so like the title states, i need some info.
i let my friends drive my car, friend 1 has built multiple stangs and friend 2 knows his fox lol. SO ANYWAY, after friend 2 drove it he said it was very nice but but it felt a little as if i had less torque than stock. he told me its because i dont have enough back-pressure
then friend 2 drove it and said its very nice for wat i have done to it but puttin on some real mufflers would help me me some.
when friend 2 drove it i was wasnt with him an i finally heard my car and it is LOUD AS FUCK
i just have a few things done to my car but nothin major: explorer intake, cai, 67mm TB, 73mm MAF, flex-a-light manual fan, mac pulleys, msd 6al, msd coil, diablo chip, cobra clutch,bbk adjustable fuel pressure regulator set at 41 lbs, mac equal-length headers, 2.5" custom h-pipe with dynomax race bulets where the cats usually go.

so with all that said, do u think i have too much back-pressure or too little or wat. or r they just talkin out their ass lol

 

i was thinkin maybe a would add mufflers to my set up so i could quiet it done and make it look like i have cats if a cop says i dont lol.
or just replace wat i have, but it depends on the whole back-pressure thing

 

I have heard about the mythical backpressure theorys, and as far as I have tested, they are all crap. My experience in general, less backpressure = more power.

I have seen a few 'oddball' cases where seemingly positive exhaust changes produce unexpected results, but I am not 100% sure what is at work in those cases. They need more study to determine the real cause.

Having said that, I am open to hear about anyone elses real data on the subject.

Brian
EFI-Unlimited

 

thats wat makes sense to me, but wat iv read it needs some backpressure

thanks for the info

 

V8 engines are odd fire motors. The exhaust pulses are not even. NA V8 engines gain power by utilizing exhaust scavenging. This is mainly done in 2 area's. With long tube headers the size, shape, length of the collectors can make or break an NA power band. Custom long tubes will be made to optimize the exhaust stroke and the cam. The size and length of the collector can actually be tuned move the torq curve of a power band. Shorty headers have no collector,.. thus no real scavenging if offered by using them. They only thing shorties would offer in the way of a performance gain would be by virtue of using larger tubes and less restrictive bends that cast manifolds create. But the full potential of any scavenging would be lost by using shorty headers.

The next area that would focus on scavenging would be in the mid pipe. A cross over in the mid pipe can open up as much as 5 - 10 hp. Running simply straight pipes with no cross over would be missing out on this.

With a basically stock motor like what your running, off the shelf parts will work best. If you run regular Flowmasters or any other chambered muffler,.. they will create all the back pressure the engine needs.

 

ok u sound like all the other pages iv found on this stuff. lol
not bad, im tryin to understand it each time i read it.

so do u think i should replace my muffler/resignator or add a muffler to it?


and i love flows, they sound sexy, but EVERYONE has them. lol so if theres others that do the same ill get those.
im lookin at gettin a set of 07 stock GT mufflers, is that a good idea?

 

and does the size of the collector on equal length make a difference or no?

and curious, is there a difference between equal length and shorties?
i would think equal lenth would be better but iv read and heard that shorties r better

 

Equal length OR shorties?

What are you asking?

You can have equal length shorties AND you can have equal length long tubes. Equal length headers means that all primary pipes from each cylinder have the exact same length to the collector. With most average headers the front primary pipes are longer and the rear pipes closer to the collector are shorter. These are called UN-equal length headers. And again,.. can be short or long tube.

Shorty headers have almost no collector and compared to long tubes will come up short on low end torque when looking at a dyno graph. Long tubes can gain low end torque by adding 6 - 8 inches of pipe the same diameter as the collector before the mid pipe. This is called 'tuning' the collector. By changing where the torque comes in at on the RPM band at almost no cost to HP. The size and length of the primary pipes is what generally effects HP. Bigger is not always better with primary pipes. This is where backflow comes in to play. When primary pipes are increased in size this will force the HP farther and farther up into the RPM band until it exceeds the cam specs or efficiency of the engine size and will fall and lose HP once that threshold is passed.

Here are a couple articles to read that explain more.
Header Basics - How Headers Contribute to Horsepower - Car Craft Magazine

Header - Exhaust Manifold - Tech - Jack Burns - Popular Hot Rodding

Hurst

 

im with this 100%

 

To a degree guys.

Lets use a stock 5.0 HO motor as an example.

Which headers will make the most HP with the best torque curve for drag racing purposes? This would be an essentially bone stock car with an off road exhaust.

Stock shorty headers with stock exhaust was used as the base line.

1 5/8 long tube headers with a 6" 2.5" diameter collector

1 5/8 long tube headers with a 10" 2.5" diameter collector

1 5/8 long tube headers with a 6" 3" diameter collector

1 5/8 long tube headers with a 12" 3" diameter collector

1 3/4 long tube headers with a 6" 3" diameter collector

1 3/4 long tube headers with a 12" 3" diameter collector

1 7/8 long tube headers with an 8" 3" diameter collector

1 7/8 long tube headers with a 12" 3" diameter collector

2" long tube headers with a 12" 4" diameter collector

I have a dyno chart here that shows the difference between each header.

Each headers had exhaust matching the collector diameter. That was the only difference in the tests. The same Borla mufflers were used in each test.

According to Brian and your theories,.. the 2" long tubes would offer the most HP and Torq. Do you agree with your theories or care to elaborate on why you chose a different header?

Hurst