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Hello everyone. Over the last couple of months we've been fine tuning the 351C 2V in our 73. I pulled the stock motorcraft distributor and tore it down, luck was on my side as the mechanical advance had 10l and 15l slots on it and it was already set in the 10l position woohoo!. Next up was the advance springs, I swapped those out for the accel 925d spring set and bent the spring retaining tangs in a bit to have timing all in at 2500 rpm verified with a timing lights. Initial timing was set at 16 + 20* max mechanical 2500 rpms makes for a very snappy very strong feeling engine. I'm using a custom tailered vacuum advance as well and this car cruises like a dream and requires almost no pedal to keep it moving. I guess what I'm saying is there is alot of almost free performance to be had by tweaking the distributor and setting the timing curve more aggresively vs the very lazy stock mechanical timing curve.

351w - Ford racing GT40X 178 cc aluminum heads - Ford racing(crane) 1.7 roller rockers - Comp Cams 280H magnum cam .544" / .544" lift - ARP hardware - hedman longtubes - magnaflow exhaust with X pipe - Duraspark - MSD digital 6al box - MSD TFI coil - optima red top battery - tuff stuff 140 amp alternator - weiand stealth intake  - edelbrock 1406 600 carb  - march pullies and brackets - Be cool fan controller - derale electric fan - FMX trans - motive 4.11 gears - traction lok - lakewood traction bars.                                            

 

 

 

 

 

 

 

 

 

 

 

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All I can say to that is "Amen Brother"! As somebody who used to rebuild distributors for a living, I can relate. Most of our customers considered us "tuning wizards" when it came to that stuff. Especially the marine customers. Glad to hear you found some new power and driveability.

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Distributor tuning is becoming a lost art, in the day of computer programmed cars.

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Question for you guys then: I think I just had my mind blown by another site and I want to confirm that it is correct. I have found a few things on this site that have talked about ported vs manifold vacuum and I am still trying to figure it out. I was under the impression that you needed less timing at idle and more timing at higher RPMs. But this other guy was saying kind of the opposite. That manifold vacuum advance would give more timing at idle and while cruising, but during WOT the mechanical advance would keep the timing at around 36 degrees. This does kind of make sense. But just so I understand correctly. the initial timing will be the only thing affecting the engine while starting the engine correct? because there is no vacuum until it actually gets running. Then during WOT there is also no vacuum, so no advanced timing there. The mechanical advance then, is where I need to build my total timing in order to be around 36 degrees at higher RPM.

 

I did read about a good way to check all this, that I think even a novice like me can figure out. Using the idle speed screw to hold a higher rpm while idling in order to check the where the mechanical advance takes it.

 

What are some other good practices to check all of this?

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Just paint a line on the 36* BTDC mark on the balancer using silver or white paint for good visibilty when checking it with a timing light. I just have a buddy do the throttle control and check rpms while I run the timing light, much easier that way.

351w - Ford racing GT40X 178 cc aluminum heads - Ford racing(crane) 1.7 roller rockers - Comp Cams 280H magnum cam .544" / .544" lift - ARP hardware - hedman longtubes - magnaflow exhaust with X pipe - Duraspark - MSD digital 6al box - MSD TFI coil - optima red top battery - tuff stuff 140 amp alternator - weiand stealth intake  - edelbrock 1406 600 carb  - march pullies and brackets - Be cool fan controller - derale electric fan - FMX trans - motive 4.11 gears - traction lok - lakewood traction bars.                                            

 

 

 

 

 

 

 

 

 

 

 

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Vac advance senses engine load, mechanical advance is rpm specific only. You have vac at idle, none at wot. Is t there a sticker on the cowl? You need 2 people, and you have to put it in gear with the lights on. And dont forget the anti-diesel solenoid!

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I am going to go against the previous post made here and say most cars of this vintage like a bit more initial timing then the spec on the cowl sticker. I like to run alot of initial advance at idle being 16* degrees in my case with the mechanical advance being limited to 20* max all in by 2500 RPM. This gives very good low end as well as mid and top end performance. Vacuum advance tuning is more involved and involves putting the car under a load like pulling hills in high gear to dial in how fast it comes in. It is all a balancing act as carb tune and timing work together. Just my opinion.

