Author Topic: CB750 chambers differs in volume - Result in HP & Nm (Read 4642 times)

Erny · « **Reply #25 on:** October 01, 2020, 05:23:15 am »

Wau, such equal pressures for all 4! Congrats!
Wondering your compr tester - can you share picture of whole tester/tool case? Looks like mine where I suspect it either measures lower that reality is due to long hose (it is intended for cars) or I have lower pressures

PeWe · « **Reply #26 on:** October 01, 2020, 09:21:00 am »

Yes, the even result is nice. I thought it should differ +/- 5 PSI.

Bike runs very smooth and evenly. Had another +200km ride today after I raised needles 1/2 notch and carb sync.

Photo of box, sold by low priced car parts and tools shop. Made for cars, bikes with various plug dimensions. The long hose is what I use for the bike with correct threads.

The real compression will be higher when excluding the hose.
ID 5mm printed on it, 375mm long adds 7,36cc! 30% more of chamber volume 23,8cc
Link where this has been described before
http://forums.sohc4.net/index.php?topic=369.msg476032#msg476032

PeWe · « **Reply #27 on:** October 02, 2020, 05:34:32 am »

A ride during my lunch to find a restaurant went very well.
The head and cam (125-75) combo is working fine. My speedo and tacho needles rotates quicker now.
An even power from 4000 to after 8000 rpm without any big power bump. It feels like it enters a small notch up at every 1000 rpm like programmed to compensate for the wind.

I needed one more gear when I tested WOT from 2nd and up on a good road leaning a little upwards. I was too focused on the tachometer when I tried to gear up at around 8500 rpm.. out of gears.... needed one more...speedo needle was just going to cross the 200 line.
Carbs are finally working fine all they way. Time for another dyno

The tire look flatter after each ride

Soon finished 2nd rear tire this year

Modern bikes fatter rear might have a point.
My rear tires lasts max 6000km, mostly 5000km or slightly less.

Old Scrambler · « **Reply #28 on:** October 03, 2020, 04:37:39 pm »

Per..........very nice work

Be sure to have extra air-pressure in the rear for the dyno-test

PeWe · « **Reply #29 on:** October 04, 2020, 12:11:10 am »

Thanks Dennis, good to know.
I have a feeling that it will not pass the minimum power this setup should deliver, 100whp.

Need a plan B to eventually crank up the compression a little bit more

Piston crowns and chambers in a perfect marriage.

PeWe · « **Reply #30 on:** October 05, 2020, 10:34:49 am »

Dyno day today!
Head from this thread delivered the minimum accepted result which is good news!!

2 runs
Red: Lower value with old head with issues and RC295 cam, over a month ago.

Blue: Higher values and better carb jetting: This head and 125-75 cam, today.

Now get the remaining stray horses lurking inside begging to be released!

Old Scrambler · « **Reply #31 on:** October 05, 2020, 05:50:46 pm »

REAL increase in Street Power..........

johno · « **Reply #32 on:** October 05, 2020, 07:32:07 pm »

Love that torque curve Pewe, flat and keeps going strong and smooth, the HP is screaming for MORE air above 6,500, Per its saying give me more air I want to go 120HP

As you say there are horses lurking in there Pewe, Lots of them baby. It shows what big displacement does on a SOHC but also shows were we are restricted.
Johno

PeWe · « **Reply #33 on:** October 05, 2020, 10:58:22 pm »

How to get more air?
It must be the head that is the limit? Carbs TMR 32mm.
34mm in valves. If ports are opened more, valve is still only 34mm.
Maybe possible to carve more around the seats ....

Open too much and too big carbs will reduce torque and response at lower rpm, right?

Bigger exhaust valves?
28.5mm will not do much, right?

Chambers are not shaped for the pistons. Just a saved old ported head.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #34 on:** October 05, 2020, 11:15:20 pm »

This is one way. Take a peek at what Kenny has put on his site at CycleX. may be just what you need. Notice the size of the spigots.

http://www.cyclexchange.net/Honda%20Page.htm

PeWe · « **Reply #35 on:** October 06, 2020, 01:00:29 am »

I have seen them, beautiful!!. Lots of work must cost lots of $$$$

I'm happy to get 5-7 hp more as Mike's dyno runs

1 more upon that level enough!!!

Use my 32mm carbs, finally with OK jetting.

I do not want to suffer lower rpm power to get 10hp (or more) at the top.
If the hp graph can follow the torque 1000 rpm more would be nice

Erny · « **Reply #36 on:** October 06, 2020, 01:11:28 am »

PeWe, great results from dyno, wish to ride that bike!!

PeWe · « **Reply #37 on:** October 06, 2020, 01:33:36 am »

It work fine....need power a little bit longer.
This is easier to see on dyno than on the seat on common roads

It would be nice if it can rev up to 9200 rpm on 5th gear rather quick.
220km/h 17:48 gear

Today 210kmh.
Quicker is better so it will be road left when top speed is reached

Erny · « **Reply #38 on:** October 06, 2020, 01:35:38 am »

220 kmph? Wauuu! My K7 (stock) up to 160..

