2.5 complete exhaust VS a 3.0 complete exhaust

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hardcore5657

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I just got dougs headers. Now i am going to do a x pipe or h pipe dont no which one yet and either 2.5 or 3 inch exhaust. I have a 360 with 10 -1 compression, rhs magnum heads, comp cam with .545 lift, edelbrock magnum air gap intake, holley 770 carb. I don't no how much HP i am making. Does 3 inch exhaust sound to big. Will I lose bottom end torque or is that just a myth?
 
I would say a 2.5" system would be good up to 450-500 HP. I'm using a 3" system with my 408 that has 530Hp...but i could be wrong...
 
i built a fairly moderate 360 with intentions of adding a power adder. used TTI headers, x-pipe, and 3 inch exhaust.

if this is primnarily a street car, go with 2.5. youll be much happier. the 3 inch is tough to fit without heat and rattles, is louder, and kills ground clearance.

also be honest about wether or not youll actually be stepping up the motor later. that way you only have to buy one system.

im still looking for someone to trade my 3 inch with a 2.5. im never actually going to go power adder, and need the ground clearance, not the extra exhaust flow. im making 425 at the rear wheels, by the way.

michael
 
I'm running a stock Magnum with Airgap, Doug's headers, Jeg's mandrel X-pipe kit, and 2.5 inch all the way with cheapo turbo mufflers and my car runs and sounds perfect for me. I wanted something quick that was quiet and no drones. It's actually much faster than I thought it would be!

The only 3" or larger I will ever install will be a turbo downpipe.
 
hardcore5657 said:
I just got dougs headers. Now i am going to do a x pipe or h pipe dont no which one yet and either 2.5 or 3 inch exhaust. I have a 360 with 10 -1 compression, rhs magnum heads, comp cam with .545 lift, edelbrock magnum air gap intake, holley 770 carb. I don't no how much HP i am making. Does 3 inch exhaust sound to big. Will I lose bottom end torque or is that just a myth?
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I talked to Doug Thorley personally about 1997 about all of this. I actually got the third set of Doug's Headers for the early A when he reintroduced them. I got them for 500 bucks delivered. Nickle plated. I had a very long conversation with him. He's a nice old dude. He said that he had done extensive dyno testing at that time and any form of crossover pipe had little to no effect and in some cases lost power. It was completely contradictory to what everybody else was claiming at the time...and still claims today. He said that it was all marketing hype. He also said something else that I completely agree with. that any form of crossover lessens the exhaust tone. That is, takes away from the exhaust note. Makes it sound "less crisp" if you will. His words, not mine. He also said that going up from the collector size showed no gains either. Hell, he's still kickin and workin everyday. You can probably call him yourself.
 
hardcore5657 said:
Stroker, are you saying go with a h pipe or just straight headers back?
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I am saying when I spoke with Doug Thorley, he had no recommendation for any type of crossover whatsoever. He had dyno proof that they were not effective. He seemed to think all the hype over them was just that hype. Yes, his recommendation was two completely separate pipes. Of course, I am sure the arguement will ensue. lol I find that's probably a pretty honest assessment, because since he is in the exhaust business, I think he would offer some form of X or H and he does not, because his opinion (based on dyno fact) is that they are not worth the money. I find that interesting from someone with a 40 plus year racing history.
 
When I put in my X pipe, I also ran full length pipes to the bumper at the same time. When I did all of this, I could tell a huge difference in the power output. Since I added two items at the same time, I cant really pinpoint what made the car feel better-the X or the complete exhaust system. One thing I will say is true about an X, is that id made the exhaust note quieter, and somewhat muffled, just like what was said above that the note was not as crisp. I like the way it changed the tone though, it really helps with the "sleeper" vibe of my car cause its fairly quiet.
 
.............I know for sure a H pipe/cross over pipe quiets the down........Ford has had a H pipe from about 1965 up...........kim.........
 
After a decade dyno-ing motorcycles, I have a couple observations that are relevant. We did a few thousand exhaust swaps in that time.
Note that I just put new exhaust on my car, and it runs great. I did not dyno before and after. Why? Because I don't really care, as long as it beats up on ricers.

#1. If your vehicle has a dip in midrange torque, it will feel faster. Why? Because it feels like it's "coming on the cam" when in reality it's just getting to where it's running "right". A full torque curve feels much slower...but in reality is much faster.

A LOT of aftermarket manufacturers sold their goods not because they made the vehicle run faster, but because it felt faster. On a street car, this may not be a bad thing to an ignorant driver.

#2. Simple fluid mechanics is what it is, and there's no real reason that X pipes or H-pipes wouldn't add power. I'm not saying they do or don't, just that there's nothing that says they will not.

#3. I go by empirical evidence whenever possible. That rules out a lot of maybe's. Mopar Action had a proven dyno increase in peak power on their Bold Beeper 'Runner. See note #1.

Increase in power, and increase in peak power are two WAY different things. If you could have 500 horsepower from idle to 6000 redline, or 100 horsepower from idle to 4400, 900 raging ponies from 4400 to 4600, and 100 horsies from 4600 to 6000 redline, which would you choose? Which one makes more horsepower? One has more overall, one has more peak. More importantly, one is easier to brag about.

