In the quest for greater power I have decided to build up a high spec A15. Plan is to use my A15 block with A14GX head, Charcade turbo pistons, GA16 crank and motorbike fuel injection, semi racing cam D1 coby type extractors and skimmed head. Any thoughts on this monster project would be great.

Are you sure the ga16 crank is better than the e16 crank for machining and fitment?

If you want to go all out you could perhaps consider a spacer plate with billet sleeves machined into the block. This can allow for longer rods and also lower comp with the pistons youve chosen with the right spacer height. Youll need slightly longer pushrods and Arp head bolts.
Using a modded e16 crank will give 88mm stroke which would be nice for capacity and torque under boost. Bore spacing of the E series crank are the same however the crankpins are very small (great for extra performance) which lend themselves to motorbike forged rods. If you go even more radical you could have the deck machined open and have removable sleeves with rubber sealing rings for ease of replacement and the spacer plate can be bonded easily. Then if you have an engine block that has easy to replace sleeves and spacer plate in case it needs re decking.

Not sure if the GA16 is easier then the E16 for fitting. I like your ideas but they are a little extreme for me at this point. The aim is to get 120 flywheel hp NA that is useable in a street car, and then if I see fit wild cam, re tuned ECU for a rally hack

120hp is easy to get out of an a15. Bore it out at least 40thou and fit flat top or domed pistons from daihatsu and the like motors so you can get compression to at least 11 to 1. Open up the ports on your head a bit more and go oversized valves around 40mm inlets and 33mm exhausts with double valve springs on top. A 30/70 cam will get you 120hp and it is streetable. It will also be a lot easier to just go twin webers rather than mucking around with other induction methods. And finish it off with extractors.

Mitch I'm not sure why you're after the stroker crank and all that but my motor makes more power than that even in the smoking state it is in now. Without fancy crank or injection. If you want 120hp why not stick to the tried and true methods you won't even need a big valve head if you do it right. High compression big cam twin 40s extractors and a decent port and polish. get it tuned on a dyno and if it's all done right you should get 90-100hp at the wheels I would think.
If you go injection what ecu are you going to use? That's the main reason I'm running carbies on the CA, the costs of buying a link etc is prohibitive at the moment.
Sounds like a interesting project though!

to my knoledge the reason for longer rods is this: Under operation the longer rods are actually pivoting less near the piston and therefore arent exerting as much stress on them. It's probly why Honda opt for a longer stroke on thier sports bikes

Long rods and long stroke are two different things. You can have a long stroke engine with either long rod or short rods. In automobile engines, the long stroke engine is more likely to have shorter rods to keep the engine small.

Sure, you can get like 1/10 of one percent better horsepower with longer rods...which is a big deal for a multi-million dollar racing team.

when "high spec" was used I thought max hp say 300hp or so

the F1 engines that run really high rpm use a short piston movement with a long linkage to multiply it back out, it lets you rev over 20,000 rpm without your piston tops breaking the speed of light.


to make a high HP A15 - turbo(or whatever to get the cr up to 12:1). burn decent octane fuel, use real EMS.

everything else will just get more.

you'll need lots of cooling capacity and and oil cooler too.

f1 engines have crazy rod stroke ratios by using the bigger bore very short stroke but long rods for their design.

The longer rods improves harmonics also but the a15 needs to be made taller to allow this with the bigger strokes, hence sleeving and spacer plate.