I'm looking for advice on tuning my Pertronix GM HEI style distributor (PND1061). Pertronix advised I can use any GM HEI weight/spring kit to tune this thing. Currently I'm already getting into 8 degrees mechanical advance at 1000. It idles sporadically. I think this is due to the timing changing as idle speed is adjusted. In addition, it's way too much timing at the top. I have a few spring/weight tuning kits I'm looking at. You can see each of there specs in the table attached. The motor is an 11:1 closed chamber 396 (402 now) with a comp cams 294s solid cam (.595 lift , 294 advertised duration, intake/exhaust lift at .050 is 248), harland sharp roller rockers, and a crane stud girdle. 3500ish stall by freakshow convertors, through a turbo 400 with stock 3.08 gears (not ideal but I'm working on that.) Motor seems to want low 20s initial timing. My issue is that with that amount of initial timing, it would be way too much up top if going with a lighter spring set. If I were to go with heavy springs to limit the total, it's not going to be enough down low . Am I going to have to choose the lesser of two evils? I'd like to have all the timing in earlier on in the rev range. I've seen people put a screw or bolt in the center plate to limit mechanical advance but I'm wondering if there was another way. Another thing to note is this thing has an adjustable vacuum advance. I know stock style HEI's aren't an exact science or the best way to make a perfect curve but I have it and want to make it work. That was long and drawn out, but I'd rather give as much info as I can off the top. I've read every GM HEI post on this forum & the other popular sites. I may have missed something but maybe somebody has a solution for me. Any help would be appreciated.
mikev65
I'm looking for advice on tuning my Pertronix GM HEI style distributor (PND1061). Pertronix advised I can use any GM HEI weight/spring kit to tune this thing. Currently I'm already getting into 8 degrees mechanical advance at 1000. It idles sporadically. I think this is due to the timing changing as idle speed is adjusted. In addition, it's way too much timing at the top. I have a few spring/weight tuning kits I'm looking at. You can see each of there specs in the table attached. The motor is an 11:1 closed chamber 396 (402 now) with a comp cams 294s solid cam (.595 lift , 294 advertised duration, intake/exhaust lift at .050 is 248), harland sharp roller rockers, and a crane stud girdle. 3500ish stall by freakshow convertors, through a turbo 400 with stock 3.08 gears (not ideal but I'm working on that.) Motor seems to want low 20s initial timing. My issue is that with that amount of initial timing, it would be way too much up top if going with a lighter spring set. If I were to go with heavy springs to limit the total, it's not going to be enough down low . Am I going to have to choose the lesser of two evils? I'd like to have all the timing in earlier on in the rev range. I've seen people put a screw or bolt in the center plate to limit mechanical advance but I'm wondering if there was another way. Another thing to note is this thing has an adjustable vacuum advance. I know stock style HEI's aren't an exact science or the best way to make a perfect curve but I have it and want to make it work. That was long and drawn out, but I'd rather give as much info as I can off the top. I've read every GM HEI post on this forum & the other popular sites. I may have missed something but maybe somebody has a solution for me. Any help would be appreciated.
GM HEI Mechanical Advance Tuning
I'm looking for advice on tuning my Pertronix GM HEI style distributor (PND1061). Pertronix advised I can use any GM HEI weight/spring kit to tune this thing. Currently I'm already getting into 8 degrees mechanical advance at 1000. It idles sporadically. I think this is due to the timing changing as idle speed is adjusted. In addition, it's way too much timing at the top. I have a few spring/weight tuning kits I'm looking at. You can see each of there specs in the table attached. The motor is an 11:1 closed chamber 396 (402 now) with a comp cams 294s solid cam (.595 lift , 294 advertised duration, intake/exhaust lift at .050 is 248), harland sharp roller rockers, and a crane stud girdle. 3500ish stall by freakshow convertors, through a turbo 400 with stock 3.08 gears (not ideal but I'm working on that.) Motor seems to want low 20s initial timing. My issue is that with that amount of initial timing, it would be way too much up top if going with a lighter spring set. If I were to go with heavy springs to limit the total, it's not going to be enough down low . Am I going to have to choose the lesser of two evils? I'd like to have all the timing in earlier on in the rev range. I've seen people put a screw or bolt in the center plate to limit mechanical advance but I'm wondering if there was another way. Another thing to note is this thing has an adjustable vacuum advance. I know stock style HEI's aren't an exact science or the best way to make a perfect curve but I have it and want to make it work. That was long and drawn out, but I'd rather give as much info as I can off the top. I've read every GM HEI post on this forum & the other popular sites. I may have missed something but maybe somebody has a solution for me. Any help would be appreciated.
