>From what I have gathered from reading books/list and owning an L18 and L20b engine: L20b will yield ~10-20hp extra for the same cost as an L18 L20b won't rev nearly as hard in stock configuration, but much more low rpm torque. cya! zac ----- Original Message ----- From: abrahamk <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Saturday, May 06, 2000 7:47 PM Subject: Re: Mild L20B vs. Mild L18 for PRC (Long & involved) > 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]/ ---------------------------------------------------------------------
