Topic: Theoretical discussion CB 750 making more horsepower.

[slikwilli420]

.....
My purposes would be for road racing so it cannot look out of place. Changing some of the key characteristics of the original design (cam cover being one) makes it of no interest to me personally. Still a very cool project though. I want to improve the original head to the extent of keeping its outward appearance to all but the CB750 enthusiast stock.

Believe me, I understand totally. I have been wanting such a piece for long time! I have a head sliced up in many pieces trying to figure out how to do it. 

Can you guys use a DOHC frame in your road race classes?

No.

[Cb750 Racer]

I'd like to see a sohc 4 valve head personally but theres no way to keep the head looking stock in that scenario. Spark plug location would the biggest problem in making the head look stock and keeping the engine a sohc. It would probably be best to make the cam towers part of the head much like a cb550 or cb400f. Of course to make a 4 valve sohc head the location of the lobes on the camshaft would most likely have to be changed as well to make everything fit and have the correct tappet geometry.This would require custom camshafts which would complicate things a bit though.Something like Mirko suggested would be spot on. I'm not sure if I could justify to myself spending 2000$+ for a head with more modern ports/combustion chamber even though I said the same thing about Mike's cylinder  . You have to remember that the cylinder studs are only 8mm to I feel like we're just climbing up a hill only to see a mountain on the other side.

[754]

Is the 750 Auto frame allowed in roadracing ?

[kmb69]

Is the 750 Auto feame allowed in roadracing ?

Just fixing to ask that question as well.

[slikwilli420]

Is the 750 Auto frame allowed in roadracing ?

Grey area and open to interpretation. Rules say pre 1972 and like design. You could infer the like design part of the rule on the Auto frame since, aside from the rails being moved, its identical to the pre-1972 frames it copied. Nothing in the rules about gusseting frames or adding material. You could argue that you would have made the mod (moving the frame rails) to a stock frame but this was already done from the factory.

[MessnerMoto]

there is no way of changing valve angles port angle etc without heavily modifying the look of the engine/frame etc... even if keeping 2 valves per cylinder.

If one is to cnc head from scratch it needs to be a minimal amount of HP that will justify huge amount of money spent. And changing angles(valve, port) a little bit to keep stock head look(height of head, position of intake ports) will not justify money spent. For that I recommend modifying stock head and that has been done many times before...

...my feel is that making custom CNC head would cost end user 4k of some units and above 

[slikwilli420]

there is no way of changing valve angles port angle etc without heavily modifying the look of the engine/frame etc... even if keeping 2 valves per cylinder.

If one is to cnc head from scratch it needs to be a minimal amount of HP that will justify huge amount of money spent. And changing angles(valve, port) a little bit to keep stock head look(height of head, position of intake ports) will not justify money spent. For that I recommend modifying stock head and that has been done many times before...

...my feel is that making custom head would cost end user 4k of some units and above

Tell that to Kenny at Cycle X. He moved the ports and changed valve angles on heads he built for his drag bike and the superbike heavyweight he built back in 2011-2012.

[MessnerMoto]

Yes like I said for just changing angles it is better to do stock head modification

[kmb69]

.....
Tell that to Kenny at Cycle X. He moved the ports and changed valve angles on heads he built for his drag bike and the superbike heavyweight he built back in 2011-2012.

Very similar to what is being discussed here: http://forums.sohc4.net/index.php/topic,174383.msg2029208.html#msg2029208

Don't think Kenny's road race head was modified to the extent his drag bike head is. Too early to know how "fragile" it may be. 

[calj737]

Interesting discussion and I have no doubt the ideas and knowledge are right here. Even sourcing outside parts this is an expensive venture and the "ponying up" part will be the problem! 

We'll want a straight shot inclined port, better than the original horizontal, so then the carbs will foul the frame. There should be an airbox for best power so the frame problem gets worse. I know a good frame guy or maybe there's a more modern surround frame that could be made to work! Roadrace guys will want the engine forward plus canted forward for a better swingarm angle.

Just kidding. 

Someone else thought along those same lines...
http://www.motorcycle.com/blog/wp-content/uploads/2014/10/100714-michael-czysz-motoczysz-Czysz-engine-side-cutaway.jpg

[simon#42]

Interesting discussion and I have no doubt the ideas and knowledge are right here. Even sourcing outside parts this is an expensive venture and the "ponying up" part will be the problem! 

We'll want a straight shot inclined port, better than the original horizontal, so then the carbs will foul the frame. There should be an airbox for best power so the frame problem gets worse. I know a good frame guy or maybe there's a more modern surround frame that could be made to work! Roadrace guys will want the engine forward plus canted forward for a better swingarm angle.

Just kidding. 

Someone else thought along those same lines...
http://www.motorcycle.com/blog/wp-content/uploads/2014/10/100714-michael-czysz-motoczysz-Czysz-engine-side-cutaway.jpg

pity it didnt work

[calj737]

But it did work. What they couldn’t do, as a privateer and start up, was chase and re-design perpetually with ever changing MotoGP rules. The limits of money have often extinguished innovative designs and revolutionary changes in long held processes.

[754]

 What my thought initially was is to raise the cam to allow for raised ports and room for springs etc. Off course it means new rockers, new cam cover.
 I think casting may save some money, more saving if you skimp on finning.
 Might safe a few buck by casting after the first run is done .  Way less machining..

