Topic: Theoretical discussion CB 750 making more horsepower.

[gschuld]

Just how much more HP will this theoretical head develop, compared to a stock head with a port job, over-size valves and thin valve stems?

One straight port head that I am aware of:
At 10 Inches Mercury and .400 Lift:
Intake    110 CFM
Exhaust    92 CFM
Converted to 28 Inches of Mercury:
Intake    184 CFM
Exhaust   154 CFM

Keith,

Thanks for sharing.  To put those head flow numbers into context, could you share the basic specs of the head you are referring to?

Guessing here:  I’m assuming it’s a 410 F2/3 based head.  Splayed intake valves to allow 36-38mm intakes, exhaust valve size and not splayed?

George

[kmb69]

.....
Guessing here:  I’m assuming it’s a 410 F2/3 based head.  Splayed intake valves to allow 36-38mm intakes, exhaust valve size and not splayed?

George

I38/E34. Pretty sure both were moved 1 degree.

[kmb69]

Material under the springs gets quite thin resulting in the "fragility" mentioned by Mike earlier.

[PeWe]

It must be possible to get similar as a Kawasaki Z1-900 can reach

140 Whp / 134 Nm

This must be a possible goal for a CB750 too.
The bore of that bike was rather big. I saw it in the shop, the PO had gone wild to carve the upper case for fat sleeves. I do not recall the displacement. JE pistons mentioned. Max on JE website is 1200cc
http://www.jepistons.com/Catalogs/Powersports/Street-Cycle/Kawasaki/kz_900-1000.aspx

[gschuld]

.....
Guessing here:  I’m assuming it’s a 410 F2/3 based head.  Splayed intake valves to allow 36-38mm intakes, exhaust valve size and not splayed?

George

I38/E34. Pretty sure both were moved 1 degree.

Thx, very helpful.

George

[turboguzzi]

.....
if a good all around motor is the goal, then a 16 valve head would be even better and still could be concealed in a stock looking casting.

Very difficult to do as both Piper and Honda found out. The cylinder studs in the SOHC cases don't allow enough room for the valves.
Piper "got around" this with the funky stock studs through the cylinder only, then DOHC placement between the head and cylinder.
Honda's RCB1000, based on the SOHC bottom end, had custom "sandcast" cases with the typical DOHC cylinder stud arrangement.

you can just 3D print new studs wherever you want them

[MRieck]

It must be possible to get similar as a Kawasaki Z1-900 can reach

140 Whp / 134 Nm

This must be a possible goal for a CB750 too.
The bore of that bike was rather big. I saw it in the shop, the PO had gone wild to carve the upper case for fat sleeves. I do not recall the displacement. JE pistons mentioned. Max on JE website is 1200cc
http://www.jepistons.com/Catalogs/Powersports/Street-Cycle/Kawasaki/kz_900-1000.aspx

Go out to 1260 with a KZ1000 block, put 37.5 intake valves, cams, porting and 36mm TMR or RS carbs and 140HP isn't hard to achieve. Getting 125HP out of a street CB750 is a little more challenging.

[gschuld]

Out of curiosity, how far can one realistically go with a 410 head without resorting to splayed valves and weld up straight intake ports?

Brian(Bear) has managed to put in I believe 35.5 intakes and (reduced to) 30.5 exhaust valves for barely clearing the valves with a high lift short duration 125-75 cam on his 410 head.

What would something like this be capable of putting out power wise with a mid 1100s cc 10:1 compression steeet engine(light pistons, decent squish area, cx7/cx10, etc cam)?  And is the head so modified capable of real street miles or is is too fragile?

How would a head like that compare to a well ported 33.5/28 valve k head that has proven reliability?

George

[754]

Welding and relocating studs in the cases, is easier than  Welding and raising ports, but then you have to find existing cylinder that could work or make new ones..

[scottly]

Just how much more HP will this theoretical head develop, compared to a stock head with a port job, over-size valves and thin valve stems?

One straight port head that I am aware of:
At 10 Inches Mercury and .400 Lift:
Intake    110 CFM
Exhaust    92 CFM
Converted to 28 Inches of Mercury:
Intake    184 CFM
Exhaust   154 CFM
The maximum POTENTIAL horsepower for a head with these specs is 189.2 HP.
Highly unlikely this can be achieved for many obvious reasons.

I think you mean inches of water, Keith? The best head for a 750cc engine would be different than the best head for a 1000cc+ engine. Someone here once said something to the effect of "Yeah, a sewer pipe has a lot of flow, but it isn't a very good port".

[PeWe]

It must be possible to get similar as a Kawasaki Z1-900 can reach

140 Whp / 134 Nm

This must be a possible goal for a CB750 too.
The bore of that bike was rather big. I saw it in the shop, the PO had gone wild to carve the upper case for fat sleeves. I do not recall the displacement. JE pistons mentioned. Max on JE website is 1200cc
http://www.jepistons.com/Catalogs/Powersports/Street-Cycle/Kawasaki/kz_900-1000.aspx

Go out to 1260 with a KZ1000 block, put 37.5 intake valves, cams, porting and 36mm TMR or RS carbs and 140HP isn't hard to achieve. Getting 125HP out of a street CB750 is a little more challenging.

OK, the question now is how to make a prepped KZ1000 motor to look like a CB750? 
A few mm bigger inlet valves make that much? Plus additional 200cc.
Twin cams allow more tuning combinations when timing, a sohc must be able to lift the valves as needed too.

[kmb69]

.....
I think you mean inches of water, Keith?
.....

Duh, Yeah! 
Getting tired and lazy! Should be proofing my post. 
Corrected the original post. Thanks Scottly

[Don R]

 So with the current combustion chamber thinking a flat top piston and a closed chamber head seems popular, flattening out the valve angle would require a bigger bore to fit the valves in. How big can we reliably bore one of Mikes cylinders? Modern springs are light years ahead of what we used to use, I don't think springs are an issue.
 The last big improvement in nhra pro stock was reducing deck height, bigger bore and shorter stroke which lowered the heads, that pulled in the intake runners close together to the point where you could look through the carb and see the intake valve. We could raise the intake port until it got into the rocker cover, maybe a bolt on intake manifold? We aren't talking a stock frame any more either.