T-Moss or M.Yount,or exhaust guru's come in

willys1 · Jun 10, 2005

Hey Mike and Tom,A year or so ago I was updating my exhaust from the headers back.You guys told me to keep the stock headers and H-pipe being my motor was stock, and the stock motor needs a certain amount of back pressure,,well I found out the hard way you guys were rite..So I have a new exhaust question Im getting my Thumpers put on and really want a Bassani X-pipe with cats,,but the new metal cats (they flow extremely well) Is this OK or am I still gonna need that back pressure from the factory H-Pipe? Keep in mind Im looking for ultimate "low end" torque!!

vikingpower · Jun 10, 2005

Its not back pressure thats important, its scavenging and velocity. stock headers are not good at either. What you need to do is choose headers based on primary diameter and length, smaller primarys support higher velocity, longer primarys work better at low RPMs; all of this is good for low end torque. Stock headers are OEM stuff just barely better than cast iron manifolds, and swapping to aftermarket shorties and X or H-pipe will see no loss in low end torque. Reading up on some dyno testing and engine theory would be in your best interest.

BaXTeR3221 · Jun 10, 2005

The bassani X with the cats shouldn't hurt performance much, if any at all. The stock pipe is there to decrease sound and pass emissions, its not the best for performance.

willys1 · Jun 10, 2005

Well guys I dont have to read anything,I have hands on experiance.First I replaced the stock headers with FMS shorties and noticed a loss in low end torque.The stock headers are the best set up for a stock motor till you get up over 260HP,and I "do" believe this to be fact!! Next I put on an off rd h pipe and noticed even more loss of low end torque Yes,it does make it quieter,but it also provides a good amount of back pressure which "is" needed with a stock motor.I put the stock H pipe back on and noticed a gain in performance!! I was told this would happen but had to find out for myself So thats why Im asking about the X pipe.

vikingpower · Jun 10, 2005

OK, I've got some numbers: In my "5.0L Ford Dyno Tests" book by Richard Holdener, a 93 GT w/90000 miles and a few bolt ons ran the following numbers on a Dynojet before and after installing MAC shorties and a ProChamber offroad pipe:
stock: 217hp@4800, 273lb/ft@3600
MAC: 232hp@5000, 284lb/ft@3700

at 2600 rpms, the numbers were the same for both setups: 124hp, 250lb/ft. As you can see, there was no loss of low end torque.

willys1 · Jun 10, 2005

vikingpower said:
OK, I've got some numbers: In my "5.0L Ford Dyno Tests" book by Richard Holdener, a 93 GT w/90000 miles and a few bolt ons ran the following numbers on a Dynojet before and after installing MAC shorties and a ProChamber offroad pipe:
stock: 217hp@4800, 273lb/ft@3600
MAC: 232hp@5000, 284lb/ft@3700

at 2600 rpms, the numbers were the same for both setups: 124hp, 250lb/ft. As you can see, there was no loss of low end torque.

Im just telling you what I experienced in my car,and what some other very knowlegable people have told me..Yea,,you will gain some HP and torque,but its give and take,take away down low and put it up top..I dont want to get in a debate about this,its a straight forward question that mite save me some money.

1993SSP · Jun 10, 2005

Ive had em all 3 guys, the H pipe, the X pipe and the prochamber H pipe, and out of the 3 I wish i had my prochamber back, it was the best, but i like the sound of my x pipe. The prochamber hands down made the most low end torque.

vikingpower · Jun 10, 2005

Ok, an X pipe will do a better job of scavenging than the factory H-pipe, but its gonna give you a lot less backpressure because it flows a lot better. If you want the backpressure keep the factory stuff.

willys1 · Jun 10, 2005

1993SSP said:
Ive had em all 3 guys, the H pipe, the X pipe and the prochamber H pipe, and out of the 3 I wish i had my prochamber back, it was the best, but i like the sound of my x pipe. The prochamber hands down made the most low end torque.

I would love to try a pro chamber,but NJ is strict with emissions

89MustangGX · Jun 10, 2005

I think you'd be safe going to headers and an h-pipe now -- but that's just my opinion...