[simon#42]

But it did work. What they couldn’t do, as a privateer and start up, was chase and re-design perpetually with ever changing MotoGP rules. The limits of money have often extinguished innovative designs and revolutionary changes in long held processes.

no it was nothing to do with rules changing . what they couldnt do was make an engine that made any power , make an engine that could actually run for 10 minutes without exploding ,  design a chassis that handled . i do admire him for trying but they tried to reinvent the wheel and none of it worked . to try and design a motogp engine from scratch you either have to be very very clever or very very stupid

[754]

Kudos to John Brittens efforts and success in creating his own motorcycle..

[calj737]

no it was nothing to do with rules changing . what they couldnt do was make an engine that made any power , make an engine that could actually run for 10 minutes without exploding ,  design a chassis that handled .

A then-current review of actually riding the bike, not reading about it. It seems the author disagrees with most of what you posit.
https://www.motorcyclistonline.com/american-beauty

[simon#42]

watch this cal , it is very good

[calj737]

I saw it when it first released years ago on TV. I was always impressed with the undertaking and the approach of starting anew, versus improving what’s there.

Hence, my earlier post about “someone already thought of that”...

[MRieck]

But it did work. What they couldn’t do, as a privateer and start up, was chase and re-design perpetually with ever changing MotoGP rules. The limits of money have often extinguished innovative designs and revolutionary changes in long held processes.

Cal...I think the biggest problem was Michael Czysz was his own worst enemy. I know 1 very talented fella who refused to work with him (after being approached) and another that was tied in to battery research when Czysz pursued that electric bike.
 Apparently difficult to work and had a well known reputation for being so.

[calj737]

But it did work. What they couldn’t do, as a privateer and start up, was chase and re-design perpetually with ever changing MotoGP rules. The limits of money have often extinguished innovative designs and revolutionary changes in long held processes.

Cal...I think the biggest problem was Michael Czysz was his own worst enemy. I know 1 very talented fella who refused to work with him (after being approached) and another that was tied in to battery research when Czysz pursued that electric bike.
 Apparently difficult to work and had a well known reputation for being so.

Yep, I’ve met many like him in my career. Seems to be a Silicon Valley trait  The “tyrant” management model made famous by Frank Lloyd Wright, made epic by Charles Eames, then modernized by Steve Jobs. Everyone wants be someone... 

Nonetheless, it was a brilliant undertaking speaking from an motorcycling perspective.

[simon#42]

shame it didnt work

[turboguzzi]

the one off works CB500R had modified valve angles and looked like a perfect stock 500 head mirko

simon, wood patterns are a bit our fashion now... there are quite a few companies that nowadays 3D print a part in low temp melting resin. then it is simply used as the core for a single investment casting, i.e. covered in ceramic and then the resin is melted away. you dont even need to make sand cores for the internal air passages and ports, what you print is what you get . in car racing where they have bigger budgets people do heads too.

with current tech a full new head that would look externally close to stock but re-engineered inside is doable, just expensive.
With CNC you will never be abloe to machine all the internal air passages between fins even with a 5 axis

http://www.sycastinc.com/tool-less-casting.html

[PeWe]

Invent a 3D printer that can print a head direct. Just machine the result, install valves.....

[MessnerMoto]

the one off works CB500R had modified valve angles and looked like a perfect stock 500 head mirko

simon, wood patterns are a bit our fashion now... there are quite a few companies that nowadays 3D print a part in low temp melting resin. then it is simply used as the core for a single investment casting, i.e. covered in ceramic and then the resin is melted away. you dont even need to make sand cores for the internal air passages and ports, what you print is what you get . in car racing where they have bigger budgets people do heads too.

with current tech a full new head that would look externally close to stock but re-engineered inside is doable, just expensive.
With CNC you will never be abloe to machine all the internal air passages between fins even with a 5 axis

http://www.sycastinc.com/tool-less-casting.html

Yoss I saw some pictures of cb500r. I cant see how much the angles were modified. But it looks not a lot. Also cb500 head is originally higher then cb750 head... cb500 has incorporated rocker towers.... so it is probably a lot higher than cb750 head. More meat to play around and keep stock look.

My logic was that if someone is going to make custom head it is a good idea to squeeze every possible hp out there. Because price for making head with this two philosophies "lets alter angles a little bit" and "lets incorporate every possible advantage in to a new head and make as much hp as we can" is minimal and later will kill original look for sure.

...yes that additive process is available in company were I 3d print parts. I think they even have that material for casting. But it is not cheap. But probably cheaper than CNC ing head? Maybe you are on right path here yoss. 

...and you can 3d print head in metal now. It is just to expensive to do it. 3d printed Al and Ti have same strength as cast counterparts....after you can temper them to T6 state.... But current price for printing 100cm3 of titanium is around 2500eu... and head is around 10000cm3
...

fun fact... space X is printing majority of parts in there engines. Also there is no modern jet engine without 3d printed parts the primary part being compressor/turbine blades...

[NitroHunter]

The head and valve cover could be blown out to slightly larger dimensions provided they retained their stock external 'appearance', this on a larger finned big bore cylinder could be made to look factory proportionate.
Think "chopped & sectioned" in reverse...