Distributor setups for L78 or L72 engines?

Jeff H · #1 10-13-2006, 07:19 AM

Just wondering what kind of distributor setup you guys are running on L78 or L72 engines. My 70 L78 has an HEI and I found out that it appears to be quite old with some rusty internals. I like the HEI and plan to keep it but I was wondering what kind of advance to run(springs and weights). I'm guessing it should be around 36-38 degrees total advance but what to do about the curve? I need to rebuild the stock carb first before I can do any real tuning but it never hurts to ask.

Chevy454 · #2 10-14-2006, 12:59 AM

What are your plans for the car? Is it the GM hei setup??

Jeff H · #3 10-14-2006, 03:04 AM

The car is just going to be a fun driver and it has a GM HEI distributor in it now. It starts right up and the plugs look great so I plan on keeping the HEI. I checked timing after work tonight and with the vacuum advance disconnected I had about 10-12 initial and 36-38 total timing. It seems to like these settings and idles around 625 to 650 rpms. My factory tach is reading high around 1050-1100 rpms but the multi-meter is reading the 625-650. It felt pretty good tonight doing a quick test drive so I'll probably leave it as is.

**WILMASBOYL78** · #4 10-14-2006, 03:25 AM

625-650 rpm for an L78 motor seems a little low...??? what kind of vacuum reading do you have at idle?

wilam

Jeff H · #5 10-14-2006, 03:36 AM

The vacuum reading is around 14-15 at idle. It's definitely a low idle but the car has no problem at this idle speed. If I advance the timing a little I will get some pinging. If I turn up the carb idle speed it tends to get hung up a little so I like it where it's at right now. The carb is a tweaked Holley 750 that I don't really like with the modifications to it so I'm trying to get an original 4557 rebuilt. The engine has some 71 oval port heads so the compression is probably lower than a stock L78.

**WILMASBOYL78** · #6 10-14-2006, 04:20 AM

14-15" of vacuum for an L78 cam motor is good...maybe the lower compression of the oval ports helps. I only get 11-12" on any of the original cars. Eric (vintage musclecar) is a good source for a rebuild of that 4557.What intake you running on those oval port heads?? Does the motor ahve the L78 cam??

wilma

@wot · #7 10-14-2006, 05:06 AM

My L78 points distributor has a max mechanical advance of 18 degrees all in by 2750 rpm ( autommatic car). There is another 18 degrees on the crank for a total of 36, with no vacuum advance. The car has about 12 inches of vacuum at 900 rpm in drive.

**WILMASBOYL78** · #8 10-14-2006, 05:11 AM

Dean, that's a good setup for that motor...everything before 3,000 rpms
..just when an L78 starts doing it's thing. then hold on till 6500-7000 or whatever your brain can stand....

wilma

@wot · #9 10-14-2006, 05:18 AM

yeah... it seems 3000 rpm is the on/off switch for this engine. Once it is above 3000, you're really starting to roll. Although not applicable with the HEI, the dwell angle I use is 30 degrees.

Chevy454 · #10 10-14-2006, 05:55 AM

[ QUOTE ]
The car is just going to be a fun driver and it has a GM HEI distributor in it now. It starts right up and the plugs look great so I plan on keeping the HEI. I checked timing after work tonight and with the vacuum advance disconnected I had about 10-12 initial and 36-38 total timing. It seems to like these settings and idles around 625 to 650 rpms. My factory tach is reading high around 1050-1100 rpms but the multi-meter is reading the 625-650. It felt pretty good tonight doing a quick test drive so I'll probably leave it as is.

[/ QUOTE ]
I'm not a fan of the GM hei pieces...while they will work, *IMO* they look out of place, and believe it or not a good points system can work just as well. Anyway, when is your total timing in? And what compression & pistons you running?

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