I'm having a hard time getting my brain to wrap around the fact that after market true dual headers will restrict more than 2/1/2 with x-over. Can anyone help me understand how the x-over helps these headers breath better than a true dual? Or, how a 2 into 1 performs better than a true dual? Is it because the x-over splits the exhaust? I would have thought that it wouldn't have mattered since the cylinder is still choked by the initial header size of each system anyways and would have expected a true dual to perform better without any weird backpressure the x-over might cause.

Obviously I'm not well versed in exhaust systems. Just looking for a little knowledge. Thanks.

 

Scavenging is the reason for 2 into 1 and cross over systems.

https://www.baggersmag.com/exhaust-p...mentals#page-4
https://www.hdforums.com/forum/gener...cavenging.html

 

Perfect links. Thanks. Lot more goes into tuning an exhaust than I realized.

 

In addition, if you get a high lift cam, you have more valve overlap (time where both the exhaust and the intake are partially open). You have to have more back pressure to prevent reversion. There is a lot to it as you said.

 

Well stated. I am running true duals, and was running B&E Superflows with a 2 inch baffle. A b**ch to get a good tune, poor mpg with loss of low end torque due to the free flowing cans. The Crusher Mellows provided more back pressure and made a world of difference in getting low end torque back along with an increase in mpg

 

Drag pipes are true duals, look kool, sound kool.
But they turn on and work at a very high RPM! hence- Drag pipes...LOL
The two into one is a lot of little actions making a big one .
Extraction is the definitive action we strive for.
Two into one is all making both cylinders work together as partners,
rather than two single cylinders pumping away singularly independently.
The two into one relationship with proper cam creates a venturi action much like
blowing across the top of the straw and fluid will rise or come up and out.
There are many other things to consider, but this is the nutshell answer.

 

he same problem a couple of weeks ago. I had the tru duals and really liked the low end power of the pipes until the pipe coming out of the back cylinder cracked at the mount over the starter. These were the old style "they were put on in 2005". I checked and could have brought a new replacement pipe for 325. and not being sure if it would match the front cyl I went ahead and bought a Rinehart 2 into1. Everybody said I would not have to retune because of the exhaust but the ole horse did not run right until I had it on a dyno and Brian did his magic and now I got the same torkie curve as I had with the true duals if not a little more. I've got a e-glide with a 88 that has heads ported, a screamin eagle 95" inch big bore kit bored twenty over, 510g cams from s&s, roller rockers and a assortment of other goodies. Hope this helps your decision, i was in the same boat