hi guys... im planning to bore one of my a15 to 79mm.

is the power gain is worth? please advice guy...

Boring the block to 79mm is a common thing for racing, as this makes the engine 1608cc's, which is allowable with CAMS' +3% rule. For the street, It depends on how you want to use the car. If it's a daily driver with a little cam, in my opinion the difference is not worth the cost. If it's an all out street racing engine, every little bit counts. It also takes away a lot of engine life, if you rebuild every 5 years or so with a 1mm overbore each time, that's 2 engine lives you've bypassed. You can get good quality 77mm pistons for about $100 Australian. I don't know what a good quality set of 79mm pistons would cost, but probably a lot more than $100. So, what do you want to use the motor for? If for a daily driver, they're not worth it, again that's just my opinion. If for racing, street or track, go for all you can get.

hi b310gx.

thanks for you advice.. this is for my daily drive b310. standard a15 (block and internal parts from a15egi, except the head) with lightened flywheel,4-2-1 extractor and twin SU. BTW i want as quite as possible car for this set up.

if i have to sacrifice the engine life... better i stay away..

I had a 1200 wagon with an A14, twin SU's & extractors. Not even electronic ignition. Was a wonderfully torquey engine, until it burnt an exhaust valve. I rebuilt it with a 79mm bore, a 70 degree cam, factory efi, an aftermarket fuel computer & an electronic dizzy. It had less horsepower, torque & was a lazy engine, due to the fuel computer being too crude. Should have just serviced the head with new valves, got some 76.5 mm pistons & not worried about efi. would have given it the cam though, as I've used the 70 degree cam before with great success. Doing the same with an A15 would be just as good.