Identical with the exception of the wear plate on the arm. Performed equally as well today with about 20 miles on it.... Bill in TR
So the first stupid question before we get in to this is whats the advantage of retarding the vacuum upon deceleration? To keep from backfiring in the exhaust? At part, or WOT theres little to no vacuum so it only occurs when fully backing off? Bill in TR
My take on it is when you close throttle you go into a full vacuum condition; more if you downshift or are engine braking going downhill. On a good day youd reach absolute vacuum. Man I hate theory... So whats the vacuum advance doing at full vacuum? Holding the unit retarded or pulling the unit past full retard and even past the mechanical advance. I kind of realize at an easy throttle application the V.A. is going to hold back the mechanical a tad for smooth drivability around town, but again, at a stop sign, whats it doing? Keeping a smooth idle/no surge feeling? I guess in a nutshell, that this is where I am having a problem getting it. I know when we are done with this chapter Ill have mastered the concept, and I cant tell you how much I appreciate you explaining the theory end to me and the masses! Bill in TR
Bill, there is no theory, just fact. Vacuum is an excellent indicator of engine load. Light load = high vacuum. Heavy load = low vacuum. The vacuum advance canister has a spring that opposes the vacuum pull. The high vacuum overcomes the spring and advances the timing. Under high load and wide open throttle, vacuum drops off and the spring wins out pulling the advance that was there out. At part throttle and light load, a smaller amount of air/fuel enters the cylinder and is less highly compressed. More timing insures optimal combustion. When you close the throttle and vacuum is high, it advances the timing. The vacuum advance doesn't retard the timing unless you consider the canister spring function. The mechanical advance is independent of the vacuum advance. It advances the timing with increasing engine speed. The timing at all times is the sum of the initial setting, the mechanical advance, and the vacuum advance. In a completely stock engine with stock distributor, the mechanical advance isn't at it's maximum until 4600 RPM. Vacuum advance tops out (14-18*) at 16" of vacuum and higher. Vacuum advance starts to advance the timing at 6-8". So lets look at a situation where the car is going 60 MPH out on the highway. Your foot is lightly on the gas, and engine vacuum is high. With typical gearing, the RPM is up around 2300-2600 RPM. Only part of the mechanical advance is in because the weights aren't spread all the way out. The stock springs won't allow that until 4600 RPM. The vacuum advance has advanced the timing above and beyond the partial mechanical advance so that timing is up around 40* or so. There is no problem at light load with that much advance, and it actually helps to get the best mileage. Now you go to pass a truck, and you floor the gas pedal. Vacuum drops to zero, the canister spring pulls ALL the vacuum advance out, and at the same time, the increasing RPM forces the weights all the way out and at 4600 RPM and higher, your timing is the initial setting plus maximum mechanical advance. You finish passing and come off the throttle, vacuum returns and if your running your vacuum advance off manifold vacuum, the canister again advances the timing. At the same time, RPM drops back and the stock springs pull the weights back to their partially retracted position. If you run the vacuum advance off ported vacuum, when you close the throttle, vacuum drops off because there is no vacuum at a ported vacuum source. In any case, the amount of vacuum advance is dictated by engine load. You can boost low end power by bringing in the mechanical advance in sooner than stock, sooner than 4600 RPM. You do that by changing the distributor springs to lighter ones. A good target is to get all the advance in by 2500 RPM. Lets say we use springs to do exactly that. Let's look at the same scenario with the car going 60 MPH. Now instead of having only partial mechanical advance, we have maximum mechanical advance because of the lighter springs we installed. We still have high vacuum so the vacuum advance has added it's maximum advance. Now we have too much because the mechanical advance is at it's maximum, and the engine surges from too much advance. That is why we must decrease the total vacuum advance in the canister to more like 8-10* instead of the 14-18*. A typical set up would be a distributor with a maximum of 20* of mechanical advance. We could run an initial timing of 12*. We set the springs in the distributor to let in the full mechanical advance at 2500 RPM. We then limit the vacuum canister to 8*. Here we are cruising along at 60 MPH again. Ignition timing is 12* initial + 20* mechanical + 8* vacuum advance for a total of 40*. We get our best MPG that way. Now we stomp the gas to the floor. Vacuum drops to zero, the canister spring pulls the 8* out leaving us with 12 + 20 = 32* of WOT timing for as long as our foot is on the floor. We come off the gas suddenly and vacuum returns, and we either have 8* added to the total timing if we have our VA connected to manifold vacuum, or no added advance if the VA is connected to a ported vacuum. If the vacuum advance is connected to manifold vacuum, that 8* can be available at idle, so our example above will idle at 12* initial + 8* vacuum advance = 20*. I tell everyone to try both ported and manifold vacuum with their vacuum advance. There will be no difference in the timing at our light throttle 60 MPH cruise example. The difference will be at idle, and full closed throttle deceleration. You try them both to see which feels better to you with your combination. Now, you have an HEI from an unknown engine. It could have a lot of mechanical advance built into it, or a smaller amount. We don't know. All distributors are not the same. It would be nice if it only had 18-20* in it, but odds are it