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Old 03-29-2008, 09:20 PM
Ristow Ristow is offline
 
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motorcraft distributor tuning. eliminating ping. several pics.

i set the distributor up for the plow truck engine tonite,same way i do all of mine. mine all burn 87 octane without ping/detonation,and i run 12~15 degrees intial advance and manifold vacuum to the advance unit. so,here's the way i set mine up...

my engines are fully stock,or 4 barrel holley with edelbrock performer grind cam,all emissions equipment removed from both. this tune works equally well with both. i have my first 8600 cam'd 360 on the stand,this distributor is going in that engine.

i use a cheap plastic hand vacuum pump and T in a vacuum guage. i like this better than the pump with the built in guage,because this way i can put the guage where it's easy to see,not having to look at the pump for the reading.



first the vacuum advance. it's important to know the vacuum advance is the engine load monitor for the ignition. it is not the advance for increased rpm,the mechanical advance takes care of that.

also,leaner charges (higher vacuum)-like idle,cruise throttle positions-take longer to burn than richer charges (low vacuum)-like acceleration,or wider open throttle positions,or anytime the powervalve is open.

so,high vacuum= low engine load,leaner charge,and increased advance from the vacuum unit.

low vacuum= higher engine load,richer charge,and lower to no advance from the vacuum unit.

some people eliminate the vacuum advance,to overcome the pinging issue,but they do so at the cost of throttle response and economy. some think since racers don't run an advance,they don't need to on their street car either. thing is,racers run around the track at near to full throttle all the time,with a carb setup to run richer for power,often eliminating the powervalve,because it'd be open all the time anyways. racers don't need a device monitoring engine load,it's always high.

so,first,get a reading of the vacuum advance,to see where it's at. this one started advancing at about 2.5",and was fully advanced at about 10.5". this is a common reading on these distributors.



that's a problem. the powervalves on these trucks are usually dual stage,rated at somthing around 11"/8.5". the single stage units will be 6.5-8.5" units. when the carb goes rich,and the powervalve opens,the vacuum unit will still be nearly fully advanced. this is where the ping/detonation comes from. the ignition is firing too soon for the rich charge.

to tighten the vacuum unit,a 1/8" allen wrench is stuck in the vacuum nipple,inside is an adjuster,you will feel the wrench engage it. turn the wrench counter-clockwise to increase the vacuum needed to advance the ignition.



i set mine so the unit begins advancing at the vacuum level the power valve opens,or very close to that number. meaning,when i get into the throttle,my vacuum level drops as the butterflies open on the carb,gradually backing the timing off in my advance unit,until the vacuum dips low enough to open my powervalve,at which point my vacuum unit is backed out completely. i run a 7.5-8.5 valve in my holleys,that is the vacuum at which my vacuum advance begins moving,or,advancing the ignition.

you will find when you get the advance dialed in,that it will be fully advanced at around 15" vacuum,a bit high,but with a mild cam,and properly set up carb,you'll be running strong vacuum at cruising speed. also. also,these units give a lot of advance. most are 12 degree units.thats in distributor degrees,so it's 24 crank degrees.a lot. even if you vacuum wasn't strong enough to be fully advanced at cruising speed,you'll still be gettin a lot of advance from the unit. i believe it's more important to have the unit backing off the advance at the correct time.

you should now be able to run 12~15 degrees initial advance,and i recommend manifold vacuum to the unit. you will have a smoother idle,and much crisper throttle response. and ping should be gone now!

