Professional Answer to Exhaust Size Question 2.5" vs 3"

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Dustedu2

Dustedu2

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I asked
("I am installing a 422 stroker in my Duster. About 520HP with TTI Headers. Will I benefit from a 3" exhaust vs 2.5") to an exhaust manufacturer and got this reply:

"550hp would be the minimum for 3" unless you were building a race car."

I still want the 3" so I will probably go 3" anyway.
 
Dustedu2 said:
I asked
("I am installing a 422 stroker in my Duster. About 520HP with TTI Headers. Will I benefit from a 3" exhaust vs 2.5") to an exhaust manufacturer and got this reply:

"550hp would be the minimum for 3" unless you were building a race car."

I still want the 3" so I will probably go 3" anyway.
Click to expand...

One thing lots of folks dont know about pipe is that it has internal drag or friction. The bigger the pipe the more friction created. Just like a car trying to "push" thru the wind,now the exhaust is the wind and it's moving instead.I have no clue where the break even point would be or if it really matters in your situation. Probably not unless your looking for every last h.p.

A bigger pipe will add more weight too.

3" is probably not neccessary but it's what you want so...go ahead and do it!
 
yes 3" probably better, but might be hard to run all the way to the back next to the tank, if your using the smaller TTi headers i don't think the 3" would give much more HP, you could also go 3" to the muffler and 2.5" out the back.
 
3" has a habit of being alitle harder to tame down when it comes to decibels,but alot of the times you also get a bigger and deeper sound and with bigger i dont mean louder just a "bigger" rumble. at 500+ REAL hp 3" is what you want for power.
getting the pipes to fit over the axle and betwen the springs isnt that hard if you are good at cuting and welding universal mandrelbent tubing!
 
There is a lot more to do with the size of the pipe than the HP of the engine. Camshaft plays a critical role in designing an exhaust system. An engine with a high overlap camshaft can not use a small exhaust system as it will be overscavenged. To say it plainly if you got a big cam in it use the 3" pipes. If you have a small cam use the 2 1/2" pipes. There is much more to exhaust then production header manufacturers know about as the dont build real high end systems. I only build high race headers, and all my work is designed for each combination. PM me the overlap of your camshaft, if you dont have that give me the lobe seperation and and the duration at .050 and I can give you an educated guess at what size exhaust pipes to use.

Mark Lelchook
Performance Welding
Racing Headers
 
there is another pipe size that i wish where more comercialy available and not just from the OEM 2 3/4" its a size that would be alot easier to package and soundvice i think it would be a great alternative to get a bit more of the 3"rumble while still being able to tame the decibels easier..
i gues the original recomendations was from Magnaflow by the way.
perfweld its nice seeing a highend builder in this forum!

i do exhaust everyday and helping others descide on size of exhaust and what type of mufflers are very difficult,and the camshaft spec is one thing i havent thought much about,it has passed by in my thoughts but im not that good yet:)
 
perfweld said:
There is a lot more to do with the size of the pipe than the HP of the engine. Camshaft plays a critical role in designing an exhaust system. An engine with a high overlap camshaft can not use a small exhaust system as it will be overscavenged. To say it plainly if you got a big cam in it use the 3" pipes. If you have a small cam use the 2 1/2" pipes. There is much more to exhaust then production header manufacturers know about as the dont build real high end systems. I only build high race headers, and all my work is designed for each combination. PM me the overlap of your camshaft, if you dont have that give me the lobe seperation and and the duration at .050 and I can give you an educated guess at what size exhaust pipes to use.

Mark Lelchook
Performance Welding
Racing Headers
Click to expand...

Here it is and Thanks much!
Cam StyleMechanical roller tappetBasic Operating RPM Range2,500-6,500Intake Duration at 050 inch Lift242Exhaust Duration at 050 inch Lift248Duration at 050 inch Lift242 int./248 exh.Advertised Intake Duration280Advertised Exhaust Duration286Advertised Duration280 int./286 exh.Intake Valve Lift with Factory Rocker Arm Ratio0.570 in.Exhaust Valve Lift with Factory Rocker Arm Ratio0.576 in.Valve Lift with Factory Rocker Arm Ratio0.570 int./0.576 exh.Lobe Separation (degrees)110Intake Valve Lash0.016 in.Exhaust Valve Lash0.018 in.Computer-Controlled CompatibleNoGrind NumberCRS XR280R-10
 
David Vizard did a good article on this. It came down to 2 things, 500hp and up it was 3", but the deciding factor is also the flow of the muffler. Many mufflers don't flow enough air to support 500hp. It is critical to consider muffler CFM when making this choice. I have an 11:1 410 w/hyd roller and went with the 2.5, but used Goerlich 18" can length mufflers that flow 485cfm each. Since I'm just under 500hp, this worked out well, and fits well. TTI head pipes from their headers should fit a lot better, but they don't. I'd recommend purchasing only the TTI tails and muffler hangers if you have a talented exhaust guy (rare) in your area.
 
