I've gotten my coupe to 16.3's with a fairly warmed up A15...I did get it running better with additional tuning on the Dellorto's, should be 15's, but now I've got the EFI I'm waiting to put on in a month or so. If you want the cheapest speed I'd say go for an engine swap, CA18, SR20, or KA24...but it's also gonna weigh the car down a little more, cause along with that you're gonna need a stronger/bigger diff, radiator, brakes, suspension, etc. Even though I've got a lot of expensive go-fast parts on my A15 I'm still probably gonna do a swap, cause the A15 can only go so far, and I'm going to see just how far too with the EFI and turbo. If/when it gives then it'll be time for the swap I think because $10,000 USD for the Japanese Pitroad A15 is a little far fetched for 150-200 hp.