4-into-N exhaust, N being 1, 2, or 4... reasons? benefits?

[zack]

Most of the cb750s I've owned have been DOHC with 4-into-4 exhaust, with double megaphones on each side of the bike, for four "megaphones" total. I've owned a couple with 4-into-2, with one pipe on each side of the bike. If you look at exhaust systems for sale (say, eBay), it seems the people try to pitch 4-into-2 as good or special. Also, a number of custom builds appear to feature 4-into-1.

I was wondering the logic behind it all. Is 4-into-4 the default or majority rule for how cb750s rolled out of the factory? Is it universal for factory original?

More importantly, is there a reason *why* one would or should want 4-into-2? 4-into-1? it seems to me like the following would hold: the more dedicated output channels (i.e., 4 muffler pipes), the less total resistance to exhaust flow that is presented to any given cylinder. That is, for each cylinder, the exhaust will flow away the most freely if that cylinder has its own dedicated full exhaust pipe.

Does anyone have any knowledge re: why different 4-into-N configurations exist, or benefits of each? I am dying to know.

[Re-run]

It is simple, lift a 4 - 4 set, then lift a 4-1. Big weight difference. However, the info you are looking for is this:

A 4-4 is going to have more torque at lower rpm to mid range while costing a bit off the top end.

a 4-2 is going to offer a bit more midrange at the expense of a small amount of low end and top end.

a 4-1 will give best top end performance but will reduce midrange and a low rpm.

The biggest draw for going with a 4-1 is weight reduction, you can shave off 20+ pounds with some systems.

Since I don't race nor constantly ride at top rpm ranges, I stick with the 4-4, it just looks right imo.

[birdmannn101]

Cost when restoring a CB750K model.  I have seen the 4 into 4 going for $1000 to $5000 easily on Ebay.

[Re-run]

For a stock exhaust, yeah it gets really expensive. Glad I am not a purist. I put on slash-cut megaphones and I think they look really awesome.

I kept my header pipes and just hacksawed off the rotted out mufflers. Our header pipes almost never go bad unless really treated poorly.