ccing heads and such

Rocketdog
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ccing heads and such Oct 19, 2010 19:18:55 GMT -5

Quote

Post by Rocketdog on Oct 19, 2010 19:18:55 GMT -5

I've been checking compression ratios on a QMB 139 bored to 47mm <72cc>. I've seen GTs specs on the stock and NCY 50mm head, but I have to do things myself. My combustion volume came out a little bigger.

Now these ratios are with no base gasket.

Figures

Stock QMB139 49cc Head-5.4ml=5.4cc

NCY 50mm Head w/.20 inch Shaved off-6.0ml=6.0cc

I didn't take a pic of that.

Instead of measuring the piston volume and the distance between the highest part of the piston to the cylinder deck. I measured the volume to the deck@TDC. I think it's more accurate.

47mm bore piston to Cylinder Deck Volume @tdc-2.7ml=2.7cc

Here's the rest.

QMB139 47mm Bore Head Gasket Thickness Compressed-.32mm X 49.62mm
Bore 47mm=1.85 inches
Stroke 41.4mm=1.63 inches
QMB139 Base Gasket Thickness Compressed-.5mm
Base Gasket Thickness effect on a 47mm Bore @ TDC =.87cc

Since I used the total volume to the deck@TDC I set the Deck Height to Zero.

I used this calculator

www.rbracing-rsr.com/compstaticcalc.html

Stock head no base gasket-9.27-1
W/ Base Gasket-8.81
NCY 50mm Head w/.20 inch Shaved off/ no base gasket-8.74-1
W/ Base Gasket-8.33-1

If you find a fault with the math speak up. But I'm sure of the measurements. I checked them twice.

RD

Last Edit: Nov 12, 2010 18:58:50 GMT -5 by Rocketdog

Don't ever become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.

90GTVert
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Posts: 601

ccing heads and such Oct 19, 2010 21:02:16 GMT -5

Quote

Post by 90GTVert on Oct 19, 2010 21:02:16 GMT -5

Nice work! It's good to see other people checking for themselves. It looks like your stock head came ready for a bigger bore, mine didn't. At that rate, I got 5.3cc and you got 5.4cc. I got a lesser volume from the head I had with no bevel at all, just a hemi combustion chamber.

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Brent
103cc Vento Triton 2T : 72MPH
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bige Non-Com "PREFERRED VENDOR" LtCol Southern 2 & 4 wheeled mechanized LRRP's Posts: 71	ccing heads and such Oct 20, 2010 5:53:04 GMT -5 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by bige on Oct 20, 2010 5:53:04 GMT -5 thats some good info
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Rocketdog
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Posts: 824

ccing heads and such Oct 20, 2010 6:06:19 GMT -5

Quote

Post by Rocketdog on Oct 20, 2010 6:06:19 GMT -5

Oct 19, 2010 21:02:16 GMT -5 90GTVert said:

That would account for the difference. The edges of my stock head are beveled a bit.

I've suspected, for a long time now, that my Chinese scoots weren't running the comp ratios that are posted on some spec sheets. 10-1 would be nice or 10.5. I've been looking for a piston with more of a flat top, instead of the common dished one. So far no luck.

RD

Last Edit: Oct 20, 2010 6:44:44 GMT -5 by Rocketdog

Don't ever become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.

90GTVert
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Fat Ghost Rider

Posts: 601

ccing heads and such Oct 20, 2010 7:48:53 GMT -5

Quote

Post by 90GTVert on Oct 20, 2010 7:48:53 GMT -5

You might wanna talk to Enviromoto. My NCY 50mm kit has a flat top piston. Not sure if the 47mm kits are like that or not. You could always go to 50mm and bump the compression like crazy if you want. ;D I had a cheap 47mm kit before the 50mm. Looks liek it might have been what you have, but it's hard to tell with the piston covered in fluid. It was a dished piston and pretty far from deck @ TDC. The NCY 50mm is closer to deck on top of being a flat top. I have had to mod my heads out to closer to 7cc to keep from having spark knock on 92-93 octane. Right now, it's at 6.8cc and right on the edge with 1-2 degrees of timing advance. If I run heavier weights and put it under more load it will knock.

