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  #16 (permalink)  
Old 08-03-2019, 10:49 PM
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Okay, so I was at the shop all day today and this is what I found out: First I bought a piston stop and flywheel turning tool. Then I put a pointer on my balancer and marked it both ways against the piston stop. I measured between the two marks and put a mark, then turned the engine to that mark on the pointer. I looked at the etched TDC mark that came on the balancer and compared it to my timing tab and it showed 4* advanced. This shows that the balancer marks are not off by much. Next I checked the distributor play against other dizzys on the shelf and play was about the same. After that I took the dizzy advance apart and checked it all out. No sticking. I put lighter springs on it and reassembled it. Put it back in the car and fired it up. Tried to set the timing with the timing light at 18* initial and revved it up. Again only 10* mechanical advance. And the idle sucked. I set the light down and timed it by ear. I advanced it until I got the smoothest idle, then retarded it a bit so when the vacuum advance is hooked up the engine has a clean idle and doesn't fight the starter. I checked it with the timing light and the initial timing was at 36* after figuring in the 4* difference on the timing tab. When the timing is all in w/o the vacuum advance I have 46* total. Add the 12* on the can and I'm at 58* going down the highway. Why does this engine want so much timing? What is with this dizzy only giving 10* mechanical? Have others had problems like that with a Pertronix flame thrower HEI?

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  #17 (permalink)  
Old 08-04-2019, 08:01 AM
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JMHO, and no disrespect intended, but I think two things are working against you:

1). According to Pertronix instructions the light springs (copper) you say your using in post #16 will give 9 mechanical advance at 500rpm and 12 at 1000rpm. In your post #1 you say your idle speed is 750rpm, which according to the instructions would bring in approximately 10 +/- mechanical at idle, leaving only 13 +/- left (23 total mechanical per instructions), explaining the short curve.

2). Also, is it possible you may be using your adjustable timing light's dial setting with the timing tab's degree scale, then adding the two together? Usually when timing with dial settings, the 0 mark is used and no math. It's also possible your light is calibrated inaccurately, you could check with another light.

Personally, I always set timing at Total (4000rpm), then check initial to see where it rests. I never set initial and assume total will be OK...
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Old 08-04-2019, 09:52 AM
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Quote:
Originally Posted by 36 sedan View Post
JMHO, and no disrespect intended, but I think two things are working against you:

1). According to Pertronix instructions the light springs (copper) you say your using in post #16 will give 9 mechanical advance at 500rpm and 12 at 1000rpm. In your post #1 you say your idle speed is 750rpm, which according to the instructions would bring in approximately 10 +/- mechanical at idle, leaving only 13 +/- left (23 total mechanical per instructions), explaining the short curve.

2). Also, is it possible you may be using your adjustable timing light's dial setting with the timing tab's degree scale, then adding the two together? Usually when timing with dial settings, the 0 mark is used and no math. It's also possible your light is calibrated inaccurately, you could check with another light.

