I know how to figure total timing... now what?
I didn't have a tape on my balancer; but bought a timing gun with advance DIAL to figure out optimum timing settings for my 74 El Camino.
I set initial timing at 10° with my stock gm 2 bbl on a 350. Results showed a total of 35°.
OK, now what can I do with this info to increase power or economy?
My book says initial timing should be 8°@600 rpm. This figure seems dated when factoring in the high corn-fed state of the regular unleaded gas I have been using. Can my el camino with a mild cam (E-921-P) run well at, say 12°?
The fuel i am using with my 347 with a mild cam is supposed to be around 93. I had initially set my timing at 12 with a total , all in timing of 32 at 3000 RPM. Under wide open throttle it began to "ping" or detonate so i had two options, increase the octane of the fuel or retard the timing. I chose to retard the timing back to 8 degrees to stop the detonation.
If you advance your timing and the engine pings then you can damage rod bearings, so you back the timing off 1, 2, 3 degrees (detonation...... fuel explodes before piston reaches TDC which tries to push the piston down as its coming up.)
If you want a bit more throttle response you can limit your mechanical advance curve to about a 16* swing and set the initial at 20*. Also, make sure you have 34* to 36* all in by 3000 rpm. Use a vacuum can with an advance of 10* and use manifold vacuum. You'll have to reset your idle speed and mixture afterwards.
IMO A stock 350 is in most cases not going to take 20 degree base timing. Worth a try but it could be a bear to startup when hot. Tend to ping itself silly up hill in the wrong gear etc. But it all depends on the rest of the tune and other factors.
14 ish initial/base should be plenty as a performance tune stock engine. Much is dependant on vac advance ported or manifold because if manifold then the idle timing is base + vacuum adv. The engine vac should be pulling 17 "wg +. The vac advance will be all in at idle no matter what. So keep this in mind when factoring in everything.
Run it on ported and at light trottle you are still way high with mechanical coming on,,,it could rattle like a nursery. The cam is tight and cylinder pressure maxing out at low rpm. etc.
Too much emphasis on base or initial seems to be the going concern. Target the total timing first (initial + mech) is 35 the magic number at 3500 rpm and beyond? do some WOT pulls. When you know this number 32-35-38 whatever keep it as gospel, everything else on the distributor revolves around it. (no pun;))
You have 25 deg of mechanical, so how much vacuum adv? could be another 20? test it out, maybe you have no vac adv? tell us.
This is 1974 car so just shy of HEI, what type of dist?
I am unwise to the ways of corn gas, but have had a laddle or two of corn squeezings on occasion:drunk:
fuel economy or mileage,pick one.10-12 initial is good for that era with a stock ish engine.34 total is probably ok.make sure vacuum advance is working as per stock. HEI was available in 74.check plug gap and do not use more than 35-40. set everything else to factory specs. Dual exhaust helps these cars.make sure the ther mac is operating properly. Check base plate of carb for loose screws.check battery and charging system and belts.just a thourough standard(deluxe) tune up.
check cap for white residue inside.dont use a cheapo cap or rotor. use good wires.Check timing chain slack if higher mileage,,,they had plastic cam gear that retarded the cam when worn and the chain also stretched a lot back then.
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