has more. That is why I advise setting the total advance with the vacuum advance disconnected and plugged. Use the lightest (yellow) springs to set the total to 32*. Once you have done that. Stop the engine and install the heavy stock springs and lower the idle down as low as it will go without stalling. Use the timing light to see where the timing is at idle. Subtract the idle timing from your total (in this case 32*) and you will know how much mechanical advance is built into your HEI. The more mechanical advance you have, the less initial timing you can run for a given total advance. If there is too much mechanical advance in your HEI, you will have to limit it if you need more initial advance. Once you have your initial and mechanical set up for the total you want to run, then you limit your VA canister to 8-10* and hook it to ported or manifold vacuum. You road test the car and listen for part throttle ping. If you detect any, you can use the allen wrench to increase spring tension so the VA is pulled out at a higher rate. If you cannot eliminate part throttle ping, you then have to limit the canister to less degrees. You play with it until you get it right. Trial and error. Look at the various distributors for 1972. See how they are set up stock. look at the specifications. Everything I just explained is in the Power Timing thread. All of it, including how to use a conventional timing light or advance light to set the total advance. You have everything you need to do the job.
Still digesting that Larry and its starting to make sense. Spent today buying, selling and moving couches and in the lull managed to get out to the shop and check out the new kit. We were discussing different advance weight weights(?) and since Ive got a '73 Electra 455 core motor sitting on the cart I decided to pull the cracked (housing) HEI off and have a look. The PO busted the housing moving the motor around sometime in the past so I cant take credit for it LOL. Pulled the clamp and it was outa the block in 5 seconds, so I know the guy didnt bust it from being frozen in situ... Got it in the vise and pulled the cap and rotor and marked all the parts with a YELLOW marker. Pulled the cap and rotor off the car to compare and marked all those pcs. with RED. Got interesting in a hurry. Other than the caps and rotors being the same, the advance units were completely different, and I am not sure how to proceed. Spent an hour reading the shop manual, but alas, its a 1972 and doesn't broach the subject of HEI. Hmmm... Aside from having similar springs and identical vacuum modules the shape of the weights are WAYYY different, the weight mounting plate is way off too and even the rotor mount is shaped different. Im probably gonna use the red stuff that came out of the car, but now Im curious about the weight shapes and ramping rates for the advance like we spoke about. The difference aint a little; its a LOT! Bill in TR Left hand and right hand weights? The yellow have shiny spots from the plastic guide buttons as do the red, but the red ones has numbers stamped on what I would guess would be the upper side. Now theres a ramp rate difference (is this a "cam" action thing?) , and length on the tips. Side by side in the car theres a pretty evident difference as well. We'll call the rotor notch 12 o'clock on both yet the advance plates are off 90* Is that a problem? I have no idea what the PO did (and neither did he LOL). In the "static" or non running position, the weight pivot pins are equal on the red but behind equal on the yellow. Any HEI exspurts feel free to pipe aboard! Thanks guys,; should a distributor curve be such a learning curve too? TIA.... ws
I don't know a ton about HEI's but I know some stuff. Certainly...Larry knows more! I don't think there are LH or RH weights. They can go up or down, it doesn't matter. There were many different weights, there were many different dist shafts, many different vac cans, and many different springs used by GM. Each of these parts affected the advance in some way. The aftermarket spring kit just limits the variety to lt, med + heavy. The weights were the same way, some were heavier than others. So...let's say you put the Lt springs in and the advance comes in at 2500. Suppose you drew a graph and made a line from 0 to 2500. That line would not be straight if you graphed it at say...every 100 RPM. It would have an amount of curve, because the weights just don't snap on + off. A lighter or heavier weight would give you a different curve. What does it mean? Up to 2500, probably not a lot! So the springs alone should do what you want. Actually...GM sold special kits over the counter of springs + weights for high altitude use. At least...that's the way I see it and hope I don't get detention or homework from Larry!
Nah... Larry's pretty good about the PT's (penalty tours) as long as you bone up on the reading part! BTW Larry, do I need to get an advance degree limiting cam like in your earlier post? It was not included with the Summit kit but it seems a bit superfluous from most of the feedback... When I replaced the Mercruiser distributors on my boat with HEIs, they provided me a curve graph in the manual. No vacuum advance (Under full load 100% of the time) so its mechanical only. The graph is a smooth curve from 0 to 2500 I believe. As soon as I can get up on the boat Ill grab a pic of the graph outa the book. Now Im kinda curious about the total*'s etc. Had those units spun up on a machine at Stepuls Dynomometer on Ogden Ave. in Lyons Ill. in about 1990 Bill in TR
Those pics Larry posted were the first time I had ever seen that limiter plate. Loved it, jumped right on Ebay + bought one for 3-4.00 + SH. I've seen other things and home made things, but not that piece. I like it because you can use the stock cannister for a stock look. Now...what's not clear to me is the bushing under the weight plate (not sure if HEI has it), if you need that with the limiter plate. There's a lot that goes on under Rubik's cap, huh?
