4perrev Posted March 11, 2015 Report Share Posted March 11, 2015 Hello all, I was trying to decipher the engine section and it's still confusing. If anyone could give me a real good break down, I would very much appreciate to words of advice. So here's the idea: 1980 L20B with 86mm flat top Z pistons from Datsun Llc. Stock crank and rods. Cannon intake with twin 40mm DCOE carbs. Matchbox dizzy 280ZX 5-speed Head choices: A87 open, stock cam U67 open, stock cam W58 open, stock cam Biggest questions are; do I need to shim the cam towers, use and bigger head gasket or any other special work? I've read about detonation and dieseling, but is this a factor that I can get around? Thanks in advance for the help! Quote Link to comment
uberkevin Posted March 11, 2015 Report Share Posted March 11, 2015 Head gasket stock.. works fine.. At least that's what I used on the l20b with flat top z car pistons I had. Also had the u67 on that, there was dieseling but you get really used to killing it slowly so that it doesn't diesel.. I didn't have 40s.. Quote Link to comment
4perrev Posted March 11, 2015 Author Report Share Posted March 11, 2015 Did it ping when you drove it? And the dieseling, was it every time? Plus I suposse you run premium? Thanks for the update. Quote Link to comment
uberkevin Posted March 11, 2015 Report Share Posted March 11, 2015 Yeah i ran premium.. I didn't have any pinging problems at all. Dieseling wasn't always... but I treated it like it did. One of my back valves started to sink into the head.. Quote Link to comment
Doctor510 Posted March 11, 2015 Report Share Posted March 11, 2015 Hello all, I was trying to decipher the engine section and it's still confusing. If anyone could give me a real good break down, I would very much appreciate to words of advice. So here's the idea: 1980 L20B with 86mm flat top Z pistons from Datsun Llc. Stock crank and rods. Cannon intake with twin 40mm DCOE carbs. Matchbox dizzy 280ZX 5-speed Head choices: A87 open, stock cam U67 open, stock cam W58 open, stock cam Biggest questions are; do I need to shim the cam towers, use and bigger head gasket or any other special work? I've read about detonation and dieseling, but is this a factor that I can get around? Thanks in advance for the help! IMO, the U67 is the best starting point, the W53 would be 2nd. You will need cam tower shims ONLY if the head has been milled more than .015". Stock HG is fine, use a good one, I have used FelPro for more than 25 yrs. Pinging and dieseling is a function of TOTAL timing and throttle plate setting. Be sure to get your "dizzy" mechanical advance system curved appropriately: 12* BTDC at idle, 34-36* BTDC total @ 2,800 RPM's, do not hook up the vacuum advance canister, there will not be any ported vacuum available with the Weber's anyway. I done mean to shoot down your project, but you read too much, the motor will tell you what you need to know. Books are good for basic settings. I never met a Datsun that could read yet. Quote Link to comment
datzenmike Posted March 11, 2015 Report Share Posted March 11, 2015 Hello all, I was trying to decipher the engine section and it's still confusing. If anyone could give me a real good break down, I would very much appreciate to words of advice. So here's the idea: 1980 L20B with 86mm flat top Z pistons from Datsun Llc. Stock crank and rods. Cannon intake with twin 40mm DCOE carbs. Matchbox dizzy 280ZX 5-speed Head choices: A87 open, stock cam U67 open, stock cam W58 open, stock cam Biggest questions are; do I need to shim the cam towers, use and bigger head gasket or any other special work? I've read about detonation and dieseling, but is this a factor that I can get around? Thanks in advance for the help! L20B with flattops and any 45.2cc open chamber head will give 10.11 compression. Pinging should be correctable with higher octane gas and with higher compression the burn time will be shorter. Shorter burn means the ignition timing must be retarded from the stock 12 degrees... perhaps 10 or even less. Trial and error. In addition the combustion chambers can be ground away to unshroud the valves making the volume larger and dropping the compression slightly. There's lots of room for dropping the compression here and better higher RPM breathing is the gain. Roughly speaking, place your gasket of choice on the head and scribe circles around the combustion chamber. Grind away material around the arc of each valve and down into the combustion chamber in a smooth curve towards the valve seat. Cam tower shims and thicker gaskets are only needed to correct for excessive chain slack from milling the head surface down. The U67 and W58 are about equal, the A87 may have smaler valves and ports. I would rum the U67 as it has the square exhaust ports that match your L16 cast iron header. Quote Link to comment
4perrev Posted March 11, 2015 Author Report Share Posted March 11, 2015 Thank you all for the advice here. Doctor 510, I do read a lot, but just trying to make sure I go in the right direction without back tracking. DatzunMike, I will look into un shrouding the valves to get the compression down as it seems to be the right answer and gives better airflow in the end! I have both headers, so the W58 may get the port and polish treatment, remove the liners and leave it on based that it was already a matched set with the engine. Quote Link to comment
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