63 L84 timing question

[Michael G.]

I have chart that lists the recommended initial timing for my 63 FI engine at 10 degrees advanced at 700 RPM. Is this correct?

Thanks, Mike

[William C.]

Re: 63 L84 timing question

Yes, as log as you have the vac advance disconnected and the original curve configuration in the distributor. The Mechanical advance should not start working under 850 RPM.

[Duke W.]

Re: 63 L84 timing question

Run it as high as you can - up to 18 degrees - to the detonation limit. The timing tab is not accurate - 14 on the tab is about a true 11-12. You can verify this with a dial back timing light, and the subject has been discussed before.

You can also achieve more low end torque if you quicken the centrifugal curve. The OE curve tops out at 24 @ 4600, which is pretty lazy.

Also for some inexplicable reason, the '63 L-84 has ported vacuum advance. Converting it to full time will improve idle quality and fuel economy, but you'll also need to install a 8" VAC like the NAPA VC-1810 or equivalent in another brand.

Duke

[Joe C.]

Re: 63 L84 timing question

Run it as high as you can - up to 18 degrees - to the detonation limit. The timing tab is not accurate - 14 on the tab is about a true 11-12. You can verify this with a dial back timing light, and the subject has been discussed before.

You can also achieve more low end torque if you quicken the centrifugal curve. The OE curve tops out at 24 @ 4600, which is pretty lazy.

Also for some inexplicable reason, the '63 L-84 has ported vacuum advance. Converting it to full time will improve idle quality and fuel economy, but you'll also need to install a 8" VAC like the NAPA VC-1810 or equivalent in another brand.

Duke

That's good advice.

But Duke forgot to mention that a SBC likes total WOT timing (total initial plus max centrifugal)at no more than about 38 degrees. I suppose that you can go as high as about 40 degrees instead of 38, but Lars, and others have found that peak power on a small displacement SBC begins to dropoff as total WOT timing goes beyond about 38 degrees. Large displacement SBC's and BBC's typically "like" 2-3 degrees less than 38.

http://65corvette.nonethewiser.net/technical/vacuum_advance.pdf

If you dial in 18 degrees initial timing (like I did), then that, plus 24 mechanical, gives you 42 degrees total. I limited the travel on the flyweights by bending the "heels" slightly, so that they contact the autocam at 20 degrees centrifugal. Another way to achieve this, is to shorten the advance slot, by either brazing or using JB Weld (or similar). My method is faster, easier, and easily adjustable/reversible.

[Michael G.]

Re: 63 L84 timing question

Thanks, I've got it at 12 with the vacuum ine off, but I'll have to shift the distributor over a tooth to get higher than that, the VA can is running into the FI plenum.

Mike

[Stuart F.]

Re: 63 L84 timing question

Michael;

Was the distributor apart, in particular was the drive gear off and then replaced? Reason I ask is that it is common for the VAC to bump the plenum (L-84) or manifold (L-76) if the gear was put back on 180 degrees off. The dimple on the gear should face forward with the distributor position on #1, but then you probably know that. I guess I was the only one who did not and had to learn from Duke and others.

Stu Fox

[Michael G.]

Re: 63 L84 timing question

The distributor was redone, but I'm not sure if the gear was off. Sounds Like I need to pull it out anyway, so I'll take a look at the dimple
tomorrow. Mike

[Duke W.]

Re: 63 L84 timing question

That's good advice.

But Duke forgot to mention that a SBC likes total WOT timing (total initial plus max centrifugal)at no more than about 38 degrees. I suppose that you can go as high as about 40 degrees instead of 38, but Lars, and others have found that peak power on a small displacement SBC begins to dropoff as total WOT timing goes beyond about 38 degrees.

I didn't "forget" anything. I've seen recent dyno test data where a 10.5:1 327 made best power with 45 degrees, but that was with high octane leaded race gas. There's nothing magic about 38, and most vintage high compression engine total WOT timing is limited by detonation on pump gas.

You forgot about the timing tab error that I mentioned; 18 on the tab is 15-16 at the crank, which is 39-40 total with a 24 degee distributor.

Typical engine power drop is about one percent if the timing is 3 degrees from optimum. That's within the range of dyno test accuracy/repeatability, so you can't nail down a specific number - just a range.

Duke

[Michael G.]

Re: 63 L84 timing question

The distributor is out. I think the gear is on properly. The dimple on the gear is facing the same direction as the rotor.

In the position the distributor was in, (about 12 degrees advanced, vacuum can touching the plenum) I could move it about 22 degrees clockwise before it hit the coil. At 12 degrees the car starts and idles well.

