- 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.