Chevy Nova Forum banner
1 - 20 of 30 Posts

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #1 ·
I went to the junkyard today and picked off some center plates and weights from the HEI distributors that I could find (only 4 cars there had HEI distributors!). So I've got 4 sets with part numbers stamped on them, but I have no way of determining what amount of mechanical advance they will provide.

Here the part numbers I found today:

Center Plate:
375
365
445
469

Weights:
41
053
60
106

Do any of you have a chart or reference for what these various plates and weights will put out in terms of mechanical advance?

I believe the 375 and 41 combo will give about 21-22 degrees based on what I've read elsewhere, but that's about what I have now in my distributor. I was hoping that one of these combos might yield only 18 degrees or so, that way I could run more initial timing without overdoing it with my total timing.

There is a giant thread on some Rocky Rotella chart where the guy pieced together a bunch of info on these parts, but they all used 139 weights, which I dont have.

Any help would be appreciated. If there is no resource online, I wonder if there are any old school manuals that might have this info in it.

Otherwise if no one has any info and I can't find any info anywhere, I guess I'll just have to use the trial by error method and test each one out.

Thanks!
 

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #3 ·
Update - additional research

That would make sense since the larger center would essentially reduce the travel of the weights from spinning outwards. Smaller centers would let them continue spinning outwards.

Here's some info I put together based off of a large thread from another forum. This guy used the 139 weights for all of his combos, but apparently the weights dont vary too much when it comes to mechanical advance. According to his testing, most were within 1-2 degrees of each other.

The 60 weights are equivalent to the 139 weights.
The 053 weights provide 1 degree LESS than the 139 weights.

So the weights aren't too big of a factor in changing the mechanical advance. Its the center plate that primarily determines how much advance is put out. So I compared the center plates that I found today in the junkyard do the ones listed on the chart this guy put together. Its pretty extensive, so it seems like the guy knew what he was doing. Of course I wont know for sure until I actually test these out. But here's what I came up with...

Center Plate 445 + Weights 60 = 19 degrees
Center Plate 445 + Weights 053 = 18 degrees

Center Plate 469 + Weights 60 = 21 degrees
Center Plate 469 + Weights 053 = 20 degrees

Center Plate 375 + Weights 60 = 26 degrees
Center Plate 375 + Weights 053 = 25 degrees

For some reason on his chart it shows center plate 365 as only putting out 6 degrees of advance, which I believe may have been a typo, so I left that one out here.

So if that information is correct, I can basically choose the amount of advance I want ranging from 18 degrees up to 26 degrees. My current distributor has around 23 degrees built into it, which is usually fine for most engines. However, I was looking for a way to bump up my initial timing while keeping my total timing the same. Since my engine has a larger cam, I'm hoping it will respond well to the increased initial timing for more low end response while retaining the WOT feel it has now which is great.

I'm not sure if anyone else on here has done much research on these center plates and weights, but there seems to be a zillion combos made over the years. But if anyone else has any input or results that they'd like to share I'd appreciate it as I'm just learning all this stuff myself for the first time now.

From what Ive gathered, a lot of guys dont bother with all this center plate/weight crap and they just weld up the slots that they travel in. This is a workable solution, however its not really how it was designed to work. The center plate is the piece that governs how much timing you get out of your distributor based on the curvatures on the plate itself. The weights just swing out to produce the additional advance, and the springs determine how fast or how slow the total advance comes in. I dont know if I'm 100% right or not here, but that seems to be the general consensus from various sources across the internet.

My main motivation behind doing all this crap is to see if I can create my own recurved distributor without having to go blow $350 on an MSD unit when I can change it around myself using GM parts.

By the way, the junkyard charged me a whole $1.00 for all four sets of center plates and weights, haha! They were greasy and grimy and I need to clean them up a little, but for $1.00 an an hour in the junkyard, I think it was well worth it. The real deal though will be to put these to the test to see if they actually produce what this guy says on his chart.

Hopefully I'll get to this soon and I'll try to post up my results whenever I can.

Any additional input would be appreciated!
 

