Thread: carb size ?

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O.K., school's in session....

"Set a cam "straight-Up" set the initial timing at 8degrees BTDC.."

O.K., the crank gear is installed on the crank in the zero position, neither on an advance groove nor a retard groove and the cam is installed on the marks with no offset dowel.

"now pull the front cover....degree the cam 4 degree advance....put it all back together....run the engine...."

O.K.

"Now read the timing light....Notice I did NOT mention touching the distributor.... cause I did NOT...."

O.K.

"The timing light WILL read 16 degrees BTDC.... bet you a Dollar...."

You bet it will, because when you turned the cam in the direction of rotation, you also turned the integral rotor drive cam gear which is engaged into the distributor rotor shaft gear, thus advancing ignition timing at the same time you were advancing cam timing.

"The cam is fased with the distributor in this situation.... we moved the timing in relation to the crankshaft"

Yep, the cam is always phased with the distributor rotor because the cam gear drives the distributor rotor gear and we did indeed advance the ignition timing in relation to the crank. No argument.

"Some will argue when you adavnce a cam you have to reset total time you have to bump it back 8 degrees...."

Yep, some guys are funny that way. If I had my ignition timing optimized, I wouldn't want to add any advance to it either.

"Oldsmobile would argue in it's day the fact that the more you advance a cam the more total it can handle....."

I can't speak for Oldsmobile, but as for myself, If I advance a cam and move the intake closing point to earlier in the valve event, I'm going to make more cylinder pressure and therefore might be looking at taking a little timing out of the motor if I was marginal on pump gas in the first place.

"Also running a cam "straight-up" you will be lucky to get the initial timing up to 16 degrees and it will still start most time it wont.... It will drag hell out of the starter/ kill the battery"

This is where you're starting to lose me. Initial ignition timing is set with rotation of the distributor housing and a timing light on the harmonic damper. You can dial in any ignition lead you want, no matter where the cam is in relation to the crank.

"Advance it 4 and initial at 16 it will crank easy as pie.....I have rebuilt umptine Olds motors...Tis how I know...."

Now I'm starting to get the picture of what you've been doing. When you advance a cam, it's easy to fake yourself out and move the cam sprocket clockwise instead of moving the cam clockwise.

"Same theory works on any engine you can adjust the cam without pulling the distributor...."

Yes, of course you can adjust the cam phasing without pulling the distributor.

"Do you supose thats why in computorised vehicles the General may run as much as 55-60 degrees total"

I suspect that if a motor can tolerate that much ignition timing, it's under a no-load situation or very light load. I've seen fellows run 50 degrees total on a SBC under light cruise conditions and that's on a non-computerized carbureted motor. The motors that are controlled by an ECM would probably be able to tolerate 55-60 total, because the computer could pull the lead back to reality in a nanosecond the very instant the motor saw some load.