[Sun Tuned]

I figure now would be a good time to give a little back to a hobby that has given so very much enjoyment to me over the years. Some of you will have seen this elsewhere on the web; so to speak,so be patient, there are probably some here that have not. At the risk of offending those who would wish this to be kept shhhhhh, you may want to leave now so as not to be mad again. I say again, because this is not the first time I have performed this trick for an audience. It was FREE the first time so I figure why change up the deal now.

Centerplate=======Weights=======Dist.Degrees
368=================139=============10======
406=================139=============12======
349=================139=============15+=====
371=================139==============9======
489=================139==============14=====
375=================139==============13+====
364=================139==============12=====
397=================139==============12=====
370=================139==============12=====
346=================139==============11=====
396=================139==============11.5===
398=================139==============10.25==
383=================139==============12=====

That should be enough to get you started. The springs I'll let everybody figure out on their own. These are probably the most common ones, but that will give everyone a basis with which to get started anyway. Anyone need any help, you now know where to find me.

[Sun Tuned]

I figure now would be a good time to give a little back to a hobby that has given so very much enjoyment to me over the years. Some of you will have seen this elsewhere on the web; so to speak,so be patient, there are probably some here that have not. At the risk of offending those who would wish this to be kept shhhhhh, you may want to leave now so as not to be mad again. I say again, because this is not the first time I have performed this trick for an audience. It was FREE the first time so I figure why change up the deal now.

Centerplate=======Weights=======Dist.Degrees
368=================139=============10======
406=================139=============12======
349=================139=============15+=====
371=================139==============9======
489=================139==============14=====
375=================139==============13+====
364=================139==============12=====
397=================139==============12=====
370=================139==============12=====
346=================139==============11=====
396=================139==============11.5===
398=================139==============10.25==
383=================139==============12=====

That should be enough to get you started. The springs I'll let everybody figure out on their own. These are probably the most common ones, but that will give everyone a basis with which to get started anyway. Anyone need any help, you now know where to find me.

[Bud Lyons]

Could you explain that for us knuckle heads that don't have a clue what that means. Have you been drinking some of 1/2" Studs coffee?



My Rig's a little old, but that don't mean she's slow.

[momo ´70 formula]

Sun Tuned,
thank you that is good information for all the people using HEI´s. I don´t right now but I will print it for future plans.

[zippy]

Thx Sun Tuned, I have copied and pasted in my Pontiac Knowlegde notepad hehe. Bud, I belive it's the centerplate# and the weight# combo will give you that certian# of dist degrees of advance. Could be real usefull to me in a couple of months hehe

Dan "zippy" Pesonen

[Half-Inch Stud]

I don't believe any of those values...(wish I did).

My experience has been to baseline on the 139 weights...that's the good news.

My experience has been TOOOOO MUCHCHCH timing with any centerplate. Numbers: I see 20 to 30degrees variation in timing advance vs RPM with most combinations.
--------------------------------------------------
Sooo, I'll be picking the combos from your list tonight, and setting the HEI up. With this list, ANY combo is better than what I've experienced to get teh advance to a smaller range. Yeap, I've resorted to HYD Lifter checkballs inserted into the HEI plate slots...to limit the range.

Time for some Kona coffee.

Half-Inch Stud

"tbdET/1xxMPH/1.xx 60foot/28"/3.54:1/10"/469 #48/Flat HYD/DualQ-Jets/Offyl/3xx0Lbs
11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/469 #48/FlatHYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/469 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/469 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[momo ´70 formula]

HIS, that´s distributor degrees. Which will be doubled at the crank. 12 distributor degrees= 24 crank degrees.

[MarkJ]

Here is a tip I got from an online article referenced in a Classical Pontiac post:

Tip#2: If you are experiencing part throttle pinging with the HEI, you probably have a 20 degree vacuum advance can. Most HEIs have a ridiculous amount of advance here, which is a detriment when you start experimenting for optimum timing. Pull the distributor cap and you will find a number stamped on the top of the support bracket near the can. This is the cans advance, it can be anything from 8 to 24 degrees. A 10 degree vacuum can is ideal. It is available from AC Delco Parts, or your dealership. Canadian AC Delco part number: D1370A

Is this true?

If so, I can tell what my total advance will be from Sun Tuned’s list, the number on the vacuum advance can and what I set initial timing at.

[Half-Inch Stud]

I believe that.

