Technical How Much Timing Do You Have ?

How much total timing
do you run on your SBC ?

Please don’t include vacuum
advance !

also: What RPM is it all in ?

Anyone 40’ ?

 

Timing should not be a set number across the board. It's dependant on engine combination. Either way WOT on pump low 20s will be your sweet spot. If you can get light load/cruise areas in the 40s you'll gain mileage


Edit. Bring it in as quick as possible without ping, probably in the mid to high 2k area

 

36 -38 crank degrees at 3,000 has been a ball park figure for me, but no dyno tests to back me up. Greg

 

Like others have said, it depends on what is in the engine. Probably 32 - 34 total advance would be a good starting point. 40 sounds a little high for a gasoline engine especially if it has 10:1 compression or higher.

On the race car we ran close to 45 initial, but we had fixed advance and were running straight methanol. It would spark knock if you tried to take off too slow, like after a spin out. Never did at race speeds.

 

Should add gasoline fueled.
Prolly cap at 93 as that’s as
high as pump gas gets ?

 

I think it is a common misconception that more timing advance from stock specification equals better performance. This stems from the fact than manufacturers have to market a vehicle that performs well under all climatic conditions - cold, dense air, sea level and sub sea level barometric conditions, dry moisture content, etc. - without encountering detonation when using the fuel specified for the engine. Less harsh conditions will tolerate more spark advance. You may be able to see a small performance gain by advancing spark advance if you are not operating under the most adverse conditions vis-à-vis spark advance.

Igniting the charge before TDC starts the charge burning and building pressure as the piston is rising. This pressure rise generates negative work, but it is necessary because the pressure rise has to be timed to take fullest advantage of the (relatively slow) burning fuel.

What is often overlooked is most performance enhancements actually will increase the burn rate of the charge, thus requiring LESS spark advance than with a stock engine.

Increasing airflow will increase the charge density requiring LESS spark advance.
Ported and polished heads will mean LESS spark advance is needed.
Aftermarket heads with higher flow will mean LESS spark advance is needed.
Increasing compression ratio will mean LESS spark advance is needed.
Adding more or bigger carburetors to reduce pumping losses will mean LESS spark advance is needed.
Adding boost will mean LESS spark advance is needed.

As others have said each combination requires a careful consideration of the amount of spark advance needed. This is best done on an engine dynamometer. Lacking a dyno, drag strip experimentation can establish optimal WOT spark requirements. Mileage measurements can establish optimal part throttle spark requirements.

Not an easy task, but it helps to be clear on why you are changing spark advance. I hope this helps.

 

Re: Type of fuel used

Indeed, some fuels other than pump gas will require more spark advance because they burn more slowly. Here is an ad by SoCal fuels to explain that. Study that if you plan to use a different O/T fuel.

Also, pound-for-pound, many race fuels produce less BTUs per pound but because so much more is used there is a net performance gain.

 

Have been lucky enough to talk to people that designed cylinder heads at Chrysler while I worked there. Combustion chamber shape is also a major player in how much timing is required and engines that have the piston too much below the deck of the block at TDC will tend to detonate. Modern chambers with a heart shape and the spark plug biased towards the exhaust valve will require less advance and will not respond to too much advance beyond this point. These chambers on 5.2L (318) Dodge stockers were called fast burn chambers and responded to fast burn (regular) fuel and unless there were other problems like carbon build up would not detonate easily. Look at the chamber shape on most aftermarket heads and you will see the heart shape.

 

Vortec heads are heartshaped, and use less timing than traditional sbc heads.

 

Pound for pound is the wrong term here! [but yes you're correct]

Most fuels are very similar BTU by weight, but higher octane fuels weigh less by volume.[Hence less BTU per gallon]
This is why higher octane fuels need to have richer air fuel ratios to get a stoichiometric balance.
And lower octane fuels can deliver more MPG and is cheaper.

The longer the hydrocarbon chain ,the heavier the fuel . Diesel packs more energy than gasoline by volume [and can also run very lean]
Also "Ship Bunker Oil" is purchased by weight not volume.

