Due to legal reasons I can't swap my engine block, but I can swap any other part of the engine. I recently bought a 98 ej9 hatch, D14A3 (removing the limiter of course, to make it D14A4 effectively)
The current plan is: D15B head swap, vitara pistons, aftermarket rods (not sure if eagles fit?), a turbo ran at 12.5 psi.
according to zealautowerks, if I do some port work, I should reach around 200whp.

What else could I do to make sure I reach my goal? What would you do differently?

 

Looks like Pauter makes an aftermarket D14 connecting rod (138mm length, 43mm big end): https://pauter.com/shop/rods/acura-honda/d14-rods/

My guess is the Vitara pistons won't work and you'll need to contact someone like Traum to build you a custom piston to match the compression height of the stock pistons.

Refresh all the bearings, seals, and gaskets. Check your oil pump clearance and replace if it's close / above the service limit. Install some head studs, an OEM gasket, a clutch to hold the torque you plan to make, and get a good tune with relatively conservative timing.

 

Why would the pistons need to match the compresson height? I thought, since I'll turbo it, I should have a smaller compression ratio, right?

 

Compression height is not the same as compression ratio. Compression height is the distance from the center of the wrist pin bore to the crown of the piston. While compression height does contribute to compression ratio, the piston's dish/dome volume will ultimately be used to dial in the engine's compression ratio.

If the compression height is too tall, the piston will stick out of the block at TDC. If the compression height is too short, you'll have an extremely low compression ratio and your engine may run poorly or not run at all (this will be the case with a Vitara piston in a D14 engine).

Using this compression calculator and entering the specs for a D14 engine with Vitara pistons and 138mm length connecting rods, you'll end up with a compression ratio of around 6.5:1, which is terrible. Ideally you would want to end up with something between 9:1 and 10:1.

You won't be able to use the "Vitara" length long-rods (which are 138.63mm long) to compensate for the low compression height of the Vitara pistons in a D14 engine either, as the big end bore of those rods are 48mm and your crank has 43mm rod journals. You'll have to either go with a stock length (138mm) rod and a custom piston or a piston of your choosing (could be Vitara) and a custom length rod. Or you could mill a ton of material (we're talking like 3-4mm) off the block or head, but then you get into messing with mechanical timing issues. If you're set on doing this, the best bet is to buy the Pauter rods (or some other aftermarket rod with the same specs) and order a custom forged piston.

 

I get that, but if I put the comp ratio at 9 or 10, I don't get enough boost before reaching 12 effective comp ratio (which is around the limit I heard for D series engines AND pump gas) at 9 ratio, I get around 5 lbs of boost, but at 6.5, I get 12.5. Sure, I'll get less power at the low end, but with a D-valve and some other adjustments, my mid and top power will be way better?

Thanks for you patience, I'm very new to this stuff

 

You're doing rods and pistons right? That's the weak point on the D-series engine. Focus on sizing the turbo appropriately (a small, modern turbocharger will meet your 250 whp goal) and getting a good tune. The smaller turbo will require more boost pressure to flow the same amount of air, but it will spool quicker and give you a broader power band. If you go with a 6.5:1 compression ratio and a turbo that's too big, it's going to be a dog out of boost and take forever to spool.