Does this timing curve seem okay....

[beanhead]

So I've been doing some adjusting on my recently-started 440. It's .040 over, with unmodified edelbrock RPM heads and intake, a speed demon 850 carb, comp XE274 cam (.488/.491 lift, 230/236 @ .050 duration, 110 lobe sep.)..right around 10 to 1 (maybe +/- only a couple of decimal points but haven't done an actual comp check yet) 1-7/8 headers out 2-1/2 pipes with dmax super turbos...using the MP orange box/elec. distributor kit I got about 10 or so years ago, autolite AR3933 (non-resistor version of the 3924) My vacuum gauge took a crap so I'm just using the timing light for now. I started the motor with about 16 degrees initial, I've advanced it to the point the rpm just starts to flatten out and I'm at 25 initial, and it kicks up after I increase throttle and tops out at 37 degrees, around 2500 or so...seems like a lot of initial to me, but it doesn't ping or anything and the exhaust temps went down a bit...now, of course this is all in park because I can't drive it yet, which is when it will be fully dialed in...I then set the carb idle stuff and that seems to be real close too...I know every engine likes different settings I just don't really have experience with these higher flowing aluminum heads and this cam, which isn't all that wild or anything but it's definitely a little choppier than stock. Also of note, while I expected it to be a small adventure to start it with no choke, especially this cooler time of year, it sometimes likes to get a small fire going in the top of the carb, which I promptly smother with a wet rag...it might pop once but not real bad while trying to start it, I thought this was usually a symptom of too much advance but it did it when I had it back down around 15 too...and like I said it seems like it wants the added advance when it's running...I've dealt with mostly stock or only slightly hopped up stock stuff over the years so I thank you all for your advice!

 

[AR67GTX]

If I understand you only have 12 crank degrees mechanical (centrifugal) advance in your distributor. That is really low - has it been modified for that?

I'm surprised it will crank over with 25 degrees initial advance. That is with any vacuum advance plugged? Are you determining it with a dial back timing light? Sometimes if you are using really light weight springs you will have mechanical advance partly in at idle and when you are setting the initial timing with a light - part of it is your mechanical that is partly coming in. In other words, 8 or 10 degrees of what you think are initial timing is actually part of the centrifugal advance you are reading. You can wrap the weights with rubber bands to hold them in and verify your real initial timing figure if you think this could be a possibility.

In any event, 37 degrees total initial + mechanical (vacuum advance plugged) should not be too much advance. I think anywhere around 35 to 37 degrees is pretty safe.

FWIW I have 16 degrees initial timing on my stock 440 with 20 crank degrees mechanical advance. But your engine has a lot of higher performance parts on it.

 

[beanhead]

If I understand you only have 12 crank degrees mechanical (centrifugal) advance in your distributor. That is really low - has it been modified for that?

I'm surprised it will crank over with 25 degrees initial advance. That is with any vacuum advance plugged? Are you determining it with a dial back timing light? Sometimes if you are using really light weight springs you will have mechanical advance partly in at idle and when you are setting the initial timing with a light - part of it is your mechanical that is partly coming in. In other words, 8 or 10 degrees of what you think are initial timing is actually part of the centrifugal advance you are reading. You can wrap the weights with rubber bands to hold them in and verify your real initial timing figure if you think this could be a possibility.

In any event, 37 degrees total initial + mechanical (vacuum advance plugged) should not be too much advance. I think anywhere around 35 to 37 degrees is pretty safe.

FWIW I have 16 degrees initial timing on my stock 440 with 20 crank degrees mechanical advance. But your engine has a lot of higher performance parts on it.

Thanks yes the vacuum advance is disconnected and plugged, I will try wrapping the springs to get a true reading...the dist is out-of-the-box and I thought it wasn't kicking in the mech. advance until the rev's got up around 1500 or so but I will double check that too. It seems to crank easy enough and doesn't kick back, so maybe it is a mix of the mech. at idle...using a standard light btw.

 

[moparnation74]

Wonderful world of cams......

 

[IQ52]

16-20 degrees initial, more likely 20. Generally 25 would be excessive for that camshaft.

 

[beanhead]

16-20 degrees initial, more likely 20. Generally 25 would be excessive for that camshaft.

This is what I was kinda thinking too...however the engine rpm drops at that degree, I was always under the impression that you wanted the timing advanced enough to level the RPMs out so that you were burning all the fuel in the cylinders? again, this engine is a little different animal than what I'm used to so I am open minded at this point..

