3 inch exhaust

[Master Gunner]

Does anyone think there's any benefit to running a 3 inch exhaust behind HP manifolds?

Mark

 

[Don Frelier]

I doubt it, @andyf might want to chime in.
I think your muffler choice and an H-pipe or X pipe would be bigger considerations for backpressure and throughput.

 

[dadsbee]

No... and pending what engine specs are there's probably no advantage with headers either..

 

[steve340]

No that large a pipe size will probably kill torque and power.

 

[Under Pressure]

Not really sure on a benefit, but I put on my 70 behind stock manifolds with Dyna Max’s and it sure sounds good

 

[Ron H]

I think 3" is for huge output motors maybe 450-500 horse...I got talked into 3" on my built poly. Waste a money.

 

[Kern Dog]

No... and pending what engine specs are there's probably no advantage with headers either..

There are always advantages to headers.
Whether those advantages are negated by their drawbacks is up to debate.

 

[dadsbee]

There are always advantages to headers.
Whether those advantages are negated by their drawbacks is up to debate.

Headers wasn't the question... 3" exhaust was.. IE no advantage to 3" pipes with headers either.. pending his engine build..

 

[diesel_lv]

I run 3" w H-pipe n headers on my 496 w 610 crank hp, but I never turn more than 5,500 rpm. Way too much. 2-1/2" would have been more than enough.

 

[Master Gunner]

Cool, didn't think there would be.
Engine specs are: 440 .030 over with KB step top pistons, 10.3 static 8.6 dynamic CR, Hughes Engines 228/232 -110ºLSA cam, mildly ported 346 heads.

Mark

 

[Kern Dog]

Headers wasn't the question... 3" exhaust was.. IE no advantage to 3" pipes with headers either.. pending his engine build..

YOUR response had the word HEADERS in it....

 

[dadsbee]

LOL Greg. guess you have to read the entire context to make it work. And it's NO to 3" pipes, manifolds or headers..

 

[Don Frelier]

My memory was better than expected.
Andy did this on his 65 Coronet and wrote an ariticle on it:
https://www.hotrod.com/articles/mopp-0501-1965-dodge-coronet-500/

 

[Charged440]

No, as I understand it, there may be no difference unless you have a 700 horse big block that shifts at 6500. I'm currently removing a 3 inch set up from my BB Skylark for that very reason.
The Power of 2.5- vs. 3-Inch Exhaust - Engine Masters Ep. 9 - YouTube

 

[69a100]

The only benefit you'll get is that it will sound like ****! Good Luck

 

[Master Gunner]

Factory was 2.5, and that is what I was going with, but I saw that 3 inch was only $14 more for head pipes and the same for the H pipe. Really didn't think it would do anything with my build and manifolds, but thought I'd throw it out for the experts.

 

[66 Sat]

YOUR response had the word HEADERS in it....

Yeah, but the original question was relating to 3" exhaust behind HP manifolds, so the response was " no advantage behind HP manifolds, nor behind headers". Nothing to do with headers not being advantageous.

 

[Kern Dog]

I don't spend money because my pockets get too full nor do I make changes that have zero benefit.
Stock exhaust manifolds are great for a stock engine with a 4500 rpm HP peak. Yes, a 440 Magnum did peak below 5000 rpms, look it up. They would still benefit with headers. I have read that a 400 HP point is where a 2 1/2" system becomes a bottleneck.
Headers allow engines to make more power. To argue that is to ignore thousands of examples from the past and present.
The F.A.S.T. and Pure Stock drag racers use manifolds only because of the rules in the class. They run fast despite the use of iron manifolds, not because of them.
I do understand the support of manifolds. Some don't want to deal with the fitment issues. I agree, headers can be expensive, fit poorly, rattle and have other problems.
Also, it is believed that as the exhaust travels to the ultimate exit point, it cools dramatically and as it does, the pipe size can be progressively smaller with no loss of power. The tailpipes can be 1/4" to 1/2" smaller than the intermediate pipes which is great since fitment around the axle and gas tank can be difficult.

 

[4mulas]

Factory was 2.5, and that is what I was going with, but I saw that 3 inch was only $14 more for head pipes and the same for the H pipe. Really didn't think it would do anything with my build and manifolds, but thought I'd throw it out for the experts.

Weren’t most factory duals 2.25” ?

 

[Master Gunner]

440 cars used 2.5" pipes, at least on the runners and chargers in 73.