That's why I thought it was me being stupid! I think the adjustable Vacuum Canister doesmt need the cam plate, and is self limiting internally and really don't mind making adjustments on stuff, but Im an old fat guy that has to lean over a plastic (1972) grill that was fragile 40 years ago, or reach over the fender dealing with buttons, buckles and zippers. Just want to do it right once and the first time. As mentioned, I am not a theory guy and so far Larry has been straight up with facts and how to's, but its' just a little confusing on the natural progression. Heck... Ive timed and tuned stuff from Electro-Motive diesels to Rolls Royce gas turbines (ground mounted jets for generators) but am seeming to struggle with this one fine tune subject... I will get it, and master it; eventually!!! Bill in TR
Guys, I'm not the authority on HEI's, not really all that fond of them myself, but I understand the allure of them being low cost and effective. The HEI does not have a pin and slot under the advance plate like the points distributors. The shape of the center plate and advance weights change the amount of mechanical advance amount. There are other ways to limit the mechanical advance, and those ways are in the Power Timing thread. You'll need to look for them. As far as that cam goes, Crane should have included it. Look in the instructions and see if they mention it at all.
WILL DO!! After the DS that is (domestic ****) on this mornings list. Wifes really good about my shop time, but theres some signatures needed in town today so that's a priority. Shes also making a trip by car from here to Springfield, MO. and then on to san Antonio Tx next weekend. Bill in TR
That cam should be included in the Crane kit. It is right there in the picture Bill. look in the box. http://www.summitracing.com/parts/crn-99600-1
Howz about some good feedback bout Summit... just got off the blower with them about the missing black cam that limits the advance. It shows in the picture but not in the description. The gal called Crane Cams and couldn't get an answer from them either so she's flipping one in the mail today for free. OUTSTANDING! I ordered the kit last Friday at 10 a.m. and they said there was a 8 day back order, and the kit appeared the next morning (Saturday) at 10 a.m. on the front porch. !00% good on the Buick outside door handle mentioned earlier here as well. Summit has my vote! https://www.youtube.com/watch?v=NoptofKbQ04 Bill in TR
Just keeps getting better and better ya know??? Yes, theres a few combinations of weights and cams available.. Ha ha !!! So I cleaned the yellow spare take out and heres some thing interesting... 1112803 4E23 out of the 455 1974 Buick then off of google, some HEI page about various GM units: 1112871 4E17 By a photo, is 68 units behind mine with a 4E17 mfg date of 4(1974) E (april) and 17 the day of the month and this is quoted as for being off a 455 1974 PONTIAC ! WTFF???? I know the B-O-P trans patterns are the same and differ from chevs, but are all the distributors the same for B-O-P ???? Gonna pull the HEI outa the car this afternoon. Couldn't find a number with a flashlite and mirror and now Im determined to figger it out for sure! BTW... the two different sets of weights are NOT interchangeable between the yellow and red units against the advance cam. KRYYUMMINNY YUMPITS! Bill in TR
No, they differ between Buick, Olds, Caddy, and Pontiac, (and, of course, Chevy.) Inards, like vacuum advance, module, weights and springs, rotor, etc do interchange. Bodies and shafts are what differ.
http://www.pro-touring.com/threads/29320-Mechanical-advance-vs-vacuum-advance-article The link is to a decent article explaining the difference between mechanical vs vacuum advance.
Lux... that was really good and helped me understand even more yet. Thanks for the link. Another good read. I especially like the advance at highway cruise part dealing with lame timing, yes that's an "M", due to early emissions control attempts via exhaust gas temps (EGTs) and A.I.R. pumps. Mines missing the AIR pump but still has the AIR intake manifold which will be looking at the scrap yard soon, one day. The other issue is the ported versus manifold vacuum. I know mine is ported right now and that will become part of the equation of the change over. So for now, Ive got a long block (1973) 455 to trade for an early 455 intake manifold. The blocks' complete from pan to intake manifold, and from oil filter back to the crank flange. No accessories tho. FOB HERE! Nick... I would hope the BOP sizes vary, but regardless of that, the spare Ive got is dated 1974 and Im about to pull the running unit outa the car momentarily. They are both Buicks, no doubt, but vary vastly from one to the next internally... more to follow! Bill in TR
