Timing advance???

[747mopar]

I'm ready to put my 456 on the road and will be tuning it this weekend. As of now it idles great, pulls 17 lbs of vac, runs cool, has great throttle response but blubbers just a bit at part throttle. This weekend I plan on checking float level, timing, fuel pressure etc. Carb is an 870 holley vac sec that is running the factory setup at this point and the ignition is a 6AL box with a mechanical advance distributor. My big question is what is the best method of getting the full advance set without a trip to the strip or a dyno.

 

[Hemi Rebel]

A dial back Timing light and a tach is all you need to set the ignition timing.

 

[747mopar]

A dial back Timing light and a tach is all you need to set the ignition timing.

I guess I should be more clear. I'm pretty happy with my initial timing but being new to the mechanical distributors just wanted to know what was the best method of checking the full advance (What determines the rpm at which it should be all in)?

 

[Mopars & Missiles]

.........(What determines the rpm at which it should be all in)?

The mechanical advance springs and counterweights. Counterweights are pretty much fixed, so you change springs to adjust. Lighter springs = earlier advance and vice versa.

How MUCH mechanical advance is a different adjustment. Some distributors have an adjustable stop on the advance plate, others just have slots that you have to tweak with a file and/or a welder.

Also, FULL advance includes vacuum advance. Street driven cars SHOULD always have vacuum advance as well as mechanical.

 

[Meep-Meep]

I guess I should be more clear. I'm pretty happy with my initial timing but being new to the mechanical distributors just wanted to know what was the best method of checking the full advance (What determines the rpm at which it should be all in)?

I'd say your cam choice and over all engine design is a starting point. To get the most out of an engine you basically want to be on the verge of detonation, but finding that spot takes a lot of trial and error and can be dangerous. Generally speaking you want 36-38 deg total all in by 2500 RPM or sooner in some cases. If your engine makes a lot of cylinder pressure then a slower curve may be required. If you have a full race engine you will end up locking the dizzy at full advance at idle. Agreed that street cars should always have a vac advance that adds about 10 deg under light load conditions (ported port).

 

[brasil]

@ meep meep you are talking about 10 degrees of advance from the vacuumcanister.... you you mean crank deg. or distributor deg. ? I am asking beause you wrote 36-38 deg. total ( which are crank deg. right ? )


Greetings Juergen

 

[Xp29h]

Just a thought..I may be way off but I fixed a little burp in throttle response with a different size shooter in the carb. I had set my timing, initial and all in and still couldn't get rid of that pause when I stepped on it. I changed a shooter to one size larger giving just a little more shot of fuel and it was gone. Hope it helps. Just a thought..

 

[Meep-Meep]

@ meep meep you are talking about 10 degrees of advance from the vacuumcanister.... you you mean crank deg. or distributor deg. ? I am asking beause you wrote 36-38 deg. total ( which are crank deg. right ? )


Greetings Juergen

Yes, 10 additional deg from the vac canister. The idea of using the ported port for the vac canister is to make it operate only under part throttle conditions. The ported port also ensures (supposed to anyway) that you have no signal at WOT, thereby not providing additional advance when you don't want it. Of course it is best to test this under actual load conditions so Tee in a sensitive vacuum gauge in the ported line and floor it. To quote Bill Cosby, find "any old side street" and have someone observe the gauge while your foot is in the carburetor and you are at max RPM. You should have no significant vacuum signal. Try not to run over stray dogs and old ladies while performing your supervised acceleration trial. If you see any vac signal record the number then use a hand vac pump and actuate the canister at idle to see if it moves at the recorded vac level. If you have part throttle pinging then you need to dial back your vac advance canister. Your initial timing setting should produce a nice idle that is crisp with equally crisp throttle response. Tip in should also be smooth. My 440 is at 10.1:1 with 190 PSI and I'm running 12 BTDC. The throttle response is like a motorcycle but that is due to good port velocity and a mild cam. Total timing is 36 deg. Vac advance adds about 8 if I recall.

 

[Mopars & Missiles]

Sample of how one of mine is setup

 

[brasil]

That curve looks interesting... all in @ 1800 rpm...?? I ve read about this fast curve in a JENSEN Forum , while I was searching for the "Right Curve " for my 440 HP Engine from 1969.... The Jensen guys in England use a similar curve... around 10-12 deg @ idle...
and 36 deg @ 1800 -1900 rpm.... plus the vacuum advance..

I am thinking to chance my curve to this setup...also, but I have some fear, because the curve is so ...."agressive "... doesn´t that hurt the main and rod bearings while accelerating ?

