LandoJMZ Posted May 1, 2015 Report Share Posted May 1, 2015 Guys im trying to reach higher compression in my L20 by shaving the cylinder heads i would like to know from you gurus previous experiences, to start, i have a stock L20 with the Hitachi carb and stock heads tjethe only thing ive added is the headers ive already prepared myself with a big cam and a webber carb and all of the gaskets the only thing i do not have info on is the specs on how much material i should shave off so please enlight me,, Quote Link to comment
datzenmike Posted May 1, 2015 Report Share Posted May 1, 2015 Shaving the head will allow it to sit slightly lower. This will add slack to the timing chain and this will advance the cam timing. You can add equal thickness shims under the cam towers to correct this..... something to think about first. A stock L20B compression is 8.4 if you shave 0.1mm........ 8.46 0.2mm........ 8.52 0.3mm........ 8.59 0.4mm........ 8.65 0.5mm........ 8.72 0.6mm........ 8.80 0.7mm........ 8.86 at this point you have shaved about 0.028" Quote Link to comment
flatcat19 Posted May 1, 2015 Report Share Posted May 1, 2015 That's a lot of risk and cost for minimum gain. L18 pistons will drop in. Machine for late 280zx flat top pistons. Locate a peanut chambered head. Welcome to Ratsun, new guy. Get to reading before you going messing up a set of valves. Quote Link to comment
Dolomite Posted May 1, 2015 Report Share Posted May 1, 2015 ^^^what he said. I'm getting ready for zx flat tops, seems the best rout to me. Quote Link to comment
datzenmike Posted May 1, 2015 Report Share Posted May 1, 2015 If the head is not flat you can skim a small amount off to true it up but not the best way to raise compression. A closed chamber head would give .............................................8.9 compression Z20 rods and 85mm flattop pistons and open chamber head..... 9.941 The above but with closed chamber head................................. 10.68 L28 flattop 85mm pistons open chamber head.......................... 10.11 The above but with closed chamber head................................. 10.87 Quote Link to comment
LandoJMZ Posted May 1, 2015 Author Report Share Posted May 1, 2015 Well my best bet is to remove the least amount of material and having the valves adjusted perfectly with the cam i really don't want to mess up a set of valves.. lol Quote Link to comment
flatcat19 Posted May 1, 2015 Report Share Posted May 1, 2015 What cylinder head do you have? Getting a peanut will be you easiest bang for the buck mod. Quote Link to comment
LandoJMZ Posted May 2, 2015 Author Report Share Posted May 2, 2015 What cylinder head do you have? Getting a peanut will be you easiest bang for the buck mod. Its the W58 head and this is on a 1979 510 guys i think i will go ahead and shave like 0.02 off. Quote Link to comment
datzenmike Posted May 2, 2015 Report Share Posted May 2, 2015 If running and not warped this is a waste of your time and money. You won't notice a thing unless taking the head off corrects another unknown problem like a loose gear clamp on the rad hose. If shaving, think big, take 1mm or 0.040" off. Now the compression is 9.08 But as mentioned this will add chain slack because the cam is now sitting 0.040" lower. You may have to buy some sheet brass or shim stock and cut out your own and stack them to get the correct thickness. Hardly worth it as one point of compression increase will add maybe 4% to 6% more power. (maybe) You have only gone half that. 8.4 to 9. That's 2 or 3 HP at almost 6K and less at driving speed. Quote Link to comment
LandoJMZ Posted May 2, 2015 Author Report Share Posted May 2, 2015 So only installing the cam and adjusting the valves perfectly will be the safest bet? im having it sent to the shop soon and,later will come more upgrades Quote Link to comment
datzenmike Posted May 2, 2015 Report Share Posted May 2, 2015 A sportier cam and a weber will be more than enough increase for you. Some things like increasing compression is a 'racing' thing to do where the expense and bother are not an issue... I mean that it's raced at WOT, (wide open throttle) not driven on the street, having to idle at lights and started in all kinds of weather. Racing requires that you do anything to gain an edge over the competition but forces you into 'the law of diminishing returns' This states that the first 50 hp increase costs $800, the next 20 cost $1,100, the next 10 cost $1,500. 1 Quote Link to comment
LandoJMZ Posted May 2, 2015 Author Report Share Posted May 2, 2015 A sportier cam and a weber will be more than enough increase for you. Some things like increasing compression is a 'racing' thing to do where the expense and bother are not an issue... I mean that it's raced at WOT, (wide open throttle) not driven on the street, having to idle at lights and started in all kinds of weather. Racing requires that you do anything to gain an edge over the competition but forces you into 'the law of diminishing returns' This states that the first 50 hp increase costs $800, the next 20 cost $1,100, the next 10 cost $1,500. You are amazing thanks for all the help i will definitely come back to ask more stupid questions because that is my super power my next project will be a stage 3 clutch and a 5 speed tranny! Quote Link to comment
