RE: Compression ratio testing

[Terry Rudd]

Rob,   Good one (about the beers) There must be something in the air on Saturday, as I got one of the calculations wrong too i.e. the stock bore capacity is 1952cc (not 1972cc) and  each cylinder capacity is 488cc (and not 493cc.)   The formula out of the book would have been a lot more complicated as it probably had a detailed method of how to calculate the chamber volume i.e. allow for piston dish, head gasket thickness etc. but you had already worked out the chamber volume by injecting fluid - too easy and very accurate.   The book would also have shown the calculation for working out cylinder volume i.e. 3.142 * (bore mm/2 ^ 2) *  stroke mm)/1000 = Capacity in cc and depending on how it was shown could have been more complicated than it really is.   Stock L20B bore x stroke is 85mm x 86mm Capacity per cylinder is:  PI (3.142) * (85/2) = 42.5 ^ 2 (squared) = 5675.2375 time stroke = 488070.425 divided by 1000 is 488cc   CR is (488 + 45)/45 = 11.85:1 (rounded a tad)   Do the same calculation for a 2190cc L20B (bored to max i.e. ~88mm) and you get (523 + 45)/45) = 12.6:1   After all this, even with a stock bore, with that head you've got yourself some serious compression and all of the problems that go with it to make it perform as you want on crap Aussie pump fuel i.e. nothing explodes if you use WOT a couple of times.   regards Terry     -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Rob P Sent: Monday, 2 December 2002 12:48 AM To: [EMAIL PROTECTED] Subject: Re: Compression ratio testing Terry, Thanks for the info. The formula my mate used out of a Nissan book looked alot more complicated than that! Coupled with the fact he'd probably had 4bph x 3.5 (4 beers per hour x 3.5 hours) = 14 beers (according to my formula ;-) probably means he had punched in a wrong number, possibly?   Regards, Rob P ----- Original Message ----- From: Terry Rudd To: [EMAIL PROTECTED] Sent: Saturday, November 30, 2002 8:55 PM Subject: RE: Compression ratio testing I wonder how big the bore is on this engine - it's huge or the math is a bit dubious to me. A L20B capacity is 1972cc or 493cc per cylinder.   Take a L20B +40' which is all but 500cc per cylinder (it's around +7cc per 1mm per cylinder on L20B)   CR is chamber volume + cylinder volume then divided by chamber volume   (500 + 45)/45 = 12.1:1   OK, that's still up there, 98 octane is good for around 11:1 +-.5:1 depending on a lot of things i.e. chamber design (squish properties), cam specs (wild). This engine is in Avgas territory by the looks of things anyway.   regards Terry -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Rob P Sent: Friday, 29 November 2002 7:46 PM To: [EMAIL PROTECTED] Subject: Compression ratio testing While we're on the subject, here's an update on my L20B rally motor (as yet still not tested since purchased complete). I put number one piston to TDC and tilted the engine on a stand so that the sparkplug hole was facing directly up. Filling a 60cc syringe with oil, I then squirted it into the chamber and filled it to the top of the spark plug hole, fully covering the threads (accidently). It came to 45cc exactly, less if you remove the sparkplug volume. My mechanic buddy calculated a compression ratio "of 12.84 to one, let's call it 13:1" We all stood around grasping our beers, shaking our heads and looking suitably impressed. ;-P Does this sound right? (Flat top alloy pistons, head still within 3 mm of maximum shave) If so, do I need to run 101 racing fuel or will BP Ultimate 98 do to avoid pinging? Will a Bluebird series II/III fuel pump adequately feed the twin 45 Webers? I have a Holley Blue fuel regulator but am told a Malpassi rising rate regulator may be the go?   Any advice always greatly appreciated --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/membersozdat@datascribe.com.au/ --------------------------------------------------------------------- --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/membersozdat@datascribe.com.au/ --------------------------------------------------------------------- --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/membersozdat@datascribe.com.au/ --------------------------------------------------------------------- --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/membersozdat@datascribe.com.au/ ---------------------------------------------------------------------