also, as 69427 said, the muffler outlet tube is so short that the increase in backpressure won't amount to anything.

PeteZO6

C6 Corvettes have 2.5" exhaust pipes from the (short) headers back. My 505hp LS7 (ZO6) has 3" pipes all the way back. On a car GM made heroic efforts to reduce weight, they spent the weight and $$ for 3" exhaust pipes. Does that answer your question.
For those who who say you lose torque with larger diameter pipes, how does >400 ft.lbs. of torque from ~2,200 - 6,800 rpm sound? It means you have a one gear car much of the time.

Pete

roscobbc

Can't speak for SB's but my 69' BB C3's had a twin 2 1/2" system as stock - however tail pipe from muffler was 2 1/4". Tailpipe trim inlet is 2 1/4" - tail pipe trim is 2 1/2" diameter. On the scale of things unless the engine has been modified it will make little difference in terms of lost power.

LT-1 kid

I think a stock 69 BB pipes are 2.5 from manifold reduced right a way to 2.0 all the way out with 2.5 chrome tips

qwank

the reason why his current exhaust is 2.5'' in and tapers down to 2.25'' out is so the stock chrome exhaust tip will still work, since it's 2.25''. Corvette central makes their exhaust this way too.

diehrd

Balance it , all sizes remaining equal.

But for the OP . I doubt he will suffer anything he can notice with his tail pipe size changing to 2.25 . I doubt even a dyno would pick up any change with 2.25 or 2.50.