Cam swap complete, timing suggestions with comp 260

[Anonymous]

I got everything buttoned up two days ago, and broke in the cam. I have the timing set at about 10 degrees now. I also installed an E0 head with bowl work and ported exhaust side(.060 cut felpro gasket). It pulls alot better on top than before, even with stock exhaust and carter 1 barrell. It seems I lost a little on the bottom though. Not much, just a little. Thanks to everyone for their help so far.

 

[Anonymous]

As for timing suggestions, play with it a little and see where it likes to run. Don't get stuck on even numbers, if it likes 15.3 degress, then that is what it likes!

 

[wsa111]

Peyton, what year engine do you have??

If you have a mechanical advance distributor-68 & up or a duraspark distributor.

You need about 14 degrees of initial + 24 crankshaft degrees = 38 degrees total advance.

This will put you in the ballpark for the best power.

Just to keep adding initial advance without knowing your centrifigul advance total is not the direction you want to persue.

Just adding initial advance will cover up a weak hole on low RPM acceration, but possibly will produce less top end power due to to much total advance.

These engines are not computer controlled. It takes someone with knowledge to get the best performance,power & fuel economy from these engines.

You laptop computer boys can control a late model, but it takes someone with the old time experience to get the best from the old school engines.

The only tool that is helpful is a modern air fuel ratio sensor to get the fuel mixture correct. William

 

[Anonymous]

The engine is a 72 200 with 53k in a 72 mercury comet. Shortblock is stock save for the cam. I am using the duraspark II with a gm 4 pin module. I will have to play with the timing as linc said, I am not getting any ping yet. How much is generally too much initial timing. The mark on the timing cover only goes to 14. I am checking the timing with the vacuum advance disconnected, then when I hook it back up it goes way past the timing marks. I guess this is normal since vacuum is highest at idle. Is there a way to hook the vacuum advance up above the throttle blade(ported vacuum)?

 

[Anonymous]

The vac advance should indeed be connected to "ported"vacuum. Look above the throttle blades for a small slot, and trace that slot with carb cleaner spray (witht he red straw) or light compressed air to see where to port comes out of the side of the carb at.

WSA is right about initial timing and total timing. They are two dynamics that need to be optimum at two different RPM ranges. It sounds like you are willing to play with this a bit, so here we go....

(Do all measurements with the vac advance hose off, by the way....)

Fiddle with initial timing until you find where you get best off-idle throttle response and low end torque. you won't need to go over 2000 RPM's ever while testing this. Find an abandoned street or parking lot to do this in, because if you make any torque at all, you will be making lots of tire noise and laying rubber as you find your best "off idle" torque timing!! Record the number you have found......

Now, having done that.....put the light on it, and get it above 3000 RPM's so you can see how much total you have. If you are around 42 degrees total (easy to do if you added a lot of initial advance timing) then you will need to take some mechancial advance out. Find your best "total" timing by finding where the engine runs the strongest at higher rpms (lots of distribuotor moving around)

Now you have best initial and best total. Subtract the differences between the two numbers that you had to move the distributor around to get, and now you know how much mechanical you need to take out. For example, if you car has best initial at 16 degrees, but the best total was achived at 9 degres intial, then you need to take out 7 degrees of mechancial advance you you can run your ditributor at 16 initial and not be over-advanced at higher RPMs'. You can do this pretty easily by slipping a little piece of washer tube over the mechanical advance limiting pin that is under the moveable plate inside the distributor. You may not get the exact timing you need, but to do that maens the dist has to come apart and you have to move the advance limiting pin to the other stop in the advance plate or do some welding and filing to get it where you want it.


Most people don't want to get that in depth, and just find a nice compromise between the timing marks (less initial that what the engine really needs) but your engine will not be at its max potential doing this.