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L20b rebuild


john510

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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.

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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.

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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.

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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.

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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?

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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

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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

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