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boosted79 boosted79 is offline
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Join Date: Jan 2015
Posts: 1,317
Does anyone understand the ignition curves in the WSM?

I'm trying to figure out the centrifugal advance curve on pgs. 28-4d in vol1 of the turbo supplement WSM.

On pg 28-4d it shows a centrifugal advance curve for USA, Cali and Japan from model 78. At 2000 rpm dist. speed it shows 8* advance of dist shaft. It also shows at 500 rpm dizzy speed it has a +-1* advance of dist shaft from TDC. So since dizzy turns 1/2 crank speed that means at 4k crank rpm the centrifugal advance is 16 crank*and at idle speed centrifugal advance effect is +- 2 so essentially zero effect at idle as expected. On pg 28-4c for USA (not Cali) it says timing must be 26*+- 4* BTDC at 4k rpm with vac hose disconnected. Ok so max total timing for USA version could be 30* at 4 k rpm. So since centrifugal only gives 16* advance that means the timing at idle with vac hose disconnected would be 14* (30 total less 16 centrifugal), correct?

Of course then the vac pot pulls out 20 crank* at idle so that gives timing at idle of 4* ATDC (14 BTDC - 10 = 4* ATDC). That agrees with the sticker on my engine lid that shows timing of 5* ATDC.

I'm assuming this retarded timing crap at low rpm was to keep the exhaust hot for the reactors to work?
Old 06-27-2017, 05:24 AM
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