@ meep meep so with my 10 deg. MSD vacuum canister I can only get more or less 46-48 deg of advance totally ?

Greetings Juergen

 

[Mopars & Missiles]

......but I have some fear, because the curve is so ...."agressive "... doesn´t that hurt the main and rod bearings while accelerating ?

Aggressive = FAST
Timid = LAST

The only things that get 'HURT' while I'm accelerating are my rear tires, and the feelings of the Ford and Chevy guys behind me.

:3gears:

 

[Meep-Meep]

That curve looks interesting... all in @ 1800 rpm...?? I ve read about this fast curve in a JENSEN Forum , while I was searching for the "Right Curve " for my 440 HP Engine from 1969.... The Jensen guys in England use a similar curve... around 10-12 deg @ idle...
and 36 deg @ 1800 -1900 rpm.... plus the vacuum advance..

I am thinking to chance my curve to this setup...also, but I have some fear, because the curve is so ...."agressive "... doesn´t that hurt the main and rod bearings while accelerating ?

@ meep meep so with my 10 deg. MSD vacuum canister I can only get more or less 46-48 deg of advance totally ?

Greetings Juergen

Should only be that much during light load cruise. True total advance at max RPM under load needs to be about 38 deg max.

 

[Mopars & Missiles]

There seems to be some confusion on this subject, so here is the text straight from MOPAR PERFORMANCE. You can read it and come to your own conclusions. I thought this was pretty common knowledge over the last 15-20 years.

This procedure assumes you are starting with one of their MP distributors that already has the correct rate and amount of mechanical advance built in. Therefore they don't state specifically a value for Initial advance, and they go right into setting full mechanical advance instead. You should double check YOUR distributor to verify that the mechanical advance mechanism is properly curved for rate and amount of advance for best performance results.

Initial plus mechanical is shown in the table and also TOTAL advance (initial, plus mechanical, plus vacuum) is also shown in this document. Hope this helps.

 

[brasil]

Hello Mopar&Missiles

I have the same information about the timing of a Mopar distirbutor..... 38 deg all in... 54 deg with vacuum ... so in this d´case I need to switch over to a canister that can be "tuned" the OEM MSD canister is not adjustible...

According to the mopar Instructions the 38 deg should be reached within 2000 rpm.... so I have to
change my distributor set up.... to your set up.

Greetings Juergen

 

[dragrazor]

While, possibly not optimum and certainly can be checked with timing light and tach afterwards. One method is to tune via driving, accelerate while going up steep long uphill section of hi way while in top gear, but fast enough not to need to gear down, advance the timing till pings, then back off till quits. If cranks freely and easily when at operating temp chances are very much right on what the engines likes........

 

[Mopars & Missiles]

Hello Mopar&Missiles

I have the same information about the timing of a Mopar distirbutor..... 38 deg all in... 54 deg with vacuum ... so in this d´case I need to switch over to a canister that can be "tuned" the OEM MSD canister is not adjustible...

According to the mopar Instructions the 38 deg should be reached within 2000 rpm.... so I have to
change my distributor set up.... to your set up.

Greetings Juergen

Yes, if you can get to 50-54 degrees with vacuum you will be fine. I haven't worked with MSD before, so I don't know if they have interchangeable vacuum canisters to give you more vacuum advance. Sounds like you are on the right track, Good Luck!

 

[brasil]

i will change the canister.... still have an adjustible one here .... if it´s done I will report here

Greetings Juergen

 

[747mopar]

Keep in mind I have no vacuum advance, straight mechanical. Thanks guys

 

[Mopars & Missiles]

Keep in mind I have no vacuum advance, straight mechanical. Thanks guys

747, just do the initial and mechanical setup then, that's all you can do without switching out distributors. With about 36-38 degrees mechanical, you will still have all the performance benefits for acceleration, you just won't get the economy benefits while highway cruising that you would have if you were able to add vacuum advance to get in the 50-54 degree advance range for cruise.

 

[747mopar]

747, just do the initial and mechanical setup then, that's all you can do without switching out distributors. With about 36-38 degrees mechanical, you will still have all the performance benefits for acceleration, you just won't get the economy benefits while highway cruising that you would have if you were able to add vacuum advance to get in the 50-54 degree advance range for cruise.

Thanks Missile, I'll look into a vacuum distributor upgrade in the near future. When should it be all in? My setup is built to make it's power in the 1,500-6,000 rpm range.