EXAMPLE:
If my engine needs 34 deg Total ADV, and I install 371 with 139weights, then 18degrees down (9deg*2) would be the idle advance = 16.

Sounds perfect...if it were true. With my HEI parts, and a hit or miss attitude, I've seen 12degrees at idle. Sooo, 34-12 = 22.. 22/2 = 11.

So, I presumably stumbled over 346 centerplate.

Overall, this list may be halpful to get rid of the BACK-BREAKING hit & miss effort....thanks in advance. tiiming advance that is.

Half-Inch Sparkgap

"tbdET/1xxMPH/1.xx 60foot/28"/3.54:1/10"/469 #48/Flat HYD/DualQ-Jets/Offyl/3xx0Lbs
11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/469 #48/FlatHYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/469 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/469 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Half-Inch Stud]

MarkJ,

I've de-hosed my Vac ADV cans. Also, I've been slotting the Vac ADV mount for Cap-Rotor Phasing.

Finally, I've compared Vac ADv cans, observed the stamped numbers, and have found Vac ADvance to be a loser with 11:1 + 455 engines.
-------------------------------------------------
This time around, the 68GTO project sports 8.3:1 compression...and can use a little vacuum advance, without risk of ping.

Thanks for the reminder

HIS

"tbdET/1xxMPH/1.xx 60foot/28"/3.54:1/10"/469 #48/Flat HYD/DualQ-Jets/Offyl/3xx0Lbs
11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/469 #48/FlatHYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/469 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/469 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Kenth]

My experience with HEI-systems is that you have to retard the curve some from the original.If you copy the original curve you will have pinging.Seems like a HEI and wider plug-gaps burns off the mixture faster that the points system?
I guess you have to optimize whatever system you´re using to actual circumstances.
Kenth

[MarkJ]

Hmm, my center plate is a #396, but my weights have “053” stamped on them. What will that give me?

Rotor Phasing: They just did this on Horse Power TV the other weekend on a Chevy HEI. Looked like a simple process, but my Pontiac HEI doesn’t have any way to adjust the pick up coil. So, that’s why you’re slotting the vacuum advance Half-Inch.

I’m slowly getting this.

Hey Keith, you may be right about the performance gains (or lack there of) with using an HEI distributor. A while back, Car Craft did an article on comparing the performance difference between stock points, a stock HEI and an aftermarket HEI ignition system. Their conclusion was that an HEI is more reliable and accurate, but no noticeable performance gains were achieved over a well-tuned points distributor.

I would think an HEI would also give better gas mileage over a longer period of time simply because it won’t wear out as fast as a points distributor.

[Sun Tuned]

Well all the dist machines at Performance Distributors aggree with mine, 2 accross town, and an engineer at plant 20 in Indiana all are within 1/2 degree of each other. Strange. The way this works is is the numbers in the above table are all what is "capable" of being achieved with each combo. The ones marked XX+ are the ones that exhibit excessive override. The rest you can take to the bank. Now if the springs are way too light as is the case with most curve kits, then even the ones that don't have a + beside them will allow excessive advance over what is listed. ANY spring that allows the advance to start too early will negate these numbers. The advance can not begin under the highest idle speed or it's not operating properly. With the right center cam that does not exhibit override there is no need to artificially limit anything on the HEI, the cam will limit it for you. Some will not and those are the ones that will show a wild amount of advance. If you take your example with the 371 center plate and 139 weights we see 9 dist degrees. Double that to get crank degrees and we get 18. Say you want 34 total. Then 34-18=16. Set the initial at 16 and you will get a total of 34 at what ever rpm you have the curve brought in. if you see more then I would respectfully ask you have your timing light serviced or at least checked. We have spent more time and way more money verifying what is in that chart, and I will stand right by it and the rest of what I didn't print on it.

The vac adv deal is no big deal either. 11:1 455's running all over with my distributors in them and the customers are thrilled with them. The trick is not to get one with a certain number of crank degrees of advance. That is not the only parameter that has to be addressed. The real meat and potatoes part of the deal is, is where the vac adv starts and where it finishes expressed in terms of In.Hg. vacuum specifications. That is probably more important than how much crank degrees of advance you've got followed very closely by that next. Next time someone is in Memphis and wants to see that chart duplicated with the numbers verified on up to 16 different dist machines e-mail me.

[Sun Tuned]

And to answer another question above. The use of 045 or 053 weights will knock exactly 1 dist degree from each of those numbers.

[Will]

Excellent info! Thank you Sun Tuned.