·
Super Moderator
Joined
·
12,033 Posts
The center plate is the piece that governs how much timing you get out of your distributor based on the curvatures on the plate itself. The weights just swing out to produce the additional advance, and the springs determine how fast or how slow the total advance comes in. I dont know if I'm 100% right or not here, but that seems to be the general consensus from various sources across the internet.
That is absolutely correct and good to see someone willing to make the HEI work for them. The mechanical assembly moves the rotor to gain advance, the vacuum can moves the base plate to change the advance. Both when working together properly produce a very good running engine, more power, smooth idle and improved economy.
 

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #5 ·
Thanks Philip! I'm not that great of a mechanic, but I'm willing to learn a few things if I can save a few bucks and get the same results.

Sevenzeronova...first of all I finally realized what your name means after spelling it out, haha! Guess I'm a little slow. :) But I just went outside to check on the center plates based on what you said and I think you're right.

Check this out though, I thought the 365 center plate had a typo on that chart, saying it only produced 6 degrees of advance. I think its right though. You should see this center plate compared to the others, its huge! If you put a weight up to it, you can see it cant move out very far at all. I cant remember what car I got that out of, but what would only use 6 degrees of mechanical advance? It must have had a ton of initial and vacuum or something.

I looked at the others, and honestly I could not tell much of a difference. They had slight variances on how quickly the weights would swing out. Some had more gradual curves, others were more quick. But to the naked eye, they're all pretty close for the most part. But that makes sense too since they are all within a few degrees of each other, outside of the 365 center plate that is just gigantic compared to the others.

Anyway, since I'm running vortec heads, and they supposedly prefer 32-34 degrees total vs old school heads that typically prefer 36-38 degrees, I may try running the 445 center plate and 053 weight combo since that is supposed to put out 18 degrees. That would enable me to run 14-16 degrees initial and 18 degrees mechanical and get me to 32-34 degrees. If it ends up liking 36-38 degrees after some dragstrip testing, then 18 degrees initial may not be that bad since I've got a larger cam anyway.

I hope I'm on track here. If there are any glaring errors in my logic please chime in and let me know. Hopefully I'll get a chance to mess with this a little this weekend.
 

·
Registered
Joined
·
2,188 Posts
I think your right on track, I would try all the centers with the same weights and record the results. I have heard some have filed the edges on larger ones to creep up on total. Just remember all centers and weights are hardened steel. Which is why they last so much longer then the aftermarket advance kits. If you decide to file or use edge of belt sander cool the piece a lot with water as this will help retain the hardness of the steel. Good luck! Post some results.
 

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #7 ·
I've heard of guys doing that as well to modify them. I want to test them out as is first though. I'd like to leave them alone and just use the correct ones if possible.

If I get a chance to test some out soon I'll post up the results.
 

·
Premium Member
Joined
·
8,405 Posts
Do you have a link to this chart you are talking about? I'm surprised no one has reproduced center plates, but maybe because there are so many, it wouldn't be cost effective to tool up for, especially when there's new, adjustable performance distributors.
 

·
Banned
Joined
·
26,231 Posts
i looked yesterday trying to assist with info... found a couple websites with some info, no charts. also found basically the same info that's been posted at Team Chevelle... again, no charts though.

that info, if available, would be helpful to others researching the same subject matter...
 

·
Registered
Joined
·
2,188 Posts
I have not found a chart either just the above posted. Someone whom has done a bunch of distributors on the machine maybe have some charts or notes of their own. Finding that person is the hard part. I will ask a few of the old school guys I know, at the next show this coming Thursday.
 

·
Premium Member
Joined
·
8,405 Posts
This sounds like something that needs to be done. Collecting and cataloging all the weights and plates and making a chart. the biggest problem I see is, the supply of HEI's in the junkyard is drying up, so even if you knew what plate/weight combo you needed, trying to find the right ones may be really hard.
 

·
Registered
Joined
·
2,188 Posts
I agree a chart will help tons of people. Having a chart with numbers and the actual curves of the centers in real size would be better.
This way someone will have options of getting the stamped
Oem part or having one cut, waterjet, laser what have you.
Seeing they aren't easy to get. Just thinking out loud.
 