 

[lewtot184]

that distributor should have a 13 degree plate (26 on the crank) and 12 degrees initial would be 38 total. light springs would let the distributor idle at more than 12 degrees. i have a little different combo but same heads and 9.75:1 compression. i limit my total to 36-37 degrees, use a 9 degree plate, light primary spring with a semi-light secondary. initial is 18 degrees but idle is about 25 degrees due to the light spring letting the centrifugal advance early. this set-up seems to work very well in my combo. if you have a tight quench between the piston and head a lot of total timing isn't always needed.

 

[beanhead]

that distributor should have a 13 degree plate (26 on the crank) and 12 degrees initial would be 38 total. light springs would let the distributor idle at more than 12 degrees. i have a little different combo but same heads and 9.75:1 compression. i limit my total to 36-37 degrees, use a 9 degree plate, light primary spring with a semi-light secondary. initial is 18 degrees but idle is about 25 degrees due to the light spring letting the centrifugal advance early. this set-up seems to work very well in my combo. if you have a tight quench between the piston and head a lot of total timing isn't always needed.

Oh, I always considered initial and idle the same? Maybe I've had that screwed up...

 

[moper]

A few comments...
Your engine is not the same as everyone elses'. Even when the exact same parts are used. So these are just starting points. The real perfect setup is tested for and discovered through your efforts. I like between 12-18° initial. I am of the opinion that more initial can be a problem, and many use it as a crutch for not knowing how to really tune a carb. I also believe in vacuum advances on any street driven car (primary use). Again - if the first step is disconnecting, you probably don't know what they do or how they do it, or how to adjust it. Centrifugal is pretty easy... It's the filler between those two...lol. It's also the harder one to dial in on an MP or factory type distributor. Some MPs have adjustable mechanical advance, some you need to play with more. The combination of head material, chamber shape and size, gasket, piston design, rod and stroke package, and fuel type all go into the right timing curve. You don't have all the specifics, and the car can;t be driven, so its just an educated guess.
16° of initial, 18° centrifugal, and slow the centrifugal to start at 1600 and end at 3K. Hook the vacuum advance to ported vacuum, and adjust it to remove any surge at cruise.
BTW - you should rev the engine up to 4500-5K to really see what the ignition does. The MP orange bix pulls out timing above 4K IIRC. It's supposed to. If you ditch int and run the Standard Ignition (brand) stock replacement ECU you will have the same spark power, and no timing changes put in by the box. Also make sure your coil is getting good voltage on the positive side. Sometimes poor splices and old connections lead to weak voltage to the coil.

 

[beanhead]

A few comments...
Your engine is not the same as everyone elses'. Even when the exact same parts are used. So these are just starting points. The real perfect setup is tested for and discovered through your efforts. I like between 12-18° initial. I am of the opinion that more initial can be a problem, and many use it as a crutch for not knowing how to really tune a carb. I also believe in vacuum advances on any street driven car (primary use). Again - if the first step is disconnecting, you probably don't know what they do or how they do it, or how to adjust it. Centrifugal is pretty easy... It's the filler between those two...lol. It's also the harder one to dial in on an MP or factory type distributor. Some MPs have adjustable mechanical advance, some you need to play with more. The combination of head material, chamber shape and size, gasket, piston design, rod and stroke package, and fuel type all go into the right timing curve. You don't have all the specifics, and the car can;t be driven, so its just an educated guess.
16° of initial, 18° centrifugal, and slow the centrifugal to start at 1600 and end at 3K. Hook the vacuum advance to ported vacuum, and adjust it to remove any surge at cruise.
BTW - you should rev the engine up to 4500-5K to really see what the ignition does. The MP orange bix pulls out timing above 4K IIRC. It's supposed to. If you ditch int and run the Standard Ignition (brand) stock replacement ECU you will have the same spark power, and no timing changes put in by the box. Also make sure your coil is getting good voltage on the positive side. Sometimes poor splices and old connections lead to weak voltage to the coil.

Ok thanks, I do realize since I can't drive it I'm just ballparking it for now. I do plan on using the vacuum advance, I've got the dist that adjusts with the tiny allen wrench through the port. It does kinda suck not being able to run it up through the gears to really set it up, I know I will be able to get timing and the carb locked in at that point, for now I just want it close enough not to hurt it when I fire it up and run it for a bit. Thank you also for the ignition box info, I didn't know these MP boxes altered the timing...

 

[cdr]

on my 512 I run 24 in,34 total + 7 on ported vac, but I guess I dont know how to tune my Carb LMAO!!!

 

[beanhead]

on my 512 I run 24 in,34 total + 7 on ported vac, but I guess I dont know how to tune my Carb LMAO!!!

I bet that charger is a beast... What kind of distributor are you using

 

[cdr]

I bet that charger is a beast... What kind of distributor are you using

I have the Firecore with module inside.