Topic: Theoretical discussion CB 750 making more horsepower.

[754]

 Just a few thoughts I will grow out there if anyone want to discuss.  Or shoot down completely.
There us current discussion on large valve , large port engines and the oroblems encountered.

 So I must ask, would raising the cam higher above chambers  or head surface help ?
I realize it brings its own new problems, first being newly designed cam holders and probably a whole new design of rocker arms. . Where i am going with this,  i think it would give more room for valve springs, without the danger of breaking through into the port, and easier sourcing of valves springs. And maybe a bit better guide life.
  BILLET HEADS.. I suppose it will eventually come to this which may open new doors but , it's very pricey to even get started on making them.  Of course common sense would perhaps suggest going to twin cams. However there are enough SOHC fans in the world , that maybe enough of them are willing to stick with single cam.
 I am not up on current top fuel 4 cyl components. I did notice a billet head for another brand using skull caps  in their design.  Is that often used? Is it not similar to I think cb 450 dohc motors ?
 Any thoughts  on any if this, please share.,

[MRieck]

 Frank...a lot of "compromised" features inherit in the 750 head could be corrected now. Unfortunately...like you said...it would be expensive. I know only 2 people that could do that. Making those cylinders was relatively easy....a head is a bit more.
 One of my friends said he would do it but i think the benefit would be changing valve angle and intake port placement. Believe me...it costs some money to get it going for design and material.
 Maybe I'll do it sometime....it would complete the circle for me.

[Jerry Rxman Griffin aka MuthaF'er]

Or just use a head like Kenny's with 38mm intakes and straight runners. That almost has to be the limit short of CNC'ing a new design by one of Mike's 2 friends.

[PeWe]

Other bike's head that can be slightly modified to fit?

[simon#42]

making a new cylinder head is quite an undertaking , on the plus side the 750 head is a pretty simple design . once you have got it cast the machining would be straight forward . from my experience with having two stroke racing cylinders made the two hard bits are making the patterns ( there is bound to be someone on here good with wood ! ) and finding a decent foundry who can actually do what they promise.
in addition to that you need a design that is substantially better than the original to make it worth while and a dozen people to put there money up to make it economical enough to do . 

[MessnerMoto]

I have some ideas and I was exploring...

My idea is to source parts from existing bikes... rockers cams valves springs. That will bring down the cost a lot

CNCing the head I can do easily for not that much...

My idea is to keep SOHC thing by replicating honda V-TEC system from cars. For that to work I need to source parts from existing bikes. Price will skyrocket without that.

But before that I think beneficial will be to improve cooling. There is no point of increasing HP without increasing reliability. Also primary chains need to go out and similar small things...

The first thing would be do incorporate something similar to oiling cooling system from 80" GSXRs https://en.wikipedia.org/wiki/Suzuki_Advanced_Cooling_System

With just that one could increase compression ratio considerably and make more HP.

Even without GSXR system it would be beneficial to install oil pump with at least 20% more flow on pressure side. From my data recordings of oil temps, head temps and oil pressure, OEM pump is not up to the task of keeping oil flow when bike is driven in warm city conditions with modified engines... don't forget that pressure side is helping to cool the engine by circulating the oil in top end. If you use the bike only on track you will never have a problem because u are always in top rpm range... But if you are using bike in all conditions it is a different story...

but back to the topic I did even some 3d scans of valve geometry in cb750

[MessnerMoto]

I would go in direction of scavenging the parts from current 2019 crfs.... And I think CRF150 exactly what we need in terms of piston , valve, rocker etc sizes....

And from what I see there are 3d models of complete engine floating around the internet

[simon#42]

i think what people will want is a standard looking head with a different valve angle and better ports , they can then use that for racing as well as on the road .

[MessnerMoto]

i think what people will want is a standard looking head with a different valve angle and better ports , they can then use that for racing as well as on the road .

yep but that is probably achievable with some welding/modifying of existing head

And it would cost the same regarding CNC machining etc... compared to 4 valve configuration. So one would pay pretty large amount for less hp

And I think in majority of European racing classes it is not allowed to use head that was not available in the time...

So it comes to money at the end

[simon#42]

tell that to all the manx norton and g50 riders that race replicas that are nothing like the original internally .

[754]

Piper I think, had a twin cam. Maybe 4 valve head for cb750 around 1970..