Dustedu2 said:
Here it is and Thanks much!
Cam StyleMechanical roller tappetBasic Operating RPM Range2,500-6,500Intake Duration at 050 inch Lift242Exhaust Duration at 050 inch Lift248Duration at 050 inch Lift242 int./248 exh.Advertised Intake Duration280Advertised Exhaust Duration286Advertised Duration280 int./286 exh.Intake Valve Lift with Factory Rocker Arm Ratio0.570 in.Exhaust Valve Lift with Factory Rocker Arm Ratio0.576 in.Valve Lift with Factory Rocker Arm Ratio0.570 int./0.576 exh.Lobe Separation (degrees)110Intake Valve Lash0.016 in.Exhaust Valve Lash0.018 in.Computer-Controlled CompatibleNoGrind NumberCRS XR280R-10
Click to expand...

that cam in a 4"stroker should make some serious midrange power:cheers:
i have that same cam in my 3.31"stroke 340 and its pulling hard in the midrange and gets mean at the top end. a friend has that grind in a 3.75"stroke sbc and it runs hard with big traction isues on the street, i cant even imaginge how much fun that cam would be with a 4" stroke:toothy10:
 
As per your cam specs you have a decent size cam with roughly 40 - 44 degrees of overlap. As Duster 340 said he wished they made 2 3/4" tubing more readily available, I think that 2 3/4" pipe in your situation would be perfect. They do make 2 3/4" tubing in 304L but its very expensive. Its used in very very lage displacment NOS Pro Mod engines, or exhaust systems. While the 2 3/4" is out of the question price wise, with that much cam id use 3" tubing. The key to a good header and exhaust system is carring enough exhaust speed to scavenge the engine. But using too small of a tube will create a choke in the system, while too large will not create any exhaust speed, this in turn will slow down acceleration of the engine. This is why youll see a small exhaust work so well at low / mid RPM but it will eventually choke off as its not big enough. I could go on for days but cant due to time. Theres a lot of good articles on my website to help you guys on exhaust theory if you have time to read. While I specialize in high end headers it might be a good read for many of you.

www.perfweldheaders.com
 
perfweld said:
As per your cam specs you have a decent size cam with roughly 40 - 44 degrees of overlap. As Duster 340 said he wished they made 2 3/4" tubing more readily available, I think that 2 3/4" pipe in your situation would be perfect. They do make 2 3/4" tubing in 304L but its very expensive. Its used in very very lage displacment NOS Pro Mod engines, or exhaust systems. While the 2 3/4" is out of the question price wise, with that much cam id use 3" tubing. The key to a good header and exhaust system is carring enough exhaust speed to scavenge the engine. But using too small of a tube will create a choke in the system, while too large will not create any exhaust speed, this in turn will slow down acceleration of the engine. This is why youll see a small exhaust work so well at low / mid RPM but it will eventually choke off as its not big enough. I could go on for days but cant due to time. Theres a lot of good articles on my website to help you guys on exhaust theory if you have time to read. While I specialize in high end headers it might be a good read for many of you.

www.perfweldheaders.com
Click to expand...

Thanks so much for your time. I will look at articles on your site.
 
What's the problem with the 3 pipe and the rear axle clearance??? Am considering a 3 system but hear that there are clearance problems????
 
I have a 3in X pipe off header extensions then mufflers welded right to the back of the X pipe, seems to work fine with me. Motor should have 460-480 flywheel hp with the cam being 240 @50
 
does it make much difference down low or just on top end. Im thinking too big could make the air lazy on the exit end and cut down on the venturi effect. i went with 3.5 inch collecters necking down to 3 inch to the h pipe and then 2.5 thru flow 40s to the back bumper.
 
Personally Im going 3"to the muffler and 2 1/2 over the axle if it's possible to order that at Summit. Then I'll just install electric cut outs after the headers. Restriction smiction!
 
I used TTI headers and 3 inch TTI exhaust on my 408 Duster. The car has a Dana 60 and I had plenty of room. It runs good and it sounds great...
 
dustaar said:
I used TTI headers and 3 inch TTI exhaust on my 408 Duster. The car has a Dana 60 and I had plenty of room. It runs good and it sounds great...
Click to expand...

It's good that the TTI stuff fits so well for ya but I know there are folks on this board who cannot agree. My self I can afford the summit el cheapo but I'll buck up for the walker super hemi turbo's and get good electric cutouts.
 
I'm so happy I read what was said here as there is much information for my future builds. On my end I personally have 2 1/2 inch pipes from the fenderwell headers straight back under the rear going to 5 inch supertrapps which are adjustable for sound as well as low, mid and top end. I've run these on this car on 3 motors so far, without a clearance problem or any problem for that matter that I have noticed and the car is lowered. For my next build which I won't discuss here because its not a mopar, chevy or a ford and have considered going with headers like the old Lola and GT40's exhaust which are sometimes called the bundle of snakes, sorta hard to explain but you can search for it on Google. I believe they are great for low rpm motors like strokers but will cost you big dollars if you haven't welding experience.

The info given here is so intense and truthful that I have been very impressed with the FABO members who replied to the poster and where I too have learned something.
 
perfweld said:
As per your cam specs you have a decent size cam with roughly 40 - 44 degrees of overlap. As Duster 340 said he wished they made 2 3/4" tubing more readily available, I think that 2 3/4" pipe in your situation would be perfect. They do make 2 3/4" tubing in 304L but its very expensive. Its used in very very lage displacment NOS Pro Mod engines, or exhaust systems. While the 2 3/4" is out of the question price wise, with that much cam id use 3" tubing. The key to a good header and exhaust system is carring enough exhaust speed to scavenge the engine. But using too small of a tube will create a choke in the system, while too large will not create any exhaust speed, this in turn will slow down acceleration of the engine. This is why youll see a small exhaust work so well at low / mid RPM but it will eventually choke off as its not big enough. I could go on for days but cant due to time. Theres a lot of good articles on my website to help you guys on exhaust theory if you have time to read. While I specialize in high end headers it might be a good read for many of you.

www.perfweldheaders.com
Click to expand...

i hear you on the price of 304L, i have also found it to take a litle diferent setup to bend but it welds very nice
 
I found this in one of my books a while ago, I use this as an estimate for the exhaust pipe diameter.

Jeep025.jpg
 
And that's right on the money. So many people go overkill and it's just not necessary.


JGC403 said:
I found this in one of my books a while ago, I use this as an estimate for the exhaust pipe diameter.

Jeep025.jpg
Click to expand...
 
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