jeffsims

How do you confirm total timing at 3000 RPMs? I have a timing light and can see the timing mark way advanced, but how do you tell for certain the total degrees since the timing gauge next to the harmonic balancer only goes to like 10deg?

oldcutlass

Is your timing light a dial back?

joe_padavano

Without a dial-back timing light, you need either a fully degreed balancer or a timing tape on the balancer. Either of these puts degree marks on the balancer that go far enough to allow you to see the timing at higher RPMs. Just read off the degrees opposite the zero mark on the tab.

http://www.summitracing.com/parts/su...ake/oldsmobile

jeffsims

So I just bit the bullet and purchased a digital timing light. The parts stores in town did not have the tape and would have to order. So......

Based on reading others comments in this forum, I am looking for ~34-36 deg BTC of mechanical advance at 3000 RPM. I removed the hose to my vacuum advance can and blocked off the port on the carb. Using this cool digital timing light, I adjusted the throttle linkage to get to 3000 RPM. I then set the timing light to 35deg advance. I adjusted the distributor until the mark hit 0deg. After slowing dropping the throttle back to idle, I reattached the vacuum advance. I forgot to measure how much vacuum advance I have......Adjusted the idle down to 800 RPM. Holy moly the power I now have.

Since it pretty much had no top end power (sluggish), when I set the timing to factory 7.5deg, do I need to get an adjustable vacuum advance and/or try to recurve the distributor? By the way, the distributor is the original that has been rebuilt. Reused the weights and springs with new vacuum advance (Standard). It has no points with the Pertronix ignition.

oldcutlass

You need to repeat the exercise of running your engine up past the 3000 rpm to around 4500 and ensure your not advancing anymore. Then do it again with the vacuum advance connected and note what your timing climbs to. It needs to be limited to no more than 50-52 to prevent pinging at light throttle. Then check your timing at idle and note what it is for future reference on tuneups.

MDchanic

Bottom line is how well it runs, whether it pings, and how easily it starts.

It will generally run better the more you advance it, up to a point, and then it will run worse.
The exact point will vary with the individual engine.

If you advance it too far, and it is not a low-compression engine, it will ping, which is destructive to the engine, so if you hear any pinging, retard your timing at the appropriate point in the timing curve where the pinging occurs.

If you advance it too far, it will be hard to start, so if you advance it and all else is well, but it doesn't want to start, you need to increase the span of your mechanical advance, so that the engine stays advanced at higher RPMs, but is more retarded around idle and cranking speed.

- Eric

jeffsims

I will do it over today to confirm what I have max. Another question. I keep reading in other places that vacuum advance should be attached to ported vacuum, which is just above the throttle blades and has no vacuum at idle. Is this correct? I ask because the factory position on my quadrajet is just below the air horn and it has ~17 inHg at idle. Do I need to change something?

oldcutlass

The argument of ported vs manifold vacuum has been on going for decades. The stock position for your vacuum advance is ported, no vacuum at idle. The reason they say to disconnect and plug the line while checking timing is to ensure that there is no way for it to interfere with setting your timing. You can do a site and/or internet search on the subject instead of resurrecting this argument.

jeffsims

Hmmm....So what is my problem if the stock position does have vacuum at idle? It has about 17". 400ci w quadrajet carb. The only other port on the carb is the vacuum pull of for the choke and the one on the throttle body for the PCV valve.

jeffsims

Ok guys. I have been sick for awhile and just now getting back to this little task. I have been doing a lot of reading through this forum and a few others. From what I gather 35-36* is the max total advance. I set my timing at 3500RPM to be about 35* total with my digital timing light. Not a whole at top end. Seems to bog down or run flat.

I then decided to go the max vacuum route. With my vacuum advance disconnected I was able to achieve 21", but was not steady. I then backed down until I reached 20". Nice and smooth at 850RPM. I then checked my timing was at at 23.6*. Holy crap. I took it for a quick ride and another holy crap, but in a good way. A lot of power. After bringing it back to the garage I thought I would check timing through several RPM ranges.

