2.5" vs 3" pipe size for high powered FE; which is better?

[Redcap]

'Morning Aaron, thanks for the photo (worth a thousand words)!

Why are these gadgets desirable?

Thanks again,
-Robroy

No worries! Better scavenging than a normal H pipe.

[robroy]

Hi Aaron! Please excuse my ignorance, but what's scavenging and what's a normal H pipe? Maybe I could find an article somewhere that explains some of these things?

Thanks!
-Robroy

[Redcap]

H pipe.

While I understand the principle, someone else will be able to explain the scavenging effect better than I can.

[robroy]

Hi Aaron! Thanks for the H-pipe photo!

I'm guessing that these H and X pipes are designed to go after the headers and before the mufflers--is this true?

-Robroy

[mrtleavitt]

The "X" allows a perfect balance of pressure between both banks. As I was told by the exhaust shop that they create more top and bottom end! If you are making a serious engine, an "X" exhaust is a must. I would say anything over 350 hp. And yes, they go before the muffler. "X" gives a better flow, but "H" is a good way to go if you want to save $100.

[Redcap]

Hi Aaron! Thanks for the H-pipe photo!

I'm guessing that these H and X pipes are designed to go after the headers and before the mufflers--is this true?

-Robroy

Absolutely correct.

[robroy]

Hello Mrtleavitt, thanks for your reply! Fascinating. A great exhaust system is more complex than I thought!

-Robroy

[69NVF100]

I have Dual 3" all the way thru with an h pipe and I am pushing close to 400 HP It is probally a little overkill but it sounds good and I did it before I knew better oh well next time I will research more

[robroy]

Hey 69NVF100, it's good to know that it works okay, and I guess you benefit from a different sound so it's not all bad! Plus the tailpipes probably look nice.

-Robroy

[69NVF100]

Yeah it Definitely looks BEEFY but as for low end loss I don't know ? I haven't really noticed but I am sure there is some.

[robroy]

Hey! Very nice looking job! -Robroy

[averagef250]

Dual 2.5 should be perfect. 3" is overkill for most engines. I know many making 450+ HP through 2.5 duals. A friends 63 Nova runs a dyno'd 470 HP/430TQ 383 through 2 1/4 duals with 3 chamber flowmasters. It runs 11 flat in the quarter. He shifts it at around 6800 and there is no lack of top end power.

[fomocoguy]

2.5 inch with an "x" or "h" will serve you well. Just remember if you want to take advantage of all those ponies that you should use quality flow through style mufflers, like Hooker Max Flows or Magnaflows. Your Borlas are probably flow throughs, but I'm not 100% certain. I DO know that the recipe for a finely tuned performance exhaust is proper scavenging (achieved by not going too big on the pipe) and high flow (achieved with high quality flow through mufflers).

As for scavenging, the idea is that the exhaust pulses will pull each other out as they leave the pipe. This creates a higher exhaust gas velocity, which in turn, for lack of better words, "sucks" the exhaust out of the heads when the exhaust valves open. Use pipe that is too big and the gases lose their velocity. By the end of their travel the pulses are pushing each other out, clogging the system so to speak. Restrictive mufflers also clog the system.

Here's a link to some neat flow bench results. I've posted this before, but I like it because it backs up some stories I've heard about mufflers that killed power when added, or shocked people when they removed them and added a higher flow design: http://www.broaderperformance.com/muffl ... _tests.htm

[crazyhorse]

just so you know before you decide you could also look at a pro-chamber box too. the h pipe , x pipe & pro chamber all have some advantages/ disadvantages . decide which is best for your set up. and as usual super advice here.

[Dragon]

Last but least a study done in Britain in the late sixties and published in Hot Rod Magazine later showed that on muffler equiped cars the best power was when the mufflers front end was 3/4s of the way back from the manifold exit. I have done my cars and trucks that way ever since. If the car design does not let me move the mufflers I change where the pipes exit. The muffler entrance causes the scavenging pulses to reflect and they said that distance made more even power.