What you need is a mechanical stop to limit the amount of advance to what you desire. You have to take into consideration what you want your initial to be first. Using the springs is an unreliable way to do it and causes other issues when it come to the rate. Once you get the mechanical advance limited most use a combination of a light and a medium spring to get the rate of the all in advance to around 2800 rpm.
You can find the correct weight set, which is not so easy anymore. I've done the screw method and some you can weld the guide slot shorter. Both ways work.
Do they make HEI distributors like this one with mechanical advance stop bushings?
I have this one, or a similar one, and for a knucklehead like myself, its so easy to work with. i found on ebay someone making 10 and 14 degree stop bushings for them. i have my car set at 20 initial, with the 14 stop.
I have this one, or a similar one, and for a knucklehead like myself, its so easy to work with. i found on ebay someone making 10 and 14 degree stop bushings for them. i have my car set at 20 initial, with the 14 stop.
mikev65, Is the mechanical advance curve shown in post #1 for the Pertronix D1016 just what is shown on some literature you are reading?... or have you verified this with a timing light and tach?
Since you already have a Pertronix HEI, don't waste your money on the advance kits shown in post #1. The Moroso advance set is probably the exact same advance set that is already in your current distributor... and the summit advance set is just a cheap/pot metal copy of the Moroso/Pertronix advance set.
My guess to the erratic idle is that the centerplate in your Pertronix HEI is installed upside down. For some strange reason, Pertronix seems to be doing this on purpose when the distributors are being assembled.
Below is a link to a post that you might find helpful in tuning your HEI. I started the link at post #57... as this refers to the OP's centerplate within their HEI distributor being installed upside-down. The post then continues with suggestions on how to fine tune the advance curve... and also how to limit the vacuum advance with a stop plate.
www.chevelles.com
Since you already have a Pertronix HEI, don't waste your money on the advance kits shown in post #1. The Moroso advance set is probably the exact same advance set that is already in your current distributor... and the summit advance set is just a cheap/pot metal copy of the Moroso/Pertronix advance set.
My guess to the erratic idle is that the centerplate in your Pertronix HEI is installed upside down. For some strange reason, Pertronix seems to be doing this on purpose when the distributors are being assembled.
Below is a link to a post that you might find helpful in tuning your HEI. I started the link at post #57... as this refers to the OP's centerplate within their HEI distributor being installed upside-down. The post then continues with suggestions on how to fine tune the advance curve... and also how to limit the vacuum advance with a stop plate.
Pertronix Dist. & Timing
I was messing up another thread so thought I should start my own, I have a 10.8:1 comp. 489, Lunati 231/239 @ .050 dur. .600/.600 lift 110 lsa 107 icl hyd roller cam, 3 spd auto trans with 3.73 rear, 850 Holley, street car that might see the track, I'm using a Pertronix Billet Flame Thrower III...
www.chevelles.com
For the street in my MSD distributor I always ran the black bushing and the heavy springs, why? so I don't have any detonation issues. Besides how many WOT blasts are you going to do anyway before the po po gets you and you wont notice the 3hp loss when using the light springs.
Ive always limited the mech advance with a bushing if I could not find the right factory cam
check the center cam stamp look underneath it should be stamped with amount of built in advance look for an old gm cam with the lowest degree
Or check out FBO they make custom bushings
Your 248@ .050 cam wants at least 16 initial not surprises it likes 20
Pick your springs that dont allow the curve to start at least 200 rpm above your hot idle you want initial rock steady at hot idle not mech advance
Then limit your vacuum can to about 10-12 with 16-20 initial
check the center cam stamp look underneath it should be stamped with amount of built in advance look for an old gm cam with the lowest degree
Or check out FBO they make custom bushings
Your 248@ .050 cam wants at least 16 initial not surprises it likes 20
Pick your springs that dont allow the curve to start at least 200 rpm above your hot idle you want initial rock steady at hot idle not mech advance
Then limit your vacuum can to about 10-12 with 16-20 initial
mikev65, I looked at the photo of your advance weights and centerplate and they are installed correctly. It looks like Pertronix is now using the same advance weights and centerplate that many of the other aftermarket HEI's are using. There is nothing wrong with these advance weights and centerplate... and they normally provide about 22 degrees of mechanical advance. It also looks like your HEI distributor has the stiff advance springs installed (normally, these stiff springs would not introduce any mechanical advance it idle speeds of less than 1300-1500 rpm... but your total mechanical advance does not come in until 4500+ rpm).
You have a couple of options...
Keep the advance weights and springs that you have, but remove the 2 stiff mechanical advance springs springs and replace with 2 medium tension advance springs. This will get your total mechanical advance to come in at lower rpm's (but should still not introduce any mechanical advance at idle speeds less than 1000-1200 rpm).
