Why does the 400ex/xr400 have 2 exhaust port holes?

[SpasticR450]

It's 1 cylinder yet 2 exhaust ports. Reason?

[beastlywarrior]

2 exhaust valves?

[Blodg]

It is not because of two exhaust valves as most sport 4-stroke motors have 2 exhaust valves.

With the EX/XR motor having separate exhaust ports and two opening for the hide pipe was a way to improve flow back in the day. A lot of different Honda engines did it this way but as technology improved over the years I think they determined that two exhaust valves that combine into one exit hole for the exhaust can flow as much air so the separate head pipes are not needed. It is the same concept as the intake from the carb being one opening and separating into two ports for each intake valve.

There were engines that had two separate intake ports as well as two separate exhaust ports like the early 80's XL 500R which came with two carbs each fueling a separate intake valve with a single cylinder.

[Stickman400]

My friends '02 660 Raptor also has 2 separate carbs that feed 1 cylinder, which has 5 valves and 2 exhaust ports. Idk what they were thinking when they designed it that way. It's alittle overkill if you ask me.

[blacknblue#2]

Originally posted by Stickman400
My friends '02 660 Raptor also has 2 separate carbs that feed 1 cylinder, which has 5 valves and 2 exhaust ports. Idk what they were thinking when they designed it that way. It's alittle overkill if you ask me.

The engineer that designed the 660 raptor had too many left handed cigarettes.....Lets make the front end 4 inches wider than the rear, make it set high as heck, feed a single cylinder with 2 carbs, hang a 4cylinder chevy can oil filter off the side of it and put yz80 tranny gears in it and call it a race quad!!!!!!! Genius

[JOHNDOE83]

Originally posted by blacknblue#2
The engineer that designed the 660 raptor had too many left handed cigarettes.....Lets make the front end 4 inches wider than the rear, make it set high as heck, feed a single cylinder with 2 carbs, hang a 4cylinder chevy can oil filter off the side of it and put yz80 tranny gears in it and call it a race quad!!!!!!! Genius

LMAO!!!!!!

Thats some funny stuff right there!

Its even more funny because its tru!

[BIGTEX400EX]

Ha ha ha..............

Never heard "left handed cigarette," I literally laughed out loud.

[bcleveland]

Originally posted by blacknblue#2
The engineer that designed the 660 raptor had too many left handed cigarettes.....Lets make the front end 4 inches wider than the rear, make it set high as heck, feed a single cylinder with 2 carbs, hang a 4cylinder chevy can oil filter off the side of it and put yz80 tranny gears in it and call it a race quad!!!!!!! Genius
I don't get the 2 carbs part being bad. To small carbs will flow more air have more port velocity and a better fuel signal then one big carb. On a single cylinder engine. Now to carbs that are too big or to small will kill performance.

[HondaRider18]

one carb is a pain, let alone 2 carbs

[tayyo789]

Two carbs flow better than one. It's not user friendly, but they perform better if you're looking for peak numbers. Especially in a big displacement engine.