2 inch exhaust??

[MrBelvedere2]

I am finally going to ditch the flowmasters on the 67 barracuda, going with dynomax ultra flows. I thought the tail pipes looked a little small, so I measured them with calipers and they are 2" diameter from front to back, I measured in several places. They are dual exhaust coming from headers with an H Pipe installed. The motor is a mild built 360, comp 268 cam, air gap intake, J heads, headers, 750 holley carb, MSD distributor and box. Do you guys think it would benefit more to upgrade to a 2-1/2" system or even a 3"? I just feel that the 2" is kind of small for the motor. The pipes are in good shape and everything no leaks, and it would be nice to not have to do a complete new system, but if that is what it needs then I will do it. What do you guys think?

 

[Grinder]

Haha are you kidding? Enjoy the new found power and torque!

My advice: If you are keeping the motor the way it is 2.5 but if you might want to bump the comp and go with a bigger cam later the 3 in. would be optimal

 

[jamesdart]

the straight thru type mufflers should make a good difference especially with undersize pipes. what are you trying to do, are you going to be hitting the track looking for every last tenth? if so then you will want to go bigger. if not, well the 2" will work. its just not optimum.

 

[MrBelvedere2]

Thanks for the info guys!

 

[T67POWER]

3":headbang:

 

[2 Darts]

If you're looking for improvement and keeping the cost down, try going 2½ to the muffler and leave the rest at 2". This is similar to what Mopar did with the single exhaust Commando/Charger 273s.

I'm told that dropping the interior pipe diameter at the tail pipe helps maintain exhaust velocity and improves the scavenging effect of headers. Never tried it personally.

FWIW: The Dart has a 2¼" system front to rear with a turbo muffler. The Demon has 2¼" tail pipes. Depending on what I can do with the exhaust manifolds, I'm thinking about doing a 2½" exhaust pipe and muffler. If that won't work out, I plan on 2¼" all the way.

 

[memike]

If you're looking for improvement and keeping the cost down, try going 2½ to the muffler and leave the rest at 2". This is similar to what Mopar did with the single exhaust Commando/Charger 273s.

I'm told that dropping the interior pipe diameter at the tail pipe helps maintain exhaust velocity and improves the scavenging effect of headers. Never tried it personally.

FWIW: The Dart has a 2¼" system front to rear with a turbo muffler. The Demon has 2¼" tail pipes. Depending on what I can do with the exhaust manifolds, I'm thinking about doing a 2½" exhaust pipe and muffler. If that won't work out, I plan on 2¼" all the way.

I have herd the same :happy10:, X2

 

[memike]

I have put header's on a stock built 360 and it ran allot faster E/T with the header's caped up to my exhaust. I guess it needed some back pressure

 

[dgc333]

I have put header's on a stock built 360 and it ran allot faster E/T with the header's caped up to my exhaust. I guess it needed some back pressure

FYI, no engine is going to see an improvement in power by increasing the back pressure, that's an old wives tail. The full exhaust improved the overal tuning of the system to allow the exhaust to more efficiently get out of the cylinders compared to the open headers.

To the OP regarding tube size. I had a dual 2 1/4" system with an H pipe cross over on the cuda when it had the \6. When I swapped in the 360 (~370H) I just adapted those pipes to the 360's headers and ran it that way for about a year. I kept saying I need to upgrade the exhaust so my daughter installed a 2.5" system (she was running her grand father muffler shop at the time) with an x pipe and 50 series flowmaster mufflers. By the butt dyno there was no difference in power. I wasn't happy with the way the tail pipes were bent (they hit the shocks on big dips in the road) so this past winter I installed a 2.5" system that came with mandrel bent pipes, an x pipe and turbo mufflers. Still no change by the butt dyno.

IMHO, you will feel little or nothing by increasing the pipe size or changing the mufflers.

 

[Grinder]

Ah yes the butt dyno~the be all end all to hp gains. Get real, if you really have 370 hp you would feel a difference. Optimal size pipe for 300 hp is 2 1/4" anything above that and you will gain hp,tq,and economy by upping the pipe size. Your butt dyno may need a tune up.

 

[dgc333]

Unless you are racing an looking for every .1 second you can find the butt dyno makes perfect sense to gage changes. The generally accepted number is 3-4 HP to be noticeable by your butt in the car.

As far as my car having 370 HP it's never been on a dyno so the number is an approximation and that is why I prefix it with ~ , that means approximately by the way.

I came to this number by the fact that the car with me in it weights 3650 lbs give or take depending on how much gas is in the tank and the fact that it runs between 102-103 mph trap speeds in the 1/4. I have also run the build through several dyno software packages that predict the engine will make ~390 HP so I feel pretty comfortable that the 370 number is reasonably accurate.

When I first installed the 360 I hooked the headers up to the 2 1/4" compression bent H-pipe system that had been behind the built \6. I ran it that way for several thousand miles before swapping in a 2 1/2" compression bent x-pipe system. I did not detect any change in the power by the butt dyno. This system was in the car until this past winter when I swapped in a mandrel bent 2 1/2" x-pipe system. I didn't make this change for power, I did it to get more accurately bent pipes that would not interfere with the shocks. Again no noticeable change in power.

A few years back one of the mopar rags took a 340 Challenger that had headers hooked to an other wise stock 2 14" exhaust system and base lined it on a chassis dyno. The first change was to swap out the mufflers for performance mufflers (If I recall they were Dynomax Turbos) and the picked up about 7 HP, a change easily detected by the butt dyno. They then swapped in a 2 1/2" system using the same model muffler and got another 4 HP right a the edge of whether you will detect it by your butt dyno. They then swapped in a 3" system with the same model muffler and only got more noise with zero additional power.

This dyno testing between the 2 1/4" and 2 1/2" systems pretty well aligns with my experiences so I figure my butt dyno is reasonably able to detect the generally accepted 3-4 HP number.

You can believe my comments or not it's your business but it helps no one to dump on some ones actual experience when you have offered ZERO evidence to the contrary.

 

[alpha13]

I don't understand where people get this whole "Back pressure" term. I must be one of the few people who know there is no such thing. Velocity of incoming or outgoing air is what you want to build torque at any given RPM. Skipping the intake velocity charge as that gets into another aspect of this. Exhaust size and length is used to tune power and sound. Obviously if your driving a 500HP big block only on the track, go for the 3 inch. But if your driving a mild 360 on the street go for an exhaust pipe diameter that flows well in the rpm you typically drive in. I've heard so many people ask me why their car got slower after putting on a dual 3 inch system. Isn't it obvious? You don't lose "Back pressure", you have just effectively reduced your exhaust velocity. Which in turn reduces the torque in that street RPM you drive in. 1800-3500 rpm. Velocity,heat and exhaust pulses tuned correctly build torque. Now if your taking this mild 360 to the track on the weekends and it's also a daily driver I would say find a middle ground in pipe size. But BACK PRESSURE is not a thing.