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Discussion Starter #1
1980 001A powerplant.7 valves per cylinder!
no 1 is the 1977 OW34.7 and 8 are the 82 XJ750E TT-F1 racer



 

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V4 CyclePath...
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More cool stuff out of Japan... Saved... someday I predict Yamaha will race a V4 in MotoGp...
 

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I'll fix it.
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I want a better look at the cam setup. the 3 exhausts are easy, they prob used offset lobes like the 3v intakes of genesis 5v heads.

The 4 intakes, Im not sure how they did it. looks like one really wide intake lobe, I wonder if it pushes down on something that opens all 4 valves at once.
 

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I recall reading how they experimenting with 6 and 7 valve designs before finally settling on the 5-valve set-up. The reason given in the articles for abandoning the 6 and 7 designs related mostly to issues related to the cooling of the middle exhaust valve. Would love to see the numbers they got from the featured 7 valver.....

Thanks for sharing :)
 

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Discussion Starter #12 (Edited)
wow...knarly!

how come they don't have the balls to make crazy shit like this anymore?
in the mid eighties there was some incredible developmental work.
basically the regulations were TT F-1,which were extremely loose(like the FX series maybe?)

the coolest bikes were the reverse headed FZ750's by daishin in Osaka(heads were reversed,exhaust out under the seat like a 04 CBR1000RR etc

There was a lot of money and enthusiasm then so very easy to have been creative
Daishin now are just a small little company making silly banana shaped(curved) mufflers for 400cc and 250cc bikes....
pretty sad
 

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Right you are, hence Yamaha`s on-going abandonment of the five-valve design. I recall reading that Ferrari experimented with the 5-valve design on its F1 engines some years ago and eventually ditched it too.

I had spoken to Kevin Cameron about this a few years back and he said that apparently the center intake valve stream causes turbulence, hence its inferior performance. Not sure if this was his opinion or if he had gotten the info first-hand from engineers (too loang ago now....)

Doesn`t Audi still use it on some of its high-performance engines?
 

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Opinion

Its one of those it depends questions.

For a given bore size there is an trade off between valve size and airflow until you get into problems with the valve being shrouded by the cyl wall. For most of the engines we see that answer as stated above is 4 valves. Yamaha's stated purpose for the 5 valve was more midrange.

Yamaha and Ferrari were the only two that really did the 5 valve and the fact that it is gone is proof enough.

I could see going to more valves if you get into a larger bore and started running into airflow problems at a given RPM
 

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virtually real
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Doesn`t Audi still use it on some of its high-performance engines?
I haven't kept up with them too well lately but they were big into five-valve a few years ago, and as I recall the reason had to do with those engines also using an unusually long-stroke, narrow bore design. The five valves allowed for the small diameter heads to have similar valve circumference to a four-valve engine with more conventional dimensions.
 
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