Topic: Highest horsepower CB750

[TerryK]

Anyone know what the world's most powerful normally aspirated sohc Honda cb750 was or is? No turbos or blowers please!

[chewbacca5000]

Some have made in the high 90s.  Not sure anyone has made it over 100 hp natural.

[BobbyR]

MReick has a dyno reading of 100 or over. Normal aspiration with his magic head work. I saw the bike in person. Very impressive.

[Jerry Rxman Griffin aka MuthaF'er]

 I just asked Bill Benton if he will be visiting the dyno soon?  If the engine he has in Cobra Girl doesn't break 100 I'd bet his new 'spare' will.

Looking forward to Mike's results when he takes his new JMR 1000 to the dyno.

[Retro Rocket]

Some of the Aussie race bikes in post classic run 120/130 HP, I think forum member Bear's sohc engines push 120 HP..

[MRieck]

 A little over 98 HP on pump fuel with a 915. Some race fuel would have broken 100 easy. Will see what the 1000 does....it needs some more miles. Feels very strong at a 6,000 RPM highway roll on. Carbs are almost right everywhere. It runs on VP small engine fuel , 94 octane, non ethanol now...that's it.

[chewbacca5000]

A little over 98 HP on pump fuel with a 915. Some race fuel would have broken 100 easy. Will see what the 1000 does....it needs some more miles. Feels very strong at a 6,000 RPM highway roll on. Carbs are almost right everywhere. It runs on VP small engine fuel , 94 octane, non ethanol now...that's it.

Very impressive!  When can you build me one?

[MRieck]

A little over 98 HP on pump fuel with a 915. Some race fuel would have broken 100 easy. Will see what the 1000 does....it needs some more miles. Feels very strong at a 6,000 RPM highway roll on. Carbs are almost right everywhere. It runs on VP small engine fuel , 94 octane, non ethanol now...that's it.

Very impressive!  When can you build me one?

Whenever you have the funds.  That was with CR-31's too.

[Stev-o]

A little over 98 HP on pump fuel with a 915. Some race fuel would have broken 100 easy. Will see what the 1000 does....it needs some more miles. Feels very strong at a 6,000 RPM highway roll on. Carbs are almost right everywhere. It runs on VP small engine fuel , 94 octane, non ethanol now...that's it.

Very impressive!  When can you build me one?

Whenever you have the funds.  That was with CR-31's too.

Is 130 hp possible, Mike?  [normally aspirated]

[chewbacca5000]

A little over 98 HP on pump fuel with a 915. Some race fuel would have broken 100 easy. Will see what the 1000 does....it needs some more miles. Feels very strong at a 6,000 RPM highway roll on. Carbs are almost right everywhere. It runs on VP small engine fuel , 94 octane, non ethanol now...that's it.

Very impressive!  When can you build me one?

Whenever you have the funds.  That was with CR-31's too.

Does this mean you are taking on more work?

[Retro Rocket]

A little over 98 HP on pump fuel with a 915. Some race fuel would have broken 100 easy. Will see what the 1000 does....it needs some more miles. Feels very strong at a 6,000 RPM highway roll on. Carbs are almost right everywhere. It runs on VP small engine fuel , 94 octane, non ethanol now...that's it.

Very impressive!  When can you build me one?

Whenever you have the funds.  That was with CR-31's too.

Is 130 hp possible, Mike?  [normally aspirated]

Yes Steve, but on methanol, not pump gas, and a lot of modifications... ...

PS, and a lot of money...

[PeWe]

A little over 98 HP on pump fuel with a 915. Some race fuel would have broken 100 easy. Will see what the 1000 does....it needs some more miles. Feels very strong at a 6,000 RPM highway roll on. Carbs are almost right everywhere. It runs on VP small engine fuel , 94 octane, non ethanol now...that's it.

Very impressive!  When can you build me one?

Whenever you have the funds.  That was with CR-31's too.

Cam is Megacycle 125-75, right?

[lrutt]

To better define this, are we talking still 750cc or are we talking big bore. If big bore, IMO that doesn't count.

[jaguar]

To better define this, are we talking still 750cc or are we talking big bore. If big bore, IMO that doesn't count.

Why not?
Still has the limitations of the architecture.

Who just wants to compare what stock engines put out on a dyno?

[bwaller]

Jag, I like to see what a builder can coax from a stocker for whatever reason. As an example Rob (Voxonda) built an endurance racer and wanted stock components. He made 17% over stock just with tight tolerances, carbs & a pipe.

[jaguar]

I see what you are saying. 
Thought you just meant from a "stock" motor.

Agree 100% that it is impressive to see what someone can do with a given displacement.  And that you can not compare the HP of a 750 to that of a 1160 stroker motor.

[lrutt]

I never said stock motor, I said 750cc. Do what you want but keep it at or below 750cc. Often times there are displacement limits for classes. It's one thing to get 100hp out of a 1000cc motor, quite another to do it from a 750cc motor. Just bringing an SOHC up from 736cc to 750cc would help but that would be about it.

[MRieck]

A little over 98 HP on pump fuel with a 915. Some race fuel would have broken 100 easy. Will see what the 1000 does....it needs some more miles. Feels very strong at a 6,000 RPM highway roll on. Carbs are almost right everywhere. It runs on VP small engine fuel , 94 octane, non ethanol now...that's it.

Very impressive!  When can you build me one?

Whenever you have the funds.  That was with CR-31's too.

Cam is Megacycle 125-75, right?

correct

[Don R]

 So to make big hp from 750cc, maximum RPM would be the limiting factor and you'd need to build it backwards from there, figuring the flow and velocity, ports, carbs and exhaust become more important. I'd suspect a class racer somewhere has the record.

[Jerry Rxman Griffin aka MuthaF'er]

Don,

You must be talking about Bill's newest engine?!! 

[BobbyR]

When you increase the HP to 100 or more I am wondering if the frames need modification to minimize twist.

Also, with large increase in HP come increased speeds. When mods to the suspension and frame do you need to make to improve the handling.

I have often wondered what it would take to mount a modern inline 4 sportbike motor in the frame thereby getting instant HP. 

[Jerry Rxman Griffin aka MuthaF'er]

Bobby,

After 100 it's pucker up time.    Hope to be able to tell you soon 

I'm gonna say straight line no, road course of course. Sure wouldn't hurt for either.

[754]

Bobby what would it take?  Tell you..a sick mind....

[BobbyR]

Bobby what would it take?  Tell you..a sick mind....

Bobby,

After 100 it's pucker up time.    Hope to be able to tell you soon 

I'm gonna say straight line no, road course of course. Sure wouldn't hurt for either.

Yes I agree. While I have done some things in the past, but that was my job and  those days ended with my discharge papers.

This was more of a mental exercise. I wondered, rather than take what is an Antique inline 4 motor and fiddle with it to try and get more power, just take a modern inline 4 motor with the power already designed in and expend the effort to do a transplant. 

I have done 100 a couple of times on my K8 and it was very interesting as Jerry said. Pucker is a good word.

[chewbacca5000]

After riding Pop-A-Wheelie 100 miles at sometimes at 100 MPH I think I may have the fastest.  There are no flat spots with this bike and it accelerates instantly.  That 100 MPH was at 6000 RPM tons of throttle left.  It literally sounds like one of the bikes you see out of the old Daytona clips.  Sounds like it too!  There is no way it is a stock bike.  It is more akin to a vintage crotch rocket than a 43 year old motorcycle.  I don't push it as I have no idea what it has for an engine.

This crazy bike just goes faster and faster.  As for the engine I have no idea, and I kinda like the mystery of the whole thing.