351w - Ford racing GT40X 178 cc aluminum heads - Ford racing(crane) 1.7 roller rockers - Comp Cams 280H magnum cam .544" / .544" lift - ARP hardware - hedman longtubes - magnaflow exhaust with X pipe - Duraspark - MSD digital 6al box - MSD TFI coil - optima red top battery - tuff stuff 140 amp alternator - weiand stealth intake  - edelbrock 1406 600 carb  - march pullies and brackets - Be cool fan controller - derale electric fan - FMX trans - motive 4.11 gears - traction lok - lakewood traction bars.                                            

 

 

 

 

 

 

 

 

 

 

 

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Mike i will certainly agree that 2500 rpm is a good spot for all in on a street car, but i am not sure you mean that your initial is 16 and total is 20? because 351's like 32-36 total.


i go with 12 initial and 32 total because i play with the vac advance. my dyno tuner does mostly straight line cars and doesnt believe in vac advance. everything is wot to those guys, but Ford did make the factory vac advance adjustable. unfortunately it is a labor of love with shims, and can be too much for people in areas with elevation changes and when you throw in dramatic temp changes and chokes...lots of confusion. fortunately adjustable vac advances are available for OEM distributors that only require an allen wrench, if you are not running a concours car. even guys like me with MSD distributors can get the adjustable GM style vac advance from Crane for our Distributors in order to reduce "partial throttle detonation" problems. when you set initial too far you can get pinging on partial throttle acceleration, especially with highway gears. Most cans advance too quickly. the factory version allowed you to unscrew the front of the diaphram housing and custom fir the shims under the springs. too much work today. now you can shove an allen wrench in there and adjust the vac advance so that you can get the most efficient burn for performance and fuel economy without risking detonation of our precious museum pieces.

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maybe i misread and you wrote 16 initial +20 for a +36 total...in that case i apologize, +36 total is right in the range i work with.

 

That's the way I read it, too, wwhite. 16 initial + 20 total mechanical advance for a total of 36* max all in. Sometimes posts are best read a couple times. That's what I have to do to make sure I get what is being said. ;)

 

No harm, no foul. And thanks for clarifying. Our bottom line here is supporting all 71 - 73 enthusiasts, in whatever they are envisioning for their 'stangs. I appreciate your knowledge and interaction in the forums.

Doc

Project started 8-7-10

Completed: All new suspension, rebuilt 351C H Code bored .030 over with mild cam and intake, new 3.50 TracLok, custom exhaust system

Current "mini-project": interior upgrade :-/

[button=http://www.7173mustangs.com/forum-garage?filterxt_uid=76]Doc's Garage[/button][button=http://www.7173mustangs.com/thread-1973-mustang-convertible-restoration-and-modification]Doc's Wiki[/button]

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I have noticed the plates in some distributors lie, it will say L12 or L10 or L6 which is suppose to be a range of 24 degrees and 20 degrees , which is suppose to be 12 degrees

when you setup the total timing, you expect say 34-36 total timing, (initial+ no vacuum advance) yet when put the timing light on the balancer and rev the motor you will see 40-54 degrees of timing. I spoke to an engine builder about this and he has seen it also on a lot of re-manufactured distributors he told me that he has had to take distributors apart reweld the timing plates then Cut them out to proper specs, or you can use a piece of vacuum hose over the stoppers to shorten the throw on the distributor timing.

I had to do this.

 

as for my distributor tune.. I had a wicked mid throttle engine ping/detonation, my builder installed a set of mr gasket 2500 rpm springs. in addition to using a piece of vacuum hose to limit max timing, i had to swap out the mr gasket springs for a set of OEM springs(heavy spring for over 2000rpms and the light spring for the instant off idle timing advance. It was a pain setting the play on the heavy spring so the heavy spring would not hold back the timing below 1500. This held back the distributor mid throttle so over 2500rpms i get my total 36 degrees. The rule is you want all mechanical timing in before 3000rpms for performance. in my case my engine would not tolerate this due to low compression due to open chamber heads and piston combination.