 

40ish in old BBCs, 34ish in old SBCs

in by 1500-2000

 

It all depends on the engine combination, vehicle weight, etc.
I run a locked early tach drive GM distributer with a start retard ignition box, mine is 26* initial and 36* total @ 2200 rpm on 89-91 unleaded

 

Put it on the dyno and find out what it wants. Lippy

 

It is important that people have verified where real TDC is .

 

Piston dome, chamber design, valve angle and cid have a lot to do with it. Ran a small displacement 23 deg sbc with big dome pistons in a Bonneville engine at 52 total. The engine in the avatar is a little bigger 23 deg sbc with better heads and not as much dome and runs best @ 42. Another Bonneville SB2 engine @ 362 ci had very small domes but dyno'ed best at 32. These heads are not 23 deg. All engines were on the dyno.

 

My timing has always been a bit off. If it wasn't, I might have been a millionaire by now!

 

Always used similar #'s as Squirrel in my back-yard tuning, stockish. Higher compression, bump it up some.

 

Has anyone compared HP say 36’ to 40’ on engine dyno (350-406 SBC) ?

 

35 total by 2400
Any more I get pinging

 

Or experiment and road test, repeat as necessary. There is no magic number.

 

Might I axe “What octane gas”

From
Engine Builder Magazine
”Ignition timing trends
As RPM increases, more ignition timing is needed

For higher octane fuels, more timing is needed due to slower flame speed

For large combustion chambers, more ignition timing is needed

For richer fuel mixtures, more timing is needed due to slower flame speed”



Bill Jenkins had a vacuum device on his ‘63 Z-11 to pull a few degrees out of timing Advance when he shifted to 4th gear. I hear we can do this electronically now with MSD AL6 box ?

 

With 87-89-91 and 93
I also have an adjustable vacuum advance that I had to play with and move from ported to vacuum and plug and back around

 

Think I’m running 35 degrees at 3500 (total timing, not with vacuum). Probably watched too many episodes of Engine Masters.

‘62 327 with the original small valve 283 heads on 91 ethanol free gas. Doesn’t ping, seems to like it a lot, not hard to start. Then again, I’ve heard a lot that SBC compression ratios were overstated, is listed as 10.5:1 but based on what I read it’s probably not that high.

edit: also has L79 cam.

 

SBC 355cid, alum heads, 2X4bbl, cam 230-235 @.050 with 110* lobe separation, comp 9.7:1, 2200# roadster, wide ratio 4 speed, and 3.70:1 gear, 93 octane gas. Running 38* total all in by 2200rpm.

 

Just thinking about it, a light car like a A with a SBC and 3.73’s vs a 4500lb car with the same engine and 3.08’s, seems that if the same engine was used in each car, the A could take all the timing in sooner than the heavier car.

I recall going with a buddy to a Speed shop 40+ years ago, he handed them his distributor and the guy asked several questions, I do remember rear ratio, auto or 4 speed, his car, etc.

 

As a couple of guys have already mentioned,it is dependent on combination,several engines including SBC's over the course of their production have been equipped with "slow" and "fast burn" style combustion chambers which will affect how much ignition timing they prefer,as FTF pointed out power enhancing mods will also affect the timing curve.To determine the optimal ignition timing for your engine will entail some trial and error lacking a dyno,using acceleration runs and a G-meter or stopwatch.If you can gain access to a chassis dyno it will speed up the process.

 

Agree with this........the "old" build SBCs (283, 301/302, 327) like lots of advance. I have always used all mechanical, no vacuum distributors....36 degrees all in at 2000 RPM.....with 93 octane gas. very good results. My old school 327/375 HP w/Rochester FI runs best at these settings. Ditto for my son's Hilborn injected 302 motor.

 

That's how I have done it for many years. I have run a mixture of fuels, propane, etc, and never had the "sweet spot" in exactly the same place on the same type of motor. I was once told by an engine rebuilder that the figure quoted in the manual is only a starting point, nothing beats a test run up a hill and a final adjustment with the 9/16" spanner.

 

36 degrees all in by 2400 rpm for distributors I set up for street and drags . I ran 38 degrees at 2400 for my dirt track stock car but that was with c-12 race fuel

 

My Caddy mill in the 37 Ford I run total of 33 degrees all in by 2500 rpm. When I was on alky I ran 38 degrees .