I have a Camaro with an LG4 carburated ( non computer controlled and with vacuum timing advance). No EGR. Stock Cam. Spark plugs are AC delco R45TS. Stock quadrajet carb. The distrib advance is connected on manifold vacuum. I want to know the best BTDC number at idle with vacuum advance disconnected, both with 87 octane and 91 octane.

It would Also be Nice to know the best timing at 3000 rpm with vacuum advance disconnected (87 and 91 octane)

10 deg initial timing at idle and 36 at 3000 rpm (both with advance disconnected), is it too Much with 91 octane ? Maybe 8 deg initial Will be Safer??

 

I setup a 1985 LB9 305 in a 1983 El Camino for a friend at one point. Basically a L69 at that point. $20 junkyard Edelbrock performer intake, non feedback Q-jet off a random junkyard 305 van I rebuilt and stock 90s 350 Van manifolds. 2 1/4" exhaust to a dual in/single out cat and single 3" out magnaflow. HEI distributor that gave 22° centrifical. It ran best at 14 initial and 36 total with the vacuum advance on the manifold fitting. Would not roast the tires off of it but ran very well for having a stock converter in the TH350 (200c went out 5 miles after I got the engine running well, lol)despite having 2.42 gears. With a Vortec starter it never had a hot start issue and never pinged or knocked on 87 octane.

 

Efff the timing mark and a bunch of "numbers". Your mark is ALMOST CERTAINLY not accurate. They hardly ever are.

Set it to where it runs the best. Advance it until it just starts to ping, then back it off until it quits; and go from there. That setting won't be "right" but will give you a good sensible starting point.

The way to think of it is, don't hallucinate that you're going to TELL the motor what timing YOU THINK it needs, according to some yutz on some Interwebz forum. Instead, ASK IT WHAT IT WANTS. Which you do by setting it somewhere, then changing it, and seeing what happens; and if it runs better, adjust it some more in the same direction, or if it runs worse, go back plus a little further. "Better" would be, "better" to YOU: could be any imaginable combination of most power, best throttle response, cool engine temps, good gas mileage, freedom from pinging, starter able to do its job, ability to run the fuel you can actually buy in your habitat, and so forth. YOU get to decide what's important to YOU, rather than being some kind of slave to "spec" in "book" that was most likely designed for best emissions compliance. "Better" is different for just about everybody, even apart from the fundamental inaccuracy of having the mark located on a blob of spooge that lets it flop around out in space somewhere; so whatever Skillet on the web "likes", may or may not be best FOR YOU.

 

I just the number out of reference.

Not all timing marks are inaccurate either. The timing marks on my new 383 build will never not be accurate. I used a dial indicator to verify TDC before I started degreeing in the cam. Between Holley, Fluidamper and Scat everything is perfectly accurate.



On the other hand I tried to time a small block that would not even stay running if you even got the timing mark on the balancer anywhere near the timing tab. Luckily that engine was in a G-van and performance testing to see what it responded best to was stupid easy. Just left the clamp loose enough I could turn the distributor and advance the timing as I held the throttle WOT until it pinged and backed off a little. Pulled a little more out and it was a dog. Advanced it back and it ran like a bat out of hell. Pulled over tightened up the clamp and drove home.

 

LOL. I've done that in a van also. Advanced until it pinged. Backed off until it got sluggish then advanced it a little more.

The downside is that you've changed 2 different timing settings. Advancing it as we've mentioned gets a good ballpark total timing setting but to do this, you've changed the base timing. Base timing mainly depends on the cam grind. With a stock cam, I don't think I would want more than 12* of base timing.

Typically, it's recommend
10- to 12-degrees of initial timing when the duration of the camshaft is less than 220-degrees @ 0.050” of valve lift
14- to 16-degrees of initial timing with a camshaft duration of less than 240-degrees @ 0.050”
18- to 20-degrees of initial timing when the camshaft duration is less than 260-degrees @ 0.050” of valve lift.

So if you've advanced the timing as we've mentioned above to where it makes the best power then check where the base timing is. Lets say it's now at 15*. That means you need to drop the base timing down 3* and increase the mechanical advance 3*. How much total timing an engine wants depends a lot on the engine setup. It could be anywhere from 28-40* but the base timing will still depend on the cam grind.

Vacuum advance is for part throttle operation and is not part of base/total timing settings. It simply adjusts the timing depending on the engine load based on the manifold vaccum.

 

Also depends on compression ratio. A 8:1 smallblock can run 14 to 16 degrees of initial with a stock cam and be quite happy...

 

I have had them quite happy at 16-20° as well. The old Goodwrench 350s have a 7.8:1 compression ratio. They could almost run on Kerosene.

 

I set the initial timing at 12 deg BTDC. At 3000rpm, the timing is at 36deg BTDC. All with vacuum advance disconnected.

Now it pings under load (more than half throttle when going upHill) but I'm on 87 octane. Do you think it Worth it (Power and mpg together) to keep that timing and switch to 91 octane? It's 10-12% more expensive per liter but if I get 3-4% more mpg and more Power it could be nice. And if it pings again, I Will set the initial timing at 10 instead.

 

Leave the base timing alone and lower the mechanical advance about 4*

 

Manifold or ported vacuum on the vacuum advance? Also how much vacuum advance and where does it start to advance vacuum wise.

 

Manifold vacuum.

I think it advances by 13-14 degrees with vacuum.

I tried 91 octane with 12deg BTDC base timing and it was still pinging.

So i set the base timing to 9.5 BTDC and its not pinging anymore (on 91 octane). Its approximately 32deg BTDC at 3000rpm without vacuum, si maybe 45-46 degrees BTDC at 3k rpm with the vacuum advance connected.

Next tank i'll go back to 87 octane for a couple of tanks to see if it pings.

The Power is better (the a/t no need to downshift on some Hills it downshifted before). I drove 150k miles today and it made 23.5 MPG highway.