john510 Posted August 29, 2010 Report Share Posted August 29, 2010 I just got an l20b complete motor.I tore it down and checked piston and bore sizes.The bore is right at 84.98 mm, so i dont think anything has been oversized yet.My question is should i use the stock piston with 11 sommething cc's dish or the L-18 piston with less dish.I will be putting an A87 closed chamber head on it and a cam with about 450 lift.I will be running SU carbs.Are flattop pistons even possible? i want to keep the compression up but not to extreme. Quote Link to comment
banzai510(hainz) Posted August 29, 2010 Report Share Posted August 29, 2010 This is my opinion here. Run the stock pistons so you can run cheap gas. Unless they sell 94 in California. If they sell 94 I would get the L18 pistons. If in dought just run the stock pistons. just rering it. I would get the A87 head match poerted to the SSS manifold. which is 1.5inch. Felpro makes their intake gasket to SSS spec hole size. and sold at Schucks /Kregon/ checker or at Rockauto.com. as for cam selection get minimum the Isky 475/275 cam. or bigger I have the Webcamshaft 488/252 but havent run it yet I got a Scheider 460/260 and Delta regrind 475/275 Scheider dont sell new cams anymore. they will do a regrind. but I say get New and pay the money. New cams need new rockerarms and they getting expensive. olddatsuns.com in tech section read up. http://olddatsuns.com/620tech.htm PS get a Jap made timming set. Do not buy Cloyes or Melling or brand you dont know. Only the Jap ones if in dought ask before buying. dont be in a rush. Quote Link to comment
datzenmike Posted August 29, 2010 Report Share Posted August 29, 2010 L20B with stock 11.36 cc pistons............... 8.4 Above with p-nut head............................... 8.9 Above p-nut with L28 flat top pistons....... 10.68....... with open chamber head....... 9.94 P-nut with L18 4.36cc pistons.................... 9.9......... with open chamber head.......9.27 To get the maximum benefits from a p-nut head flat top or small dish pistons are best. Dished pistons defeat the purpose of the high quench areas. Quote Link to comment
john510 Posted August 29, 2010 Author Report Share Posted August 29, 2010 Thanks Hainz and Datzenmike,i think i will start looking for a set of L-18 pistons.Hainz my A87 head is match ported to the SU manifold its in my car now on an L-18.Do you guys know where to get the L-18 pistons,i checked rockauto they dont have them,my local Nissan dealer doesnt know shit.The last time i tried to order parts for my 510 the guy didnt know what a Datsun was.Hainz you think i should use more cam ? i didnt want to get to crazy. I have read just about everything i can on ratsun and 510realm and its hard to decide what to do.This car is not a daily driver just a toy i like to haul ass in.Anyways thanks for the info and opinions they are definitely appreciated.Pictures and more questions coming soon. Quote Link to comment
datzenmike Posted August 29, 2010 Report Share Posted August 29, 2010 I just got an l20b complete motor.I tore it down and checked piston and bore sizes.The bore is right at 84.98 mm, so i dont think anything has been oversized yet Did you do the measurement a couple of inches down the bore or at the top? Quote Link to comment
john510 Posted August 30, 2010 Author Report Share Posted August 30, 2010 Datzenmike,i measured near the top about an inch down,the middle and close to the bottom.Im getting nothing but 84.97mm to 84.99mm on all four cylinders.Im taking these measurements also at 90 degree intervals around the cylinders. Quote Link to comment
banzai510(hainz) Posted August 30, 2010 Report Share Posted August 30, 2010 Like I said Use more cam.I got my pistons from Rockauto.com Sealed Power was the brand I think Off my head it was 12159P was the part# But could be NLA now Silvolite has L20 pistons. Also Motivsated on here had a source of L20pistons for like 40$ aset. I dont worry about raisn compression ratio much myself. if you got a closed chamber head your doing goodRemember you can spen alot on these so dont thinks its going to turn in to a V8 for the amount of money spent Quote Link to comment
zed Posted August 30, 2010 Report Share Posted August 30, 2010 Do you guys know where to get the L-18 pistons, Did you see what Mike said about losing the benefit of the peanut head quench area if you use dished pistons? I did a similar build to yours - I put L28 flat top pistons in an L18 block with a peanut head. Compression is around 11:1 and it runs so sweetly on 93. I believe the squish effect is good for several octane points Quote Link to comment
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