SBC Ignition Tuning

I have an 350 small block with an HEI ignition. I quickly found out that the stock timing plate was not going to suffice as it was either not matched to the balancer or my motor truly needs more than 10* of initial advance. Regardless I stopped trying to set timing with the light and marks and with the vacuum method, in which you increase timing at idle to achieve the highest vacuum then back it of a couple of degrees. I immediately noticed positive results with how the car was running and eliminated some of the problems I was having with snapping the throttle open. When I first started this process the gauge was reading under 10 and now I am around 15in at idle, the car drives and pulls great. The thing is that the starter now has a hard time turning the engine over which is a classic sign of too much initial advance. Do any of you small block tuning gurus have tips on what direction I should be going here? The car runs great and does not ping but is hard to turn over. 

Also wanted to note that once the engine does start to turn over quicly it fires right up. 

Running HEI, Holley 650, no vac advance hooked up right now, and I do have a mild cam. 

Thanks

If you pull the coil wire and turn it over, will it spin right up? 

(Just trying to eliminate timing as the culprit)

You may have a mismatched timing tab and balancer. Here is some info on SBC timing marks, may help tell if yours is off. 

Timing marks

It is common for a SBC to want more than 10 degrees of initial timing, especially if modified. 

Twisted46 said:

Running HEI, Holley 650, no vac advance hooked up right now, and I do have a mild cam. 

 

Thanks

How does it behave if you use the same timing method, but leave the vacuum advance hooked up (including when setting it) so the timing is a little less advanced when cranking?

It won’t be a big change at idle, but the small change may be enough to get things spinning easier. 

Most of the ones I throw together end up at 12-13 initial with advance hose clamped off.  

Using a dial back timing light, set the max mechanical advance where it needs to be for you (32* should be a safe start). Hook your vacuum advance up on the base plate of the carb, not ported vacuum. Initial timing is mostly irrelevant, maximum is what's important. 

First, fix your timing marks.  All this "set the timing by ear/vacuum/plug colour" E36 M3 went away a very, very long time ago, and it was performed by grizzled veterans.

Wait... before you get too involved in checking timing, there are a few zillion reasons why this could be happening.  First, many of the SBCs of the lower-compression era called for 14-17 initial, and if you've added more cam duration, you can expect initial advance to be closer to 20.

Post specs.  I have build chevys with mismatched cams and compression and have gone as far as locking the mechanical at 34 initial.  Head chamber design, compression, cam, manual vs automatic, ported vs manifold vac... tons of factors here to consider.

ross2004 said:

Using a dial back timing light, set the max mechanical advance where it needs to be for you (32* should be a safe start). Hook your vacuum advance up on the base plate of the carb, not ported vacuum. Initial timing is mostly irrelevant, maximum is what's important. 

This times 1000.  Initial vacuum is only used as a benchmark because the engineering of the dizzy makes the proper curve in the rest of the load range.  Its just a little hard to set total timing on the highway at WOT and redline.  The actual amount of initial timing is pretty inconsequential.

Most hei Dizzy's will not allow a 25* advance,  but 10 to 12 degrees base is Taxing a Starter or Just Starting too , a Base plate with a Longer Adv,Stop Groove will give you Low initial and High Max.

RPM 650-750 I Don't know Cam Specs. Vacuum should as high as you can see at this rpm ,10* should be enough  adjust Idle Jets NOT Timing,

Most hei Dizzy's will not allow a 25* advance,  but 10 to 12 degrees base is Taxing a Starter or Just Starting too , a Base plate with a Longer Adv,Stop Groove will give you Low initial and High Max.

RPM 650-750 I Don't know Cam Specs. Vacuum should as high as you can see at this rpm ,10* should be enough  adjust Idle Jets for Vacuum NOT Timing,

HEIs will allow whatever advance you want.  If the dizzy itself doesn't turn far enough, just move the wires around to the next post.  That's an easy way to get 50 degrees, then back the dizzy off as far as you can to take out about 25-30.

There is zero way of knowing if 10-12 is taxing a starter since we don't know the other hundreds of factors going on in there.  As I said, I have locked them at 34 to cover for a mismatched cam and compression until I got around to swapping heads.  It didn't tax the starter at all.  Initial timing is only a means of using a baseline for proper advance everywhere else, but initial timing makes very little difference.  As long as it isn't kicking back on the starter and as long as it starts, initial timing could be anywhere from 4 degrees to 25 degrees or more depending on the combination.

Okay cool it's not just me. I also have a 350 with HEI and noticed the same thing. If I set timing using the stock marks to 6 or 8 bTDC like the sticker in the engine bay says to, it runs like a turd in all conditions. But if I keep advancing until it actually drives great, the timing light says I'm well past the timing marks, probably 10 to 15 bTDC.

No idea on the specs of my engine. 72 El Camino (2-barrel originally) with a GM 350 crate replacement, whatever cam it came with, 550 CFM, and I added the HEI distributor.