But with the above option, you would set your initial timing to 14° BTDC and with your added mechanical of 22°... it would put you at 36° total mech advance. You would then need to limit your vacuum advance unit with a stop plate to get about 10°- 12°... and then plug your vacuum advance into a full time/manifold vacuum source. This should give you about 24°- 26° of timing at idle. If you do not limit your VA, most aftermarket adjustable VA units can provide 20+ degrees of additional advance (and this could be too much). The MSD 84281 stop plate is a very easy way to limit the vacuum advance on a HEI distributor.
If you wanted a higher initial timing (with less mechanical advance) you could make some kind of "home-made" mechanical stop that limits you mechanical advance (kinda trail and error with fitting/adjusting)... or you could purchase the Moroso 72300 advance kit (this is the same exact kit as the MSD 8428... but the Moroso kit cost less $$). You would also get some different tension advance springs to play with by purchasing the kit. If you remove your existing centerplate and weights and replace with the Moroso kit, you would get about 16° of mechanical timing (many people, including myself have confirmed this). Don't go by the advance charts shown in the literature... they are wrong. You could then set your initial timing to 20°... and still maintain 36° total mechanical advance. You would still need to limit the VA as mentioned above.
Now suppose you wanted set your initial timing to somewhere in between 14°- 20° BTDC... but still maintain a total mechanical advance of 36°. An option would be to "modify" the centerplate of the Moroso advance kit to achieve your desired results. You would still need to install a stop plate to limit your VA.
Below is a link to a post where I modified my centerplate to tailor the mechanical advance curve on my HEI distributor.
Be sure to click on the "See More" option within each post to see the entire contents.
www.stevesnovasite.com
You have a couple of options...
Keep the advance weights and springs that you have, but remove the 2 stiff mechanical advance springs springs and replace with 2 medium tension advance springs. This will get your total mechanical advance to come in at lower rpm's (but should still not introduce any mechanical advance at idle speeds less than 1000-1200 rpm).
But with the above option, you would set your initial timing to 14° BTDC and with your added mechanical of 22°... it would put you at 36° total mech advance. You would then need to limit your vacuum advance unit with a stop plate to get about 10°- 12°... and then plug your vacuum advance into a full time/manifold vacuum source. This should give you about 24°- 26° of timing at idle. If you do not limit your VA, most aftermarket adjustable VA units can provide 20+ degrees of additional advance (and this could be too much). The MSD 84281 stop plate is a very easy way to limit the vacuum advance on a HEI distributor.
If you wanted a higher initial timing (with less mechanical advance) you could make some kind of "home-made" mechanical stop that limits you mechanical advance (kinda trail and error with fitting/adjusting)... or you could purchase the Moroso 72300 advance kit (this is the same exact kit as the MSD 8428... but the Moroso kit cost less $$). You would also get some different tension advance springs to play with by purchasing the kit. If you remove your existing centerplate and weights and replace with the Moroso kit, you would get about 16° of mechanical timing (many people, including myself have confirmed this). Don't go by the advance charts shown in the literature... they are wrong. You could then set your initial timing to 20°... and still maintain 36° total mechanical advance. You would still need to limit the VA as mentioned above.
Now suppose you wanted set your initial timing to somewhere in between 14°- 20° BTDC... but still maintain a total mechanical advance of 36°. An option would be to "modify" the centerplate of the Moroso advance kit to achieve your desired results. You would still need to install a stop plate to limit your VA.
Below is a link to a post where I modified my centerplate to tailor the mechanical advance curve on my HEI distributor.
Be sure to click on the "See More" option within each post to see the entire contents.
Dialing-in the Timing Advance Curve with my GM Style HEI
Dialing-in the Timing Advance Curve of my GM Style HEI - Part 1 Last year, I wanting to “dial in” the advance curve of my aftermarket GM Style HEI that is used on my SBC (I have a Pertronix D1000). What started me on this project was I could not get a steady initial timing reading at low RPM...
www.stevesnovasite.com
Regarding vacuum advance, make it easy on yourself.
VC1852 / AR22 Starts adding vac advance at 7-9", Full vac advance of 10* @ 12-14" vacuum (this is the one I used)
or if you engine pulls even lower idle vacuum
VC1862 / AR31 Starts adding vac advance at 2-4", Full vac advance of 18* @ 6-8" vacuum. ( tried this one but found it to be too eratic).
VC1852 / AR22 Starts adding vac advance at 7-9", Full vac advance of 10* @ 12-14" vacuum (this is the one I used)
or if you engine pulls even lower idle vacuum
VC1862 / AR31 Starts adding vac advance at 2-4", Full vac advance of 18* @ 6-8" vacuum. ( tried this one but found it to be too eratic).
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