PeWe · « **Reply #39 on:** October 06, 2020, 04:23:03 am »

That's the goal

PeWe · « **Reply #40 on:** October 07, 2020, 07:16:02 am »

Quote from: Erny on October 06, 2020, 01:35:38 am

220 kmph? Wauuu! My K7 (stock) up to 160..

My K2 has cheap Cruzin Image K7 pistons with K6 head. Piston domes add extra compression. 170-180 PSI measured with same gauge as used here.
K7 cam just bolt in. Yamiya no number 4-4.
56-57 whp on dyno.
http://forums.sohc4.net/index.php/topic,183810.msg2130979.html#msg2130979

I have not tested top speed, 160kmh easy. Probably 170-180kmh.
But this is with a fresh built engine, new 61.5 pistons/bores, head job with good guides and valves.

Fun and relaxing to ride!
My wife's favourite as passenger!

simon#42 · « **Reply #41 on:** October 07, 2020, 09:54:13 am »

why do you measure your compression level in psi ? the cam profile and timing can affect this figure . that is why people normally measure compression ratio with the engine static .

PeWe · « **Reply #42 on:** October 07, 2020, 10:36:09 am »

Just to compare all 4 cylinders and verify they do not differ too much.
I can check later on if changed which can show issues like leaking valves or worse if the drop is high.
This was one of the reasons I understood to change head asap when my old had suddenly dropped around 20 PSI on 2-3, 1,4 as before.

I tested different cams before and noted the pressures. This verified the cams overlaps and how it affected compression.

DP315 with different lash changed compression rather much.
And yes, it worked better with the 0.12" recommended lash, compression difference compared to less than half lash used by many other cams.

Interesting to see relative measurements.
With same tool I can compare the change when replacing cam, head and/or pistons.

Compare one build with another.
My K2 had around 140-150PSI with stock type pistons. 30 more with different pistons, everything else same.

Now I know how this build is working. If I should change head, I do not want to see lower values

Maybe not too much higher either, forcing me to use thicker gasket, increase the squish or even worse, use another cam with more overlap when this cam work fine.

Very useful simple tool, note the compression.

PeWe · « **Reply #43 on:** January 08, 2022, 05:43:12 am »

Update:
Now running 970cc and another head with Kibblewhite 33.5/28.5mm valves.

Same cam, 125-75. A little bit more compression.
Same gauge showed 205-209PSI.
Rather equal that indicate even chambers and maybe good grinded cam as well.

No pinging heard. But it was too rich jetted at low up to needle area. Too lean main jet.

This is now hopefully sorted. I'll see how it will behave at the 5000 rpm pinging area.

Previous build with 1005cc and 101whp could have had better values with thinner base gasket. It used the thicker RCS.

Below from late October 2021 dyno, 970cc build.

Still std tap fuel, Shell V-Power.

Last ride after this dyno felt better between 3000-6000rpm after rejetting. So torque curve hopefully better there at next dyno.

I have a better tool today to measure the volumes. This is another engine build.
A little bit easier....

I found how to search for one not far away with decent shipping cost. 25cc version.

This weather from today is far from a dyno ride!

Old Scrambler · « **Reply #44 on:** January 08, 2022, 08:15:47 am »

Same scene from Pocatello................I hope to travel south about 600 miles in a month or so...........much better dyno temps and clean roads

PeWe · « **Reply #45 on:** January 08, 2022, 08:55:22 am »

I have to travel real far away for bike riding temps, Spain.
Now waiting to end of March if lucky.
I'm curious about how this blue bike will run after last adjustments. 104whp to beat. I'm positive that will happen!

Darkness with short days here at latitude 60* north make me tired.

Tracksnblades1 · « **Reply #46 on:** January 11, 2022, 03:58:24 pm »

PeWe,
Those are about as even compression readings
that I’ve may have ever seen excepting a single.
And considering in multiple cylinders the first one
checked always has the fresh battery and surfaced
charge voltage.

Have you done a leak down test on it, yet ?
We’ve primarily used a compression tester for a diagnostic tool.
It looks like you’ve got a good build on cylhead and bores…🎯

Don R · « **Reply #47 on:** January 11, 2022, 04:11:39 pm »

The head I recently got has a ding in a cylinder like something piston sized was dropped in the chamber. Fortunately, that cylinder feels like it's humped up right there compared to the others so maybe equalizing them would cure the issue.

PeWe · « **Reply #48 on:** January 11, 2022, 08:59:06 pm »

No leak down test. I have no equipment for that.
Cheap compression tester was easy to find. I bought it to verify equal cylinders and compression.

Good to save the values for future references if something change, verify builds and status too.

Last head was ported and chambers balanced by a nearby shop that also fixed the pistons.

News:

Author Topic: CB750 chambers differs in volume - Result in HP & Nm (Read 4642 times)