Horsepower increase

[BOURRET]

What is the average horsepower gain (or the % increase) obtained by removing the mufflers ?
Happy new year to everybody

[Ron61]

BOURRET,

That is a kind of hard question to answer as it will depend on the type of mufflers and exhaust you have now. On my 69 Ford Cobra with the 439 CI. the factory used MOPAR Hemi mufflers because they were the lowest restriction ones back then. I have two huge exhaust pipes and I think they told me I would gain maybe 5 to 10 horsepower if I disconnected the mufflers. Not enough to mess with unless you are racing and the noise is defening. When we started it in the garage, it shook all kinds of tools and cans off the guy's shelves. If you have the restrictive super quite type then you would gain more than I could. Try running your set up through desktop Dyno and that will give you a pretty good idea of what you can gain. Sorry I can't be of more help, but maybe some of the guys that have more experience in this area than I do can tell you more.

Ron

[SCOBRAC]

Depends,

Sometimes none. I had a 1966 GT fastback that ran worse without mufflers.

[nanard289]

Michael is right! When mufflers are removed, it is frequent to observe that air / fuel mixture become too learn and consequently you can lose some HP (even if you win some decibels!) In the worst case, you can destroy your engine (pistons can reach the melting point). So, if you modify, remove or replace header part (or air filter), you have to tune the carb accordingly (don't forget to check also the spark plugs) to maintain ideal air/fuel ratio. In this case only you can expect win some additional HP.

[DAVID GAGNARD]

That was going to be my next question.....

I do a few (3 to 5) open tracks a year with my Mustang,making some upgrades this winter,racing tires,brakes,racing seat,etc.etc....

Local machine shop that does my enigne work just got a pipe bender like the muffler shops use,bought it from a shop going out of business,dirt cheap.... He also bought most of the stock of exhaust pipe,from 1.75 inch to three inch,got a truck load of the stuff.....

He has offered to make me some tailpipes that will come out in front of my rear tires for FREE. Right now I have the Dr. Gas X crossover system with mufflers and tailpipes coming out the rear of the car... The idea was to take off my mufflers and tailpipes (takes about 10 minutes) and put on the straight tailpipes (2.5 inch diameter) for open track events....Running an iron headed 351-W,making about 350 hp....My question was how if any will it affect my air/fuel ratio without mufflers?????? I'm running a Holley 600 DP,jets are 64 front and 74 rear I think,a tad rich at idle and low speed,but just right at highway speeds and on the track....

Also will it be worth the 10 minutes of work to remove the mufflers,they are rather large flat type from an early 80"s Ford LTD??????

I kinda would like to make some "noise" at the track anyway......

David

[RACER X #99]

Dave,
I have no idea if Open Pipes will lower your lap times. I will guarantee it will increase your fun factor and even if you ain't going faster it sure will seem faster.
Nothing sound better than a screaming sb. The big blocks may bellow but the sb's scream. But you already knew that ,now you will be able to hear it.

Cranky

BTW don't forget the earplugs, you wanna hear the car today, not for the next two days.

[coyled]

David, it will depend on the power of your motor and the exhaust itself. My guess would be that with 350hp and a good exhaust system that you will not gain much hp. Try it and see if it feels faster or your lap times improve. Or, go to the drag strip and make 2 passes, 1 corked up and the other open. If the MPH picks up, you are making more power. Scott

[DAVID GAGNARD]

Thanks guys,I figured I probably would not gain enough to really make it worth the trouble,especially on a road course (I'm not that good of a driver "yet"),but I do love the sound of the Vintage GT-350's on the roadcourses with open pipes,looks cool also......

Will make the change and try it out,but I guess I should also keep an eye on my plugs too......At least they will know when I'm on the track......

David

[trularin]

SCOBRAC is correct. The designer of the engine takes into account the backpressure the exhaust presents.

A well tuned engine, from a design point, will run best with an exhaust system that allows the engine to breath, but is present.

Just my $0.02

[nanard289]

....next question

Hi Dave,

Your local machine shop dealer has a good approach: you have to replace the muffler by a pipe to keep a minimum exhaust pipe length. By this way, you will improve significantly your engine performance for following reasons:
First, when you remove the muffler, the exhaust gas way is free (without zigzag) and the pistons take only few power at the crankshaft to push the exhaust gas in the headers.
Second, inside the headers (at the middle), exhaust gas are pushing in front (to output side) but they are pulling in back (cylinder side) until to create a vacuum. This phenomenon is amplified with the gas velocity. Consequently, (if the exhaust pipe is long enough to favor it) due to the vacuum in the cylinder, the fresh gas will be strongly sucked when the inlet valve will open even if the piston still rising (that is the reason why you have to tune your carb). If the exhaust pipe is too long the gas will lose velocity and will block the inlet gas (that is the reason why you have to evaluate the total header length).
To conclude, if you replace only your muffler by a pipe (with a good carb tuning), you will win some HP. But if you change also your camshaft to optimize the vacuum phenomenon (to anticipate and to increase the inlet valve opening) the power gain will be more significant (but it is not a 10 min. operation!) Anyway as say Cranky, the open pipes will increase your fun factor and that is a very strong argument.
Bernard

[flipper35]

As I recall when tracks like Portland started requiring mufflers for the Trans Am cars they found the mufflers increased the HP and started running them required or not. This may or may not help with your question though. Just that all generalizations are false. Including this one.

[DAVID GAGNARD]

Brent;

I agree,I read some time ago (2 or 3 years) that a couple of tracks began requiring mufflers and had a decible (???) limit.... These cars where similar to the Busch cars in size/looks/power..... A couple of engine builders began expirementing with different headers and muffler combinations.... One shop found a combo that made the exact same hp and torque with the mufflers as it did with open headers,but he spent a lot of time and money on different combinations to get there.... I do not have the time nor the money nor the motor for this,but it can and has been done....

I just want to make some noise when I'm on the track!!!!!!!!!!!!!!!!! I may even switch back once I try it.... On the road course it is real easy for me NOT to have to watch the tach for shift points as I can tell pretty accurately my rpms with the noise of the motor.... After a few laps at speed,I then pretty much know approximately where I will be shifting..... When not in traffic I always watch the tach,but sometimes in traffic I'm watching my mirrors and just shift by the engine sound....

Also,nice big pipes coming out just in front of the rear tires just looks soooo gooood,kinda like the cool looking side pipes on a Cobra.......

Bernard,you are correct about pipe length and tuning... When I was with a dirt track team some years ago,we ran open headers with tail pipes..... A couple of top teams told me the way they determined tail pipe length was to use pipes longer than you would think and paint them with a cheap can of spray paint...... Where the paint quit burning off the tail pipe was the correct lenght or at least close to it.... We used that as a guide....


David