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #13 ·
Chart Info

Hey guys, sorry I didn't post this up. I'm a member on another forum and those guys get all pissy if you post up links to other forums for some reason. Sounds like you guys dont care though, so here it is...

http://www.chevelles.com/forums/showthread.php?t=327577

It's from a Chevelle forum. Its based on another thread found on a Pontiac forum where some dude experimented with various center plates and weights upside down for his Pontiac. The cool part is, upside down for a Pontiac, is right side up for a Chevy. Center plates are installed numbers facing up for Chevys and numbers facing down on Pontiacs, at least according to this site. I have no personal knowledge to say if thats right or wrong though.

Based on the info in that thread, I pieced together some combos with the center plates and weights that I was able to find in the junkyard the other day. I haven't tested these, so I cant verify them just yet. But the logic there seems consistent.

For example, the one center plate mentioned in the chart, 365 indicates only 6 degrees of advance. I thought that was a typo since it was so far off from the others. But when I looked at the 365 center plate, you can see clearly it doesnt let the weights swing out very far at all. The others are more similar in design/shape which is why they are closer in degrees.

I'll post up any results that I get, but I dont plan on testing these things extensively. I'm going to try and get 18-19 degrees from the one combo and if that works, I'm calling it a day. It'd be nice to have a distributor machine to really test these things out.

I agree, the HEI distributors are becoming a thing of the past in the junkyards. 10 years ago my buddy and I would see a ton of them in the junkyards. When I went the other day, out of all the GM cars all I found were 4 cars with HEI's in them. Slim pickings. At least they all had a unique center plate/weight combo.

Anyway, read through that chart from the link I provided above and see what you guys think. I think its pretty helpful, at least a good starting point. He says the 139 weights are similar to the 60 weights I believe and the 053 weights provide 1 less degree of advance typically than the 60 weights. He emphasizes that the weights are pretty close typically, and that the center plates are what really determine the advance degrees put out.
 

·
Registered
Joined
·
1,880 Posts
As always seems to be the case here, more good stuff to learn. :popcorn::attention::thumbsup: Peace Dale
 

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #15 ·
Small chart

Here's what I've put together so far based on the info from the thread in the link above. I'm making the assumption that the data provided there is accurate, which may not be the case of course. Until I can verify this, this is as good as it gets for now...

Center Plate 445 + Weights 60 = 19 degrees
Center Plate 445 + Weights 053 = 18 degrees

Center Plate 469 + Weights 60 = 21 degrees
Center Plate 469 + Weights 053 = 20 degrees

Center Plate 375 + Weights 60 = 26 degrees
Center Plate 375 + Weights 053 = 25 degrees

Seeing how my distributor currently has 23 degrees in it and I was shooting for something less with my new setup (to run more initial timing), I'm going to opt for the first combo above that yields 18-19 degrees.

So if I use center plate 445 and weights 053, that should give me 18 degrees of timing. That's 5 degrees less than now, which means 5 degrees more initial timing can be used than I have right now and still achieve the same total timing amount.

Here's another question for you guys:

Do larger duration camshafts tend to respond better to more initial timing?

I've read where larger duration camshafts tend to like more initial timing, due to lower cylinder pressures at low rpms due to the longer time the valve is opened vs a stock style cam. So if a stock motor that is set at 6 degrees is advanced to 10 degrees BTDC, it may respond well to that, but going much more than that it may not like that much timing. However, a cam with say 234/238 duration @ .050 may like 14-18 degrees of initial. If that is true, then having 23 degrees of mechanical advance may not be optimal, which is the issue I've run into.

My car currently responds great at WOT, hauls *** and runs awesome! But I think for street use it could use some additional initial timing for lower rpm driving. I know that vacuum advance can be used to supplement this at cruise speeds and at idle, but I think more initial timing would have a better effect than vacuum advance would since its always there and not subject to changes in engine vacuum. Correct me if I'm wrong though.

I'm thinking a good curve for my setup would be as follows:

16 degrees initial timing
10-12 degrees of vacuum advance
18 degrees of mechanical advance

This would result in 34 degrees of total timing and around 46 degrees of timing at cruise speeds. Also around 28 degrees at idle.

Using various spring combos, I would try to achieve this total timing by around 3000 rpm.

