Author Topic: Theoretical discussion CB 750 making more horsepower.  (Read 1305 times)

0 Members and 1 Guest are viewing this topic.

Offline gschuld

  • Master
  • *****
  • Posts: 1,641
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #75 on: October 05, 2018, 08:30:19 am »
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


Online kmb69

  • Master
  • *****
  • Posts: 1,856
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #76 on: October 05, 2018, 08:54:55 am »
.....
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.

Online kmb69

  • Master
  • *****
  • Posts: 1,856
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #77 on: October 05, 2018, 09:04:54 am »
Material under the springs gets quite thin resulting in the "fragility" mentioned by Mike earlier.

Offline PeWe

  • Really Old Timer ...
  • *******
  • Posts: 6,700
  • Bike almost back to the 70's 2015
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #78 on: October 05, 2018, 09:19:55 am »
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
« Last Edit: October 05, 2018, 10:31:10 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline gschuld

  • Master
  • *****
  • Posts: 1,641
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #79 on: October 05, 2018, 11:43:55 am »
.....
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

Offline turboguzzi

  • Old Timer
  • ******
  • Posts: 3,533
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #80 on: October 05, 2018, 11:53:59 am »
.....
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 :)

Offline MRieck

  • Really Old Timer ...
  • *******
  • Posts: 9,527
  • Big ideas....
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #81 on: October 05, 2018, 01:16:31 pm »
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. ;) ;D Getting 125HP out of a street CB750 is a little more challenging. ;D
Owner of the "Million Dollar CB"

Offline gschuld

  • Master
  • *****
  • Posts: 1,641
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #82 on: October 05, 2018, 02:00:43 pm »
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

Offline 754

  • Really Old Timer ...
  • *******
  • Posts: 25,096
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #83 on: October 05, 2018, 04:03:58 pm »
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..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline scottly

  • Really Old Timer ...
  • *******
  • Posts: 12,196
  • Humboldt, AZ
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #84 on: October 05, 2018, 08:13:33 pm »
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". ;D
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline PeWe

  • Really Old Timer ...
  • *******
  • Posts: 6,700
  • Bike almost back to the 70's 2015
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #85 on: October 05, 2018, 09:26:47 pm »
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. ;) ;D Getting 125HP out of a street CB750 is a little more challenging. ;D
OK, the question now is how to make a prepped KZ1000 motor to look like a CB750?  ;D
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.
« Last Edit: October 05, 2018, 09:46:47 pm by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Online kmb69

  • Master
  • *****
  • Posts: 1,856
Re: Theoretical discussion CB 750 making more horsepower.
« Reply #86 on: October 06, 2018, 07:27:43 am »
.....
I think you mean inches of water, Keith?
.....

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

 

;