Timing for Silvertop with Increased Compression

[85AW20v]

Anyone have any idea on what base timing to run on my ST with TRD head gasket plus 0.4mm off the head so total decrease is 0.8mm. Don't know what C/R it is now or cc of combustion chambers but its no longer an interference free motor! Timing is set at 10deg at the moment.

Is there a general rule of thumb - would you normally retard or advance the timing in this situation and by how much either way?

[pidge]

(nothing spectacularly helpful here...)

Generally, if you increase the compression, the static timing would have to be retarded compared with the static timing for the stock compression, all other things being equal. How much by I'm not sure (may be one or two degrees, plus perhaps another one or two for our Crap Fuel (tm))

Advancing the timing generally leads to Bad Things Happening, starting with simply poor performace (if the ECU usa a knock sensor), through to putting conrods through the block - but I think a 4AGE stops at simply bending the rods.

If you've done head work to increase the flow in and out (i.e. increase the VE of the engine), you may need to retard the timing further.

Perhaps comapring with a blacktop (CR=11:1, silver top CR=10.5:1) static timing, although the blacktop has a differnt compression chamber design as well, may be helpful.

[Mr Revhead]

both 20vs run the same static timing.

what fuel would it be running?
and what ecu?

[85AW20v]

Standard ECU and either BP98, Avgas or a 50/50 mix of the two.