Flathead spark curves.........

This is what I have for my timing (8ba and crank trigger with ecu) when the engine is warmed up. I do have the cam advanced a few degrees. It has not been on a dyno to tune it right, just using how it feels and sounds until I can. The top red dot on the table is the manifold vacuum at wot and the lower dot is at idle. I tried more advance around 26 degrees and it was prone to detination under hard pull (around 12.7 afr), backed it off and still pulls good and no detination (at 13.1 afr) so will leave it here for awhile. Just throwing this table in to see if this may off in left field. The engine is port efi pointed toward valves and wondered if this might affect the timing as to running less? I ask because I am far from knowing what I should while tuning, open to comments or suggestions.


Vergil

tried to get the picture to show bigger but this is as big as I could get it, sorry


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Hi Vergil
Could you explain that table in more detail? I'd like to be clear on what I'm looking at. I'm assuming that the top line is RPM. Are all the numbers in the center table Timing degrees? What are the numbers on the left portion ?
Thanks
Jim
 
Kahuna said:
Could you explain that table in more detail? I'd like to be clear on what I'm looking at. I'm assuming that the top line is RPM. Are all the numbers in the center table Timing degrees? What are the numbers on the left portion ?
Thanks
Jim
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You are correct Jim on what you are looking at, the top left to right numbers are the rpm and the numbers in the center table are the degrees, the numbers on the left are vacuum numbers (conversion chart below) my engine operates in the range between the red dots, if I am cruising at say 2150 rpm and my kpa (vacuum) is maybe 74 my timing at that point would be 20 degrees btdc. I am not the best at explaining things and should have been more clear on the chart.

Vergil

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38 coupe said:
Interesting. The Ford Service Bulletins say all 32-48 V8 distributors except the 40A have 18 degrees mechanical advance and the 40A has 22 degrees.
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I agree the specs are either 18 degrees or 22 degrees. Most of the crabs are 11a units which give you 22 degrees distributor engine advance.
My 1935 Motors manual lists Initial Advance Crankshaft degrees BTC as welll. I call this "pin" advance as its where the timing pointer is set from the factory.
That number is from 0 degrees (six cylinder) to 4 degrees btc (most of the v8s)

A 11 a unit with 22 degrees and a "pin" setting of 4 degrees would total at 26 degrees of advance..
Looks like 20-28 is pretty much in agreement for all concerned ??:)
 
Somehow I lost the vacuum retard number in this thread. What is the retard at WOT? I have found that the CR of most engines is a calculated number, not measured. The recomended .050" piston to head clearence is to promote turbulence and doesn't increase CR appreciated.
Virgil's Chart allows for a great deal of experimenting, be nice if you could use it on a stock or mild modified engine.
I hope to have My grandsons truck on the road this Fall I do have a 4bl intake and would like to use an electronic engine management system.
JWL used one, but the power output was less than a carbonated engine.
Richard is developing a system for measuring total advance, both Mac and vac. and recording it while driving. Now that will be interesting.
Take care.
 
I have a stock crab (rebuilt ) on my 99A but have no vacuum hooked up, have the leather and plunger in there, just wound it in enough to create a small amount of drag. My engine runs best with about 8 degrees intial, and with a timing light it advances smoothly up to just over 30 degrees at about 3000 rpm. ( i marked the pulley and made a pointer when I built it) never pings.. has milled 81T heads with the piston clearances at .050, so Im guessing the compression is maybe 7 to 1. mild Cam..only about .325 lift. twin 94s on an edelbrock super dual(which are a tad rich, new jets this weekend), headers and dual pipes.
My question is, considering how sweet this admittedly mild engine runs, is there any advantage to hooking up the Vacuum?
 
Ol' Ron said:
Somehow I lost the vacuum retard number in this thread. What is the retard at WOT? I have found that the CR of most engines is a calculated number, not measured. The recomended .050" piston to head clearence is to promote turbulence and doesn't increase CR appreciated.
Virgil's Chart allows for a great deal of experimenting, be nice if you could use it on a stock or mild modified engine.
I hope to have My grandsons truck on the road this Fall I do have a 4bl intake and would like to use an electronic engine management system.
JWL used one, but the power output was less than a carbonated engine.
Richard is developing a system for measuring total advance, both Mac and vac. and recording it while driving. Now that will be interesting.
Take care.
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Ron,

The vacuum retard could be ( depending on the adjustment) as high as 20 degrees engine !
 