Here's what I think I need to do to acheive 18 degrees advanced, please let me know if I'm all wet:

If I put it back in one tooth clockwise from where it was, the 12 degree advanced position will move 27 degrees clockwise (toward the coil) and the minimum advance (limited by contact with the coil) will be 5 degrees. If I then rotate it 13 degrees, I'll be at 18 advanced without hitting the plenum.

Any advice would be great, thanks, Mike

[Duke W.]

Re: 63 L84 timing question

IIRC the dist. gear has 13 teeth so installing it one tooth off from where you pulled it changes the timing at the crank by 55 degrees at the same housing clocking. Remember that X degs on the distributor is 2X degrees at the crank because the dist. rotates at half speed.

With an odd number of teeth, on the gear, rotating it 180 degrees results in a 27.5 deg. timing change at the same clocking. So in your case if the initial timing is 12 with the VAC against the plenun, the timing would be about 40 (or -15 depending on which one tooth change in installation direction you choose). Then rotating the dist. 14 deg. CCW will bring the timing down to 12 in the former case, and you can easily advance it beyond this as much as you like. You said you have about 22 degrees of rotational freedom, so moving it CCW 14 degrees puts the dist. in the mid-range of its rotational freedom at 12 initial, which is how it should be with correctly manufactured OE or OE equivalent parts.

Most issues that you have are the result of having the gear installed 180 degrees out of phase. Normal gear installation is gear dimple pointing the same direction as the rotor tip, however, there are (sometimes inexplicable) cases where the dimple must face "180 out", and many aftermarket gears have no dimple, so you have to use trial and error.

There are also cases reported where the gear must be installed "180 out" if an aftermarket camshaft is installed.

Do you have an aftermarket camshaft?


Duke

[Michael G.]

Re: 63 L84 timing question

Thanks, Duke, your explaination makes sense.

I'm told that the cam is an "Elgin" cam, made to original specs for the 360 HP cam. From reading a lot of your posts, I'm sure you are probably more familiar with this cam than I am, so let me know what you think.

Mike

[Duke W.]

Re: 63 L84 timing question

I can't say anything specific about Elgin cams. In those cases where it was suspected that the drive gear on the camshaft was not indexed per OE spec, which through out the distributor clocking, the actual source of the camshaft could not be positively identified.

Duke

[Michael G.]

Re: 63 L84 timing question

Duke, I've been talking to someone who says he's never seen that problem with Elgin cams, so maybe its an oddball gear or something. There are strange repro parts of every type out there, perhaps this is a repro gear.

In any case, I guess it doesn't matter too much what the cause is, it seems pretty clear that to get just a bit more more advance, one tooth is too much rotation - a half a tooth is what it will take. The way to get that is to take the pin out and turn the gear 180 degrees. Thats easy enough.

Its getting so I see this distributor in my sleep, so, I'll reorient the gear and reinstall the distributor one more time.

Thanks, Mike

[John D.]

Re: 63 L84 timing question

The distributor was redone, but I'm not sure if the gear was off. Sounds Like I need to pull it out anyway, so I'll take a look at the dimple
tomorrow. Mike

Michael, If the distributor was restored then the bottom gear had to come off. Didn't Don Baker restore your distributor. IF so then you got a read out on the specs. Sounds like you have figured out the problem though. Sounds like you are one tooth off as the Vac can is smacking the plenum.
JD

[Duke W.]

Re: 63 L84 timing question

Duke, I've been talking to someone who says he's never seen that problem with Elgin cams, so maybe its an oddball gear or something. There are strange repro parts of every type out there, perhaps this is a repro gear.

In any case, I guess it doesn't matter too much what the cause is, it seems pretty clear that to get just a bit more more advance, one tooth is too much rotation - a half a tooth is what it will take. The way to get that is to take the pin out and turn the gear 180 degrees. Thats easy enough.

Its getting so I see this distributor in my sleep, so, I'll reorient the gear and reinstall the distributor one more time.

Thanks, Mike

One other thing to check is wire indexing. Look at the '63 Corvette Shop Manual and be absolutely certain that the plug wires are indexed properly. This is another "fix" that bubba does all the time - start screwing around with how the wires are indexed on the cap, so verify before you do anything else.

Here's another tip. When you pull the dist. set #1 at 12 deg. BTC. Assuming the wires are indexed properly rotate the gear 180 deg. then install the dist. with the rotor about 45 deg. to the right of engine centerline. As the gears mesh it will back off to about 20-25 deg. If the housing doesn't seat you'll have to tweak the oil pump drive. A typical wood paint mixing stick is a good tool for this job.

Once seated the with the rotor properly oriented at the above angle, rotate the dist. housing until the points just open and the actual timing should be close to 12. The VAC should be in its midrange of available travel and the cap window should be near normal to engine centerline. If not, something ain't right!

Duke