do i really need 3" exhaust

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rod7515

rod7515

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Building a 408 for in my dart. Going with a good size roller cam, stroked, tti headers, tunnel ram and ported heads plus other mechanical upgrades. engine builder is recommending 3" exhaust, I was thinking 2 1/2". Going to be driving it approximately 1500 miles a year. Is 3" really needed of is that overkill? I'm worried about ground clearance plus I already have 2 - 21/2" flowmaster mufflers I thought I could make use of. What are your thoughts?
Thanks, Rod
 
rod7515 said:
Building a 408 for in my dart. Going with a good size roller cam, stroked, tti headers, tunnel ram and ported heads plus other mechanical upgrades. engine builder is recommending 3" exhaust, I was thinking 2 1/2". Going to be driving it approximately 1500 miles a year. Is 3" really needed of is that overkill? I'm worried about ground clearance plus I already have 2 - 21/2" flowmaster mufflers I thought I could make use of. What are your thoughts?
Thanks, Rod
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If you're not trying to squeeze every bit of HP out of that 408, the 2-1/2 will be fine.
 
Rod, you'll have more power on the street then you could ever really use regardless of the exhaust size. If you're more comfortable with the 2 1/2 pipes, go for it. It will certainly be quieter then the 3's and you can always open them at the track if you want to get the most out of your combo.

Just for my personal knowledge, i am curious as to your primary header size? I'm not real familiar with all the TTI offerings, but it sounds like the 1 3/4-1 7/8 step would best fill you needs with the 408?
 
I'd run the 1 7/8 headers from TTi, My engine builder told me to run that size,
 
There's no reason to have 3" unless you are pumping big horsepower. 2 1/2" is what I would do unless I had over 500 horse
 
you built a 408 and soon as you get used to that your gonna want more. i always build for future improvement. go 3" and be ready for the future. these cars are load and obnoxious. thats why we love em.
 
younggun2.0 said:
you built a 408 and soon as you get used to that your gonna want more. i always build for future improvement. go 3" and be ready for the future. these cars are load and obnoxious. thats why we love em.
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Did this with two chamber Flows. Not bad,a pair of long case Dynomax Ultra Flo's ,flow as much or better & quieter. My .02....
Edit: Have you checked out the Summit/Jeg's mandrel bent exhaust pipe kits? Can be had with or without mufflers.(both 2.5 & 3.0 available).
 
I built a 440 and used 3" exhaust on the street one time and will likely not go thru the trouble or expense again. Didn't run or sound any better in my opinion. So in my case I feel I was just suckered into the hype. I did have to find out for myself though. I now consider it overkill and a waste of money. Not to mention adds more weight to a car that I had bought lightweight parts for. Makes no sense.
If I was ever to use 3" pipes again and that is a unlikely if. It would be on a blown big block that was to be run on the street that I was trying to keep the noise level down on.
Race cars are not considered in my opinion here as they would have unflanged collectors or no collectors at all, you know zoomies.
I have also been accused of being a old fossil more than once. LOL.
Your results may vary.
 
several years ago one of the magazines did this same test on a street car,,if you already have a good flowing 2 1/2 keep it ,,,a nice set of headers and free flowing mufflers will get the job done
 
Check this out I was trying to figure out how much a difference in flow it might make going from the stupid 1 7/8" reducers and smashed downtubes on my shorty headers to 2 1/4" all the way to the rest of the existing 2 1/2" X-pipe system. The change would surely be noticed once I cam up the engine (360 Magnum) into the 350-375 HP range from its current 300 or so

"Science be praised" lol

Pipe Diameter (inches), Pipe Area (in2), Total CFM (est.), Max HP Per Pipe, Max HP For A Dual Pipe System
1 1/2 1.48 171 78 155
1 5/8 1.77 203 92 185
1 3/4 2.07 239 108 217
2 2.76 318 144 289
2 1/4 3.55 408 185 371
2 1/2 4.43 509 232 463
2 3/4 5.41 622 283 566
3 6.49 747 339 679
3 1/4 7.67 882 401 802
3 1/2 8.95 1029 468 935

Kinda hard to read I tried to add spaces but the site app takes them out... Basically a dual 2 1/4" system can support around 375 HP, 2 1/2" can support 465 HP and 3" can handle a whopping 680 HP... definitely not necessary for your build IMO. Ideally a 2 3/4" system would match your engine's output the best but nobody makes kits in that size. 2 1/2" should be plenty, and add some 3" dumps coming right off the header collectors when you need max output. Best way to go I think...
 
MOPEkidD-3 said:
Check this out I was trying to figure out how much a difference in flow it might make going from the stupid 2" reducers and smashed downtubes on my shorty headers to 2 1/4" all the way through.

"Science be praised" lol

Pipe Diameter (inches) Pipe Area (in2) Total CFM (est.) Max HP Per Pipe Max HP For A Dual Pipe System 1 1/2 1.48 171 78 155 1 5/8 1.77 203 92 185 1 3/4 2.07 239 108 217 2 2.76 318 144 289 2 1/4 3.55 408 185 371 2 1/2 4.43 509 232 463 2 3/4 5.41 622 283 566 3 6.49 747 339 679 3 1/4 7.67 882 401 802 3 1/2 8.95 1029 468 935
Click to expand...

Relative to the build, & the builder.... A really good 2.5" exhaust system can flow 450-500 done right. (expensive...., and worth every penny).
 
