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I am once again wading into this forum due to the depth of knowledge it has, rather extraordinary looking from the outside in.



This issue is old part numbers that I cannot seem to cross-reference to, I have no idea what I have... which means nowhere to go.

So if I may ask has anyone experience with outer weights being stamped 48..both weights are stamped 48. The center weight is 383 that is a known quantity. It looks to me like someone yrs ago did a tune-up using Bluestreak parts

The objective is to get a known quantity of weights...and recurve this distributor to something near a normal timing curve. A place to start.

1983 454 HEI RV engine all stock.
 

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Discussion Starter #2
I am once again wading into this forum due to the depth of knowledge it has, rather extraordinary looking from the outside in.



This issue is old part numbers that I cannot seem to cross-reference to, I have no idea what I have... which means nowhere to go.

So if I may ask has anyone experience with outer weights being stamped 48..both weights are stamped 48. The center weight is 383 that is a known quantity. It looks to me like someone yrs ago did a tune-up using Bluestreak parts

The objective is to get a known quantity of weights...and recurve this distributor to something near a normal timing curve. A place to start.

1983 454 HEI RV engine all stock.
And this little gem is actually plugged into the hei module...something i have never seen
 

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I don't know, but I'm a betting man.
I'd say it is something like an idle speed switch.

Good luck and enjoy your voyage.

-- Spike
 

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I don't know, but I'm a betting man.
I'd say it is something like an idle speed switch.

Good luck and enjoy your voyage.

-- Spike
Thank you for the response ..that voyage your speaking to is exactly what concerns me. Dropping new springs on this dist and finding myself or it in a place it should not be... does raise the eyes a bit.

As to the box it does not interact with the carb in any manner but perhaps it does manipulate the advance in some manner. Looking at how GM addressed emission control anything is possible. But that was 40 yrs ago and this is now so it is what it is.
 

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If you do a search on the part number on the "relay" it shows that it is an idle control switch. Apparently was used in a lot of GM trucks during that period, shouldnt be too hard to find a service manual and figure out what it is supposed to do.

As far as the weights go maybe Dave Ray will chime in, he should know the answer. What makes you think that they are not correct ?? Would be pretty unusual for them to have been changed.
 

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To try to understand the correlation between weights and center numbrs is a constant problem. Most combos do not have any specs with them, and, the ONLY performance set ever done came out of 350 and 454 late 70's/early 80's Suburban and some truck engines. Weights 41, center 375 give 22 crankshaft degrees of timing, and are common to all ZZ series carburetted engines.

The rest of the OEM GM combos are all for EMISSIONS engines, all 436 others.

Now, here come the issues. When we designed the mechanical advances, we did not adopt the start and limit pin slots ito control the start and limit parameters, we ground them into the actual center curvature and weights to get the start, curve and limit we wanted for any specific engine combo. WHY? Well, so we didn't end up with a hundred different reluctor slots and Pin stops, we added those parts tothe curve, so the weights and center could be used on ANY large HEI, one way up for tight hand rotation, up side down for left rotation.

So, one other issue, all those after market "curve kit" setups with weights and center ARE NOT FOR STREET USE. They are designed to give 16 to 18 degrees of crankshaft degrees, so the initial can be set to 20 or so static degrees, and the vacuum advance disabled, FOR DRAG RACING USE ONLY, NOT FOR STREET USE. The different spring sets are totally usable, for any large HEI, and points distributors.

AND, AGAINST ALL THE KNOW IT ALL'S SAGE ADVICE, JAMMING A SCREW INTO THE WORKS, WELDING/BRAZING THE SLOTS UP ON A LARGE HEI IS NOT THE RIGHT WAY TO RE-CURVE ONE, SELECT THE RIGHT EMISSIONS CURVE SET AND USE IT, SOME HANDFUL OF VERY FEW ACTUALLY WORK WELL FOR PERFORMANCE APPLICATIONS FOR DRAG RACING.
 

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(snippage) AGAINST ALL THE KNOW IT ALL'S SAGE ADVICE, JAMMING A SCREW INTO THE WORKS (snip)
I recall you mentioned adjusting the weight by drilling a small hole
in the weight and adding a screw, bolt, etc. for fine tuning. Didn't you
also mention the distance from center of such screw, bolt etc. would
have a different result?

-- Spike

The next H.Q. Ale is on me. :)
 

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Discussion Starter #8
If you do a search on the part number on the "relay" it shows that it is an idle control switch. Apparently was used in a lot of GM trucks during that period, shouldnt be too hard to find a service manual and figure out what it is supposed to do.

As far as the weights go maybe Dave Ray will chime in, he should know the answer. What makes you think that they are not correct ?? Would be pretty unusual for them to have been changed.
I have researched the part number and have found it does mention idle speed. With that being said the only physical connection it makes is some sort of vacuum valve/ solenoid with wiring that directed under the dashboard and the distrubutor...there is no connection to the carburetor in any manner.