 I can remember at least one  offset rod CB750 engine in the 80,s, think it was 1200cc plus.  Quite quick in the 1/4.
 The question I have... it must rapidly wear out certain parts I would think. .

[MessnerMoto]

Piper I think, had a twin cam. Maybe 4 valve head for cb750 around 1970..

 I can remember at least one  offset rod CB750 engine in the 80,s, think it was 1200cc plus.  Quite quick in the 1/4.
 The question I have... it must rapidly wear out certain parts I would think. .

My first proposal was in direction of keeping SOHC

...probably it would be possible to reuse a lot of parts from DOHC cbs.... and to replicate piper thing

But than engine will not fit in a frame. One would need to  modify the frame to accept higher engine... and so on....

[bwaller]

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. 

[cbr954]

I would go in direction of scavenging the parts from current 2019 crfs.... And I think CRF150 exactly what we need in terms of piston , valve, rocker etc sizes....

And from what I see there are 3d models of complete engine floating around the internet

This design with the CRF started in 2017,  I had a 04 also which was the old design.  I bought a 2017 last fall, did a valve clearance check after the first break in ride, its a neat and pretty compact setup.

[MRieck]

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. 

Valid points for jut "kidding".

[754]

 At this point, I think the frame is a small part of the problem..

[MessnerMoto]

the main problem is philosophical question at which point after modifications it stops to be CB750... and why I haven't buy several years old sport bike for couple grands and enjoyed 200hp

[cbr954]

I would want a stock looking head, and it would have to be sohc.  To me the 750 is one of the best looking motors made.  But thats just me.

[754]

 As long as it's a single cam  with a cb750 lower end, nobody will mistake it for brand S,  Y, or Z..

[bwaller]

the main problem is philosophical question at which point after modifications it stops to be CB750... and why I haven't buy several years old sport bike for couple grands and enjoyed 200hp

Exactly

[MessnerMoto]

the main problem is philosophical question at which point after modifications it stops to be CB750... and why I haven't buy several years old sport bike for couple grands and enjoyed 200hp

Exactly

... if you put DOHC Piper replica head on cb750 you will get engine that looks kike dohc 750.... And than why you haven’t just used DOHC engine in first place.... Dont get me wrong I would like to do custom head but I need to restrain myself with logic;)

[slikwilli420]

I want a head design that is still SOHC, takes the stock cam cover, but has more modern valve angles, straighter ports, with a better combustion chamber. Roller rockers and improved oiling to the top end would be nice bonuses as well. I want the head Honda would design if they could do it all over again, but today. A true bolt on piece that only needs piston valve pockets changed to work.

[kmb69]

I want a head design that is still SOHC, 2. takes the stock cam cover, but has more modern valve angles, straighter ports, with a better combustion chamber. Roller rockers and improved oiling to the top end would be nice bonuses as well. 1. I want the head Honda would design if they could do it all over again, but today. 3. A true bolt on piece that only needs piston valve pockets changed to work.

1. Pretty sure Honda would implement the "Unicam" with 4 valves per cylinder for a SOHC version today. Similar to what Mirko posted pictures of.

2. Valve cover would have to be different.

3. I have done several CAD layouts of such a design. There are numerous obstacles with other design aspects of the engine that make a bolt on quite the challenge!

Just guessing, it would probably need to be an over square, big bore, short stroke design. You have to look no farther than the mess they made of their '79-'83, square to under square, DOHC's.

[slikwilli420]

I want a head design that is still SOHC, 2. takes the stock cam cover, but has more modern valve angles, straighter ports, with a better combustion chamber. Roller rockers and improved oiling to the top end would be nice bonuses as well. 1. I want the head Honda would design if they could do it all over again, but today. 3. A true bolt on piece that only needs piston valve pockets changed to work.

1. Pretty sure Honda would implement the "Unicam" with 4 valves per cylinder for a SOHC version today. Similar to what Mirko posted pictures of.

2. Valve cover would have to be different.

3. I have done several CAD layouts of such a design. There are numerous obstacles with other design aspects of the engine that make a bolt on quite the challenge!

Just guessing, it would probably need to be an over square, big bore, short stroke design. You have to look no farther than the mess they made of their '79-'83, square to under square, DOHC's.

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.

[kmb69]

.....
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?