For my '03 FX4...if I currently have a 3" Maggie catback system (w/ 14" muffler), can I stay with 3" for true duals? I see a lot of folks running 2.25". Any reason behind it?

Thanks!

 

Not on a engine smaller than 350ci.

Keep it 2.5" max. I would say 2.5, my scavenging is great, X piped & 2.5. 2.25" pops and crackles way too much but some people swear by it.

 

yea anything smaller than a 5.7 you need to stay under 3" pipe, 2.5 will work perfectly, you can have 3" inlet mufflers and they can flare that 2.5 out to 3" and then run the tailpipes, my pipe is 2.5 true duals into 3"inlet and 3"outlet 10 series flowmasters, and 2.25 is a little small, best go with 2.5

 

Yes, there are good reasons behind it. Look at the factory sized exhaust system. With todays CAFE standards etc. the manufacturers are pressured to get as much efficiency as possible, and if huge exhaust pipes were the ticket, they would use them.

You want as SMALL a pipe as possible without inducing ANY backpressure at the RPM that your motor makes peak power. This will ensure maximum scavanging. While this may be easy for the manufacturer to figure out due to their millions of dollars in test equipment, it's not so easy for Joe Blow to figure out. With a small V8 gasser making ~225-275 HP 2.25" for true duals would probably be about right. Dual 3" would likely have little to no scavanging.......thats bad.

 

Awesome info fellas. Thanks. That was what I was looking for!

 

LOVE my 2.5" setup, wouldn't have done it any other way!

 

2.5" will support up to 400hp, there is no need for anything more, I go by horsepower rating for pipe size, there is no need for anything to have 2.5" unless it makes high hp or is forced induction. The big block muscle cars of the 60's run great with 2.5", and they are a far cry from the 281cid or 330cid in the F150.