90mustangGT · Jun 10, 2005

Once again, backpressure is always bad. The fact is that larger exaust will cause more backpressure if the energy and volume of the air isn't sufficient to push the gas out of the car. I have a pnumatic (sp) (air powered) vaccume cleaner with no mechanical parts except a on/off valve. So how do you turn 90+psi into vaccume? Well it has six small ports that face towards the bag. When you squeeze the trigger the air is blown away from the nozel, causing a vaccume. Exaust works the same.

Why would stock headers work best in a stock motor for low end torque? Well even though they are kinked, these kinks act like venturie tubes in a carb to speed up the air, but not allow it to blow back in. Forming a chamber of vaccume behind the kinks so when the exaust opens up there is less volume of gas and actually sucks the exaust up and increases velosity.

Michael Yount · Jun 10, 2005

Unless you can go to long tubes (1.5" primaries with your stock set up) stick with the stock HO headers; shorties won't help. On the other hand a good 2.25" or 2.5" H or X pipe with high flow cats will help.

The gains listed in the article referenced above are largely due to the rest of the exhaust system - not the headers. There have been a number of folks who've posted before and after dyno runs with just header changes - stock HO headers replaced by aftermarket shorties. Unless you get up over 280-300HP, aftermarket shorties are unlikely to help you. We lost 3HP on mine switching from stock HO headers to FRPP shorties.

5spd GT · Jun 10, 2005

Bummer...my mac headers helped on my bolt-on motor compared to stock

stang8urimport · Jun 11, 2005

I have a Prochamber, and it sounds awesome with the stock headers and mufflers. Wouldn't give it up for anything. I always recommend MAC's midpipes and catbacks. Great stuff. Their headers on the other hand....... lol... And if you did indeed "lose low end torque", there is no possible way you lost so much that you would get a seat of the pants difference.

Michael Yount · Jun 11, 2005

5spd - got any data?

5spd GT · Jun 11, 2005

Michael Yount said:
5spd - got any data?

Just SOTP...the electric fan helped out more...there was 3 different bolt-ons put on from track time to track time...so no "single" variable was changed. The headers gave it a better sound and I felt a bit more pick-up from the SOTP. Mine are equal length headers...I want longtubes.

Michael Yount · Jun 11, 2005

I swore to my buddies based on SOTP that the shorties improved mine -- the dyno data seemed to tell a different story.

SOTP data is extremely unreliable (gains or losses), and if you changed other things at the same time -- well, the fact is you don't really know with certainty what difference your Macs made.

04sleeper · Jun 11, 2005

Hey Billy,

From my personal experience, I lost power from switching from stock headers to 1 5/8" FRPP's so I decided to go with smaller headers and a friend had some 1 1/2" equal length MAC shorties. I was sure these would work with my car with my heads being stock and unported but I was wrong.
I ended up cleaning up the welds on the inside of my stock headers and it seemed to work best. On the Dyno everything went right back up.

As for the mid pipe I found the VRS OR x-pipe to be worth 9 HP and 11 ft. lbs. over the stock cats but I think the catted x-pipe would show very close numbers.

Kevin

dstanggt50 · Jun 11, 2005

I"ve read that headers on a stock motor gave around like 1-2 hp depending on rpm (5.0 mag), but I've read upgrading from stock h pipe getting around 10hp (mm&ff) on a 95 gt, w/nothing else. My car came with a catted h-pipe for shorties, and I didn't put my full lengths until after heads, and my old 87 I kept the stock headers until my heads, so I have no personal data, but my friends 92lx got quicker after an off road h (no dyno, his sotp)(stock headers).

willys1 · Jun 11, 2005

89sleeper said:
Hey Billy,

From my personal experience, I lost power from switching from stock headers to 1 5/8" FRPP's so I decided to go with smaller headers and a friend had some 1 1/2" equal length MAC shorties. I was sure these would work with my car with my heads being stock and unported but I was wrong.
I ended up cleaning up the welds on the inside of my stock headers and it seemed to work best. On the Dyno everything went right back up.

As for the mid pipe I found the VRS OR x-pipe to be worth 9 HP and 11 ft. lbs. over the stock cats but I think the catted x-pipe would show very close numbers.

Kevin

Hey Kevin!! Yeah I think Im going with the X-pipe,I hear alot about the sound difference also,Im curious to see,lol,,or hear I know Im close to the line in terms of HP and not needing the stock stuff for back pressure..I will call you this week,finally got things worked out Thanks for the reply's guys

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