Would it be possible to set the rpm at say 2400, then just begin to adjust the vacuum plunger to see the affects of vacuum or the lack of it.
This may answer many peoples questions as to just what the vacuum does. ME too.
I started doing something like this back a few years ago, but the dist mach wasn't working well. I now have an Allen, will have to find an old crab.
 
Ol' Ron said:
Would it be possible to set the rpm at say 2400, then just begin to adjust the vacuum plunger to see the affects of vacuum or the lack of it.
This may answer many peoples questions as to just what the vacuum does. ME too.
I started doing something like this back a few years ago, but the dist mach wasn't working well. I now have an Allen, will have to find an old crab.
Click to expand...

Sure when i get in another crab i will play with the vacuum some.
On the last one i noticed a number of surprizes !
I loosened the vac adjustment bolt and spun the crab up to about 2500 rpm and then turned in the screw one turn at at a time with no vac applied. It took about seven turns to get the maximum drag on the leather etc. Then applied vacuum from tester adn noticed it takes a good supply of vacuum to pull the piston back.
Max spark retard occurs below 7 inches of vacuum.
Ford suggests turning the screw , then test driving and turning in until the spark knock goes away.
It doesnt appear to be a very linear progressive adjustment , but a on/off issue more or less . With the leather stop it had to be pretty hard to maintain the adjustment other than just off and on...
 
BUBBAS IGNITION said:
Sure when i get in another crab i will play with the vacuum some.
On the last one i noticed a number of surprizes !
I loosened the vac adjustment bolt and spun the crab up to about 2500 rpm and then turned in the screw one turn at at a time with no vac applied. It took about seven turns to get the maximum drag on the leather etc. Then applied vacuum from tester adn noticed it takes a good supply of vacuum to pull the piston back.
Max spark retard occurs below 7 inches of vacuum.
Ford suggests turning the screw , then test driving and turning in until the spark knock goes away.
It doesnt appear to be a very linear progressive adjustment , but a on/off issue more or less . With the leather stop it had to be pretty hard to maintain the adjustment other than just off and on...
Click to expand...

Do you recommend installing a gasket under the big screw on the vacuum system?
 
Yes , you need a gasket or a small oring or something to hold a seal for the vacuum.
I noticed that it takes a lot of vacuum to move the piston ( very hard to do with a hand pump mitti vac etc) . I used the vac pump on my distributor machine to move the test unit.
 
How much clearance can the plunger/piston have and still be effictive? It seems that even a little wear would allow vac to pull around it and thru the distributor rather than hold piston up. Just wondering.
 
Jack 34pu said:
How much clearance can the plunger/piston have and still be effictive? It seems that even a little wear would allow vac to pull around it and thru the distributor rather than hold piston up. Just wondering.
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The ford service manual shows a go/no go gauge for testing this. The clearance is pretty tight, a heavy coat of lube will not allow movement some times!:eek:
 
I've been working with this vacuum advance/retard now for several years. I've tried to determine the needs of the engine and I find very few people understand the principals involved. Yhe new engine management systems adjust the timing and A/f ration 30 times a second. Maybe that's why my Saturn gets 35MPG with 140K on it. All this from a 1.9L engine (117ci) . My friend JWL has done some extensive test at WOT with a verity of engine Modifications, however we don't drive that way. BUT, everyone wants performance, that's why the dual exhaust big carbs and lots of them. Hi compression heads and my favorite, Long cams (They sound great).
I don't think we have a good tune on our engines because we're satisfied with what we have, we don't know any better.
Why is it that to equal cars can have different performance or better mileage. For the first time someone besides me and a few of us who've been here, can seet the changes in vacuum under various conditions and this tells up something. Unfortunately I haven't figgered out just what. One problem is: on either the SBC dist or the 11a crab, vacuum doesn't control the timing the way we want it.y to.
Getting hard to see this, probably doesn't make much sense anyway.
Ol' Ron
 
