Timing Method Of Choice

[BLACK MOON]

OK here's a question. What method of timing your car do you prefer?
1. Timing light
2. Vacum gauge
3. By ear
4. Bring it to the shop

Also, after adding headers, electronic ignition and changing carb, what do you guys or girls set your initial timing to for a 327, 300hp.

Thanks

 

[WayneC]

Timing light... 8 degrees @ 600rpm (vacuum advance hose plugged)

 

[Bo Dillingham]

Many years ago, I read an article that said you can find the optimum timing in a small block Chevy with a vacuum gage by turning the distributor in very small and slow increments until it gets to maximum vacuum, then back it off until the vacuum drops 1 inch. I cannot remeber the recommended RPM for this, but I think it was around a grand.

20 or so years ago, when I was a true gearhead, and fooling around with all combinations of heads, cams, etc. I found this method to be very good. I watched and recorded fuel mileage for over a year in my 68 Chevelle, after a slight upgrade in heads, cam, intake, carb, and headers. After a year of turning the distributor in tiny increments and recording the results, I ended up with the same setting as the vacuum gage method that took about 15 minutes.

Bo

P.S. For those of you who have any idea who I am, the body goes back on my 65 Stingray Convert this week. It will sit on top of a totally rebuilt chassis (with all the new technology: this is not a restoration), with a professionally built SB up front. Much, if not all, of the engine fixings came from recommendations made to me by "Tom" in this forum. The frame also sports a removable cross member under the tranny, also from this forum.

Thanks to all.

 

[magicv8]

I try to keep the total at 36. I have an adjustable vacuum advance that is ported off the intake manifold, and with the initial set at 8 or 9 degrees, I dial in performance with the vacuum advance - usually running back and forth between 2 close expressway interchanges.

On my advance can hose connection, I clamped a needle indicator , and the chrome distributor cover has degree markings on a label behind the needle - so I can change the timing depending on octane and altitude as I wander the USA in my Chevrolet (no timing light needed).

A timing light was used to create the label (like Wayne does), and I verify the setting with every set of spark plugs. The seat of the pants tells me the car is pulling hard with no hesitation, and my ear listens for knocking when I get on the loud pedal.

If you don't travel much, you can set the timing for local conditions and buy the same octane at the same gasoline vendors.

 

[JohnZ]

A base timing setting is irrelevant until you've mapped your centrifugal advance curve and know exactly how much is being added, where it starts, and where it stops advancing. Your distributor should add 20-26 degrees - if it does, a base setting of 10 degrees will put you at total timing of 36, which is where most small-blocks are happy. On the other hand, if your distributor has been messed with or has a "smog" curve in it that adds 32 degrees, a 10-degree base setting will give you total timing of 42 degrees, which is a recipe for a meltdown.

Map the existing advance curve first so you know what you've got, and work from there.

 

[BLACK MOON]

Well mine is surging at a sustained rpm, crusing down the hwy. Also alot of spitting and sputtering. If I disconnect the vacum advance the problem seems to go away or if I reduce the initial timing to 0. I think this tells me that the dist. has been messed with and the vacum advance is adding too much advance. I found a guy with a dist. machine and I'm going to have him set it up and tune the car. Any suggestions?

 

[allcoupedup]

Just wanted to add a comment - at cruising RPMs your engine will develop enough vanuum to activate the vacuum advance. The total timing that JohnZ and Magic are referencing is the mechanical or WOT timing (mechanical + initial). At cruise you may see total advance in the mid 50s (mechanical + vacuum + initial).

If you're crusing at 65 MPH and your engine is at 3000 RPM, you may have all the mechanical advance in and the vacuum advance may be in and one of them may be too much.

Only way to figure this out is to map it with a timing light or as you suggested, stick the distributor in a machine.

Sears sells a real nice dial-back timing light for about $60. It's a must have with these old cars. A perfect christmas gift!


Brian

 

[Hib Halverson]

A degreed balancer.

36 deg total adv done at 3000 rpm with a timing light. Initial ends-up about 8-10. I'm real leary of dial-back lights because to make the dial-back feature work, there's a delay factor in the light trigger. Only the most expensive dial-back lights have a delay small enough to not affect overall timing. Best is a light, with quality circuitry such that it will trigger at over 3000 rpm, and a degreed or taped balancer.

I have 8-deg of vac. adv., too.

For that 327, I'd be conservative as the cam has short duration and you've got 60's high-compression.

Start with 32 deg. total with 10 deg initial. If the engine runs well with no detonation, try 34 or 36 but keep your initial around 10 for easy starting. You want the centrifugal all in by 2800-3000 rpm, if possible.

If you run an aggressive curve like that, limit vac. adv. to 8 or 10

 

[magicv8]

Thanks Brian and Hib for adding the stuff I take for granted. My balancer is marked 0-36 and my total is also 36 at 4000 without vacuum advance. Remember - for performance - port the vacuum off the intake.

 

[427/390]

I put a GMPP 502/502 into my 67 last spring and my observations are as follows - I am using an MSD tach drive distrib. and 6AL box, the engine has headers and other than that is exactly as delivered by GMPP:

I have one light and one medium spring in the distributor (all in at like 2,600ish)

The engine seems to run best with 18' initial timing

The engine would probably like 20' initial timing, but I already have the smallest advance stop bushing in the distributor which allows the distributor to add 20' of mechanical advance

With the spring set up and the initial, I am running about 38' of total advance (before any vacuum advance)

The car has 225/60 15 tires and 3:36 rear and Muncie wide ratio and at the drags this summer on a fairly hot evening it ran 12.9 (see www.jcir.com/joe for video)

I am generally happy with the 12.9s and the way it runs, but with John Z and Hib Halverson responding to this post, I thought I could get some additional perspective on areas where I can improve this combo - Thanks in advance - Joe

 

[BLACK MOON]

Well I'm going to start a new post because this problem has gotten worse. This started after rebuilding the motor, removing and cleaning all electrical connections. Well I took it to a shop and low and behold the motor has the wrong timing cover and welded tab on it. The guy puts in heavier springs and corrects the timing. The car runs ok for about 10 minutes and then starts hesitating, pulsing, spitting thru the pipes and what sounds like backfirring. The sidepipes makes this racket sound like gunfire and the pedestrians don't seem to care for it. This occurs at a steady speed or decelerating. Acceleration is strong and no popping. I've changed coil, and plugs but neither helped. I'm using an MSD tach drive dist. and a 6A box. Does the box need to be grounded? Could I have missed a ground when I detailed the engine compartment? We're all scratching our heads and butts trying to figure this one out. Any help would be appreciated.:J :crazy

 

[BLACK MOON]

Well the 'mechanic' made the problem worse so I'm back trying to fix it myself. Changing the spacer to limit the advance before I try recurving.