ForMySon

I'm lost. With the cam, I don't know anything about tunning this beast. It's a 71 350 that last owner build with a cam. I need a list of all the things to do to check to see if it's tuned right.
Where does it redline at?
Can I use a timing light like normal to set timing?
What about HEI hi-performance vacuum advance of 24 degrees? Is this too much advance?

Any help to get me started would be great.

camaronewbie

You need to either 1) use a timing tape - sticks on the balancer and shows timing marks into high numbers), or 2) a digital or dial-back timing light.

Start with timing at about 10 BTDC, have the dist bolt tight enough to dist from turning on it's own, but loose enough where you can still twist it by hand. Take timing light and screwdriver for idle adjustment with you in the car.

When engine is warmed, make a WOT run - if you don't get any spark knock (shouldn't at 10BTDC), then bump it up to 12BTDC, and make another WOT run. Keep doing this (WOT runs and bumping up by 2 degrees), until you get spark knock at WOT - when you get the spark knock, come back down 2 degrees, and lock it in place. This sets the timing at the highest position possible without getting the spark knock at WOT.

Of course, changing timing means you'll need to do idle adjustments along the way as well, to keep your idle at a reasonable range (mine's about 850rpms in park).

Then, you can see what your total timing is at about 3000 rpms. The "magic number" is about 32 - 36 BTDC at 3000 rpms. But most off the shelf distributors will noty achieve this "magic number" without having weights and different springs installed into the distributor to enable it to mechanically advance that far that fast.

Mr. Gasket makes both the timing tapes, and the weights/springs kits for the distributors. Just measure the diamter of your balancer to order the tape.

For a reference, I did this on mine - I ended up with about 15 degrees BTDC base timing (17 made mine knock), and that gives me about 28 degrees total timing at 3000 rpms (I need the weights/springs kit to meet the "magic numbers").

It's not a perfect method, but it's easy, and gets you where you need without fancy tools or expensive dyno runs.

ForMySon

Thanks. I can do this. With a few questions:

1. I'm not sure I know what spark knock its suppose to sound like. Doesn't it sound like lifter rattling?

2. I have the 3 sets of springs/weight combos. I put the middle set in, which I think was a 24 degree advance. If I can't retard the timing enough to reach 32-36 BTDC with this set of springs/weights then would the next best weights/springs allow me to achieve this? or Is it more a matter of what cam I have?

In other words, if its just a mediocre cam, then I won't be able to retard the timing far enough to use better springs/weights?

3. How far can I advance an engine before spark knock? Ahhh, I'm guessing this is also in relation to the cam. Some lights in my head might be going on.

thanks much.

camaronewbie

1) spark knock - remember the old days when you sometimes heard a "pinging" noise from a car as it was travel;ing under load (like up a hill)? That's spark knock, ie detonation. Alot of us rememeber it from the days of swapping to unleaded gas - our old leaded gas cars didn't like unleaded gas, and pinged alot.

2) haven't done the weights/springs thing yet myself, so not sure I can answer other than to say it's a trial and error thing - just have to play with different combos.

3) yes - dependant solely on YOUR motor - some cars detonate at lower timings, some at very high timings - just depends on your particular baby and what she likes/doesn't like.

izcain

Once the timing has been setup put a fresh set of plugs to do your carb tuning.

If you have access to a wide band this would speed everything up greatly.