Clocks and Springs and Carbs

[Lee B.]

Re: Clocks and Springs and Carbs

Duke,
The cam that is in it is 210/214 @ .050 intake at .429 exhaust at .439 with a centerline of 110. Had another round of storms tonight and did not get a chance to mess with it. I set the timing by Lars Grimsrud's recommendation and came up with the 14d initial timing. I will try it at 6d tomorrow and re adjust the air fuel and see what I get. Will also get the vacuum readings and map the advance. The VAC is new and holds vacuum. Will get the number off of it, but it is the correct one I am pretty sure. Will also post a pic of the top of the distributor. Can you tell me how to map the centrifugal curve? I assume you disconnect the VAC and record the timing at every 200 rpm or so up to 3000 rpm? Do you also need the manifold vacuum reading at each of these points?
Thanks
Lee

[Duke W.]

Re: Clocks and Springs and Carbs

For starters that camshaft probably has a lot more overlap than OE, and there's likey no way it will idle at 500 with the AC compressor engaged. You have to select an idle speed - as low as possible commensurate with acceptable idle quality. Use the vacuum reading and apply the Two-Inch Rule to determine if the VAC is properly matched to the engine configuration.

What is the lobe separation angle (LSA) of the installed cam. You said "110 centerline". Did you mean 110 deg LSA or 110 deg. ATDC inlet POML?

The correct VAC is may not be the OE equivalent. When you have an aftermarket high overlap cam you need to know normal idle speed vacuum and then apply the Two-Inch Rule.

Look at the specs for the OE centrifugal curve in the CSM or AMA specs. Then with a dial back light installed and the VAC disconnected and plugged determine the start point. Then take readings every 500 revs starting at 1000 (assuming the start point is less than 1000) until it stops advancing, which is about 5000 if it still has the OE curve. It's best to have a helper operate the throttle and record the readings you take, so you will have the start point, intermedicate points at 500 rev increments and the maximum at whatever RPM it maxes out.

Use a test tach for the centrifugal start point and idle speed measurments. The in-car tach may not be that accurate at low revs, but it's okay to use it for the higher RPM centrifugal readings if the test tach doesn't have a high RPM scale that will go to 5000 or more. Idle vacuum readings without specifying idle speed are meaningless, so make sure you specifiy both speed and vacuum at the two specified operating points.

The only necessary manifold vacuum data is at idle speed with both the AC compressor engaged and not engaged. Set the idle speed as low as you find acceptable with the AC compressor engaged. Then specify idle speed/vacuum with the compressor not engaged.

Duke

[Lee B.]

Re: Clocks and Springs and Carbs

Duke,
Thank you for the information, just found out I will be out of town tonight, so I will get this done tomorrow after work and post the results. Yes the overlap is 110 degrees. When I do this, do I need to set the initial timing to 6 degrees or a little more to account for the larger cam? or does it matter?
Thanks
Lee

[Duke W.]

Re: Clocks and Springs and Carbs

When you take the centrifugal curve you can leave the initial as is and record the total. But you MUST determine the start point so you know what the initial really is. If initial is set above the speed where the centrifugal starts it's actually less than what you think. This is a common problem. Once you have the total values and have verified what the initial is, measured at less than the centrifugal start point, you subtract the initial from each data point and you have the centrifugal curve.

If the LSA is 110 degrees then at 210/214 durations it likely has more effective overlap than the L-79 cam. It's certainly not a camshaft I would recommend for for a 327/300. It has too much overlap, which kills low end torque and results in poor idle quality.

Duke

[Lee B.]

Re: Clocks and Springs and Carbs

Okay, finally got a chance to map the distributor. At idle the vacuum is at 15" without the A/C off. Forgot to turn it on. The idle was at 550 with a static timing of 6d. The vacuum advance pulled in 16d at 10". The distributor had the original springs in it and here is what it was at:
500-0d. 1000-5d. 1500-16d. 2000-17d. 2500-19d. 3000-21. 4000-28.

I replaced the springs and came up with the following:
500-0d. 1000-13d. 1500-17d. 2000-19d. 2500-22d. 3000-26d. 3500-30d.

I did not get a chance to test drive it.

[Duke W.]

Re: Clocks and Springs and Carbs

The first data set sounds pretty close to OE although the OE 360-16 VAC should not provide full advance until 12", but 10" is probably within or very close to maximum production tolerance. Idle vacuum at 550 with the A/C off is higher than I expected (the OE cam would pull about 18-19" at 550). but does it idle okay with the compressor engaged? You should set the idle speed at the minumum for acceptable idle quality with the compressor engaged, and the VAC must meet the Two-Inch Rule in this idle condition.

You took readings at 500 and 1000, but at what engine speed does the centrifugal actually start to add advance?

The lighter springs are a good idea. It should have more low end torque and better around town fuel economy. You can now set total WOT advance by revving up the engine to over 3500, and setting it at 38-39, which would be better as long as it doesn't detonate.

Whether it has any effect on the original reported problem remains to be seen.

Duke

[Lee B.]

Re: Clocks and Springs and Carbs

I actually got a chance to drive it around late last night and it did drive much better. Will try it out over the next couple days to make sure the WOT problem is gone, but much better right now. Thanks for the help.
Lee

[Lee B.]

Re: Clocks and Springs and Carbs

So, I replaced the original coil and drove the car again and it drove like crap. I think all this problem stemmed from a coil that went bad after it got hot. Although all the timing corrections needed to be made, the bottom line is if you have a bad coil, nothing works as it should. Will replace with a good coil and drive again to be sure.