3" exhaust? 2.5" exhaust...??

-
dusterdoug

dusterdoug

FABO Gold Member
FABO Gold Member
Joined
Sep 26, 2007
Messages
1,092
Reaction score
309
Location
Tracy, CA
**Sorry for the typo in the title; fat fingers, small keys.

Has anyone done and comparison of a 3" vs 2.5" exhaust on a mild stock stroke small block?

For reference: stock stroke 360, kb107, EQ magnum heads, mid 240 degree (@ .050) cam. In a 69 orig slant six Dart.

Discuss...
 
I'd do a 2-1/2. There maybe a increase with a 3 inch, but I don't really see much. IMO
 
There is an episode on youtube by Engine Masters comparing this exact thing. I know its not Mopar specific but moving air is basic to all ICE. Give it a look and see if it clears a few questions up for you. But 2.5 is going to be plenty in most street applications.

Try episode #9 and #12.
 
Last edited:
All in what you want performance wise.... All in what you want with comfort when driving....

20 years ago I would want loud and fast... Today I would want no parts of a 3" exhaust on a street car... 2.5" is plenty of exhaust to make good power. I am actually going to use 2 1/4" right now and see where that leads...

Good luck,
JW
 
Up to 450 hp a 2.5 system will be more than fine. Smaller primary tube headers will build more torque, but lay down on the top end. larger primary tubes on the same motor may be dead on the bottom but allow for more rpm. it is all based on the combo of the motor etc rpm you plan to run and parts etc HP goal. Its a recipe if you will some work some dont.
 
Heck, I put a 2.5" exhaust on my 408 stroker. It made 523 hp on the dyno, but the 2.5" tubing would have cleared my custom trans mount better. So what if I lose 10-30 hp?
 
I had 2 1/2 with turbo mufflers on my streeter running 11.70, friend had a 3" system with flowmasters for sale. Spent the money and put it on with no change in ET. Should have saved the money!
 
340doc said:
I had 2 1/2 with turbo mufflers on my streeter running 11.70, friend had a 3" system with flowmasters for sale. Spent the money and put it on with no change in ET. Should have saved the money!
Click to expand...
Live and learn. Only one true way to really know what is good for your car and unless someone has the exact or near exact combo.......
It's the old school way.
 
Good info, thanks all. 340doc summed up all of your thoughts! 2.5 it shall be.
 
Where are you getting the exhaust from? A kit? Local shop? What muffler are you thinking about?
 
SLOPAR72 said:
All in what you want performance wise.... All in what you want with comfort when driving....

20 years ago I would want loud and fast... Today I would want no parts of a 3" exhaust on a street car... 2.5" is plenty of exhaust to make good power. I am actually going to use 2 1/4" right now and see where that leads...

Good luck,
JW
Click to expand...

Same mufflers on both systems the larger system is quieter.
 
340doc said:
I had 2 1/2 with turbo mufflers on my streeter running 11.70, friend had a 3" system with flowmasters for sale. Spent the money and put it on with no change in ET. Should have saved the money!
Click to expand...

So you put 2 totally different systems on a car, didn't change the tuning, and saw no changes. In your mind this results in a theory proved true?
 
roccodart440 said:
So you put 2 totally different systems on a car, didn't change the tuning, and saw no changes. In your mind this results in a theory proved true?
Click to expand...
Never said I didn't check the tuning. I spent the money and wanted an improvement. I don't think were trying to prove or disprove a theory here. I was just relaying my results. Results may vary. The OP asked for info.
 
Mid 240's cam could be making 500ish hp. :)

2.5" is much easier to route/fit under the car. If you plan on squeezing it, go with 3"
 
lxmodguy said:
2.5 is more than enough. It is more than enough on a small block motor.
Click to expand...
your statement is way too broad - not all small blocks are created equally - nor are all big blocks... MOST mid-level performance engines will do well with a 2.5" system - big or small block.. but once you get into the higher HP ranges (I think someone aptly stated above 450HP) a 2.5" system could be restrictive - again, big or small block. I would venture a step further - if you are approaching 400HP - a 3" system will likely work well for you.
 
lxmodguy said:
2.5 is more than enough. It is more than enough on a small block motor.
Click to expand...

Maybe on a stock or lightly modified small block it is,but you start stroking them and making real power I'll take my 3" system any day..
 
ScampMike said:
your statement is way too broad - not all small blocks are created equally - nor are all big blocks... MOST mid-level performance engines will do well with a 2.5" system - big or small block.. but once you get into the higher HP ranges (I think someone aptly stated above 450HP) a 2.5" system could be restrictive - again, big or small block. I would venture a step further - if you are approaching 400HP - a 3" system will likely work well for you.
Click to expand...
stroked340 said:
Maybe on a stock or lightly modified small block it is,but you start stroking them and making real power I'll take my 3" system any day..
Click to expand...
I don't find the statement to broad. I see it as accurate and very much so to a degree.
I guess this truth depends on the end users use of the car followed by the ears abilty to put up woth the noise. I don't consider his build particularly powerful. I'm sure he is making a bunch of it (HP & TQ) and it is a barrel of fun for sure. The engine masters exhaust tube video is an interesting one. it was a 15.7/13 TQ/HP gain on that engine. Of course, your results may vary.....
620hp/580 - TQ open header
614/569 HP/TQ - 3 inch exhaust
601/554 HP/TQ - 2-1/2 exchaust

I like Steve B's exhaust sound mention at 6:52 into the video. A lot of truth there.
 
Last edited:
You must log in or register to reply here.
-

Back
Top