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Head CC https://slantsix.org/forum/viewtopic.php?t=38351	Page 1 of 3

Author:	dakight [ Sat Dec 19, 2009 10:44 am ]
Post subject:	Head CC
I measured my head this morning, and found it empty... but I digress... The chambers are all at 56CC + or - .5CC. Is this close enough to even or do I need to work them a little to even them up? Putting the numbers into the engine calculator as Follows: Chamber Vol. 56 Piston Vol. 0 Bore 3.460 Gasket bore 3.670 (Permaseal Gasket, measured with a caliper) Comp. Gasket .040 Stroke 4.125 Deck 0.086 (after planned .100 cut). I come up with static compression ratio of 9.344. My target is 9.5 so I'm in the ballpark. Should I stick with the planned .100 cut or bump it to .110 to get closer to my target?

Author:	dakight [ Sun Dec 20, 2009 4:23 am ]
Post subject:
Anyone?

Author:	66aCUDA [ Sun Dec 20, 2009 5:35 am ]
Post subject:
David I would go ahead and bump it to .110. You can all ways use one of the Aussie gaskets to get a little less volume if you need it. Although that amount is not likely to make much difference. Frank

Author:	james longhurst [ Sun Dec 20, 2009 5:42 am ]
Post subject:
Hi David- I'm sure if you're within .5cc you're probably ok. I don't think you'll notice much difference but I'd probably spend the time to get them all equal. That includes measuring each chamber a few times to make sure I didn't screw up. Of course you could probably drive yourself crazy during the process. As for deck height, (were it me and I haven't been to the machine shop yet) I think I'd have them take a little more off to get the compression where I want it. I don't think and extra .010 will hurt the deck. After all, what's the point of making all these calculations and not ending up with what you want? -James

Author:	68barracuda [ Sun Dec 20, 2009 5:51 am ]
Post subject:
Hi Dak, My head volume is also zilch OK The Cylinder head volume was 59cc +- 5cc They are all now 45 cc on the dot. my static ratio works out to 9.485 For some reason my pistons are way down in the hole did not want to cut the block as it has just been redone and the engine is in the car

Author:	dakight [ Sun Dec 20, 2009 11:16 am ]
Post subject:
Would it make sense to get another .020 taken off the head, then cut the block accordingly? The machinist told me that he initially took .035 off of it to get it where it is. I had intended for it to be at 52 CC before I started cutting the block but when I measured it was at 56. How much will another .020 reduce it? edit After some quick and dirty measurements and calculations, it looks like I need to take another .030 off the head to get it down to 52 CC... does that make sense?

Author:	WoodyB [ Sun Dec 20, 2009 2:59 pm ]
Post subject:	CC'ing chambers
The closer the volumes are 'matched' the more even cylinder pressures, that is also taken into account IF the deck clearances of the block/cylinder are even, or close, not being relevant but say within .002" or better overall/end-to-end. The closer the cylinder and head volumes, the more even the cylinder pressures and the more even the power band per cylinder, IF the components are close (SCR, filling volumes, etc etc). If you're building a street engine, it's fine but if you're building a race engine, the volume variants should be less than .5cc, not +/-. Hope this helps...wb

Author:	dakight [ Sun Dec 20, 2009 3:17 pm ]
Post subject:
It's a street car and I have no intention to race it. Still, I want it done right and to run well.

Author:	emsvitil [ Sun Dec 20, 2009 3:29 pm ]
Post subject:
Even out the head volumes............. So later on you won't be saying to yourself 'Maybe I should have done it.............'

Author:	Dart270 [ Mon Dec 21, 2009 9:09 am ]
Post subject:
What is the error in your measurement of cc's? I bet it's as big or bigger than +/- 0.5 cc. I wouldn't bother evening them up more than that. Think about how much CR that changes - almost none. The biggest question for what CR you want: What cam will you run? Closely followed by: What fuel grade will you use? Lou

Author:	dakight [ Mon Dec 21, 2009 1:32 pm ]
Post subject:
The burette is graduated at 0.2 CC increments. My eyes aren't as sharp as they were when I was in Chemistry classes back in the mid 60's but I like to believe that I can resolve that much difference in my reading. I suppose there might be +- 0.1 variation in the fill technique and there is a certain amount of parallax due to the place I'm working and the height at which I have to hold the burette. I didn't buy a stand, I'm guessing my average error is +- 0.3, maybe 0.4 at most. The cam is an Erson 270 and while I'd like to run 87 fuel, I wouldn't be overly concerned if I had to go up to 89. 91 might have a little bit of a pucker factor, but considering that I won't be driving it everyday even that probably isn't a killer. I do not want to have to buy race fuel or aviation gas. That would be a no-go.

Author:	DusterIdiot [ Mon Dec 21, 2009 6:33 pm ]
Post subject:	Lol...
Quote: The cam is an Erson 270 and while I'd like to run 87 fuel, I wouldn't be overly concerned if I had to go up to 89. A 270 Erson with a 108 LSA would be able to run much more compression and still use pump gas... if it's a 111 LSA I'd say it might be 87 or 89... I'm running the 280/270 at 10.3:1 static...and it's fine on 89, and can do 87 if I dial out the vacc. advance a couple degrees.... Get a DCR calculator and see if you can run the DCR up a bit...I'll bet you'd be suprised. -D.Idiot

Author:	dakight [ Mon Dec 21, 2009 7:51 pm ]
Post subject:
I don't know much about DCR. What kind of numbers should I be looking for.

Author:	DusterIdiot [ Mon Dec 21, 2009 8:48 pm ]
Post subject:	DCR as a tool...
Quote: I don't know much about DCR. What kind of numbers should I be looking for. DCR is a better tool as it measures your compression ratio at the time the intake lobe actually is closing the vavle and the piston is starting to upsweep to build pressure...So in essence if you had a high duration cam with a tighter lobe separation there would be a large enough time where the overlap occurred and the cylinder would "bleed down"/loose compression...that might be able to deliver performance with lower cylinder pressure to allow use of lower octane fuels... DCR calcs for V-8's run a ruler of something like 7=Arco Regular, 8= regular maybe 89, 9=super and greater... With the slant we get some benefits of the long rods causing some dwell at the top and bottom of the stroke, so we might be able to tolerate a bit more on the DCR scale than the short stroke wide bore crowd... There are a few to choose from online, you will need to enter all the pertinent information on the engine, the cam, and punch the calculate button... The one I have downloaded isn't too bad... Assuming you are going with the numbers included and the 52cc chambers it's about a 9.8SCR +/- measurements... Assuming the 270/270 cam is 108 LSA and ground or bushed to advance 4 degrees... puts you at about 8.17DCR which is right on target for running 87/89...you might be able to run it up to 8.4 and be ok with that octane rating-a BBD it won't be happy... but any of the bigger 2 barrels or the 4 barrels this should be very fun when you are done. Play with it a bit and see what your options are... -D.Idiot "You have just crossed into....The Outer Limits!!!!"

Author:	sandy in BC [ Tue Dec 22, 2009 10:19 am ]
Post subject:
You are ending up in the same place ,give or take, as Rob and me. My DCR is about 8.2 (too lazy to look it up) Robs is a little higher with the same cam and higher compression. Your static compression is is closer to mine ....but with a little less intake duration. I run my car on 89 .....but could run on 87 (3.55 gears and a 5 speed) My BBD runs out at the top end of a very fat torque curve. If you are not the type to wind it up a BBD gives you one hell of a vacume signal for street use and ridiculous low end torque. You will need a good curve to keep it out of detonation in the midrange. My curve is very close to the stock 65 manual trans curve.... You are on the right track.

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