Ignition timing vs. quench

[Dave Erickson]

I read some articles on quench that claim that as quench is lowered (down to .030 - .035"), ignition advance should be reduced, because the time required for ignition is reduced. So how does that impact 356 engines? Should a 356 engine with .030" quench use an 050 distributor (with 26 deg. of advance) rather than a BR18 with 30 deg. of advance, or is the effect less than 4 degrees?

[Kevin Wills]

There are a lot of factors that go in to how much advance an engine will take or need. It might help if you provide some other information about the build. FWIW, I built my 1925 to .035" deck and run 34* total advance with a BR18.

[C J Murray]

I read some articles on quench that claim that as quench is lowered (down to .030 - .035"), ignition advance should be reduced, because the time required for ignition is reduced. So how does that impact 356 engines? Should a 356 engine with .030" quench use an 050 distributor (with 26 deg. of advance) rather than a BR18 with 30 deg. of advance, or is the effect less than 4 degrees?

Theory vs reality. Because there are so many factors that determine the best spark timing you really need to test the actual engine. Without a dyno you can experiment on the road but feeling a difference will be difficult. If your timing is too far advanced the typical sign is that the car pings if you quickly press the gas pedal to the floor while cruising at 3300rpm. Third gear works well. The idea is that you want to be at full advance, above 3000rpm, in a gear that accelerates slowly, and induce detonation. If it detonates then reduce timing slowly until it stops, or use better fuel.

The vast majority of 356 engines run best near the factory setting. If the engine runs hot you may not have enough timing.

[Kevin Wills]

Thanks for your expert advice when I was going through my tuning, Cliff. I used your exact method above to test. BTW, 160-180* oil temp at the gauge once I dialed the jetting in more closely. It runs great.

[David Jones]

I am 100% in agreement with Cliff. F Vee engines are theoretically all the same in that the combustion chamber, capacity, volume, cam profile are very close to identical. Even so on the dyno each engine to extract the maximum performance required surprising variations in timing and carb jetting. One engine made most hp at 41 degrees BTDC. That was an anomaly though.

[Wes Bender]

... if tuning was only as simple as adjusting timing to match quench....

[Dave Erickson]

... if tuning was only as simple as adjusting timing to match quench....

Tuning is not simple, but theory is useful to guide practice...