Personally, I always set timing at Total (4000rpm), then check initial to see where it rests. I never set initial and assume total will be OK...
I first checked it with the original springs in it and they were quite stiff. I now have the silver springs in it. Having it already start advancing at low RPMs actually makes sense to me. I did notice that no matter what springs I used I could move the rotor a little bit with little effort then the farther I moved it the more it fought the spring pressure. The timing light is a brand new OTC digital timing light and I did the last timing with it set at zero.
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  #19 (permalink)  
Old 08-04-2019, 10:30 AM
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Well, according to all the videos I just saw online my entire advance kit is installed backwards which means it was assembled that way from the factory. Will double check things today and post results later
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  #20 (permalink)  
Old 08-04-2019, 10:48 AM
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Quote:
Originally Posted by jjjaffo View Post
Okay, so I was at the shop all day today and this is what I found out: First I bought a piston stop and flywheel turning tool. Then I put a pointer on my balancer and marked it both ways against the piston stop. I measured between the two marks and put a mark, then turned the engine to that mark on the pointer. I looked at the etched TDC mark that came on the balancer and compared it to my timing tab and it showed 4* advanced. This shows that the balancer marks are not off by much. Next I checked the distributor play against other dizzys on the shelf and play was about the same. After that I took the dizzy advance apart and checked it all out. No sticking. I put lighter springs on it and reassembled it. Put it back in the car and fired it up. Tried to set the timing with the timing light at 18* initial and revved it up. Again only 10* mechanical advance. And the idle sucked. I set the light down and timed it by ear. I advanced it until I got the smoothest idle, then retarded it a bit so when the vacuum advance is hooked up the engine has a clean idle and doesn't fight the starter. I checked it with the timing light and the initial timing was at 36* after figuring in the 4* difference on the timing tab. When the timing is all in w/o the vacuum advance I have 46* total. Add the 12* on the can and I'm at 58* going down the highway. Why does this engine want so much timing? What is with this dizzy only giving 10* mechanical? Have others had problems like that with a Pertronix flame thrower HEI?
This may be a gear tooth off there is about 12 degrees per tooth.

How much timing the engine wants is variable to compression pressure (not to be confused with ratio), the shapes of the combustion chamber and depth to which the spark plug penetrates toward the bore center, and certainly the cam timing.

Compression pressure has a relationship to compression ratio but it is flexable through the effects of throttle position and cam timing. Idle develops less cylinder pressure simply because the the throttle blades obstruct how much air the cylinders get. Compression ratio applies how much force is applied to what ever amout of air (mixture) gets into the cylinder. At low rpm the cam also can work against how much mixture remains after the piston blows some mixture back into the intake which depends on how soon or late in the compression cycle the intake valve is closed.

The end result is that the thinner the mixture trapped in the cylinder the more advance s needed to get it burnt at the point in crankshaft rotation that optimizes that force through the connecting rod into the crankshaft. Low cylinder pressure, lean mixtures, and overly rich mixtures burn slowly compared to more ideal conditions thus need more advance to optimize combustion forces at the optimum time for the crankshaft to utilize the input. This happens in a range around the mid stroke in a fairly tight set of degrees.

The combustion chamber shapes come into play where subtle changes have large effects. The opposite ends of chamber design represented by the early SMOG era open chambers, not just large but essentially featureless. These were designed to run cool to reduce NOx formation which at the time there wasn't a catalyst to break this up, but there were several means to post combust excess HC's so combustion chambers got their nuts cut off, so to speak. Modern chambers represented by the L31 Vortec have a lot of elements to thrash the incomming mixture and position the spark plug as deeply into the chamber as mechanically possible, these burn faster and hotter so you get more power on less spark lead, more compression for the fuel's octane rating, and of course more NOx which now can be cleaned with a catalyst. These chambers greatly reduce HC emissions, generate a lot more power doing that on lower fuel consumption and because of the fast burn do not need anywhere as much spark lead as older open chambers. So head selection is of major importance especially with cams getting into the 220 degree range at .050 lift and bigger.

Modern heads show peak power on about 34 to 38 degrees spark lead total. If you need something else greater then there is an error in configuration selections, set up or both.

Vacuum advance is not active at wide throttle positions so its 10 to 12 degrees at idle goes away as the throttle is opened. This of course is variable to load on the crank. Sitting in the shop with no load it doesn't take much throttle to get high rpm thus vacuum advance needs to be disabled to see what the centrifugal is doing. There is always slop in the centrifugal mechanism, this needs to be tested to see how his effects the initial settings, that can require that you wire the thing out first then retest with the springs to see how the innate free lossness can effect the zero base setting you're hunting for.