----------------------------
'72 Formula 400
12.77 @ 108 / 234/244 cam / Q-jet / 3840# / 3.23s / street tires (not DRs)
'73 Firebird 400/4-speed

[Half-Inch Stud]

With all that said and agreed to. My last peel of onion has to do with Timing-Bounce, at total advance.

How do we minimize, or eliminate HEI timing bounce with mechanical advance?

Half-Inch Stud

"tbdET/1xxMPH/1.xx 60foot/28"/3.54:1/10"/469 #48/Flat HYD/DualQ-Jets/Offyl/3xx0Lbs
11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/469 #48/FlatHYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/469 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/469 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Sun Tuned]

O.K. Stud, seriously, and believe me when I say I mean no ill will against anyone here, I don't want to turn this into a whizzing contest. Let's see... the timing bounce you speak of is a very real concern. Generally the point distributors were the worst ones to exhibit that problem, as they limited the centrifugal advance by means of a specific length slot and pin arrangement. Since that was a total metal to metal deal unless the hypalon sleeve that was installed by the factory on SOME(not all) models, was still there(most flew off after a year or two) bounce was a very real problem. At least it could be on fast winding engines. When the pin went sailing down to the other end of the slot, it would frequently hit the end and bounce off the end of the slot and then rest back at the full advance position. Not a good deal at all. This did not cause a problem on most cars but for the few that wound up like a rocket it was a real pia. With a little work it could be rectified.

On the HEI there are 2 slots that the center cam pins ride in. These are way longer than need be, as their purpose is NOT to act as a limiting device as most think. On the HEI it is the center cam that in fact limits the advance. However on some somebody apparently forgot to say whoa in time. These cams have a definite "lobe profile" to them. Different engines obviously require different amounts of total AND at different rates of advance. On the point dist the cam was in essence just a big lobe that the weights rode on and as they went up the slot/pin was used as a positive stop device to limit the advance. In the early days we see the cam lobe shape was real steady and fat shaped. Good for just about most anything. All you had to do was swap springs to speed it up. Some cams would be ground on to help speed up the advance when certain spring designs were not handy. O.k. idea that got the job done but I don't like to do it as it took the heat treat out of the part. As the HEI showed up all the technology that was known was used on that shaft design.

Since money is the prime deciding factor on just about anything, it was decided that in order to save money on having to manufacture 30 or so different shaft assemblies, that it would be much easier within the specific divisions to just make one shaft design and allow superior flexibility to that by using different center plate(cam) pieces. This allowed 1 shaft assy to quickly and easily be adapted to fit many different combos.

Not only does the center cam control the amount of total centrifugal advance capable. It also controls the rate of the advance(speed) along with the springs. The springs will control the actual speed of the advance, but the cam controls both the total amount AND the specific rate in conjunction with the speed the springs allow. Much more critically than the point dist did. If you look at different cams you'll see that some have a smooth slow ramp, some have a smooth beginning ramp and a quick ending ramp, some have a fast opening ramp and slow down towards the end, and on and on. Swapping these things around will allow one to tailor a curve more suitable for a particular combo than another. Sometimes it will and can cause more problems than before too. These things were not designed to be mechanically limited, except by the center cam alone. You'll see the ramps on the cams are not nearly as broad as the old point dist cams were. Although I've done it in certain applications...some circle track combo's, and in wierd instances where a guy wants or needs a very limited centrifugal amount( due to no factory cam that limits that low, that could be easily found). It is a delicate project to keep that mechanical stop from allowing the advance to bounce. The cams have such a fast rate of advance it is very difficult to fix a mechanical means to limit to a certain amount without having the thing bounce. Really the only way to do it right is, is to take the cam and place it flat on a bench grinder and "tailor"(grind) the ending advance portion of the cam flanks to where they are flat. This is very hard for me to try to explain. But it is the ending section of the cam that slows and stops the weights from advancing further. When that is done then you have the tedious task of blending the lobe portion of the advance part into the ending section, so it doesn't slam the timing in a jerky motion. Some people "tail" the weights. You can even use a fast ramp cam and a pretty stiff set of springs. These HEI cams are about as critical tolerance wise as the regular camshaft in the block is. And just as tedious as it is for the cam grinders to develop a fast ramp high lift cam for your valvetrain,that will not to slam the valve back down on the seat and damage the seat or valve, it's the same deal for the advance cam. The smoother the better. I do not personally like to mechanically limit an HEI with some sort of metal stop, although I have done it in the past. It just invites the problem your asking about...advance bounce. Best to do it with the cam itself as long as you can find one with the right amount of advance that your looking for. If you can't, well I can only offer the idea of a fast ramp cam, with the right amount of advance, and spring it stiff enough to make it act right. Can't run light springs with a big cam and make it work without float and the dist is no different. Hope that helps, I tried.

