Rear exhaust vs under car exhaust

[Newsnake]

I have heard that rear exhaust may hinder bhp production by as much as 20%. Is this true? If your goal is to limit noise and you prefer a more roadster look. Will under car exhaust exiting before the rear wheel be a better alternative? Or are there any down sides to under car exhaust. Any advice would be appreciated. Thanks.

[rustyBob]

I have under car exhaust on my 2001 Midstates and love it......
i dont have to worry about anybody ( including curious kids ) burning
themselfes on the hot side pipes....it hurts ALOT...smells bad to....
also if you are on a long drive you have to listen to the pipes roar in your
ear for the whole drive.....i only hear mine when i'm on it hard and going
through the gears.....as for loss of HP, i didnt build a race car i built a driver
so any loss of HP is not a concern of mine.....as for ground clearance,
not a problem, it goes on and off the trailer no problem and rolls over
speed bumps without any scrapeing....

[Newsnake]

Thanks for the insight.

[mickmate]

The undercar exhaust on originals with the cast iron restrictive exhaust manifolds loses about 100HP. If you use tubular tri Y headers with 2" primaries and good mufflers you'll only marginally affect performance. I have made them for originals and newer cars and they look and work good.

[dcdoug]

Originally Posted by mickmate

The undercar exhaust on originals with the cast iron restrictive exhaust manifolds loses about 100HP. If you use tubular tri Y headers with 2" primaries and good mufflers you'll only marginally affect performance. I have made them for originals and newer cars and they look and work good.

Don't you lose about the same with side pipes anyway (assuming you aren't running straight pipes). I was under the impression that because under car exhaust allows for more efficient header design, that you can actually achieve more power with under car exhaust that side pipes.

[JBCOBRA]

I really like rear exhausts and have heard this can be the case when it comes to power. Stock SPF rear exhausts are pretty restrictive, but so are their side pipes.
Actually the internal diameter of the sidepipes chokes down to 1 3/4 inch at one point.
So the rear exhaust may be better?
Now if I can squeeze some bigger pipes under there...........

Originally Posted by dcdoug

Don't you lose about the same with side pipes anyway (assuming you aren't running straight pipes). I was under the impression that because under car exhaust allows for more efficient header design, that you can actually achieve more power with under car exhaust that side pipes.

[elmariachi]

Posted on wrong thread.

[Ozgur_Tan]

my first c*bra (circa 1998) that i've built from kit has got open side pipes, it was too loud
latest my scratch built #1 has got under car exhaust and love it
frankly my scratch built #2 has got side pipes with some mufflers and still prefer #1

[SP01715]

I have undercar exhaust that exits before the rear wheels, and I love it. I am running Magnaflow mufflers and actually think it sounds better than side pipes.

[mdross1]

Had the headers on my big block car built at Tubular Automotive in Mass.Ordered custom 2 1/2" HP chambered stainless mufflers, tailpipes are the same straight out the back.Looks great,sounds even better.Lowest point on my car is flange on Lakewood bell it is also trimmed for more clearance.With the top on the car the mechanical sounds are great with a fantastic exhaust growl mixed in.Life is good everytime I climb into this hot rod and light the fire.
Had a big block Vette with side exhaust before this car which made me not want them again.

[mreid]

To really understand the effect and both hp gains and losses, you have to tune the exhaust to the engine component selection. In fact, you should look at the entire exhaust system as a vital component in the engine build if indeed max hp is your goal. Some milder engine builds actually benefit from some back pressure as it aids scavaging of exhaust gases. Also, some sidepipes are actually more restrictive than a properly designed under car exhaust. As you see in the real world examples and experiences above, it really depends on your build and end goals.

[mdross1]

The sole reason why I built my car was for it's performance potential,and to be able to experience what a Cobra is all about.We have always built and had muscle cars,one was a Corvette with a 427 BB side exhaust.This Cobra was built with road racing in mind,not to try and make a living doing it but it enjoy the experience to the fullest.At first thought about wringing every ounce of hp and tq from the 460, but settled on enough that it is a chore keeping the car on the track even with the car scaled.So for me the Cobra experience could not possibly be any better.

[fastd]

my advice: decide what you really want and go for it. As for hp, I switched from undercar to exit out the rear and picked up a lot - I changed the carb at the same time so I can't say for sure how much was due to the exhaust - I am guessing 30-40 hp.