1. I would prefer to run in the 1600-2000cc class, which is why I think the Stanza is such a good car to use (If I can find one!) - 2 litres & ~950 Kg. 2. I would like to keep the bottom end as stock as possible, including pistons. 3. The purpose of squish is, as you said, to promote turbulence in the mixture at / near TDC. A turbulent flame-front burns significantly faster than a laminar (quiescent) flame-front and so the combustion process is closer to the ideal constant volume process, yielding more power, less susceptibility to detonation, etc... However the squish areas in the closed chamber head (as I see it) won't work well unless you run flat-top pistons with about 40 thou clearance between the piston crown and squish areas, that is, you need to run a +0.2mm deck height. If you use the std. dished pistons the squish area should be only slightly greater than in the the open chamber head. Considering the -0.45mm stock deck height and dished pistons, BOTH the open and closed chamber heads should give poor squish. 4. I have a V91?? head from a Bluebird, it has 42mm inlet valves and 35mm exhaust valves. It is the same as a U67 but with bigger valves and slightly revised combustion chamber. The exhaust port is very constricted and so should respond well to 'aggressive' porting - any tips? Overall, I think the head should flow very well and the low compression ratio ( 9:1 on L20B, 9.22:1 on L18) will limit detonation. How did your mate get 10.5:1, with 40thou removed from the head I'll only get 9:1 (I haven't CC'd it yet though). 5. Your program sounds interesting, what power increase would you get running the mixture rich (faster flame-front speed), and using super extra long spark plugs (central ignition source, shorter flame travel distance - less end gas autoignition) 6.Why do #1 & #4 cylinders have a cut-out for the spark plug, but not #2 & #3. Should the cut-outs be radiused ??? 7. I am still not clear on the L18 vs. L20 question, which is more powerful when modified as discussed? 8. 180B can only run L18 Thanks - Nick -----Original Message----- From: Craig Overend <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Date: Saturday, 6 May 2000 1:37 Subject: Re: Mild L20B vs. Mild L18 for PRC (Long) >Nick, > Do the PRC rules state a maximum cubic capacity? >If your running a 1600 then the maximum capacity allowable is probably >1899cc. >And the 180B I have been told can run L20B (is this true?) which would >allow 2099cc. There is no set weight for the stock 1600 or 180B but >Wheels Magazine Oz weighs 1600=910kg, 180B=1000Kg, and I have been told >a 180BSSS=1080Kg. The 180B or SSS may increase in weight a little with >the taller/heavier L20B in it too. >Nearly every datsun book I've read recommends a maximum of 2mm oversize, >that's from 85 to 87mm for both L18 & L20B. Any further and the block >would need to be sonic tested first. >An L18 at 87mm bore and 78mm stroke is 1855cc. >An L20B at 87mm bore and 86mm stroke is 2045cc >The L18W and Japanese made L20B with Japan cast into the side of the >block seem to be the go for large bore L's. > >You haven't stated what size the valves are in your (U67?) open >chambered head. I'll Assume its a stock L20B U67 head & valves. Your >limited with a stock L20B/SSS cam (11.02mm/248deg) as to where max rpm >power is generated. I've just started writing my own engine simulation >program, and according to it, the stock L20B U67 inlet valve becomes >choked(no more air/fuel can be flowed) at approx 5550rpm. This was >calculated with the stock L20B block specs(85mm bore). Changing only the >bore to 87mm, drops max power to 5300rpm due to bore to valve area ratio >changes etc. Put an optimum lift camshaft in this engine and it will >lift it to approx 5650rpm. Put 44mm inlet valves in for approx 6280rpm >before valve choking. As long as ports/manifolds and carbies flow enough >for the valve thats the approx. max power rpm to expect. It will also >vary depending on you valve seat internal diameter/minimum port diameter >aswell. >I can't see anyone estimating power/torque figures accuratly, there are >just so many variables. >I'd recommend using closed chamber head on any L series. The added >squish/quench area creates turbulence that assists in mixing the >air/fuel better, and also increases the burn rate. Mixing the air/fuel >better reduces the amount of lean pockets of air/fuel which leads to >reduced knocking/pinging allowing higher compression ratios. From memory >Nitrous Oxide emissions can be kept lower with low compression ratios >which is probably why Nissan designed the L20B the way they did. >A friend has an OZ L20B in his 180B it's ~86mm dished pistons, U67 head, >~10.5:1CR, stock Cam, 3angle 42mm valve, stock ports, twin 38mm SU's, >ram tubes, extractors into 2" exhaust. Assembled in a hurry, not ported >& no attention to detail. Doesnt pull past 6000 at all, power from about >3000-5500 i'd say. Pings @~6deg without AVGAS. 10-12deg with AVGAS I >think. L18 Dizzy used needs regraphing too. >Hope that helps. > >Craig. > >Japanese L20B blocks seem to be the go otherwise don't bore the Oz block >very far. >> abrahamk wrote: >> >> I am/was rebuilding an ex-TRX Bluebird black rocker-cover L20B for >> PRC/club motorsport until I read the disparaging comments about this >> type of motor on the list. I would like to know more about the >> relative merits of the L18 vs. the L20B before I continue. >> Firstly let me get my facts straight. >> -The L18 block has a higher nickel content than the (Australian) L20B >> block and so is more wear resistant. The L18 is also oversquare and so >> should rev better and respond to a cam change better than the L20B. >> The PRC rules forbid connecting-rod changes e.g. L16 rods into L18. >> Now, >> -What are the power/torque/maximum rev. limit figures for these two >> engine types using twin 1-34" S.U's ( 1.50" port size), extractors, >> 9~9.5:1 compression ratio, open-chamber head and 248 degree L20B/SSS >> cam ( i.e. a fairly average 'mild' setup ) >> -I would expect 80-85 kW from the L20B, lots of torque, easy to drive, >> relatively easy on fuel, which will pull hard to about 5500-6000 with >> a 6500 rev limit. >> -What is this talk of A,B, and C type L20B cams? I have acquired a 'B' >> stamped cam from a 200B but is has the same profile and duration as >> the Bluebird (according to the manuals) i.e 248 degree 16/52-54/14. >> -A 280 degree camshaft re-grind costs ~$100. What kind of power >> increase do you get, if any, with a medium-low compression ratio and >> open-chamber head (engine spec. as above). Any detonation, fuel >> consumption, driveability etc.. effects to worry about? >> -Also, was the HA-10 Stanza homologated with an L18?. I've been >> told that a L18 Stanza will pass registration without an Engineer's >> report, but CAMS only has homologation documents for L16 and L18 >> versions (that I know of). >> -What are the weights of the Datsun 180B and 1600? >> >> Thanks - Nick. >> >> --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.datascribe.com.au/ozdatonline/index.htm >> http://www.datascribe.com.au/ozdatonline/listindex.html >> http://www.mail-archive.com/[email protected]/ >> --------------------------------------------------------------------- > > --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.datascribe.com.au/ozdatonline/index.htm http://www.datascribe.com.au/ozdatonline/listindex.html http://www.mail-archive.com/[email protected]/ ---------------------------------------------------------------------
