timing ????

[67 coronet]

was wondering what you guys are using for initial and full advance settings on your rides.running a 590 lift purple shaft in a 30 over 383.
cant seem to get the advance till hard to start,then back off trick to work well.
running 20 degrees advance at the moment and runs ok,but still seems like it could be better.

 

[Cranky]

The whole combination dictates what an engine likes and especially compression ratio. The 509 cam will bleed off cylinder pressure in the lower rpm ranges and if your static compression is low it probably will like even more initial than 20! For full advance, experimentation works or put it on a dyno.....btw, what is your cranking PSI?

 

[67 coronet]

ya,thats kinda the same thing i figured cranky.comp ratio is about 9.8 to 1 or so.its a race motor i adapted to run on the street.

 

[Cranky]

If your cranking PSI is around 140 or less, it might like more than 20 initial. I've had the 'displeasure' of tuning on two different engines that were 8-1 (one was less) that had lumpy cams and they ended up being right around 50 total. Don't remember what the initial was exactly but it was up there but anything less than 20 made them really lazy off the line. It surprised me enough that I had to check my timing light with two others! The one with less than 8-1 was a 72 318 with 360 heads. It ended up running 13.50 @ 102 in a 72 Demon with that setting. The other was a 440 in a 67 Coronet that we never could get to hook up but it ran some low 13's @ around 108. The teen had traction but with a stock converter, it wouldn't light up until 3000 rpm. Kinda figure the cam in that one was a bit retarded too.

 

[67 coronet]

thats a dam good idea,gonna check psi on wed to get a better idea,thanx.
its in a 67 coronet with 3800 art carr stall,victor manifold,457 spool.heads are a bit restrictive right now(minor smoothing and over size valves).they may change in the short future.

 

[Funship32]

If your cranking PSI is around 140 or less, it might like more than 20 initial. I've had the 'displeasure' of tuning on two different engines that were 8-1 (one was less) that had lumpy cams and they ended up being right around 50 total.

Holy cow, Cranky! 20 initial and 50 total timing? Isn't that a lot on both accounts? Not to argue 'cause they took what they needed but I am just askin' so I can perhaps learn a thing or possibly 2.

 

[Cranky]

Yup....I know it sounds crazy. On the 440, I personally checked it out for true TDC and checked the cam timing too. That car had a 3000 stall and 3.91 gears and moved pretty dman good from a 25 mph roll in 2nd gear and traction on the street wasn't there at all even if it was launched from an idle. If you nailed it in 2nd at 35 mph, it would light em up. Figured with that much timing they would be burning off the spark plug straps but neither one ever did that. On the teen, I had no idea if TDC was true or not nor where the cam was set however the exhaust note was pretty loud at idle and driving around the pits and that's usually a good indicator the cam is on the retarded side but it did run up to 6200 rpm before going flat. The guy still owns the car and maybe one day I can find out where it's set.....

 

[Funship32]

Wow. Well thanks for that info! I'm trying to solve for factor "X" on my 383 and perhaps that is the ticket as I'm running 12 BTDC and a total of about 38 which is all in by about 2400 RPM. Yet she just doesn't run the way I like from idle so maybe I need MORE timing....

 

[2059]

For what it's worth.. Set my initial at ~24* and dogged the mechanical advance to give it about 10* more for a total of ~34*. No vacuum. 9.5:1 and ~120lbs pressure (compression test) installed a "hot switch" so I can throw fire to it after the assy is rotating. Don't race it but it seems to like the settings.

 

[383man]

As said the combo makes a big difference as many hot builds will run 15 to 25 initial and some run locked out dist at about 32 to 36. Many like to set the initial to the highest vacum they get at idle but so much depends on the build like comp , quench , aluminum heads , cam and so on. My 493 has aluminum heads and 10.6 comp with quench (.045). I actually set my Mallory dist up with quick advance all in by 1800 rpm and then I set my total to 37. It idles at about 24 initial and has 37 total all in by 1800 and I have no vacum advance. That works very well for me and my combo as I run a solid flat tappet with 264 and 270 @ .050 and .585 and .592 lift. But I use 1.6 rockers and my intake valve closes at 58 degrees ABDC at .050 as its a custom grind and I told Dwayne Porter who did my cam I want to keep the cyl pressure below 190 so I can run on 92 pump which it does with no ping at all. I have found the old basic hotrod eng setup of about 10 to 12 initial and 38 total will not work the best on many combo's. Many are giving way more initial and less mech to still have 34 to 38 total but use alot more initial if the eng is built right to take the initial timing. The total all over combo has so much to do with the timing curve as there is no set in stone rule. Ron

 

[2059]

67, There a ton of discussions here about timing. Just search "timing" in general, engine and ignition forums.

I went through a similar learning process about two months ago. As stated, there is no set-in-stone rule however; there is a lot of good advice regarding starting points and you'll need to play around with it a little. One of the most "discussed" topics is the need for and how to signal vacuum advance. After I understood (relearned) why it's there and how it works, I removed it. Not saying you should, just saying understand your set-up. Keep us posted.

 

[GTX MATT]

If you're running the 590 purpleshaft just lock the timing out (34-38 degrees), it will start and idle better. I'm running 252/260 duration @ .050 in a 10.5:1 440, stock starter and no issues locked at 34. It won't fight the starter with that much duration. I locked the timing because 24-28 initial still didn't idle as good and I had to idle the engine around 1050-1100 rpm. My car cranks once and is running and my cam is much smaller than yours, and idles strong at 900-950 rpm.