__________________________________________________ _____________________________

onto the mechanicle advance. this step is not near as critical as the vacuum unit adjustment.but still worth doing. the engine speed advance. fires the plugs sooner as rpm increases,regardless of charge strength. after about 2500-3000 rpm,air turbulence is strong enough that additional advance is not needed. from the factory there is too much available,but the springs are stiff enough that it usually isn't a problem. but here goes.

remove the vacuum advance unit from the distributor body.remove the rotor,pull the felt from the top of the shaft,under the rotor.



there is a wire clip,grab it with a small needle nose pliers,and pull it out and up to release. you may need to do this with both tangs.

the clip.



next,the reluctor wheel. it has a roll pin locating it to the shaft,mark the hole on the relucter the pin is in,then gently pry it up and off with 2 screwdrivers.



pull the 2 screws holding the plate in the body.they can be stuck,heat the body underneath where the screws protrude to help.



and pull the plate. you'll need to rotate it a bit to clear the positioning tab for the distributor cap.



heres the mechanicle advance parts. note the slots,one longer than the other,that limit the amount of advance that is available,and the tab that is used in the slot to limit advance. you want the smaller slot,it'll be on the big slot from the factory.



so,release the springs,carefully. you may need to bend the ends out a bit to get them over the pegs. you don't want to distort the springs.



once released,romeve the upper shaft,clean and oil the spindle part of the lower shaft.



and put the upper back on,rotated 180 degrees,to be on the smaller slot.



light lube here...



put the plate back in the body,align the screw holes. anti-sieze the screws,install,and put the reluctor back on the shaft,tap it into position,align the roll pin hole with the groove on the shaft,set the pin in the groove at the base of the hole and tap it in.



put the clip back in. drop it into position,hold one side down in place with a small screwdriver,and shove the other side down with the pliers,snapping it into place. put the felt in,and lightly soak with oil.



if you did this with the distributor installed,the rotor will be 180 degrees off now,so you will need to pull the distributor up out of the engine and rotate the rotor 180 dgrees to get your timing back in place.
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Last edited by Ristow : 04-02-2008 at 01:42 PM.
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Old 03-29-2008, 09:31 PM
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BarryL BarryL is offline
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Very Nice write up, with pics, makes it easy. Thanks!
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Old 03-29-2008, 09:44 PM
GWChris GWChris is offline
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Nice write up Ristow! I have not modified the mech adavance on mine, perhaps I will try it on a spare distributor.

Adjusting the vacuum advance diaphram really is a key mod, and easy to do too. In the end I drove around with an allen key for a couple of weeks - I'd drive it to work and listen for ping on the way, adn adjust it until I it just barely pinged.

If you combine this adjustment with moving the vacuum advance to run on straight manifold vacuum, you should never have to worry about listening to that ratttle again and you'll have improved throttle response.
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Old 03-29-2008, 10:19 PM
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nograin nograin is offline
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Nice write up and explanations!

I was wondering if the Motorcraft vac advance was exchangable or adjustable. Now I know!

Dang! The motorcraft dizzy has the same PIA retaining spring the old Chryco dizzy's use. So going for the shorter slot cuts the total advance. That could help with higher rpm ping issues, OR, would let you get away with a little more initial advance (and end up with the same full advance).
I'm not plowing or towing so will probably skip that.

FWIW. Technically the part throttle pinging is not because of the richness - it would actually be worse if it was leaner - just like at full throttle. But at part throttle the air mixture isn't as dense* as at full throttle so it it burns slower. Plus the EGR would have to be working perfectly as designed (or were they just praying they could skate passed emissions one more year) for it to cool the combustion temperatures down. Oh yea. It doesn't help that today's fuel doesn't have the motor octane ratings as good as they had been in the early 70s.

*I had to scratch my head on that at first. Think about how the venturi and throttle create a vacuum. So the air under the throttle - especially if its not fully open and the engine is pulling hard, is not as dense as above.
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Last edited by nograin : 03-30-2008 at 11:48 AM.
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Old 03-30-2008, 06:36 AM
GWChris GWChris is offline
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Ristow - What is the difference in degrees for the max advance limit when you put the upper staft on 180deg out?
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Old 03-30-2008, 07:26 AM
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Very nice write up. Hope this ends up in the archives.

I made a stop blade to cut down how much the vac advance can move. It has a slot in it so it can be fine tuned.



Larry Miller
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Old 03-30-2008, 07:39 AM
Ristow Ristow is offline
 
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yep,i remember you made that larry,very nice modification.

