Distributor setups for L78 or L72 engines?

[Jeff H]

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]

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

[Jeff H]

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]

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

wilam

[Jeff H]

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]

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]

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]

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 http://www.yenko.net/ubbthreads/images/graemlins/burnout.gif http://www.yenko.net/ubbthreads/images/graemlins/3gears.gif

[@wot]

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]

[ 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]

"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. http://www.yenko.net/ubbthreads/images/graemlins/biggthumpup.gif http://www.yenko.net/ubbthreads/images/graemlins/3gears.gif

[mbxlesney]

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. http://www.yenko.net/ubbthreads/images/graemlins/burnout.gif

[Keith Tedford]

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.
http://www.yenko.net/ubbthreads/images/graemlins/3gears.gif

[Chevy454]

[ QUOTE ]
On my L78 Nova Iam going with a restored stock 1112000 distributor with a Crane pointless ignition with the built in rev limiter.

[/ QUOTE ]
Not to discrourage you, but I heard in Stanton this year of some folks having some problems with the Crane unit...I'm not sure if Casey Marks tried one of the Crane units or not, but I do know he found that a set of points whooped the snot out of the Pertronix on the dyno...

[VintageMusclecar]

[ QUOTE ]
...I'm not sure if Casey Marks tried one of the Crane units or not, but I do know he found that a set of points whooped the snot out of the Pertronix on the dyno...

[/ QUOTE ]

Rob;

That's the 3rd or 4th time I've heard someone say that (re: Pertronix). Can you give some details?

Eric

[Jeff H]

[ 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?

[/ QUOTE ]

Rob, the motor is a bit of a mystery to me since it was built by a previous owner. All I know is it has the 820 oval port heads which probably lower the compression a little, the stock L78 intake, Holley 750(that's been messed with), the GM HEI distributor and headers. As for cam and pistons, I have no idea but will assume they are stock. I don't plan on racing the car and I'm not worried about 100% stock appearance at this point in time. Regarding the vacuum advance, I'm reading around 36 of timing with the vacuum adv disconnected. When I reconnect it the total timing jumps up to around 50 or so. Is that correct? Should the vacuum advance still be adding in at higher revs? I don't get any pinging so it sounds fine.

[@wot]

The vacuum advance unit is non adjustable an adds 15 degrees to the mechanical advance on a stock L78, yielding 51 total timing. If you are positive there is no detonation, check the plugs to confirm, leave it alone. If it is high speed detonation, back off the timing a couple of degrees. If you detonate under load, its probably the too much vacuum advance. There is NO vacuum advance at full throttle, engine vacuum will be close to zero.

[Chevy454]

@wot nailed...vacuum advance is for part throttle...36 is where you'll be under full throttle [ie: racing]. The general rule of thumb is to back it off till you don't get detonation and it will start when hot...that's for a street car, as your trap speed on your ET slip may actually tell you something different...http://www.yenko.net/ubbthreads/images/graemlins/naughty.gif

Eric: I had lots, and lots of troubles out of my Pertronix units, and ended up ditching them...I'll try and rattle Casey's cage and get him to chime in.

[Keith Tedford]

The Crane adjustable vacuum cannister can take care of over advance at cruise speed. Start with 10 degrees and work up.

[Salvatore]

Keith, I totally agree with your previous post. The points in my Z are from November 2000. (ACCEL) My stock distributor was curved to have everything in at 3000 rpm's. No problem to 6,500 and no pinging or overheating. Would not say my car is wickedly fast just seems to run fairly efficient. I tend to run it a little on the richer side with the Podell additive. Don't know if it is doing anything (additive) but I am not fixing something that is not broke at this point. I use the R44S AC Delco plugs.

[WILMASBOYL78]

I use the Crane setup in the 68 yellow BB car..it works fine and has the rev limiter feature which works nice. All the other cars have stock points style dist. with just regular parts. I did notice on the L78 distributor the vacuum advance had 15 and 3.55 stamped on it...I assume that is the 15 degrees mentioned and guess the 355 refers to the rear end gears?????

I want to check the curve on the project car and set it up correctly...that is my next tuning adventure.

wilma http://www.yenko.net/ubbthreads/images/graemlins/burnout.gif

[@wot]

Tom,

With a decent dial back timing light and tach you can plot the curve through any rpm range. Its fairly easy to do. I use a snap-on light that gives both timing and rpm.

Dean

[L78steve]

Wilma,The 15 stamp on the vac.unit is the advance it pulls in.The 355 stamp is the last 3 digits of the vac.unit part #.