Author Topic: porting question 750-k2 (Read 2521 times)

rbirkhan · « **on:** May 14, 2007, 07:10:06 PM »

Does anyone know the stock combustion chamber in cc's I have started porting and modifiying the combustion chamber and want to see how much I need to mill off to retain 9.0/1+ CR. I know I may need to slot the cam to retain corect cam timing. I could figure it out if I knew the cc's of the dome of the piston also. I have been folowing the porting article posted here before which is quite good. The intake valve guide restriction was huge and lots of valve shrouding in the combustion chamber. 1972 k-2 750 stock bore unmilled heads.

HondaMan · « **Reply #1 on:** May 14, 2007, 08:34:59 PM »

Find my thread called "750 hemi" or something like that. It's all in there. I just did all that last summer, with my K2.

Jim F · « **Reply #2 on:** May 14, 2007, 09:27:52 PM »

Heres the link for porting the Honda head
Enjoy
Jim

http://members.tripod.com/cb750k2/Technical/porting/Porting_the_Honda_Head.htm

rbirkhan · « **Reply #3 on:** May 15, 2007, 03:08:31 PM »

Unfortunately they dont mention combustion chamber volume or piston dome volume. Someone knows

Sam Green Racing · « **Reply #4 on:** May 15, 2007, 03:34:05 PM »

You should have worked it out before you pulled the motor apart and before you started work.
There is a formula for checking CR that will give you the figures you need.
If nobody can come up with it, I'll see if I can find it when I have time,...I have it wrote down at home but can't remember it off hand.....something to do with being old.

Sam.

rbirkhan · « **Reply #5 on:** May 15, 2007, 05:13:58 PM »

I can figure out what I need with this calculator (below) but I need the cc of the piston dome. I have gasket thickness bore stroke and deck height.

http://kb-silvolite.com/calc.php?action=comp

rbirkhan · « **Reply #6 on:** May 15, 2007, 05:40:54 PM »

looks like 19.092 cc's would be 9.0 to 1 Using 2.4 inch bore, 2.475'' stroke, .010 negative deck height minus +? dome~ 0cc, .049 in thick gasket 2.472 bore gasket comes to 19.092 cc's. I will measure what I have with a syringe and plexiglass then figure out how much to mill for the desired C/R. I need to get them the same shape and volume and of course polished. should run nice nothing like a blueprinted cylinder head. still wish I knew the dome cc's though

this is a nice tool

http://kb-silvolite.com/calc.php?action=piston

Ben · « **Reply #7 on:** May 15, 2007, 07:00:36 PM »

Why don't you just work out the effective combustion chamber volume and work from there? This is much easier and probably more useful. Just put a little grease on the top piston ring, reassemble (no cam required) and crank to TDC. Get an accurate syringe and fill the cylinder with oil until you reach just up into the spark plug threads. Make note of how many mills you used. The number is your true combustion chamber volume in cc's.

Or, if you really need the dome volume, just press it into a piece of plasticence until level with the edge of the piston top. Fill the depression made in the plastecine with your oil filled syringe until level. Presto, you have your dome volume.

Cheers.

Sam Green Racing · « **Reply #8 on:** May 15, 2007, 07:11:58 PM »

Sorted

you took the words right out of my mouth Ben

Sam.

Ben · « **Reply #9 on:** May 15, 2007, 08:26:18 PM »

Sometimes the old school ways of doing things are the best and easiest!

Cheers,

Ben.

rbirkhan · « **Reply #10 on:** May 15, 2007, 09:07:44 PM »

I have used a syringe and a plexiglass cover to CC combustion chambers its the way to do it. I have ported heads with this method before. I dont want water in a newly honed/ringed/assembled bottom end. Besides if I did it this way I would need to torque the head/new head gasket down and its a one shot deal it only compresses once and I would need to do it in every cylinder then disassemble it dry it out and it still wont tell me the volume of the piston dome which is the only measurment I dont have. I cant believe no one knows the volume of the piston dome. How are people figuring out there static compression when they build big bores etc. I guess they are just assembling and hoping for the best scary.

