Head flipping?

[the bear zxr]

so... rear facing exhausts... Ive only ever seen it on a very small handful (well, a pinch really) of race bikes, and usualy 2-smakers.

So my theory is: if your building a rather custom fourbanger such as.... ooh i dont know a zxr750: what would you have to do to flip those ports around??!!!

ive given it a little thought: things like new cams and matching the valve ports to be intake=exhaust and then running that way round.. or perhaps flipping the head, (but this complicates things hugely: adding a chain reversal assembly and swapping the chain side: all too much work!!!!

has anyone got any light to shed? or experience? or brilliant ideas? cheers guys

[DrunkenMistake]

I take it by rear facing exhaust you mean the exhaust ports are facing the back of the bike and the intake is on the front side of the motor,

For what reason do you want to change it around for? out of curiosity.

Seems like a lot of work for not a lot of gain unless there is something I dont know.

[AllanB]

Like this?

[koba]

Doable on two stokes, due to simplicity.

In almost all situations with a 4 stroke it will be far too hard for no gain and likely a loss.

[Kickaha]

It's been done before, although every bike I have seen pictures of has been a drag bike

[Motu]

My brother's bike, 1971. Very easy to do on a Triumph, with symmetrical stud patterns on barrels and head...in 8 stud anyway and twin cams with vernier adjustment. That's an 8 stud Bonnie head with twin plugs.

[the bear zxr]

exactly like both pictured..

no power gains anticipated, however the packaging design and appearance are the target points

[jellywrestler]

My brother's bike, 1971. Very easy to do on a Triumph, with symmetrical stud patterns on barrels and head...in 8 stud anyway and twin cams with vernier adjustment. That's an 8 stud Bonnie head with twin plugs.

all that ability to achieve that yet he couldn't figure out suspension is useful!!!

[Motu]

He got it as an unfinished project, it did have a sprung hub, the rigid is certainly lighter, and the sprung hub only had about an inch of travel. It also had a cool looking springer front end, but we measured 8 inches of negative trail because of the longer rocker - that's a 6 inch over Rocket III front end. Most powerful 650 Triumph I've ever ridden - 3rd gear wheel stands and top gear wheelspin in the wet, could pull away from a Mach III which was the bench mark of the day. But none of that from reversing the head, that was just done for the cool value.

[Blackbird]

This is a photo of my drag bike in the late 60's. There is NO measurable performance gain from reversing the head with carbs, although ram air on later injected bikes does have an appreciable effect at speed but that's a properly designed system. The reason that I turned the head on the drag bike was twofold:

Firstly, to reduce the length of the inlet tract between the supercharger and the inlet valves to reduce pulsing harmonics and prevent fuel deposition/condensing out of the airstream. Secondly, to move the weight of the bike forward by being able to place the supercharger up front. Stud spacing between the crankcase and barrel was symmetrical so no problem there. Inlet and exhaust camshafts were independent so could simply be re-timed.

There ya go - clear as mud

[Erelyes]

And here I was expecting another fucking waving thread.

[tigertim20]

definitely doable and will be a cool talking point / point of difference if youre just looking to build something for yourself. to ease the burden on the wallet might pay to get friendly with someone who works at a machine hop or something!

[AllanB]

On any modernish sport bike I picture a issue with the injectors and frame/radiator clearance. Given the engine will have a forward tilt and the injectors point upwards there may not be room in anything standard format. Then again if you go to that effort with the engine the rest may be a piddle!

[husaberg]

Get yourself a Husaberg or a Yamaha YZF450 far easier...


the odd Harley can have a head swapped around as well