[momo ´70 formula]

Sun Tuned,
excellent information in your last post. That explains alot!
Thank you.

[Half-Inch Stud]

Sun Tuned,

Good digest on the Weights and cam block.
Let's go full-tilt, and make it a Chapter.:

You were quite clear on the Points-distributor Advance bounce, due to hitting the posts, as stops. That has been hi-lighted by others from old as an area to check after cam springs, opil pump changes. They bounce around peak torque...due to cam and harmonic balancer twists.

MY beef on the HEI is alleviated within your digest. YET, revisited with the Rotor spin direction (OK, inertia and Under-cap wind resistance). Such that loose springs will aggavate the Rotor wander (advance wander) at peak torque. Such that too firm springs will cause the Rotor to achieve TOTAL ADVANCE well into th 3500+RPM range..and keep advancing into 5000+RPM, due to the HEI camplate geometric hyperbolic leverage design.

Problem is a Timing RETARD under accelerations/decels, bumps, and upshifts. We all would notice it if we were thniking along those lines.

I've pondered super light weights: (no good because Rotor windage and inertia will dominate). Higher sensitivity to upshifts, etc.

I've pondered heavy weights: no good because they need heavy springs, and allow the timing to creep in advance well towards redline. Our engines favor a fixed advance after 3200RPM....some even earlier.
-----------------------------------------------
So, it seems to me we (I) need to key in the best set of MEDIUM springs to match the 139 weights. That allows the weights to best match the center cam's exponential stop-ramp...since it's there to avoid advance bounce. And overcome the ROTOR mass, and satisfy the accelaration, upshift dynamics. Conflicting requirements when the springs are incorrect!
------------------------------------------------
Sun, I think you've taken the mystery out of the HEI advance setting problems for me. I got homework.

Thanks,

Half-Inch Stud

"tbdET/1xxMPH/1.xx 60foot/28"/3.54:1/10"/469 #48/Flat HYD/DualQ-Jets/Offyl/3xx0Lbs
11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/469 #48/FlatHYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/469 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/469 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[romulus]

Sun Tuned:

Great info! Thanks for sharing that..

HIS:

You MUST be an engineer! You remind me of one of the guys I work with, intelligent and mildly crazy, great guy. Only fault is he is into Porsches, but still cool...

So guys, just to make sure I am not completely twisted on cheap drugs (getting my HEI just right is turning into a major sojurn.) I wanted to verify what I think I know so far.

1) on our Pontiacs, the center plate is installed number side down.

2) the factory weights and cams seem to be the best bet, since they are hardened and all the kits I have tried seem cheap and too light for timing stability.

I attempted to plot out my curve for my 9.5:1 455 by setting up a tach on the radiator support and recording the timing at 200 RPM intervals. I chickened out at 3000 RPM, the thought of going any higher made me very nervous , even with a good supply of Guinness on hand. Running the 139 weights and 389 center cam. A previous post by Sun Tuned said this should get me 10 degrees, or 20 Crank Degrees. Curve started advancing at 1000 RPM and by 3000 I was reading 16 degrees of advance. My best guess would be full advance by around 3900 RPM.
I still needed to know if I was getting the full 20, so before shutting down, I set the initial timing to 0. Opened up the dist. and by creative use of little slices of 3/8 fuel hose , propped the weights open to full advance. Fired her back up(she cranked VERY slowly) and read the timing....20 degrees! COOL!!
MY problem is I still have this fear of letting that center plate limit the total timing. Soooo...here is where I get crazy . Just inboard of the rotor mounting holes are two more holes that don't appear to have any function. 10-32 screws fit nicely thru them. Found some socket head allen screws 1/4 inch long and reduced the diameter of the heads with a drill motor and bench grinder until the center of the dist. would just touch them at full advance. Attached nuts to the bottom with some Loctite Red and repeated the full advance test. Got about 19.5 degrees. I was feeling pretty clever until reading your posts about distributor bounce. any thoughts?



-the human body is a remarkable machine that is capable of turning Guinness into Bud Light--