Author Topic: horsepower est.  (Read 2182 times)

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Offline Don R

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horsepower est.
« on: December 31, 2022, 05:23:29 PM »
  Just for the sake of fun and discussion, I'm contemplating engine sizes and over bores, if we assume a warmed over 736 makes around 74HP that's a HP for every 10cc. All other factors being equal, an 836 might be up 10HP over a stock bore 736. Does that sound right?
 
 Therefore, an 812 might make 7.6 more HP than a 736 and an 836 might make 2.4 more hp than the 812.
 Given the choice between an 812 and an 836 will the seat of your pants know the difference? I realize I'm assuming there is enough carburetor, exhaust flow, valve size and port area to support the extra CC's. 
 
 
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Offline HondaMan

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Re: horsepower est.
« Reply #1 on: December 31, 2022, 08:06:15 PM »
In the old days....when dirt was young and computers took up a whole floor of the building...

The 811/812cc kits generated the biggest bang-for-buck unless the intake valve was enlarged for the 836 size. The HP difference between 736cc and 811/812cc was more-per-CC change than the 811/812 to 836 difference. This makes sense given that the cylinder dynamics changed from undersquare to oversquare beyond the square-bore of the 811/812 size: the engine changed from the 'whirlwind' intake design of the narrower bore to an unguided intake fill that doesn't cool as well, nor does it have the stratified charge (and wider powerband) of the smaller bore.

General HP numbers I'm used to seeing/remembering:
Stock 736cc K0-K1 (post-sandcast): 67-68 HP when dyno'd and published by Cycle magazine (8500 redline)
Stock 736cc K2-K3: 60-64 HP when dyno'd and published by various magazines (8000 redline)
Stock 736cc K4-K5: 55-58 HP when dyno'd and published (8000 redline)
811/812cc K0/K1: 72 HP when dyno'd with OEM carbs (Motorcycling magazine, I think it was)
836cc K2-3: 74 HP at 7800 RPM, less above that, dyno'd w/larger carbs (Cycle Rider mag, or something like that: a short-lived, wrench-happy magazine)
825cc engine per Action Fours' ads: 74 HP@8000 RPM (never saw dyno tests)

There was a famous quote (a tech paper I read several times) from one of the Honda engine designers back in those days who described how the 750's design inspired the Honda CVCC (car) engine. This complex critter had 2 intake valves (and one exhaust), with a smaller one in a 'precombustion chamber' that had a small port into the main cylinder, and a carb that had 2 venturis (and 2 distributors, with points!). One venturi was 8:1 (to 10:1 at speed) A/F mix while the other, larger one was 17:1 (to 20:1 at 4000+ RPM) mix. There were 2 sparkplugs per cylinder, one in the 'precombustion' chamber and the other, firing later, in the main chamber. The precombustion would intake and fire (10-18 degrees) early and would jet the overly-rich mixture into the larger cylinder thru a small, angled port so as to form a 'whirlwind' at supersonic speeds to stratify the fuel-air charge out toward the cylinder walls to cool them while the main portion of the charge burned at (hot) improved MPG levels. This was all done to prevent ping, which is also a benchmark of this SOHC4 engine. They were torquey engines, and the design was said to have come from the 750 SOHC undersquare swirl-charge "success", as he put it.

What I've noticed over the years: the 811/812cc engines last almost as long as the stock-size ones, while the 836cc engines don't, given cast pistons both (forged pistons use up the rings faster). The 836 engine feels torquey at in-town, lower-RPM speeds, but loses its luster above about 6000 RPM for lack of carb and intake valve size. If the carb (and intake valve) are enlarged, it becomes a sluggish beast at in-town speeds until 3000 RPM at least, when it gets its 'legs'.

I have also noticed that boring past the 811/812cc bore size also re-starts the characteristic cylinder warping of the outer 2 cylinders, which adds to the power loss at about 4000+ miles. For this I was glad when Action Fours also realized it and made the 825cc kit, which, if the engine had gone thru the 3 steps of 760cc (4th oversize) to 811/812cc (square bore) to 825cc it could last 80k miles or more without power loss. But, since the roadracers balked at more than 812cc and the dragracers went straight to 836cc (or more), that in-between kit soon died away, too bad. It would have given 2 'big bore' steps with the stock cylinders, much extending the engine life.
« Last Edit: December 31, 2022, 08:25:04 PM by HondaMan »
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline dave500

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Re: horsepower est.
« Reply #2 on: December 31, 2022, 11:52:35 PM »
thats all because the stock rod length is used,theres a lotta locked up power and free torque in a few mm or part off in rod lengths in any over bored motor,Don you should know that.