Bogie
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  #21 (permalink)  
Old 08-04-2019, 07:36 PM
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Honestly I think you're making this a bit more complicated than it is. You found your TDC and then talk about the marker you have being 4 degrees different - why not just mark the new TDC on it? And use your dial back light the way is supposed to be used. Check your initial timing by simply watching the timing mark move back to your TDC mark as you rotate the dial. Then read the dial for the initial timing amount. When you want to see where your mechanical timing is doing plot a timing curve. Move up 200 rpm at a time and write down what the timing is at that point. I would suggest putting the parking brake on, blocking the wheels and if possible have someone in the car for safety.



Straighten out whatever mess you have with the installation being backwards, put at least one of the tight springs in there with a light one and see where you're sitting. Remember this is mechanical advance - not initial timing. Don't even consider the vacuum unit until you get all this worked out where you want it. Again, if you're looking for 36 total, 15-18 initial and the rest in by 2500 will probably put you in a good place.
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Old 08-04-2019, 08:38 PM
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Thank you for that insight, Bogie. The heads are 1971 "290" castings. They're closed chamber heads @ 101cc. I suppose it also doesn't help I have 0.070" quench either. I have 224* @.050" and the intake closes at 59*. I have 50* of overlap. The AFR meter says it runs pig rich at idle, 12.6 to 1 and doesn't like to run any leaner. I guess all the above makes for really crappy flame travel at an idle. The idle is best at 36* initial w/o vacuum advance hooked up. I tried it again today with 18* initial and had to increase the idle set screw so it would run. I put it in gear and you could hear it laboring pretty bad. I power braked it a bit in the shop and there was no power. Jacked the timing up to 36* at idle and the car came to life. Idle barely dropped when put in gear. I know people say to set the timing to like 36* all in without vacuum advance and let idle timing fall where it may. That's all well and good but before I went on this timing adventure the car was running strong on 46* all in w/o vacuum advance. No hint of pinging. I guess this engine is an enigma. I bet it will take even more mechanical and be happy.
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Old 08-04-2019, 08:58 PM
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Quote:
Originally Posted by chasracer View Post
Honestly I think you're making this a bit more complicated than it is. You found your TDC and then talk about the marker you have being 4 degrees different - why not just mark the new TDC on it? And use your dial back light the way is supposed to be used. Check your initial timing by simply watching the timing mark move back to your TDC mark as you rotate the dial. Then read the dial for the initial timing amount. When you want to see where your mechanical timing is doing plot a timing curve. Move up 200 rpm at a time and write down what the timing is at that point. I would suggest putting the parking brake on, blocking the wheels and if possible have someone in the car for safety.



Straighten out whatever mess you have with the installation being backwards, put at least one of the tight springs in there with a light one and see where you're sitting. Remember this is mechanical advance - not initial timing. Don't even consider the vacuum unit until you get all this worked out where you want it. Again, if you're looking for 36 total, 15-18 initial and the rest in by 2500 will probably put you in a good place.
So I finally fixed the timing today; or at least figured it out. The weights in my distributor were installed correctly. The center piece that the weights move was installed backwards. Took me a ton of searching the internet to figure this out. Now the weights return completely and there's no slop. There was a fair amount of slop when set up the other way. I changed to some lighter springs while I had it apart, one medium and one light and now the mechanical is acting the way it should. It's still a conservative curve, all in at 3500 RPMs and up, but it will now through in about 18-20* mechanical instead of just 10*. Now I need to get the car on the road and finish dialing in my timing.
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  #24 (permalink)  
Old 08-04-2019, 09:11 PM
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BTW, this seems to be a known issue with Pertronix flame thrower HEIs that were built ten plus years ago. I've read from other people that they had to redo the mechanical because they were installed wrong. Because of the center plate being installed backwards there's a lot of slop and the weights don't return fully. Then when you start the vehicle it automatically advances a certain amount until there's tension on the springs. By then 1/2 the advance is used up at an idle. Took a lot of research but that's the deal and good information to have.
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Old 08-05-2019, 11:12 AM
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Over 10:1 compression ratio
Disconnect and plug the vacuum source.
Loosen distributor hold down, snug the bolt so you can just turn the distributor
Set engine idle speed as low as possible to prevent centrifugal from operating.
Connect timing light to #1 or #6 cylinder

