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

Chevy454 · #7 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?

**Salvatore** · #8 10-14-2006, 07:43 AM

"A good points system can work just as well".....We agree on something! WOW. I totally agree on a good distributor set up with a set of points.

mbxlesney · #9 10-14-2006, 04:06 PM

On my L78 Nova Iam going with a restored stock 1112000 distributor with a Crane pointless ignition with the built in rev limiter. so I can retain the stock appearance and not having the hassles of points. The GM HEI units in the mid 70s are great units but seem to remember a firewall clearance issues on 1969 Camaros and same period Novas.

Keith Tedford · #10 10-14-2006, 04:25 PM

I run points on our L78 with the same curve as Rob, all in by 3000 and idle it at 900 rpm. I ran the 427 the same way. I run a stock 429 B-R coil. The HEI died a couple of years after we bought the car and I had a 1111498 distributor on the shelf so that was used. You will be hard pressed to notice whether the last number is an 8 or a 9 with the unit installed. The car starts fine and will turn any rpm that I wish to run. I used to run the Delco D112P HD points in the old days. No problems to 6500. Now I run the Accel HD points, not the race units, and have no problems. So I change the points every 4 years. That's part of the fun of owning these cars. I've run the stock 4346 carb with #73 primary jets and #76 in the rear. Power valves front and back. Fine tuning on a chassis dyno might find some gains, but this is a pretty good ball park to start with.
If your HEI is in good condition, just ad the GM 990 module. Apparently the early modules had their problems. New modules are as close as your nearest GM dealer.

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