Offline PeWe

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Re: horsepower est.
« Reply #3 on: January 01, 2023, 02:56:51 AM »
- Ported head will add some too.
- Higher compression another detail.
- Deeper valve pockets for hotter cams. Not much hotter need deeper pockets.

- High lift and relatively short duration to get OK torque from low.  RC295 and 125-70/75 cams

### One example about compression ###
My K6 had 1005cc, DP315 followed by bettter RC295 cam.
Ported K6 head with 34/28mm valves.
Power was only around 90-93whp. But it ran rather well.

I replaced the head with a ported K2 head with stock stemmed 34/28 mm valves. (Earlier was a max ported K6 head, 5mm stemmed 34/28mm valves)

Cam Megacycle 125-75. Compression tested with a cheap tester now in the +200PSI area from earlier 185-190PSI. Now smaller chambers, thinner head gasket, MLS 0.03" from 0.04".
This gave now 101Whp, better torque with  even power up to +9000rpm. Big difference when passing 180 and further above 200kmh.

- Replaced cylinder with a 970cc kit 70mm pistons.
That kit had the billet block w pistons as a template. Not lower compression.
My nearby shop milled the cylinder lower for the pistons outer edge vs head surface. Pistons were 12.5:1 so they were milled to get similar data as the 71.25mm pistons vs billet block vs head chamber sizes.
(970 cyl 84.0mm, billet block 84.5mm high. 70mm pistons were 0.5mm lower at their outer flat edge)

I changed base gasket to thinner, from RCS 0.02" to 0.01".  (0.25 mm lower cylinder)
Power now 104.5whp on several dynos during 2 seasons. Same compression tester show 210-220PSI area.

Last dyno with another ported head (392) with 33.5/28.5mm valves. Also ported Yoshi style as the previous K2 with material left in front of the guides, as sharp plows, maybe give more support to guides too.
I asked for it after reading a thread George wrote.

Last 2 dynos 107.5 whp.
Only change 1 step smaller main jets, cleaned K&N pods.
Still 33.5/28.5mm valves and 125-75 not touched since last 104.5whp a week or 2 before.

Cam that most likely is ok timed. I have tested a few degrees more advanced and retarded with several hp lost.

So, the small details with compression, cam timing and probably ignition too can add or reduce +15whp with 970-1005cc.
Dyno showed erratic graphs at higher revs with points.

Changed to Dyna-S that also use stock advancer with cut springs which is a must for good behavior from idle and up. My almost stock K2 has that too.

I have used 32mm carbs all the time. Mikuni TMR.
836 gave 80-83 whp.
Action fours SS-1, Megacycle 125-20 cam.
Compression tester in the 180-190 PSI area
I guess that thinner gaskets and 125-75 (or RC295) cam should have given some more. I ran it with RC295, more torque and easier to just twist throttle on 5th gear- 4000rpm. No dyno.

I know one guy that got 86whp with JE  62mm pistons.
Not that much ported head with 5mm stemmed 34/28mm valves.
The mechanic said "only 750cc". Pistons shaped for the updated chambers, high compression. Norris cam, CR31 carbs. 4-1.

*** The engine is like an orchestra ***
All parts have their mission. They must play the same song and correctly adjusted/ timed as the conductor (tuner) make sure.

Compression is a vital detail.
I use  street gas as Shell V-Power. No pinging unless too lean carbs as could happen in the beginning, years later found to be caused by not filtered pilot air jets. Or if less diplacement/compression need bigger jets.

I'm curious what next dyno will show when carbs now have better needles. Before too rich.

Maybe engine like a little rich.

I can accept a few less when mixture is better not carbonizing pistons-chambers and flush important oil lubrication away.

One detail the dyno guy  noted:
After several WOT's, max power reduce a little.
He ran the engine in the lower area to read AFR very careful and let engine cool down during a few minutes.
Next WOT ~1-2 whp more.

Billet block more stable than the 970 stock cylinder with 74.5mm OD sleeves -70mm bore makes 2.25mm thick sleeves and not thick material around them.

Billet block pistons will be gas ported, horisontal holes above top ring to let gases press ring outwards.  I think diam as ring groove is high, half diam in ring groove, half above.
I have a new set of rings, shop will clean the nikasil and freshen up the surface for the new rings.

It will be interesting how it will behave on dyno after that. Thin base gasket next time to ensure +105whp. ;)

Another thing when it can be tested. I have no reason to rebuild my K6 now. And make sure the carbs to be correctly adjusted before.
I have cleaned pistons and chambers several times due to too rich carbs.

My other ongoing engine build prepared for the block,  will use 29mm carbs I have and 890cc adapted for my repaired K6 head.
Build will end up in my K2 as my latest idea.

