L20B Timing Troubles

[Stoffregen Motorsports]

I used t haul my 1970 Triumph Bonneville around in my 320. Bring it up to the Berkeley hills to go riding. My '49 Whizzer looked cool in the back too.

[distributorguy]

That late model distributor has to be timed closer to 16 BTDC to get your total timing figure correct, and the engine will rev quicker with more low-end advance.  Once you get the oil pump drive gear in the correct position, and get timing set to around 16 degrees, turn the engine to those timing marks and verify the ignition rotor is pretty well lined up with the distributor cap terminal its supposed to fire to (correct phasing).  Unfortunately I've had my hands on MANY A1 Cardone distributors that just won't ever work properly, and that's where the one with yellow paint on it came from.  They use poorly made electronics, swap parts from wrong distributors, pack them full of grease to mask wear.  

 

You can use a timing light to verify how much advance the distributor offers once its running.  You can go from 32-37 degrees total, not including the vacuum.  

[Stoffregen Motorsports]

I think 32 is about max for a street engine running pump gas. And that would be total timing, with or without the vacuum hooked up.

[distributorguy]

I respectfully disagree, with the exception of CA fuel playing a role in some situations.  Lower compression engines (under 160 cranking compression with a stock cam) can run more timing very successfully.  Also, engines with advanced cams (smog era stuff 74-newer) can usually benefit from more advance to match cam timing.  Ported heads (done correctly) and better cams (chosen wisely) will lower those numbers, as will an increase in cylinder pressures.  Most stock-ish street engines can utilize 34 to their advantage.  Many can use 36-37 total mechanical, without vac included in that number.  Some specific engines like 39-41 such as the late style TR6, and many smog era MGBs, and Mopar small blocks.  If the cam is advanced (smog trick), the distributor needs to follow suit or performance will suffer.  

[Stoffregen Motorsports]

In my years of experience and Datsun engine building, we almost never ran more than 32 degrees.  Sometimes up to 35. Our dyno at Rebello Racing was not the best back then, but it did prove that just because you can add more, doesn't mean it will make more power with more.

[distributorguy]

That's the difference between you and most folks - you built high end motors at Rebello.  The average low compression stock-ish motor likely never spent a $600 day on the dyno, right?   :thumbup:

 

I've had the luxury of getting to tune a lot of used up, worn out, low compression toys that can perform better in stock (smog) form with more advance - either because the cams were (factory) advanced to pass emissions or they were just never dialed in properly.  I've seen some cars that run best at 28 total (like my Olds), others at 42.  32 is always the safe bet, not necessarily the best choice, IMHO.  A very efficient L-series motor will run best at 30-34, but not all of them are so efficient and sometimes you have to cheat the numbers to coax drivability out of them.