Sam Green Racing · « **Reply #11 on:** May 15, 2007, 11:14:48 PM »

Why do you refer to us big bore types as scary just because we can't tell you the displacement of the crown of a stock piston ?

How many people do you think will know or would want to know the displacement of a stock piston crown ?

You havn't told us what you are trying to achive yet and despite the fact that Ben has already told you the easy way of figureing it out, you are still prepaired to take the figures that someone might offer as being spot on.

Do it youself, then if you get it wrong you only have yourself to blame

Sam.

Kamal · « **Reply #12 on:** May 16, 2007, 02:09:13 AM »

Who said to use water to measure the volume of the combustion chamber? Nobody did. They said oil. Just a poor projection.

Liquid is liquid...use liquid mercury for all hell...just don't use water! Use OIL. And a bit more tact in trying to RE-convey your ideas and requests...just in case you turned out to be wrong after all.

rbirkhan · « **Reply #13 on:** May 16, 2007, 05:25:11 AM »

Its ok if you dont know no need to reply if you dont. Measuring combustion volume by assembling the head on the engine will be inacurate because you cant see if there are air bubbles when filling it and you wont know when to stop filling the sparkplug hole remember the spark plug electrode has volume as well. Also you would need to prop the engine up at 4 different angles in order to fill it. This is a tough crowd.

rbirkhan · « **Reply #14 on:** May 16, 2007, 05:41:32 AM »

Sam i am trying to achive 9.0 to 1 CR after reshaping the combustion chambers. I have figured out a way to measure the piston I will post the cc's tonight. Not trying to piss anyone off just thought someone knew. Its been a long week. Its looking like 19 cc's is close to the majic number. Sorry about the scary comment.

MRieck · « **Reply #15 on:** May 16, 2007, 07:28:47 AM »

Quote from: rbirkhan on May 15, 2007, 05:40:54 PM

looks like 19.092 cc's would be 9.0 to 1 Using 2.4 inch bore, 2.475'' stroke, .010 negative deck height minus +? dome~ 0cc, .049 in thick gasket 2.472 bore gasket comes to 19.092 cc's. I will measure what I have with a syringe and plexiglass then figure out how much to mill for the desired C/R. I need to get them the same shape and volume and of course polished. should run nice nothing like a blueprinted cylinder head. still wish I knew the dome cc's though

this is a nice tool

http://kb-silvolite.com/calc.php?action=piston

The K0 crown is flat with very, very small valve reliefs. It doesan't displace enough volume to be concerned with especially when you are so low on the compression ratio to begin with. In comparision, the F piston has a .040 higher dome which increases CR to 9.2:1. You can get the chambers exactly the same after a lot of work but keep in mind the port volume and shape are always a little different too. You never get the same amount of charge in each cylinder. After the enging is run awhile your chamber volume will change a bit too secondary to carbon build up. I wouldn't worry about getting getting things to .01 CC. I'd concentrate on tightening the squish and getting the CR up to 9.5:1.

Gamma · « **Reply #16 on:** May 16, 2007, 08:16:07 AM »

Liquid Mercury-Now that would be interesting to watch in a combustion chamber.
Sorry couln't resist commenting

rbirkhan · « **Reply #17 on:** May 16, 2007, 11:27:34 AM »

thanks, I looked at the small dome and with the negative deck height its a wash. later engines had higher comp ratio intresting. I will post some pics when the heads are done they look sweet already should breathe nice.

Fasted · « **Reply #18 on:** May 19, 2007, 11:26:19 AM »

Show us the pictures!!!

HondaMan · « **Reply #19 on:** May 19, 2007, 07:51:44 PM »

Quote from: rbirkhan on May 16, 2007, 11:27:34 AM

thanks, I looked at the small dome and with the negative deck height its a wash. later engines had higher comp ratio intresting. I will post some pics when the heads are done they look sweet already should breathe nice.

Later engines' cams ran 5 degrees later, too, for a more hi-RPM orientation. The durations were the same, otherwise.

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Author Topic: porting question 750-k2 (Read 2521 times)

Ben

Ben