*******
My K2 with CI K7 (392) 61.5mm pistons  (748cc) cranking up the compression,  stock K6 cylinder and head to look like model year 1975.
K7 cam, Yamiya no number 4-4. K6 carbs with stock airbox.
57.8 whp.
Wheel vs crank hp differ 20% as I have found when reading here and there about bike power.
57.8x1.20=69.36 crank hp  that feels possible. Higher compression and better flowing exhaust.
« Last Edit: January 01, 2023, 09:35:41 AM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Don R

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Re: horsepower est.
« Reply #4 on: January 01, 2023, 09:53:45 AM »
 I'll admit it, I love to provoke a discussion because we all learn so much. 
No matter how many times you paint over a shadow, it's still there.
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 You don't need a weatherman to know which way the wind blows.

Offline PeWe

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Re: horsepower est.
« Reply #5 on: January 01, 2023, 11:19:28 AM »
This is a very interesting topic I want to read more about.
Examples would be fun.

I'm sure there are many that has upgrade experiences.
I remember guys that only bored their engine to 890/900cc with flat Henry Abe kits. Not a racer, but less shifting.

Here also about CB750 initial limitations and how the limitations change when upgrading.

In wich order do the limitations appear in a CB750?
Maybe compression and cam followed by ports?
Displacement will add more ground torque and base for more at top.

Bigger bore pistons usually add compression. Stock cam can have too short duration?

My 836 with good ported head ran fine with a modest cam. It got a little more with higher lifting cam but not enough difference to skip longetivity when bike was used mostly for touring.

The RC and Yoshimura cataloges can tell what to do and in wich order.
Yoshi said that 836 and 8000 rpm is the limit for stock rods.

Tuning enter next $$$ level when going bigger or rev higher more often;)

The idea with 810/812cc followed by 823cc and 836cc was really good for stock rods.
Dynoman has 811cc pistons today.

This make me eager to see how much an 890cc build will reach. Hopefully + 90whp.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline HondaMan

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Re: horsepower est.
« Reply #6 on: January 01, 2023, 11:27:40 AM »
PeWe:
When you had trouble with the points: have you tried reducing the steep opening and closing ramp on the points cam? When i\I worked with the midget-car racers of the 1970s (who were using the 750 engine), they used the points with much-slotted points baseplates, making the opening ramp into a longer slope. This required idle to be 1200 RPM instead of 900, but those engines ran regularly at 14k (and one even to 16k) RPM. Those engines had the tranny cut off and just used the crankshaft, with the left (alternator) end driving into a 4-speed or 5-speed clutched gearbox, so there were other considerations, too.

The points and condensors on those engines were in their normal position, mounted to the 'front' of those engines so they could be easily accessed. The spark advancers were much modified, though, and full advance did not occur in the 14k engines before 7k RPM. In the 16k engine the advancer had additional (tricky and complex) hardware added to reduce the spark advance 2 degrees at 12000 RPM to allow that one to run up to 14.5k, then more advance was applied to reach 16k RPM. The driver-owner said it was "peaky" and had a flat spot of power when the 2 degrees retard was happening, but would "push though" it on the straights of the track to reach the 16k peak. Obviously, not a streetable approach! But, interesting work regardless. Today this could be more easily done with electronic spark controls.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline PeWe

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Re: horsepower est.
« Reply #7 on: January 01, 2023, 12:09:25 PM »
Hi Mark, I did not modify the points nor cam. The phenomenon only seen on dyno graph. Not felt while riding.
I got ideas about double point spring mod. If that could have changed it. Or using other points.
I think car points has been mentioned somewhere. Old Corvette points?
« Last Edit: January 01, 2023, 12:45:52 PM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Don R

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Re: horsepower est.
« Reply #8 on: January 01, 2023, 12:21:55 PM »
 I stumbled across this recently, on ebay at 3 am with the auction over at 7am.
  Everything inside looks new, the packing newspaper is dated 1977.
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline PeWe

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Re: horsepower est.
« Reply #9 on: January 01, 2023, 12:35:09 PM »
Photos of the content too?
NOS 1977 is still new ;)
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Don R

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Re: horsepower est.
« Reply #10 on: January 01, 2023, 04:35:01 PM »
Photos of the content too?
NOS 1977 is still new ;)
I opened them but didn't get a pic. I'll do that tonight.
« Last Edit: January 01, 2023, 06:04:42 PM by Don R »
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline HondaMan

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Re: horsepower est.
« Reply #11 on: January 01, 2023, 08:02:59 PM »
Boy, that is an ANCIENT Wiseco kit!
:D
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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Re: horsepower est.
« Reply #12 on: January 01, 2023, 08:17:50 PM »
Hi Mark, I did not modify the points nor cam. The phenomenon only seen on dyno graph. Not felt while riding.
I got ideas about double point spring mod. If that could have changed it. Or using other points.
I think car points has been mentioned somewhere. Old Corvette points?


