Reversed Heads

Yea, but it would be really cool! I'd love to see how it's done. It seems like it would be very difficult, but maybe it's not??

I was lucky enough to see Elmer Trett back in the 80's and his bike was awesome.

I say go for it! Just be sure to include lots of details and pictures for the rest of us!

KruZer wrote:

"rephasing the engine"? Not sure what you mean...

A lot of early 650 guys rephase to 277°- the early Yamaha XS650s used to vibrate notoriously. There really aren't any gains in that except the motor has a little more throat to it's purr and with less vibration the reciprocating mass moves more efficiently. I'll try it on this motor just to see what happens. What the heck- it was free.

I wouldn't say any of it is for nothing as long as I get enjoyment out of the research, the build, learning from it and, later on, riding the bike. That is plenty of reason for me to do it so long as it doesn't kill the wallet (and my girlfriend ends up killing me *snark*). So long as those qualifications are fulfilled, there is plenty of reason for me to do it. I just need to make the decisions along the way.

don't know if re-phasing is possible with a 750 twin crank as it is a forged one-piece, were the yamaha is a multi-piece, unless you are cutting and welding

Forgive me for not noticing that in your opening thread you stated that the bike is 750.

Please disregard my previous comments. For some reason I had it in my mind that you were talking about a 900 or 1000.

I don't know nothin about the 750s!!!! So I have no idea what would be involved in turning the head around.

Good luck,
Buzz

flht1997 wrote:

crank...is a forged one-piece

So were the old XS650s.

KruZer, I was wondering if you'd catch that.:woohoo:

I believe my nephew has a 70s model two cylinder 750 in his garage. Not running, needs a starter and carb work.
If you're looking for parts to experiment with let me know and I'll see if my nephew wants to part with the 750.

Buzz

what year XS are we talking?, all the ones i have had my hands in had multi-piece

Why reverse the head when you could just turn the entire engine around and make the bike front wheel drive? Now that would get some comments from onlookers! :woohoo:

If the ram air (from a reversed head in this case) has no effect than why do all the modern sport bikes run a snorkel / ram air set up on their rides? I can't believe that those lightened to the max machines would add a bunch of extra plastic for no gain....

If there is no gain from "ram air" then why do the plastic bikes have their intakes up front and lots of tubes to bring it back? (I am not being a smart a$$ I actually want to know if there is a reason...)

650ed wrote:

Why reverse the head when you could just turn the entire engine around and make the bike front wheel drive?

Why stop there? To get the full effect but without the expense, simply sit on your bike backwards...

Ram air absoluly has makes a difference in performance...above a certain MPH and if the air is channeled into the carbs correctly.

In the case of the modern sport bikes the aerodynamics of the front wheel, front fender and fairing are designed to route the air into the intake tubes that feed the injectors.

One of the reasons the fuelers started going to the reversed head was because of the weigh distribution on the bike. The engine on a fuel bike(equipped with a blower) could be moved futher back in the chassis if the blower was located in front of the engine. A side benefit was some increased ram air effect at speed.

That being said. A KZ (750 or 1000) with the head turned around is not going to have the aerodynamics that will feed the carbs air like a sportsbike. You might get some benefit but not enough to justify the trouble and expense(usless you're just going after the cool factor).

Still it a cool thing to think about and even cooled to do.
Let us know if you work it out.
Buzz

Ram air most definitely has an effect on engine performance. It goes up in an exponential fashion though. so at 35 there will be no difference basically. At 70 there maybe some gains, but at 100 it will be more noticable. Its kind of a tricky thing though. First how do you measure the gains on a dyno without that ram air?? If you start pushing more air through a carb it will lean out the jetting unless you jet it to be richer in which case you lose low end. then start considering how much extra horsepower it will take to overcome the extra drag incurred by things like hood scoops at 100+ mph, and is it worth the extra Horse that could be gained?? All this being said, on our bikes its not worth it. But it would be really cool!! I would say the biggest from reversing our heads would be that you could take in much denser cool air rather then the hot air that is coming off the exhaust headers, heads, and cylinders. You could also use an equal length exaust header system that would be really straight and would probably stay much hotter so it would act shorter then what it really is, giving more top end if you knew what length to start from.