psycho1122
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posted May 21, 2004 06:07 AM
Question for entropy or JonnyCheese
I recently reassemled my 12 engine after having Billet 2nd and 3rd gear installed.
I did a static, cold compression test on the fresh 1270 (new bearings, rings, cam chain etc.), I was suprised at what I got for #s......245 psi per hole!
Additional specs are...105.5 in. / 100 ex., no base gasket, .050 piston to valve, .027 piston to head, +2.5 timing.
A/F Ratio set to 12.9-1
Runs great after map on 91 pump (oxygenated).
Can you estimate CR? Also, would you be concerned about possible Detonation?
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VincentHill
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posted May 21, 2004 06:25 AM
I do not know if they could they could be close but I am measuring my CR tonight by putting 1-4 on TDC and 2-3 on BDC and then filling my Burette with engine oil and filling both cylinders to the top of the spark plug hole with the cylinders at 90 degrees to the ground. (Have a convex bubble of oil at the top of the hole) and divide this out to know exactly. I do not know any other way to do this!
From the pressure you have I think your CR is high Between 12.7 and 13 to 1
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johnnycheese
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posted May 21, 2004 12:03 PM
yep you are correct Vincent. That is the only way to do it. I would put it around 14.5:1 and 91 pump gas is a no no on that. also 12.9 is WAAAAYYYYYY to lean at least 12.6:1 A/F
An Entropy is sitting right next to me an this is his input as well
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psycho1122
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posted May 22, 2004 08:51 AM
Would you also agree that 0 advance would also fight off some Detonation?
Thanks again Guys!
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johnnycheese
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posted May 22, 2004 10:12 AM
I would take some out using 93
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entropy
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posted May 22, 2004 03:32 PM
 Edited By: entropy on 22 May 2004 16:35
psycho:
.027 piston to head means your pistons are sticking up out of the block at tdc (assuming you are using a .030 headgasket)??? Be careful... I had pistons hitting the head (at hi rpm) with a set up like that.
any hot starting issues???
oxygenated 91 pump gas??? I used Nutec SP5+ when my bike was at 240psi/14.2+/- CR. NO GOOD!!! detonation evident, blew a head gasket at the Texas Mile races last Oct.
vincent,
engine oil in a burette?? man o' man you'll be waiting for ever for it to drain??? Also, you do not have to do the volume at BDC w/burette. Bore x stroke = add'l vol from TDC to BDC. What type burette are you using, what are the smallest gradulations???
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psycho1122
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posted May 23, 2004 09:54 AM
Entropy;
At .027, pistons do not exceed the cylender block, even when they were rocked (w/o rings installed).
I used the "used" head gasket when doing the mock up assembly clearance check.
New Muzzy .030 head gasket at final assembly.
NEVER a Hot starting issue w/ this 1270 engine. Cam Timing is probably helping w/ this. Engine does not even run hot on the road or in traffic!
Arizona is a HOT place!
Isn't Nutec an Oxygenated Race fuel??!!
One major thing I did w/ my JE's was to widdle away all the sharp, thin edges around all the Valve relief cut outs. This does not allow ANY hot spots on the piston tops.
When you ran the Nutec in the 240 psi engine, what timing advance were you running?
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entropy
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posted May 24, 2004 12:33 AM
psycho,
if you have a .027 piston to head (in the squish area), and you are using a .030 headgasket, it seems that yr pistons are sticking outa the block .003. Are you measuring it differently????
Yep, Nutec SP5+ is oxygenated, and sure adds power, but Daniel at Nutec said don't run it if you are much above 13:1. On the 1/4 I was doing OK, but in the mile sprints I got damage.
As you point out, bigger int numbers seemed to help my hot starting problem (107/110).
I'm running 5 advanced at WOT; tried lower numbers and higer numbers and hp fell. It likes 5, but gotta be careful about what fuel.
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psycho1122
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Posts: 1608
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posted May 24, 2004 08:18 AM
Remember that your .030 head gasket will compress a few thousandth's, also...I used the OLD head gasket when we solder checked the Quench area. I may have a two or three thou. chushin in there.
We used a Machineist's rule on the deck with the piston's at TDC, only when rocked did they "Kiss" the rule.
Wow! +5 w/ oxygenated fuel?!.........With your psi/comp. #'s, sounds like a recipe for detonation.
I am definately taking precaution's to eliminate the possibility of detonation. I might even take out some compression  to minimize the possibility, i.e. a .040 head gasket.
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You say PSYCHO like it's a BAD thing!!
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