Ol' Ron said:
I've been working with this vacuum advance/retard now for several years. I've tried to determine the needs of the engine and I find very few people understand the principals involved. Yhe new engine management systems adjust the timing and A/f ration 30 times a second. Maybe that's why my Saturn gets 35MPG with 140K on it. All this from a 1.9L engine (117ci) . My friend JWL has done some extensive test at WOT with a verity of engine Modifications, however we don't drive that way. BUT, everyone wants performance, that's why the dual exhaust big carbs and lots of them. Hi compression heads and my favorite, Long cams (They sound great).
I don't think we have a good tune on our engines because we're satisfied with what we have, we don't know any better.
Why is it that to equal cars can have different performance or better mileage. For the first time someone besides me and a few of us who've been here, can seet the changes in vacuum under various conditions and this tells up something. Unfortunately I haven't figgered out just what. One problem is: on either the SBC dist or the 11a crab, vacuum doesn't control the timing the way we want it.y to.
Getting hard to see this, probably doesn't make much sense anyway.
Ol' Ron
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Makes sense to me Ron, I have two flatheads and the engines more or less are close in the builds but the tuning on them are quiet different and the seat of the pants is also noticeable. And you hit the nail on the head when you said as long as we are satisfied we stop without finding the power we should have. I guess I am lazy and now will have to start flogging them again to see what I have missed and I'm sure there will be more than a few problem areas to mess with ;).

I will say until I started playing with the fuel injection and computer control ignition I really didn't realize what a great job the carburetor does under all the conditions we run them in and as gunked up as we let them get.

Vergil
 
BUBBAS IGNITION said:
Some data to digest :

1= First curve was without vacuum piston installed, advance was bouncy and jusped around a bit. Believe unit needs the piston load to stabilize the advance. 22 degrees at 2200 rpm
2=Installed clean /lubed piston.....Advance curve moved up the scale a bit and remained steady. 22 degrees at 3000 rpm with load on piston.
3=With vacuum adjustment all the way out , 7 complete turns will retard timing 12 degrees engine timing.
4=It takes 10 inchs of vacuum to began moving piston with light tension adjustment. ( light is just having contact with advance) Maybe a couple turns inward....

Interesting observation if spark advance is in at cruise speed at 2500 rpm and 20 degrees, AND vacuum drops to between 4-7 inches of vac the unit retards 20 degrees !!!! Almost a perfect overlap of advance going both directions.

Now the discussion would be what is the actual carb fitting vacuum at different rpms.
What happens to this vacuum when multiple carbs are used ?
How much lower is this vacuum when a high lift camshaft is used.?

Can someone hook up a vacuum gauge to a single carb flathead and drive the car ?

Is the intake vacuum different from carb fitting vacuum ????????

The only thing i can conclude at this point is the fact that these distributors ( cleaned and serviced) are 22 degree mechanical advance units. AND the fact that that they do need the piston and leather stop for proper operation.

Ask away ?????????
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Vacuum for these distributors is taken from the manifold, not the carb. Multi carbs will make no difference.
Tests on one of my crab distributors shows 22 deg of advance, all in by 1600 rpm. I then ran at a steady rpm with vacuum to the piston and noted the amount of retard when the vacuum was dropped, allowing the piston to contact the plate. My results showed that the retard varied depending on speed. Maximum retard was 15 deg at 1500 rpm, 10 deg at 2000 rpm and 2 deg at 3000 rpm. This was with the adjusting screwed backed all the way out.
The spark was steady at all speeds with vacuum applied and no load from the piston. I would think that if the spark jumped around with no load from the piston, that the distributor shaft or bushings are worn. I do not agree that the piston has to be in there to make these work properly.
 
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Good comments guys , this has made a great post for all to see and read.
I will do the 49-53 Distributors starting next week in another post.
I will start with stock load a matics, then use a customers mallory and then do the chevrolet conversion with full mechanical ( we have shipped almost 300 of these units with some amazing results)..
Also recieved a couple early crab mallorys to check early next weel as well.......
 
Hello Ron
My tests agree with you. I run 15 degrees idle. Jumps up to 25 for accel. Then tapers to 17 at 3200. I get comments on the smooth idle. If I want a rough idle, I would use 8 to 10.
Dick in havasu
 
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