There was a specially-made points plate for these bikes that mounted Chevy points, I think even shown in our forums at one time? They recommended the Corvette version of points then because it had an engine that could reach 6000 RPM, and was a V-8 with distributor, so that was like running (8 x 6000/2) = 24000 RPM on these bikes. That would have been good news to the midget-car builders I knew! Those midget-car guys were doing the double-spring thing on their points, but I was told the 2nd spring came from points from another bike (never learned which one, though). I never saw their points plates (that I remember), just the advancers.

On dragrace tracks where guys were running over 10k RPM on points, sometimes you could hear the exhaust 'breaking up' near the gear shifts. I always supposed this was due to points float, or possibly carb issues with the velocity stacks they ran. On the roadrace tracks the shifts were usually more in the 7000+ range.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline Don R

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Re: horsepower est.
« Reply #13 on: January 01, 2023, 09:17:12 PM »
Boy, that is an ANCIENT Wiseco kit!
:D
I wish the 77 K sitting here looked as good.
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline PeWe

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Re: horsepower est.
« Reply #14 on: January 01, 2023, 09:47:41 PM »
It has similar design as old RC?
It had single oil control ring.
- The shiny one to the left, RC cast 836.
- RC forged, 1983.
- To the right Action Fours cast 1985


The RC cast gave 83whp in worn sleeves without smoking. Over 0.10mm total clearance
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Don R

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Re: horsepower est.
« Reply #15 on: January 01, 2023, 10:47:31 PM »
  This is the stroker motor, I think Tom (the late PO) was an action 4's dealer. His stuff has a lot of MTC parts too. I believe it is a 72mm bore, my cheap dial caliper reads 71. something at the top. Two sleeves are low in the block and don't seal to the copper head gasket. My plan is let Ken at cycleX figure out how to cure it.
   I have a K2 with another of his engines believed to be an 836 It sits a lot but runs great when it's running.   
« Last Edit: January 01, 2023, 10:51:10 PM by Don R »
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline ekpent

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Re: horsepower est.
« Reply #16 on: January 02, 2023, 06:46:02 AM »
Hi Mark, I did not modify the points nor cam. The phenomenon only seen on dyno graph. Not felt while riding.
I got ideas about double point spring mod. If that could have changed it. Or using other points.
I think car points has been mentioned somewhere. Old Corvette points?


There was a specially-made points plate for these bikes that mounted Chevy points, I think even shown in our forums at one time? They recommended the Corvette version of points then because it had an engine that could reach 6000 RPM, and was a V-8 with distributor, so that was like running (8 x 6000/2) = 24000 RPM on these bikes. That would have been good news to the midget-car builders I knew! Those midget-car guys were doing the double-spring thing on their points, but I was told the 2nd spring came from points from another bike (never learned which one, though). I never saw their points plates (that I remember), just the advancers.

On dragrace tracks where guys were running over 10k RPM on points, sometimes you could hear the exhaust 'breaking up' near the gear shifts. I always supposed this was due to points float, or possibly carb issues with the velocity stacks they ran. On the roadrace tracks the shifts were usually more in the 7000+ range.
The points plate were called Maxi-Dwell. Have one still in the original packaging. Made them for the Honda and Kaw 4's. The only drawback I have read on those was the actual plate was made of aluminum and might distort somewhat when hot.

Offline PeWe

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Re: horsepower est.
« Reply #17 on: January 02, 2023, 06:57:14 AM »
Hi Mark, I did not modify the points nor cam. The phenomenon only seen on dyno graph. Not felt while riding.
I got ideas about double point spring mod. If that could have changed it. Or using other points.
I think car points has been mentioned somewhere. Old Corvette points?


There was a specially-made points plate for these bikes that mounted Chevy points, I think even shown in our forums at one time? They recommended the Corvette version of points then because it had an engine that could reach 6000 RPM, and was a V-8 with distributor, so that was like running (8 x 6000/2) = 24000 RPM on these bikes. That would have been good news to the midget-car builders I knew! Those midget-car guys were doing the double-spring thing on their points, but I was told the 2nd spring came from points from another bike (never learned which one, though). I never saw their points plates (that I remember), just the advancers.