So, where are the x-pipes, h-pipes, no-crossover, etc. making power? A drag racer is going to look at peak power and little else, a road racer looks at midrange and little else, and a street driver looks at magazines and little else. Which one are you? What is it exactly that you are after, and what exactly is it that so-and-so told you, and what exactly were they after when they did their research?

Again, not saying wrong, right, or indifferent...just advising people to ask questions that may help them get what they want.
 
jos51700,

Pretty good observation, "Street driver looks at magazines and little else." Part of the problem is we don't have the time, money, or resources to test the claims of parts manufacturers. Unfortunately magazines are beholden to their advertisers so they are rarely if ever critical of any products in their magazine.

This is wrong.

None of us really know the cost or benefit of a 3" exhaust on a street car with 400-500 Horsepower. Does it really make it "louder" or simply "lower" and thus shake the fillings in our teeth? Does it make more top end HP at the expense of mid range torque? Which exhaust system provides more power "under the curve?" Which car is faster 0-60 and in the quarter mile the one with 2 1/2" exhaust or 3"?

We won't ever know the answers to ANY of the above questions. Why, because it would hurt the advertising dollars in Hot-Rod Magazine et. al. If everyone knew that the there was no benefit to a 3" exhaust system, or it was only worth a couple of hundredths sales of 3" exhaust systems would plummet. Can't have that.

Regards,

Joe Dokes
 
Joe Dokes said:
jos51700,

Pretty good observation, "Street driver looks at magazines and little else." Part of the problem is we don't have the time, money, or resources to test the claims of parts manufacturers. Unfortunately magazines are beholden to their advertisers so they are rarely if ever critical of any products in their magazine.

This is wrong.

None of us really know the cost or benefit of a 3" exhaust on a street car with 400-500 Horsepower. Does it really make it "louder" or simply "lower" and thus shake the fillings in our teeth? Does it make more top end HP at the expense of mid range torque? Which exhaust system provides more power "under the curve?" Which car is faster 0-60 and in the quarter mile the one with 2 1/2" exhaust or 3"?

We won't ever know the answers to ANY of the above questions. Why, because it would hurt the advertising dollars in Hot-Rod Magazine et. al. If everyone knew that the there was no benefit to a 3" exhaust system, or it was only worth a couple of hundredths sales of 3" exhaust systems would plummet. Can't have that.

Regards,

Joe Dokes
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I only subscribe to one magazine (Mopar Action), because their tech is spot-on and they post it when they make mistakes. Generally speaking, they are not sponsor-driven like most (So it seems, anyways).

MCG is OK and I'll subscribe to get a free shirt but the authoring is, um, not to my liking.

That said, I urge every enthusiast to cancel their magazine subscriptions, and go to at least one car show or race or bench-racing session a year, instead. Guaranteed more knowledge, better connections, and typically factual information about a given setup ("Here's how it sounds. Let's go for a ride and see what you think!")

Like I said, empirical evidence es el numero uno.
 
...Larry Sheppard (Mopar Performance/Direct Connection) says to install your H pipe about 12 inches past the collectors.
the only benefit is noise reduction for street cars.
 
If its too loud, you're too young. If it not loud enough, you're too old.:headbang:
 
Well I realize this is a MOPAR forum, but I couldn't find a comparison using a mopar so here is one using a 5.0 Phord motor.
The bottom one is from Car Craft also with a Phord. I have a 2.5 with an H pipe in my stroker exiting under the bumper, my .02.
 

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Honestly, in terms of OP, the 2.5 system is more than adequate for you needs, and cheaper, and lighter.
In terms of science... I think the reason you don;t see huge dyno results overall is simple: Every package is unique, and by package, I mean the chassis, engine, noise level acceptance, etc. I bent custom pipes for a couple years. Xs and Hs will quiet any exhaust. So will turning down the ends, and going from larer diameter to smaller diameter piping, adding bends, changing the position and size of the muffler or adding a resonator.... I think the main issue is with a V8 layout, X can't be placed where it might actually help.. which would be closer to the collectors. The trans and crossmember is in the way. Look at a Winston Cup car on it's roof... They do have merged pipes, and they are way rear of the trans. I'm fairly sure that's because it makes power, and they are tuned for enhancing peak power which in those cars is 8-9K rpms. It would be lighter to have them exit without traversing the chassis.
 
ir3333 said:
...Larry Sheppard (Mopar Performance/Direct Connection) says to install your H pipe about 12 inches past the collectors.
the only benefit is noise reduction for street cars.
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I've always thought about it like this...if your muffler is a restriction, but you have two instead of one (Like connecting one bank of cylinders to both exhausts by an H or X pipe), wouldn't that be 1/2 as restrictive and therefore a benefit?
 
412 Stroker said:
Well I realize this is a MOPAR forum, but I couldn't find a comparison using a mopar so here is one using a 5.0 Phord motor.
The bottom one is from Car Craft also with a Phord. I have a 2.5 with an H pipe in my stroker exiting under the bumper, my .02.
Click to expand...

I plotted the top chart, it has the curves of a pickup truck motor, and a dog at that. There's a clear emphasis on torque, and the hp falls off very early. Oddly, the X-pipe shows solid gains immediately after the 5454 crossover.

The bottom chart is worthless. Too many variables and not enough for statistical analysis.
 
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