650RPM 40.6*
1000RPM 42.3*
2000RPM 54.9*
3000RPM 58.9*
3500RPM 58.9*

It seemed to level out at 58.9* max. Wow. I am pretty sure I did something wrong. I probably should have left vacuum advance connected, when I was targeting max vacuum. It looks like I get about 17* of vacuum advance. If I go back and retry, I should be around 41.9* total timing.

So where did I take a wrong turn?

oldcutlass

I believe you still have points correct? Make sure you set your dwell to 30 before proceeding. Disconnect the vacuum line to your distributor. Set your timing light to 34 and run the engine up to around 3000 rpm, you want to see the balancer line up with 0 on the indicator. If not, note the amount of degrees you need to add or subtract to get to 34. Let the rpms drop back down to idle and move the distributor the amount of degrees difference, then repeat until your at 34 @ 3000 rpm. Let the rpm return to idle and tighten the lockdown bolt. Repeat one more time and make sure it did not move. In addition I like to monitor the timing up to about 4500-4800 to make sure it does not advance any more.

Now that you have your total set, reset your timing light to 0 and note what your initial timing is set to at idle. Write that number down somewhere for reference tuneups.

Next thing to check is your vacuum advance. Reconnect the line you removed and plugged earlier. If its connected to manifold vacuum your idle will go up and the timing will advance. Lower the idle at the carb for your desired rpm. Note what your timing is at idle. Then raise the rpm to about 3000 and then to around 45-4800 and note your timing at those 2 points. Do not adjust the distributor. If you have purchased an adjustable vacuum advance and its for limiting the amount of advance then adjust it to where your timing is no greater than 50-52. You may possibly need to install a stop to limit also. Once your done note what your idle timing is at idle with the vacuum connected and post your results please.

Initial timing at idle without vacuum= @what rpm=
Total timing without vacuum= @what rpm=
initial timing with vacuum= @what rpm=
total timing with vacuum= @what rpm

Then take the car for a ride and see how it acts, be sure to listen for pinging and whether it surges.

Octania

So, for folks whose hearing is not so good- you know, old timers- how can detonation be detected?

oldcutlass

Good question... bring a youngster. He should not get any pinging at these settings and 93 octane, but I always like to bring it up. The other option is for him to just set it at stock and not worry about anything. I only answered his question. These are a good read:
http://www.camaros.org/pdf/timing101.pdf

http://www.lbfun.com/warehouse/tech_...t%20Timing.pdf

jeffsims

Eric - Thanks for the input. I did exactly what you told me. Below is what I found...

Initial timing at idle without vacuum= 17* @ 650RPM
Total timing without vacuum= 34* @3000-4500RPM
initial timing with vacuum= 36* @ 650 RPM (Readjusted idle back to 550RPM)
total timing with vacuum= 54* @3000RPM-4500RPM

I do not have an adjustable vacuum advance. Do you have any recommendations on what to buy? 1967 442 w 400ci.

-Jeff

jeffsims

I guess I am a youngster...39yrs. My wife tells me I never hear anything she tells me though. LOL!

Before I did what Eric told me to my total timing at 3500RPM+ was 58*. I did hear what I think was pinging, but not from the engine compartment. It was from under the car and sounded like pings from exhaust pipes close to the exhaust manifold connections.

After readjusting I am not to 54* total. I do not hear that sound anymore from the pipes.

Pinging?

oldcutlass

I like to keep my total with vacuum at 46-50. You can make or purchase one of these:
http://www.summitracing.com/parts/CRN-99619-1/

oldcutlass

Does it idle and drive smooth? You should have plenty of power. Get it on a hill and run it at wot and then a good half throttle cruise. Listen carefully for pinging.

jeffsims

Oh yea, I forgot. I am not running points. I have the Pertronix electronic system.

jeffsims

Idles smooth. Better WOT than what I have been experiencing. I have not heard any pings. Will look for a good hill tomorrow.

oldcutlass

No problem its a points replacement. The distributor timing is the same. Buy or make a limiter for your vacuum advance. On hot summer days it will be a problem.

Glad you got it set and its running well.

Fun71

I made a limiter using a small bushing similar to the pic below. The advance canister originally gave 24º advance and the bushing cut that down to 16º.



I later made one out of a small piece of metal similar to the pic below and it is adjustable, so I now have it set to 10º.