how much hp with this exhaust set up 5 hp at least?

65stang289 · Aug 9, 2005

I just got some 40 series with X pipe and 3 inch dumps. How much of a difference is the X over the H? I just got it off my buddy who just sold his fox body.

12sec67 · Aug 9, 2005

what did you have before?

12sec67 · Aug 9, 2005

stock H pipe, 2" ... 2 1/4"....?

65stang289 · Aug 9, 2005

Which time In the past 2 years I have had a few different sets on. I had a 2.5 H pipe with flowtech on. Then I just ran a foot of pipe. The last one I had was glass packs to the headers before this one. I am going to the track friday with 2 new things the exhaust and the heads. I ran 9.5 NOW I want to run at least A 9.1.

66P51GT · Aug 9, 2005

IMHO, 3" is too big for your setup. You will lose velocity in the lower RPMs and it will hurt your low-end torque. You may pick up some peak HP but not sure there is an overall benefit. Average HP over the entire power band will probably be higher with the stock 2 1/4" exhaust.

X vs. H is negligible on a stock motor. With chambered mufflers like the 40 series flows, the h-pipe has proven to produce more power (2-4HP more than an x-pipe) on high-performance engines.

brianj5600 · Aug 9, 2005

Depending on the tune, it could go slower. Changes in back pressure can change jetting needs.

57fairlane · Aug 9, 2005

66P51GT said:
X vs. H is negligible on a stock motor. With chambered mufflers like the 40 series flows, the h-pipe has proven to produce more power (2-4HP more than an x-pipe) on high-performance engines.

Did you dyno this? Is this on a chassis or an engine dyno?

66P51GT · Aug 9, 2005

It was a chassis dyno. It was a test done by 5.0 a couple years ago. The test used all the same tubing (can't remember if it was 2.5" or 3") and swapped out different combinations of mufflers with H and X pipes. The maximum difference found on a ~375HP engine was about 5HP. I'd have to go through too many boxes to find the article so you will just have to trust me . One of the summary comments was "Chambered Mufflers like H pipes."

Of course I didn't listen and purchased an x-pipe to mount in front of my Delta 50s. This is mounting behind a ~400HP roller block with 2 1/4" pipes. I like the sound of the X and that is why I purchased my combination. I also didn't want to go larger on the pipes to retain some of the low-end torque. Hopefully it isn't too restrictive. If so, I will swap out for 2.5" pipes. I'd reserve the 3" for strokers and big-blocks looking at peak HP.

My basic rule of thumb is buy headers for power and mufflers for sound.

BlueMonster65 · Aug 9, 2005

exhaust science

from what i have read the ideal setup for an exhaust on a street car with 300hp to 400hp would have long tube headers with 1 5/8" primarys and 2 1/2" collectors then 2 1/4 pipe then to a 2 1/4 or 2 1/2 h or x pipe. 2 1/2 pipes out of the crossover pipe to a 2 1/2" muffler with 3" over the axle pipes. the reason you want a small pipe immediately after the collector is to increase the velocity of the exhaust gas exiting the engine to promote cylinder scavenging. as you get farther away from the engine you need the exhaust gasses to expand so gradual increases in the pipe aid in the expansion and reduction of back pressure while still promoting scavenging of exhasut gasses. the muffler is often refered to as an expansion chamber and it allows the gasses to fully expand. having a larger tailpipe will pretty much only increase volume (that's sound not flow) this is becasue with a chamber style muffler such as the flowmasters after the muffler there is no backpressure. the exhaust gases have fully expanded and are just exiting due to the pressure waves created by the engine. there is literally no restriction. higher horsepower level should use the same guidlines but with larger primary and collector pipes to accomodate the increased flow from a larger or more powerful engine.

66P51GT · Aug 9, 2005

BlueMonster65 said:
A street car with 300hp to 400hp would have long tube headers with 1 5/8" primarys and 2 1/2" collectors

Mac True-Fit Long Tube headers have these dimensions. They are available from Dallas Mustang for ~$250.

65stang289 · Aug 9, 2005

I have long tube headers they are Hooker Comps. I just have 3 inch dumps and a 2.5 pipe.

57fairlane · Aug 10, 2005

BlueMonster65 said:
the reason you want a small pipe immediately after the collector is to increase the velocity of the exhaust gas exiting the engine to promote cylinder scavenging.

Walk me through this one.

It seems like you are assuming that the motor is producing only enough power to dictate using 2 1/4 pipes.

BlueMonster65 · Aug 10, 2005

not exactly

its not that simple well maybe it is. the key is to not go with too big a pipe right after the collector for about the first few feet. general guidlines suggest 2 1/4 pipe for under 300hp 2 1/2 for under 400hp. what i am suggesting is that by mixing the pipe sizes a better exhaust can be created for a car working in that hp level of 300 to 400. and it is absolutely critical that all pipe bends are mandrel bent so that the pipe maintains the diameter thru the bend. this means avoid accordion type bends or benders that flatten the pipe. a mandrel bend 2 1/4 exhaust will out flow a cheap accordion bend 2 1/2 exhaust.

57fairlane · Aug 11, 2005

BlueMonster65 said:
General guidlines suggest 2 1/4 pipe for under 300hp 2 1/2 for under 400hp. what i am suggesting is that by mixing the pipe sizes a better exhaust can be created for a car working in that hp level of 300 to 400.

I would say even going too small has a negative effect as much as too big.
David Vizard performed Hundreds of dyno tests and found that an engine needed enough air flow for 2.2 cfm per unit of HP. Therefore a 400hp engine would need 880 cfm (400 x 2.2). However running a dual exhaust you could divide that number by 2 and get 440. So in theory you only need an exhaust system that is capable of flowing 440 cfm. But how does this apply? A typically section of 2 1/2 pipe flows around 550 cfm. So again, in theory you could support up to 500 hp with a 2 1/2 and have within 1% of the maximum power output. Would a larger diameter help? At higher RPMS, yes.

The only time I could see how changing pipe diameters would be a good idea is when they are at the tail end of an exhaust system (the axle back?) and only for the reason of keeping the exhaust hot.

Edbert · Aug 11, 2005

66P51GT said:
You may pick up some peak HP but not sure there is an overall benefit. Average HP over the entire power band will probably be higher with the stock 2 1/4" exhaust.

This is a KEY concept for most of the bolt-ons out there. Magazine articles and advertisements are all wasting our time and money discussing which one might have picked up 3-10 peak horsepower or foot-pounds here and there. The numbers you SHOULD want to see is average ones. A smaller pipe could lose 5HP at 6,000RPM but gain an average of 5HP all the way from 1,500-5,000RPM and be dead even from 5-6K. Which RPM range will you spend most of your time in?

LMan · Aug 11, 2005

66P51GT said:
X vs. H is negligible on a stock motor. With chambered mufflers like the 40 series flows, the h-pipe has proven to produce more power (2-4HP more than an x-pipe) on high-performance engines.

..hardly worth the trouble

how much hp with this exhaust set up 5 hp at least?

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