Starts just fine to me.

My 357 has 10.25:1 compression and the distributor is locked at 38 degrees.  It starts right up with no problems.  I believe you need to verify that your timing pointer is correct.

If you have an 'advance' timing light with a knob you only need to make one good timing mark to point the gun at. You don't need a whole scale or range of marks to go off of. 

It's Odd to me that Gear heads would not Think a Properly working Dizzy Is Nesessary . yes you Can 'LOCK down the Dizzy but ours started up at 12* and could Pull Over 38* above 4  grand, but we stopped it at 36*  To keep the EGT down , our engines ran 7200 rpm lap after Reliable Lap. Never Blew Up A Race Engine

See you at the Challenge!

      Edited Text   for the Masses

I do not have a set back timing light but I guess I need to quit farting around and just get one. The expense of this project does not warrant cheaping out on a necessary tuning tool. And the problem is that my timing bracket (probably from a truck) only goes up to 10* and I am well past that. 

I know that total timing is WAY more important than initial/idle but I would not think that it would be happy idling and reving out at a point where it becomes hard to start. 

Motor specs:

355 block with dished pistons

416 (305) heads with some P&P work but nothing crazy. 

compression should be around 9.5 - 10 

Cam:

My daily is a 0.020" over 350, with ported 305 heads, flat-tops, steel shim headgasket, and 231°/0.470"/108LSA. It idles at 8inHg in gear, and cranking pressure is 180psi. Should be a tick under 11:1 compression.

I am pretty sure the base timing is somewhere around 13° to 18°, 35° total, and I run full manifold vacuum advance. Honestly, I make sure I am getting full advance where I want it, and base is where base is.  Anytime I check timing, it's up to and past 3000rpm, never idle (other than idle curiosity - bwahahahahaha).

I also run a modern gear-reduction starter from a late 90's Vortec , and a 1000CCA batter, which help in cranking immensely.

Get it spinning first, then turn on the ignition. It will fire up with 34° spark.

A properly working dizzy is completely necessary, its just that initial/idle timing is not the important part.

Think of it like a suspension.  Let's say you have a stock suspension.  A stock alignment setting is fine.  Set it to zero camber, 4* positive caster, and 1/16" toe in.  Now lower it 4 inches and reset your alignment to the same spec.  The rest of the geometry is completely different and may call for different "initial" alignment in order for the suspension to perform in the correct way during its range of travel.

Once you change things (like a larger cam with no other changes) you still might need 34 total, but it idles poorly.  There is nothing that says you HAVE TO keep the same initial timing.  Maybe you need to take 4 degrees out of the mechanical advance range and then advance 4 degrees initial.  You're still at 34 total, but the reduced cylinder pressures mean that it needs more initial advance to run properly at lower loads.

Twisted46 said:

I do not have a set back timing light but I guess I need to quit farting around and just get one. The expense of this project does not warrant cheaping out on a necessary tuning tool. And the problem is that my timing bracket (probably from a truck) only goes up to 10* and I am well past that. 

I know that total timing is WAY more important than initial/idle but I would not think that it would be happy idling and reving out at a point where it becomes hard to start. 

 

Motor specs:

355 block with dished pistons

416 (305) heads with some P&P work but nothing crazy. 

compression should be around 9.5 - 10 

Cam:

 

As a baseline, try a bunch of starts and keep advancing by 2 degrees until you get kickback on the starter.  Then you'll know.  My guess is that you'll get to 24 or more before you get kickback.

I put some advance limiters in mine, so I could increase the base timing without also increasing the full advance.

I'm not so confident on what I posted for my base timing. In my notes I have various spring and weight combinations I've tried, and many are between 12 and 14° base. Some were 18° base.

And then there was the time I had to pull the distributor completely apart and re-weld the advance pins because they came apart.

I think last time I checked, at 35° full advance I was running 32° timing at idle which includes full vacuum advance at idle.

I agree it doesn't sound terribly abnormal. We used to run our stock cars around 18° base mid 30's total. 

Verifying timing marks during assembly was something I learned was necessary, the hard way, using parts from dozens of different engines etc. 

I'd confirm TDC with a piece of wire in a spark plug hole while turning the engine by hand, watching the timing marks as the piston comes up and begins to come back down. 

I've seen many dampeners that have spun on the rubber too, so there's lots of opportunities for timing marks to be incorrect. 

When I built my 350, I degreed the cam and found the NEW harmonic balancer had the timing marks off by 1°.

I can't say I'd have ever noticed 1° LOL. 

Realistically though, IMO repeatability is more important than 2-3° accuracy in a performance application. Timing will vary anyway. It really doesn't matter if it's actually 16° or 17° what matters is being able to return to a baseline if the distributor has to come out for some reason. 

Edit: Or if it changed since the last time you checked it with the same references.