On dragrace tracks where guys were running over 10k RPM on points, sometimes you could hear the exhaust 'breaking up' near the gear shifts. I always supposed this was due to points float, or possibly carb issues with the velocity stacks they ran. On the roadrace tracks the shifts were usually more in the 7000+ range.
The points plate were called Maxi-Dwell. Have one still in the original packaging. Made them for the Honda and Kaw 4's. The only drawback I have read on those was the actual plate was made of aluminum and might distort somewhat when hot.
I saw those on eBay. Not cheap plus horrible shipping so order was not possible.
Seller had an X-pipe exhaust system too.
I guessed seller had an old stock not sold earlier.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline HondaMan

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Re: horsepower est.
« Reply #18 on: January 02, 2023, 08:01:32 PM »
Hi Mark, I did not modify the points nor cam. The phenomenon only seen on dyno graph. Not felt while riding.
I got ideas about double point spring mod. If that could have changed it. Or using other points.
I think car points has been mentioned somewhere. Old Corvette points?


There was a specially-made points plate for these bikes that mounted Chevy points, I think even shown in our forums at one time? They recommended the Corvette version of points then because it had an engine that could reach 6000 RPM, and was a V-8 with distributor, so that was like running (8 x 6000/2) = 24000 RPM on these bikes. That would have been good news to the midget-car builders I knew! Those midget-car guys were doing the double-spring thing on their points, but I was told the 2nd spring came from points from another bike (never learned which one, though). I never saw their points plates (that I remember), just the advancers.

On dragrace tracks where guys were running over 10k RPM on points, sometimes you could hear the exhaust 'breaking up' near the gear shifts. I always supposed this was due to points float, or possibly carb issues with the velocity stacks they ran. On the roadrace tracks the shifts were usually more in the 7000+ range.
The points plate were called Maxi-Dwell. Have one still in the original packaging. Made them for the Honda and Kaw 4's. The only drawback I have read on those was the actual plate was made of aluminum and might distort somewhat when hot.

Yeah, that was it: Maxi-Dwell!
:D
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline Don R

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Re: horsepower est.
« Reply #19 on: January 03, 2023, 10:50:03 AM »
 So, if you had an 836 that was worn out or rusty and wanted another 836 would it be possible and/or prudent to bore that block and install thicker sleeves that might be also able to take another overbore?  Is such a sleeve commonly available?  Asking for a friend. L0L!
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline bryanj

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Re: horsepower est.
« Reply #20 on: January 03, 2023, 11:31:18 AM »
Somebody somewhere will make sleeves but cost may be high
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline PeWe

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Re: horsepower est.
« Reply #21 on: January 03, 2023, 12:26:18 PM »
CycleX has sleeves.
http://www.cyclexchange.net/Engine%20Parts%20Pistons%20Page/Sleeves%20Rings%20and%20Circlips/Sleeves%20Rings%20and%20Circlips.htm

Stepped sleeves. 74.2mm OD where it sit in block
64mm ID.

Often used with 890 or 900cc. 67 or 67.5mm pistons.
The latter end up in thin sleeves under cyl block.
Important to seal sleeve vs block very well to avoid oil weeping out thru the vents between 1-2, 3-4.

My 890 cylinder is sealed with Wurth Super RTV where sleeves stick out. 
Feels OK. Will hopefully stay dry.

My K6 has their other sleeves, with 970cc. Work fine so far.
The shop milled wider hole in the bottom so o-ring could be pressed in, covered by Hondabond equal sealer Threebond.
It has stayed dry so far, 10.000km and 4 torturing dyno visits ;)
« Last Edit: January 03, 2023, 12:32:10 PM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Don R

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Re: horsepower est.
« Reply #22 on: January 03, 2023, 12:51:24 PM »
  That sleeve may be the best option for an 836 with a turbocharger. Another note on my list of things to ask Ken about.
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline HondaMan

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Re: horsepower est.
« Reply #23 on: January 03, 2023, 04:35:57 PM »
  That sleeve may be the best option for an 836 with a turbocharger. Another note on my list of things to ask Ken about.
If the first 836 kit was done (properly) with cast pistons and 0.0010"-ish clearance, the cylinders could be honed some more for forged pistons since they take about twice that much clearance. Done that (with SuperHawk), worked out fine for 4 years (forgot how many miles) starting in 1970. I moved away from them and the bike after that.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline Don R

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Re: horsepower est.
« Reply #24 on: January 03, 2023, 08:18:59 PM »
 Sadly, this 836 and it's non turbocharged 836 mate spent time in a barn with the carbs removed and the cylinders rusted. I got the 71 freed up running but it soft seized it after a sprint down the 4 lane.  It cooled off and rode home.
« Last Edit: January 04, 2023, 03:08:05 PM by Don R »
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.