I'm shooting for 34 degrees of total timing as a starting point because I'm running Edelbrock Etec heads, which are based off the vortec design. Most guys that run these heads say they're car likes around 32-34 degrees of timing vs old school heads that like as much as 36-38 degrees. However one member on here pointed out that his car with vortec heads did best with 38 degrees, so its not a given, everything must be tested since everyone's setup is different.

If my car ends up liking more timing, then I can either bump up the initial a little, or change my center plate/weight combo again in the distributor.

So hopefully I'm on the right track here and not just wasting my time. If anyone else has some ideas/info to contribute that'd be great! I'm just trying to pick up as much as I can on here before I start doing the actual work. Years ago it was easy to get things done, but my free time is much more limited these days, but for good reasons (wife/baby, etc). Thanks!
 

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #16 ·
Update

Well this afternoon I yanked out the stock Pertronix center plate and weights from my distributor and installed the following:

445 center plate
053 weights
2 silver medium springs

I'm not sure if the stock weights weigh much more than the Pertronix weights, but I figured the two medium springs would be a good place to start. Those two light copper springs are really a joke and I could see the weights not even coming back in at idle with those.

I was about to start my car and test it out, but my daughter fell asleep inside, so I'll have to wait until she gets up from her nap, haha! I guess right now it would be nice to have quieter exhaust! Haha!

Anyway, I was looking at the play of the weights and stuff. It seemed like the stock kit allowed the weights to swing out fully and fully utilize the space in the slot that the center plate is mounted on. Now when I swing out the weights I notice it doesn't fully utilize the slot space, so maybe it did effectively reduce the total advance. Though you wouldn't think you could notice that much by the naked eye. But that's about a 25% reduction going from 23 degrees to 18 degrees, so I suppose that would be measureable.

I'll see how it works in a little bit when I can fire the car up and check the timing with my dial back light. I'll check idle first, then rev it up and see how far the advance goes. If I only get 18 degrees from the distributor then I'll be happy!
 

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #17 ·
Update

I was able to finally figure out a good combo for my car, at least for total timing. I was shooting for 32-34 degrees total for now until I can get to the dragstrip to test it. My Pertronix distributor had 23 degrees stock in mechanical advance. I wanted less than that, maybe 18 or so, so I could run more initial timing.

I tried the 445 center plate and 053 weights, but that didn't work, still gave me well over 24 degrees of advance. So I had to scratch that plan.

So I thought I'd give that big center plate, the 365 stamped one, a try. So I used the 365 center plate and the stock Pertronix weights which already had good bushings in them.

I first set the initial by using the heaviest springs in the distributor to ensure no mechanical advance was present at idle. Also plugged my vacuum advance. I then set the timing at 16 degrees initial.

I then swapped in the two lightest springs so I could test my total timing without having to rev the motor to 4,000 rpm in my driveway with my head under the hood. :) Started it up and it immediately had 8 more degrees at around 950 rpm in park, so those light springs are definitely no good. But after revving the motor up good I found that it never went any higher than 32 degrees. I determined this via my dial back timing light. I set it at 32 and the timing mark lined up with zero dead nuts the entire time. Once it hit a certain RPM it would not advance anymore.

So that means I created a 16 degree advance limit in my distributor by using the GM center plate 365 and the Pertronix weights, which is pretty close to what I was shooting for.

I then swapped out those two light springs for two medium springs. When I checked the timing at idle with no vacuum advance, this time I only got around 2 degrees of advance at idle. If I had dropped the idle lower to around 700 rpm this probably would have eliminated it. But 2 degrees was ok, so I left it.

I plugged in my vacuum advance and found I only got 8 degrees from that because I had turned it down so much. Turns out before I was running more timing than I thought, which is why I had to turn the vacuum advance down so much to prevent pinging at part throttle.

So tomorrows plan is to readjust the vacuum advance up to around 12-15 degrees so I have around 44-47 total degrees of timing at cruise. This would also give me around 30-33 degrees at idle with vacuum advance hooked up.

So I'll try 32 degrees for total timing for now and wait until I hit the dragstrip to adjust from there. I'll adjust it up in 2 degree increments until I hit max MPH and once it starts topping out I'll leave it there or back it off slightly.

The reason I'm shooting for 32 degrees total timing to start is because I'm running Vortec style heads. If it turns out I can run more, I'll just bump up my initial a little more.

