Max

I have been tunning to get the most out of my new carb set up. Now that I have that dialed in I'm looking for a little more power by fine tunning the ignition.

My distributor has 14* mechanical advance in by 2000 rpm
and 10* of vaccum advance.

I was running 16* initial advance for a total of 40* advance

I just bumped it up to 20* initial advance for a total of 44* advance and it seems to run even better.

It was originally a LO3 engine and I suppose that the compression is fairly low and I always use at least 92 octane gas.

There doesn't seem to be any problem with detonation. I have run it at WOT up a steep hill to almost 5,000 PM and it doesn't skip a beat.

Is it likely that my combination works best with so much advance?

Should I go even farther?

IHI

iTrader: (1)

As you read more of these posts you'll keep hearing that every motor likes different things and such is the case with your car. I have my 355 set at 17 intial and 32 full in at 3K, anymore and it'll desiel like a bitch. My buddies 350 malibu has his set at 40 degree all in at 2500rpm, so if that works for your runner hard.

Jester

Thats a little high but not unheard of. If you can run it without knocking..great. 14 degrees mechanical isn't much tho..what kind of wieght set are you using? Most sets have 20-22 degrees. If you could get that, even in a little later, then drop the initial a bit to keep the same total you'd be better off.


Also, there is nothing wrong with running high octane and that much timing, but if you'd like to save yourself a little cash you can probably try 87 or 89 octane and drop your curve down a bit without losing much power.

F-BIRD'88

If a sbc needs more than 36/38 deg total advance n/c vacuum adv. @ high rpm I'd suspect something wrong with my tuning method. Your balancer or timing tab may be out of wack.
Most every normal sbc needs 32 to 36 deg advance to make max power. Increasing initial timing always makes it feel more snappy
but can be decieving. Try to determine why yours wants more than everyone else in the world.
Some thing is wrong.

89formula#1

hey guys how do u figure out how much timing u have? i don't have a timing gun but i am gettin one and i am curious how u know this?

IHI

iTrader: (1)

If you get a timing light make sure to buy an adjustable one-little more but 10X better than the old gun. when you first start your motor, let it warm up, set the gun at zero degrees and slowly turn the **** till the marker on the harmonic balancer matches the notch on the timing chain cover, that's your intial timing. Then have a friend bring the motor up to usually 2500 or 3000 rpm, have the timing light pre-set to the desired timing and then turn the distributor till the marks line up again, let it idle down and re-check your intial timing, it will be different if you change the total advance, but that is ultimately what you want to base the engines timing on.

ShaneBuss2

I always get confused on this. At WOT, doesnt your vacuum go to 0?

The timing you get measuring your car at 3000 rpms in your driveway would definitely differ from 3000rpms wot in gear down the highway..??

someone help me out..

IHI

iTrader: (1)

My distributor is all mechanical-NO vaccum canister so centrifical force advances mine, it was spun balanced and tested to insure this. All my other cars that had vaccum canisters, I unplugged the hose going to the canister and plged the hose end, ran the motor till about 2000 rpm and set it to my desired timing. then reinstall the vaccum hose.

Jester

Thats why distributers are supposed to be hooked up to a ported source, not manifold. Ported sources are negligable at idle, and increase as rpm does.

And yeah..it is much different underload than in neutral. You need a dyno to really see.

ShaneBuss2

they increase as idle rises, but at WOT aren't they zero again?


I just dont see why people figure in vaccuum advance at WOT...

ChrisFormula355

16 degrees total plus 14 degrees mechanical equals 30 degrees NOT 40. That 10 degrees of vacuum advance doesn't mean didly squat when you mash the go peddle. When people post numbers in magazines referring to total timing, they are always talking about inital plus mechanical, not initial plus mechanical plus vacuum, that wouldnt' make any sense. So when you had your timing bumped to 20 initial plus the 14 mechanical that puts you at 34 total which is actually pretty good, in fact I would go a little more even and try 36-38 total as small block 305's seem to like lots of timing.

Max

Thanks a lot. That makes sense. I'll try 24* initial with 14* mechanical for a total of 38*. It should have even snapier throttle response.

Should I plan to increase the jetting to complement the additional timing advance? Does that matter?


Is there a trade off between Torque and Horsepower.
In other words, If I advance it even more and the throttle response becomes even better, will the motor produce less power up high like around 4500 - 5000 RPM?

Do I have to sacrifice one for the other or can I have both.

Lance

five7kid

iTrader: (14)

You need to understand why the timing is advanced. If the spark occurred right when the piston was at TDC, the piston would be going down (from inertia) before cylinder pressure would drive it down. The idea of spark advance is to start the fire soon enough before TDC that pressure has started to build up to get the piston moving down by force.

Starting the fire too soon or too late will result in loss of power (and throttle response). And, the rate of burn varies with engine speed and load. That's the idea of tayloring the advance curve - to get it right on time at all engine speeds and loads.

So, just changing the setting of the distributor housing (base or initial timing) isn't the total answer. How your mechanical and vacuum advance work together, along with the initial and total timing and the rate at which the advances come in and/or go off, determine whether both WOT power and throttle response will be improved.

ChrisFormula355

Well, in a nutshell, I've discovered that too much timing drops off the power just as bad as too little, even if its only off by a few degrees, and really the only way to know for sure is to go to the track. however 34-38 total for a carburated small block with a mild cam seems to be the golden rule that you can't really go wrong with.