you already have the longest stroke of any dseries engine, there are places that'll do stroker setups to take it beyond 1.7ltr but the prices are rediculous. If you want more displacement my suggestion would be to have the block resleeved and bored out to a 77-78mm bore(75mm is stock)which will put you at 1758cc-1805cc(1.8ltr) if you were gonna stay naturally aspirated you could go to a 80mm bore which would put you at 1898cc (1.9ltr).
If you're gonna get into nitrous then yeah aftermarket internals(pistons, rods) are the way to go.
|