GW,most are 21 on the long slot,16 on the short. keep in mind those are distributor degrees,so double those numbers for crank degrees. i believe i have seen advance shafts with shorter slots on both sides.

i did not go into putting performance springs in as that will require more in depth tuning,and this was aimed more at eliminating ping/detonation,and gaining some throttle response at the same time.
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Old 03-30-2008, 08:05 AM
GWChris GWChris is offline
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So that means if you flip it the max advance just goes from 21 to 16 Deg (distributor)?
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Old 03-30-2008, 08:06 AM
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Old 03-30-2008, 08:11 AM
Ristow Ristow is offline
 
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Quote:
Originally Posted by GWChris
So that means if you flip it the max advance just goes from 21 to 16 Deg (distributor)?


yes,you will lose 10 crankshaft degrees of total advance available.
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Old 03-30-2008, 09:28 AM
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Now THAT'S what I'm talking about. Good job, Mike! And thanks!!



Mods should move this one to the tech section.
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Old 03-30-2008, 09:40 AM
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Good write up Mike. I'll shoot a note to Tad to move this to the archives after a day or two.
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Old 03-31-2008, 07:52 AM
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I never knew the vac advance was adjustable. My 360 had a ping problem I could never seem to get rid of ever since I bought a parts store distributor.
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Old 04-02-2008, 11:46 AM
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Great stuff!

So, what about adding the Mr. Gasket springs that people usually mention go along well w/ doing the HEI/e-coil ignition?

That's ovbiously a V8. What about the 258?

It sounds like you're referring to the stock MC21xx carbs for this and possibly having at least EGR if not all emissions. What about 0 emissions, not even EGR?

And is this just for towing/workhorses or what about daily drivers?
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Old 04-02-2008, 11:55 AM
Ristow Ristow is offline
 
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actually i run holleys,but do run this setup with stock 2 barrels as well. i do not use the egr on any of mine.

this setup will run good for any purpose.anytime you can eliminate ping/detonation is good no matter what you're doing,although this is not a high performance setup,i think very few trucks on here need more tuning than this.

the vacuum settings will differ with bigger cams,and need to be adjusted as applied. bigger cams will have lower vacuum across the board,and need lower settings on the vacuum unit.

lighter springs on the mechanical advance will require a lot more in depth tuning,that i feel is not needed on a daily driver,not to mention hard to get to on these distributors.
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Old 04-02-2008, 12:19 PM
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malodin malodin is offline
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Ristow, in your first post you say

"you will find when you get the advance dialed in,that it will be fully advanced at around 15" vacuum,a bit high,but with a mild cam,and properly set up carb"


what about those of us that are running stock cam and stock 4 barrel? will it work with it?
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Old 04-02-2008, 01:10 PM
Ristow Ristow is offline
 
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it will. generally,the milder the cam,the stonger the vacuum will be. stock cams are real mild.the above is geared towards stock to mild engines,like with an edelbrock performer cam. 8600 may be a bit to big,but close in vacuum compatability. i should have stated the build of my engines above.

the above tune would not work on a wild cam,not enough vacuum,and the settings would need to be adjusted per the vacuum reading the engine gave.
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I LOVE how Ristow has stolen my comment about him ... "Quoted" it ... and made himself famous for being an ***hole to people. Hahahahahahahahahha!


→ Where the kids hang out...

fsjbuilder.org come for the mindless chat,stay for the hand drawn emoticons.

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Last edited by Ristow : 04-02-2008 at 01:27 PM.
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  #18  
Old 04-02-2008, 01:55 PM
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Now I'm tossing the ported vs. manifold vacuum for the advance around in my head. I know my 230 motor uses manifold vacuum for the dizzy adn it has never pinged and has plenty of off the line zip (at least for a 230), and after some Googling, it looks as if the ported vac was spawned due to emissions and the EGR.

So if you dumped your EGR, it's best to go back to manifold vacuum?

Now I'm lost .
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Old 04-02-2008, 02:02 PM
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Yes, manifold vacuum. Even if you didn't dump the egr, manifold vacuum.
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