As to manuals, this is a RV that has a modified p30 chassis, It has been improvised quite a bit..Ive yet to see a manual for all they have done

My concerns are how it operates, shorting out the distributor in some manner advancing the timing for enhanced idle speed? Or perhaps some type of primitive knock sensor?

I am stripping the emission control systems off the engine, restoring the engine to some of its potential and economy. As in all things I would have liked the salvage the dist but perhaps it is best to just pull it and pick up a new product...There is so much to go thru making my dough work is just as important finding the right curve on this engine.

I play with boats and not cars, yrs ago I've found throwing money around can be quite expensive in a rebuild...Again thank you for your reply.
 

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As far as adding weight to the weight, that is only if radical curve speed is required and cannot be met with springs too light to return the curve ti idle.

For the most part, the large HEI has enough different weight and center combos to work a lot of non-emissions engines, the only trouble is, which combo, it could take decades to identify and try all the various combos.

"I have researched the part number and have found it does mention idle speed. With that being said the only physical connection it makes is some sort of vacuum valve/ solenoid with wiring that directed under the dashboard and the distrubutor...there is no connection to the carburetor in any manner."

For some heavy weight vehicle applications with SMOG controls, there is a vacuum distribution valve, electric, that switches the vacuum advance vacuum souring between ported for lower gears, to full manifold for upper gears. This switch and vacuum diverter valve might well be one of those emissions control setups.
 

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As far as adding weight to the weight, that is only if radical curve speed is required and cannot be met with springs too light to return the curve ti idle.

For the most part, the large HEI has enough different weight and center combos to work a lot of non-emissions engines, the only trouble is, which combo, it could take decades to identify and try all the various combos.

"I have researched the part number and have found it does mention idle speed. With that being said the only physical connection it makes is some sort of vacuum valve/ solenoid with wiring that directed under the dashboard and the distrubutor...there is no connection to the carburetor in any manner."

For some heavy weight vehicle applications with SMOG controls, there is a vacuum distribution valve, electric, that switches the vacuum advance vacuum souring between ported for lower gears, to full manifold for upper gears. This switch and vacuum diverter valve might well be one of those emissions control setups.
Why thank you, Dave Ray, seeing how GM addressed the burning of hydrocarbons almost anything makes sense... I think. So I will go out and start decompiling what must have been yrs and yrs of engineering. It should be noted the system is old rusted and not functioning along with modifications done along the way...EGR delete is one along with some type of valving in the exhaust system.

I've watched you posting some interest you do seem to have quite a grip on HEI/emission systems. I do understand the weights and centrifugal advance setup, it will be interesting to play around with these springs and see how they do control that process. Timing light in hand and saying look at that comes to mind. I was raised in a shop during the 60/70's tuning up an engine was second nature...knowing what not to do was critical.....hence my anal approach. I left for college before HEI mass implementation so I know very little of how it functions. Tinkering with it now is very interesting...If one could take back this knowledge in time what is know common knowledge..he would be a millionaire in short order.

Thank you again
 

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An update is needed here, the relay switch is indeed an idle speed control switch, in my case, it had been butchered/cut off and the circuit rendered useless. Buried under old vacuum lines and yrs of dirt and grease the vacuum line was uncovered and then sourced to the carb.

As to those old part numbers those to have been uncovered, here at Chevelle tech... Again thank you and your forums are incredible.

https://www.chevelles.com/forums/18-engine/343241-h-e-i-tune-up-kit-what-should-i-buy.html

See post #6
 

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I know Rocky, great fellow, great tech.

But, his chart is incredibly useful, misses some critical points, of which, are not his fault, he did good on the chart as is.

These are ALL EMISSIONS curve specs, and they need both start and limit degrees numbers. HEI does not use a pin and slot to set the at rest and full limit degrees, they are cut into the weight/center combo.


BTW, changing the springs, spring rates does not change the start/limit points, only the rpm speed of the advance curve.


This is NOT to say to not use Rocky's info, he has given a great deal of info nobody has previously, and that is the best for all of us, use/test wisely.
 

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Most of the recurve I understand and get, once upon a time I rebuilt the old points& condenser dizzys. It will be interesting to watch advance using a restricted vacuum to control the advance ...and building advance with spring and centrifugal force..that to sounds interesting.

Now limiting the amount of advance with an add on screw..weld etc does concern me but I will cross that road when it comes. I'm quite sure once I get to that point and find the solution I will mumble to myself But Of Course...:D

In a sense, I am reliving my youth it is the adventure that matters.
 

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The mechanical advance weights and center ARE the start, limit and curve parameters, welding, brazing, screw here or there is NOT the right way to do it, no mater whom the "expert" is telling you to completely mess it up.

The various stops for the vacuum advance are only limited to a person's common sense, ingenuity, and fabrication skills. They are the extension of what a vacuum advance was called when it was designed, a "load compensator", adding timing when the engine was at no, to low load vacuum levels, via full manifold vacuum, NOT added to enhance EMISSIONS reduction, by using it as a completely useless second acceleration advance curve by ported vacuum.

I'm not allowed to relive my youth, I am too busy getting hammered for trying to help people get their cars running right.
 
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