Last Edit: Oct 20, 2010 7:52:53 GMT -5 by 90GTVert

Brent
103cc Vento Triton 2T : 72MPH
103cc Vento Triton 2T : 70MPH
96cc Keeway Venus 2T : 61MPH
49ccScoot.Com

Rocketdog
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Sargeant First Class, Rolling Gatlin Artillery & Mobile Supply

Posts: 824

ccing heads and such Oct 20, 2010 13:11:14 GMT -5

Quote

Post by Rocketdog on Oct 20, 2010 13:11:14 GMT -5

Thanks GT. Here's a picture of it.

Yeah it's Enviro's 47mm kit. Wonder if NCY makes a flat top 47mm. I want to stay in my 1a class and that's the max.

Muhahahah!!! hehe Thanks Rebel. In a few weeks I'm going to do a 150cc stock head and bore. A 59mm bore and a 4mm stock er stroke. So stay tuned.

RD

Last Edit: Oct 20, 2010 17:17:06 GMT -5 by Rocketdog

Don't ever become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.

90GTVert Global Moderator Fat Ghost Rider Posts: 601	ccing heads and such Oct 20, 2010 13:57:43 GMT -5 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by 90GTVert on Oct 20, 2010 13:57:43 GMT -5 That looks like what I had, but mine wasn't from Jeremy. I thought all he sold was NCY kits. Hmm. I still vote to shoot him a message or call him up. If he doesn't know, he can probably point you in the right direction.
	Brent 103cc Vento Triton 2T : 72MPH 103cc Vento Triton 2T : 70MPH 96cc Keeway Venus 2T : 61MPH 49ccScoot.Com

Rocketdog
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Posts: 824

ccing heads and such Oct 20, 2010 17:46:49 GMT -5

Quote

Post by Rocketdog on Oct 20, 2010 17:46:49 GMT -5

If I could take just 1cc off the piston you would get 10.38 with a stock head and a 47mm bore. Like I said, I didn't cc the dent in the piston but there is at least 1cc in it. Perhaps a bit more. Those photos really don't show how deep that sucker is.

RD

Last Edit: Oct 20, 2010 17:47:34 GMT -5 by Rocketdog

Don't ever become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.

jmkjr72 contributing staff Commander 132nd Northern Cav. Division Posts: 2,779	ccing heads and such Oct 21, 2010 18:05:14 GMT -5 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by jmkjr72 on Oct 21, 2010 18:05:14 GMT -5 how much piston to valve clearnce do you have that would be my concern as lond as you have room i would look for a piston without the valve relifes

Rocketdog Revolutionary Commander Sargeant First Class, Rolling Gatlin Artillery & Mobile Supply Posts: 824	ccing heads and such Oct 24, 2010 7:09:20 GMT -5 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by Rocketdog on Oct 24, 2010 7:09:20 GMT -5 That's next. I haven't got to it yet. RD
	Don't ever become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.

Rocketdog
Revolutionary Commander

Sargeant First Class, Rolling Gatlin Artillery & Mobile Supply

Posts: 824

ccing heads and such Nov 12, 2010 18:56:51 GMT -5

Quote

Post by Rocketdog on Nov 12, 2010 18:56:51 GMT -5

<-----------------Somebody converted mm to inches and put the decimal point in the wrong place. But it's still not far off, just a bit less compression. It doesn't take much, when your working with such a small bore, to make a big difference.

Stock head no base gasket, I split the difference I think using rtv would make-9-1

W/ Base Gasket-8.54-1

NCY 50mm Head w/.20 inch Shaved off/ no base gasket-8.51-1

W/ Base Gasket-8.09-1

Running a NCY head is hardly worth it with the dished piston. And as 90GT has commented, the bigger valves probably don't help thing that much anyway. Reduces the velocity of the intake and exhaust. Now if you went up to a 50mm it might be a different story.

RD

Don't ever become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.

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