Barnett - in Australia 98 is just your standard premium unleaded as we use the RON (Research Octane Number) - this is the equivalent of 93 on your side of the pond using the AKI rating (Anti-Knock Index). So he isn't suggesting Rocket Fuel, and probably hasn't milled the heads too much.
See https://en.wikipedia.org/wiki/Octane_rating.
And yes I think that we should leave him with what he now has!
Cheers
Shane
.
thanks for the info . . i actually use the chart below . . my the point is that all the windsors run just fine and dandy
with no pinging on us 91 octane which is generally equivalent to your 95 . . in fact, many can be run on 89 which is between your 92 and 95.
the static compression on his engine if it is bored .30 over is 9.1 which means that it will run in 100 degree heat on us 91 octane, therefore the builders recommendation for 98 which is us 93, is at least 1 grade higher than it needs to be and there s no benefit whatsoever from running higher octane gas than is necessary . . it wont hurt to do this but it wont help at all and in some cases, it can will reduce power depending on the brand of gas.
also the other point is that the additive the builder is recommending is going to increase the octane rating by at least 1 which means that even under the worst circumstances, he could easily run your 95 and this is why i think he should have the builder tell him exactly what cc's the heads are . . If the builder did not measure the heads then it;s certainly more likely that he could run lower octane gas to save a few dollars.
Also, if his pistons have valve reliefs, his compression would e around 8.5 with un-milled heads and .030 over bore in which case he could easily run your 92 even without the booster which might save him around $3.00 a tank by itself . . That alone should be more than enough to buy liter of cold, tasty, fosters lager and get change back.
EURO RON US (R+M)/2
. 90................... 85.9
. 92................... 87.8
. 95................... 90.7
. 96................... 91.6
. 98................... 93.5
100................... 95.5
105................. 100.2
110................. 105