The cool part is, at least how it looks for now, I've effectively reduced my mechanical advance in my distributor from 23 degrees stock to 16 degrees modified which enabled me to run more initial timing. And I did all this with only a few hours time today and $1.00 for junkyard parts!

So that chart may not be entirely accurate. The 365 plate shows 6 degrees of advance on the chart above from the Chevelle forum, but in reality it must have been a typo because I get 16 degrees when using that plate.

So if you guys are looking for a way to reduce your mechanical advance and limit it, try to find a 365 stamped center plate from a stock GM HEI distributor unit and you'll be all set. You'll see right away how much bigger this plate is compared to others.

The other thing I noticed right away was that the weights swung out almost all the way off the base with the stock center plate and with the 445 center plate. But with the 365 center plate the weights were not as close to the edge, in fact they had quite a bit more room left to go. But because the 365 center plate was so much fatter, the weights bottomed out and couldn't advance any further.

So there is a way to reduce your mechanical advance other than using screws, welding/brazing slots, etc. The problem is I dont know if 365 center plates are that common. I cant remember what car I got that one out of at the junkyard either. Must have been a car that didnt need much total timing or ran a lot of initial.

I'll post up my results tomorrow on how the car feels after a test drive. I'm hoping its not a total dog or running horribly now, haha! But just testing it with a timing light in my backyard all the numbers checked out good.
 

·
Registered
Joined
·
4,086 Posts
Discussion Starter · #18 ·
Update - runs awesome!!!

I was able to monkey with my car a little more this morning. Got it running AWESOME to say the least!

Set up my total timing to 32 degrees yesterday by using 16 initial and 16 mechanical (limited by the GM 365 center plate using stock Pertronix weights and two medium silver springs).

Today I bumped up my vacuum advance from 8 degrees to 12 degrees. Hooked it up to manifold vacuum so at idle I get 30 degrees of timing (16 initial, 2 mechanical, and 12 vacuum). The 2 deg of mechanical start to come in around 900-1000 rpm and when I checked my timing in park it was idling around 950 rpm or so. In gear it idles around 850 rpm so it shouldn't have any mechanical there at idle in gear.

I also replaced the stock metering rods in my Edelbrock 800 cfm carb (previously switched to one stage leaner in cruise mode) and adjusted my idle mixture screws 1/4 turn richer.

Took it for a test drive, holy crap does it run awesome now! Zero hesitation from a dead stop, no more off idle hestiation or flat spot. That was probably mostly due to the lack of initial timing and a little bit to due with a lean idle mixture. It runs great from idle to part throttle to WOT now!

Got on the road and nailed it in first from about 20 mph and it just took off! Front end came way up, pinned me back in the seat, and I was gone! Shifted into 2nd gear and same thing, just hauled like crazy! Never ran that good before!

I think before I was running too much timing. These vortec heads seem to like less timing.

Part throttle response is great too, just hums along cruising and then when you step into it it just takes off, no pinging, no hesitation, just goes like it should.

So I'm pretty happy with the results. It basically took a day or so of tuning in the backyard, testing out springs/weights/center plates, adjusting the timing/carb, etc. The funny part is the part that really helped me tune the car was a junkyard part from some old crappy car. All my car needed was a way to limit the mechanical advance, and that big center plate seems to be doing it for me. Only cost me $1.00 and an hour or two at the junkyard to get that part!

Now I can go to the dragstrip and test out different timing settings. I'll try 32 degrees to start and then try 34, 36, and maybe even 30 degrees. My guess is it will like somewhere in the 32-34 range for total timing since that's what most guys seem to run with vortec style heads.

My car also runs a lot cooler now which is an added bonus. Runs around 170-180 while cruising and never gets above 185-190 while idling or stopped, etc. And this was today where its 90 degrees outside right now! Pretty sweet!

Anyway, I'm not sure if anyone is even following this thread anymore, but I'm happy I got my car running right and I did it all on my own with just some time, a lot of reading, and $1.00 junkyard parts, haha!
 

·
Premium Member
Joined
·
8,405 Posts
Actually, this kid of first hand testimonial feedback is what is really useful. A lot of people just "twist the distributor" and have no idea how recurving can make a huge difference.
 
1 - 20 of 30 Posts
Top