To make a long story short, I wasn't aware until last week that the front hub and pulley are a matched set from the factory. As it turns out, my timing has been about 10* too retarded for the last year or two. I was having all kinds of problems - torque down low didn't seem right, spool took forever (15psi at near 5000 rpm with a .96 undivided p-trim 60-1), and power wasn't where it should have been either (estimated @ 330rwhp at 15psi boost, stock ports). To top it off, around town mileage never got above about 13mpg, and on the freeway i could only manage ~18.5mpg with careful tuning. At the time I thought the leading plugs were firing 13*btdc with a 15* split at full boost (15psi). As it turns out, they were at 3*btdc and 12*ATDC!



So my question is... how much of an effect would the timing have on these things? Is there a significant difference in power between firing at TDC and 10*BTDC?



Thanks!

Manolis



PS - I zeroed my timing this time around by marking the pulley with an apex seal at the rear trailing plug hole, and then marking it with the seal at the rear leading plug hole. TDC is centered between the two marks.

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i did that with my 20b, hp went from 220ish to 140ish. yes i have a 20b dyno sheet @12psi and 140rwhp https://www.nopistons.com/forums/pub...#>/biggrin.png

Having your timing too far retarded, and 10 is a lot, would cause the poor gas mileage, very poor throttle responce, horrible power, and also cause your water to run hot.