datzenmike Posted May 2, 2015 Report Share Posted May 2, 2015 There are no stupid questions. Stupidity can't be fixed but ignorance can. 2 Quote Link to comment
banzai510(hainz) Posted May 2, 2015 Report Share Posted May 2, 2015 If this is a must on higher comep I would try to find l18 stock pistons and a peanut head. I have a set stashed away. shit maybe 2 cant rememeber. Guy I know had lots of pinging issue with his motor on pump gas even with 91. It wasn't worth it for him. he had flattops in his l20 is a stage 3 clutch really needed? Quote Link to comment
Eriks Posted June 28, 2015 Report Share Posted June 28, 2015 What would be "too high" compression for a L20B ? Quote Link to comment
datzenmike Posted June 29, 2015 Report Share Posted June 29, 2015 That would depend on what quality (high octane) gas you have over there, how much it costs and it's availability. Higher compression increases a gas engines efficiency and there are some gains to be had. Possibly your mileage increase can more than pay for the increase cost of the gas. It may ping anyway and that's annoying. With 'good' gas and reasonable timing you could run 9.5 on 91 and 10 on 94 octane. This is plus/minus (there are variables like altitude, temp, humidity.... Quote Link to comment
Eriks Posted June 29, 2015 Report Share Posted June 29, 2015 Thanks again Mike, we have two octanes to choose from, that is 95 and 98. Anything less than 95 is not available. I have more questions, now in the clutch department :) Quote Link to comment
datzenmike Posted June 29, 2015 Report Share Posted June 29, 2015 Nice!!! We get 87 and up. Quote Link to comment
HRH Posted June 29, 2015 Report Share Posted June 29, 2015 Fing lucky with the gas! We have 87 swill here, some states have 85, highest we can get is 92 octane in Washington state. Works just fine really, but still, you can get away with a lot more compression if you're running 95-98 octane without pinging. That is one of the weak points on L series, higher compression usually ends in detonation. However, the best option for your L20 if you want to build a screamer is get the Z20E car pistons and rods and stick them in with the L20 head. I built an awesome motor quite a few years back with this combination, .030 off the head, Nismo L7 rally cam regrind copy and if I remember correctly it was about 11.75:1 and it ran like a raped ape on 92 octane. One thing to think about. Compression makes more torque, yes. But without porting the head and adding a big cam, you're only getting a little bit. The more airflow you get through the head, the higher the compression you're going to need to force the air through without causing tumble and inefficiency. Like if you strapped a SSS race head to a stock L20b block. Yeah, it can flow 800 cfm or whatever, but your compression will only allow it to be usable for 600 cfm. At that point, it's a waste. Not actual numbers, just throwing them out for reference. This was back in '09, it was still carbureted, dual SUs. Couldn't go very fast in this autocross because I had junk tires and the suspension wasn't quite where it needed to be. Had lots of fun on the way over though. Quote Link to comment
Stoffregen Motorsports Posted July 1, 2015 Report Share Posted July 1, 2015 If you have $1000 to spend, have someone do a quick port job and install big valves along with a cam and valve springs. Your biggest gains will come from a nice but not over the top port job and big valves. Obiously the cam factors into that too. $1000 is cheap and that's if you bring them the head, not the car... Quote Link to comment
shacks510 Posted July 1, 2015 Report Share Posted July 1, 2015 we have two octanes to choose from, that is 95 and 98. Anything less than 95 is not available. Wow. Average California pumps have 87, 89, and 91. There's so much ethanol in it though that makes the gas here junk. I know of a place nearby that has 100 on the pump... at $11 a gallon... Quote Link to comment
That620son Posted August 18, 2015 Report Share Posted August 18, 2015 Wow. Average California pumps have 87, 89, and 91. There's so much ethanol in it though that makes the gas here junk. I know of a place nearby that has 100 on the pump... at $11 a gallon... That sucks for you guys. Over here we have 87, 89, 93 and if you go towards the race track you can get 110 for exactly $6 more a gallon than premium. So at time of post it's 8.70 a gallon for 110. Quote Link to comment
banzai510(hainz) Posted August 19, 2015 Report Share Posted August 19, 2015 Dont ethanol raise the octane level? But you need more volume to get the same BTU out of them I think. Octane dont make a BIGGER explosion it makes you run more advance when you need it to get the most power. Lower octance just explodes if chamber to hot thus outoff at the wrong time. 1 Quote Link to comment
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