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I want to check some conflicting advice I have received with regard to waste spark cranking timing. My camshaft manufacturer recommends going with crank timing that is before any overlap occurs to avoid any chance of an intake backfire. By the specs that puts cranking at 19.5 (so probably a little later given valve train slack, so I'll measure).
A tuner I am working with and trust has setup the crank timing at 4 degrees -> -2 when warm. I am experiencing an occasional intake backfire. Once started though everything is fine even with the overlap as you would expect.
What is the recommended way to setup cranking advance for a waste spark engine?
To be honest this isn't something that I've found to be a huge problem even with aggressive cam grinds offering a lot of overlap. I'd usually set the cranking timing to about 10 deg BTDC. 4 deg cold and -2 hot are quite retarded values and it shouldn't be necessary to have the cranking timing this late. There is no danger however in just adjusting the cranking timing and seeing if you get an improvement with your backfire situation. You can find that if the cranking timing is too advanced the engine may kick back during cranking but I would simply test and see what works for you. I'd expect that 10-15 degrees will work well.
I spent some more time on that car today. 15 deg BTDC is the most cold cranking timing I can get in without kick back and about 13 warm so I setup a cranking table accordingly and problem seems to be resolved.
Great to hear!