 

I also needed to cover up the lean ping with a 50cc accelerator pump and 35 shooter size, along with a 8.5 power valve, this was on a Holley DP 750CFM

i was able to tune the motor from 10HG" to 17 HG" with the changes i made so it made sense to change the power valve. Total HG at idle / 2 +.5 = for your power valve

i didn't have a 9HG power valve so i settled for a 8.5 instead of a 9.5HG valve. I remember i did try and up my Jet size from 70 to 72 but i had a hot start issue and at WOT i seemed to be ok, it was always a mid throttle issue with too much timing too soon causing me problems.

 

So distributor tuning may also involve holding back timing just enough to work.

 

later on i tuned my Vacuum advance, getting some timing back for cruise.

 

It is a lost art but what i found also was sometimes the book rules do not apply and you really need to listen to the engine's sound when you are driving, you can hear a slight miss or ping and know your distributor may need a change or you need more fuel in a certain rpm range.

 

anytime you move away from the stock configuration on a motor, you end up in la la land as far as what works with the parts combo you have.

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c9zx described back in 2011 that the vac advance is adjustable with an allen wrench. same thing i said the other day. the vac advance will cause the mid throttle pinging when you set your initial where the car rens best (16 initial?) so install the adjustable vac advance diaphram and you can eliminate the ping and still set up with 12-16 initial and 32-36 total. you just adjust the vac advance when you are out driving.

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the oem Vacuum advance was a fixed unit not adjustable and you had to use a spark delay adapter. it is a vacuum restrictor basically that retarded the advance a little to deal with mid throttle ping.

 

the later vacuum advance after 73 was adjustable and you could install them on the old distributors, new refrub dist come with the adjustable advance with Allen screw.

 

the vacuum advance will not eliminate a bad ping it is suppose to be a fine adjustment when compensating for say bad gas in the 1970s.. have to remember also even after lead was phased out you had access to 102-110 octane gas at the pump up till the mid 1980s. after that in some areas its hard to find anything over 97 octane now. it was a big factor in mid throttle or off cruise ping. ethanol is a problem as well but save that for another time.

 

now you want the vacuum advance because it will increase mpg at cruise more timing is a good thing at low load or no load.

you want your advance right to the ragged edge of detonation then back off like .5 turn.

 

so first all basic tuning is done with the vacuum advance port plugged you do all tuning on mechanical only.

 

when you get the mechanical right then you get into the vacuum advance when you drive. if on mechanical everything is ok but then the vacuum advance is causing a problem you really have too much mechanical advance and you want to back off and let the vacuum advance take over. this is for the street, for the strip or track its a different situation.

but basically if the vacuum advance is showing the engine going lean at low load off cruise then even on mechanical that engine is close to ping and it should be readjusted. you want to have a safety margin, in a way the advance shows you how big a margin you have.

 

but there are so many factors, spark plug heat range , how efficient your cooling system is all are big players.

 

oh and the size of the exhaust is a big ping issue. back pressure is very important it can cause a mid throttle ping as well. the exhaust back pressure causes a wave inside the engine of reverse air flow that causes the carb to sort of double dip fuel from the transition slots. if the exhaust pipe is too large this wave becomes very small and the double dip effect goes away, this requires you to up the shooter size and the jet size because you are compensating for a fuel loss packing the cylinders.

 

some guys toss on 2.5-3" pipes with headers and start to have massive problems and they don't know why because they were taught if an engine breaths easier and lets out gas (LOL) easier then it must make more power, the truth is again there is a balance and if you play with one area on the motor it ripples down the line sometimes in frustrating ways.

 

that is why we all end up under the hood week after week looking for the perfect adjustment.

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if you play with one area on the motor it ripples down the line sometimes in frustrating ways.

 

Sometimes in exciting ways as well!

2rr7aiv.png

 

Just cruising along minding our own business when BAM!!! The LAWS show up.

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