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 Offset Crank keys and Effects on Timing

 Created by: Bomvida
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 Posted: Jan 18, 2022 10:22PM
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Take this with a hefty dose of "Maybe", but I seem to recall my very skilled dyno operator saying that most big bore minis operate best with a max advance of 28 degrees on US pump gas.  This was quite a number of years ago, though, and my brain is less into remembering mini stuff as it once did.

 Posted: Jan 18, 2022 02:21PM
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US
As Spank pointed out, the cam timing has nothing to do with ignition timing.

"How can anything bigger be mini?"

 Posted: Jan 18, 2022 11:44AM
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Thanks Spank for the info!  I was just trying to see if i need to adjust the timing reading to take into consideration any offset from the crank key.  currently running an Aldon yellow with vac advance timed at 10 degrees at 900 RPM and max advance 32 degrees at 5000 RPM with pipe disconnected.  I was curious if those numbers are inaccurate due to the cam timing from the offset key.      

 Posted: Jan 18, 2022 11:30AM
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Any engine builder worth their weight in salt should time a camshaft in to the crank position as designated by the cam grind requirements, whether that be with a vernier or similar adjustable timing chain setup or by using offset keys. Anyone just going "dot to dot" is missing out on getting out of the cam whatever it has been designed for. Different engine builders, based on their OWN testing and findings, may deviate from recommended cam manufacturer timing settings to achieve their desired results from their builds.

Don't confuse these cam timing settings with ignition timing settings. While there certainly is a correlation between the two, they are two separate areas for optimization and require lots and LOTS of expertise to fine tune each one. Getting everything perfected requires a bit of a spiral approach-- adjust one bit then another bit and then another bit (cam timing, compression ratio, valve sizes, head port sizes, exhaust size, ignition timing), and test, readjust, then retest, the readjust, then retest and repeat until you zero in on what you are shooting for.

The way MOST of us do it is we have an engine that we trust has been built to within certain functional specifications, then adjust the external stuff as much as we can which includes playing around with ignition timing and advance curves. That's where a skilled dyno operator comes in.

I learned that just by playing with timing on a 998 engine I could get another 15hp out of what Id been driving around on previously.

May not answer your question directly, but if you are trying to get the best ignition timing setup for your engine, using whatever numbers or figures you find printed in a book or online is only a ballpark. If you really want to know what's right for what you have in your car, you need a skilled dyno operator who can adjust your timing and your fueling and retest until they get the best numbers they can get to. When I did it, it was by FAR the best $ I'd ever spent.

 Posted: Jan 18, 2022 11:07AM
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Hello all!  I have a question regarding stroboscopic timing settings.

I have a 1380 engine built by minimania with a cam timed to 107 degrees.  Does anyone know if they use offset keys for their build?  If so, does this affect timing checked at the flywheel on an A+ engine.  If so what are the options?  Thanks in advance!