Turn distributor to read 12 deg. initial advance with timing light
Tighten distributor hold down
Reconnect distributor vacuum advance hose
Restore normal engine idle speed
Done

Timing results:
Initial (12 deg.), vacuum (12 deg.), centrifugal (12. Deg.):

Total timing (36 deg.) advance above 2500 RPM
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  #26 (permalink)  
Old 08-05-2019, 08:52 PM
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Quote:
Originally Posted by MouseFink View Post
Over 10:1 compression ratio
Disconnect and plug the vacuum source.
Loosen distributor hold down, snug the bolt so you can just turn the distributor
Set engine idle speed as low as possible to prevent centrifugal from operating.
Connect timing light to #1 or #6 cylinder

Turn distributor to read 12 deg. initial advance with timing light
Tighten distributor hold down
Reconnect distributor vacuum advance hose
Restore normal engine idle speed
Done

Timing results:
Initial (12 deg.), vacuum (12 deg.), centrifugal (12. Deg.):

Total timing (36 deg.) advance above 2500 RPM

REALLY? - you have got to be kidding. Gotta hand it to you, about time I think you got your headed screwed on straight you pop off with something like this again.


Do you not realize that there are a fair number of readers of this information out there that do not fully understand this stuff?? And that this bogus information you throw out sometimes can confuse the daylights out of them? It's a real shame that you keep doing this to people.
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  #27 (permalink)  
Old 08-06-2019, 06:52 AM
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REALLY? - you have got to be kidding. Gotta hand it to you, about time I think you got your headed screwed on straight you pop off with something like this again.


Do you not realize that there are a fair number of readers of this information out there that do not fully understand this stuff?? And that this bogus information you throw out sometimes can confuse the daylights out of them? It's a real shame that you keep doing this to people.
Gotta admit, chasracer, I found his information to be highly flawed also. After all there's no vacuum advance at full throttle. Plus my car won't even idle at 12* initial. I want to recheck the timing with another timing light because people have said mine might be flawed. My question to that is wouldn't a bad timing light read late? Mine says my car wants 36* initial. A light can't read advanced, can it?
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Old 08-06-2019, 07:37 AM
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On the timing lights I can only say that we have several of them and two of them are identical make and model. They read 2 degrees different. We use the one that agrees with a third one - an old Actron that I have had for 30+ years. I like the other one because it's battery powered, plus a smaller frame and I can get closer to the timing mark. And I don't really have an answer to your question - the odd light that we have is 2 degrees less than the other two but I am not saying that means anything.
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Old 08-08-2019, 06:53 PM
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2 cents from a old fart