Guys run a lot more than 500 whp turbocharged on a single 3-4 inch exhaust, so I'd think dual 2.5 would suit a pretty high power level. Just a guess :)
 
Oldmanrick, owning an early abody creates issues on parts availability. Headers for this body style by any manufacturer that I have found are all step headers using 1 5/8 - 1 3/4 step. That is probably another reason I ask if 3" is over kill on the system. Pricing between 2 1/2 and 3" is probably only $20 for x or h pipes. My concern is if 3" isn't needed I can tuck a 2 1/2 pipe under body for cleance of trans mount which has to be altered and road clearance. Also because I moved springs in I am probably going to have to bring exhaust out in frt of rear tires as there's no room at fuel tank and frame. Mopekid brings up a good point on using a dump for when I race.
Thanks Rod
 
I have a full 3" system on the Dart Sport.
I wouldnt waste my time with a 3" system or X pipe.
Trying to fit 3" pipe from the axle to the tips is pretty tight!
My 2 cents.
:burnout:
 
MOPEkidD-3 said:
Check this out I was trying to figure out how much a difference in flow it might make going from the stupid 1 7/8" reducers and smashed downtubes on my shorty headers to 2 1/4" all the way to the rest of the existing 2 1/2" X-pipe system. The change would surely be noticed once I cam up the engine (360 Magnum) into the 350-375 HP range from its current 300 or so

"Science be praised" lol

Pipe Diameter (inches), Pipe Area (in2), Total CFM (est.), Max HP Per Pipe, Max HP For A Dual Pipe System
1 1/2 1.48 171 78 155
1 5/8 1.77 203 92 185
1 3/4 2.07 239 108 217
2 2.76 318 144 289
2 1/4 3.55 408 185 371
2 1/2 4.43 509 232 463
2 3/4 5.41 622 283 566
3 6.49 747 339 679
3 1/4 7.67 882 401 802
3 1/2 8.95 1029 468 935

Kinda hard to read I tried to add spaces but the site app takes them out... Basically a dual 2 1/4" system can support around 375 HP, 2 1/2" can support 465 HP and 3" can handle a whopping 680 HP... definitely not necessary for your build IMO. Ideally a 2 3/4" system would match your engine's output the best but nobody makes kits in that size. 2 1/2" should be plenty, and add some 3" dumps coming right off the header collectors when you need max output. Best way to go I think...
Click to expand...

Where do you get off introducing science into this discussion? Lol.
I wish more threads contained this type of information. Assuming it is accurate, it beats single data points and wild *** guesses that pervade some of these threads.
 
Flow is proportional to the 4th power of the radius. Some folks may presume that a pipe 1/2 the size of another pipe would flow 1/2 as much. This is incorrect. 1/2x1/2x1/2x1/2=1/16
So a 2 inch pipe would flow 1/16 of what a 4 inch pipe would flow. Just FYI.
 
desmo900 said:
Where do you get off introducing science into this discussion? Lol.
I wish more threads contained this type of information. Assuming it is accurate, it beats single data points and wild *** guesses that pervade some of these threads.
Click to expand...

Lol I'm a soon-to-graduate mechanical engineering student so I guess it comes with the territory... There's nothing fancy going on with exhaust besides a few math equations, but knowing how they work is the key. You can learn from trial and error over several years building exhaust systems and engines but it's a lot easier reading a bit and then pushing buttons on a calculator lol. Don't get me wrong nothing replaces real-world experience though :thumrigh:
 
MOPEkidD-3 said:
Lol I'm a soon-to-graduate mechanical engineering student so I guess it comes with the territory... There's nothing fancy going on with exhaust besides a few math equations, but knowing how they work is the key. You can learn from trial and error over several years building exhaust systems and engines but it's a lot easier reading a bit and then pushing buttons on a calculator lol. Don't get me wrong nothing replaces real-world experience though :thumrigh:
Click to expand...
well put.from where i stand ive got some first hand know how on this subject.being a fabricator by trade ive built a few different exhausts for my car.if nothing else i can tell you this...that on my setup (street driven 340 with tunnel ram) there was a big difference between a 2.5 true dual full length system with flowmasters to a 3" x pipe system with straight through type mufflers.according to the butt dyno it felt like you pulled a cork out of the exhaust.adding an X or an H (ive built both)to the 2.5 system helped some,but ditching the flowmasters helped more .if the OP decides to keep the 2.5 system id look into swapping in some magnaflows or ultraflows.
 
Some very interesting information given. Thanks for the thoughts and flow charts. It seems that a 3" system would be the best choice for flow and power but that a 2 1/2" would do the job but may not handle any additional upgrades for future improvements. I don't have to make a decision till summer since I'm no where close to ready yet. I will probably go with a 3" dump just behind the headers. Then decide on what size goes behind that. Clearance and where to exit underbody will play a big part of the size. Since the springs have been moved in I will have challenges with fitment as well. Thanks again for your thoughts and any additional advice.
Rod
 
I love these threads where every guy except one or two is just blowing smoke.

Thanks MopeKid and FJ5. The only 2 posts anyone needs to read.
 
I appreciate all the replys. Everything considered I plan on using 3" dumps off the TTI headers then going down to 2 1/2" to the mufflers, a 90* and out in front of the rear tires. Being its on the street and I wont race on the street it shouldnt hurt me at all.
Again, thanks for all the replies.
Rod
 
Here's a detailed flow test. Lol...in my opinion mandrel bent is more important in this case. A nice 2 1/2" mandrel bent system with an x-pipe placed in the correct location is the best bet, but any decent system will do again, as long as your not racing and trying to eek out every single bit of power.

[ame="https://www.youtube.com/watch?v=CF3RfyD-DzE"]Hooker max flow muffler flow test - YouTube[/ame]
 
1971 Dodge Demon 340 have original manifolds on it, the left side down pipe is 2 inches and it seems very titght around the clutch and starter in fact who ever had it before me looks like they had to smash and squeese around that area to make it work, the right side is 2.25. what is the original exhaust size that came with the 340 Demons?
Thank you.
 
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