Quote:
Originally Posted by jjjaffo View Post
Okay, this engine has been talked a lot in my other posts: 408 BBC 9.7 to 1 compression. Stock closed chamber 101cc large oval port heads (3964290). Weiand dual plane intake and 770 street avenger. Hooker super comp headers and 2.5 dual exhaust. The cam is a comp 270 magnum hydraulic flat tappet timed 6* advanced. Cranking compression is 185 +/-. I degreed the cam to where it is now and put on a new neutral balance balancer. The timing tab I'm almost positive lined up with the balancer 0* mark on the 0 on the tab. The distributor is a Pertronix HEI street and strip flame thrower w/ adjustable vacuum advance that I bought 15 years ago. It has less than a thousand miles on it. I timed this engine by ear last year due to not having a timing light. I know, I can hear your groans. Anyway, after growing pains with the 770 SA I was quite surprised at how much fun the engine was in my 1984 Olds Cutlass with 3.42 gears and a turbo 400 with a 2400 stall. So just today I decided to throw a timing light on it and see what's what. (finally bought one). The numbers floored me! At a 750 RPM idle with the vacuum advance unhooked and the hose plugged I had 40* of timing. I verified this number by using the dial back on my light. So I checked the mechanical advance and it only advanced 10* and moved no more all the way past 4000 RPMs; and it was all in by 1800 RPMs. Checked with vacuum can hooked up and it throws another 12* on top of all that. This is suspect of the balacer and timing tab not being in sync. I will re-verify TDC this weekend. Even more weird I reset the timing to 18* BTDC and adjusted the idle and it ran. (Couldn't drive it due to tranni issue). Could shut it off and hit the key and it would fire and idle- tho you could tell it wasn't optimal. Because there was only 10* mecanical I pulled the cap. Several things were discovered: When I moved the rotor back and forth without actuating the mecanical there was a fair amount of slop. I figured this explained my somewhat erradic timing at idle. But you could also pull the shaft assembly up and down quite a bit. The mechanical advance seemed like it took alot of effort to move so I looked at it and saw what looked like light weights and heavy springs. I can recurve it once I figure out TDC but is there a shim kit to take the up and down slop out of the shaft? The back and forth slop I haven't nailed down yet. I believe it's a hardened gear on those. Is this compatable with a flat tappet cam? Should I just buy a new distributor and go from there? If so can you recomend a distributor? BTW the timing was steady above idle. Just fluctuated at idle. Does anyone know where I should time this combo to start with? To me it's obvious why this engine never detonated, not enough mechanical advance. With that said I wonder how much power I left on the table? So I'm new to proper timing tecniques to get the best power. Please guys I need all the help I can get to do this right.
no 2 engine- car combos like the same thing. if you have a local drag strip that holds a test and tune session, you can get it right regardless of where the marks are as long as you can record the readings and use marks you have. start with your timing as retarded as you can get off the line with knowing your total say like 28 total. monitor your mph on a full pass forgetting about the seat of the pants advance your total timing in 2 degree increments until the mph quits increasing, back it off to the lowest setting that had the highest mph. write that number down. thats where you want your total to end up. then work on 60 ft retard it back a few and make 60 ft passes I am assuming this car bites.advance the timing and record at what inital advance it best 60 fts. record that number. adjust your advance weights to operate between the best 60 timeing and the best mph timing. and adjust springs to have it all in at convetor lock rpm. vac advance will give more street manners if you hook it to manifold vacuum.unless your carb is way to small. vac will drop off at wide open and mechanical will be the only thime working, but at cruse and light accelleration it will have more manners
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Old 08-09-2019, 07:43 AM
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Quote:
Originally Posted by chasracer View Post
On the timing lights I can only say that we have several of them and two of them are identical make and model. They read 2 degrees different. We use the one that agrees with a third one - an old Actron that I have had for 30+ years. I like the other one because it's battery powered, plus a smaller frame and I can get closer to the timing mark. And I don't really have an answer to your question - the odd light that we have is 2 degrees less than the other two but I am not saying that means anything.
Few years ago everyone was recommending the Flaming River Battery powered single wire timing light as being one of the most accurate. Is not a dial back light - and very simple. As far as accurate dial back lights, the old 1970's-1980's chrome Craftsman lights are supposed to be good (I also have one of these but I don't use it any more). I have also heard that using a dial back feature on a timing light is inviting error. Better to use timing tape.

My latest experience was converting to a FAST crank trigger. Although it was amazingly rock-solid timing inside the garage, never could get away from high RPM misfires with my Daytona Sensors box (no matter the gap I used) and I finally went back to using the distributor pickup. Looks like the FAST crank trigger uses a Ford Cam sensor and the waveform is different for the others. Point is - that few degrees of scatter you often see in your timing is really scattered timing. I always thought it was probably just my timing light. It wasn't, as the crank trigger was rock solid at same point. Makes me wonder how much power we give away using distributors. Maybe I'll eventually go to a crank trigger sold by Daytona Sensors.
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