Posted 01 September 2017 - 06:37 PM
Velict, I got your PM and will answer it as well but wanted to post up here as well because this is a frequent question for people new to A series builds.Regardless of wheter it's an A12, 14 or 15 the parts are more or less the same.
A full race A15 is going to be 150hp at the rear wheels and isn't even remotely streetable; needs 110 octane fuel and rebuilding every 6-7 hours of run time. For a full race A12 those are between 100 &110 at the wheels. These motors make no power below 5000 RPMs.
The motor in my car now would be somewhat streetable; it's a bit unhappy under 4500rpms but will at least pull away from a stop at 2500rpms, albeit not rapidly. The idle just ok and the gas mileage is poor (9 mpg on track, maybe as hig as 15-18 around town)
We're doing some fine tuning on it and I'm expecting around 110-115hp (currently 105) at the wheels which probably equates to 135-140 at the crank. Here is the spec; A15 76.5mm JE forged pistons, stock crank rods balanced, 14lb flywheel, Delta cam 278 degrees duration .420 lift, Ported GX head, 11-1 compression, SI 37mm intake & 30mm exhuast valves (SI makes them with a narrowed stem to increase port flow), 3 angle valve job, Iskederian dual valve springs, 39mm Keihin FCR Flatslide carbs on custom intake manifold, Nissan header, 210 electronic distributor set to 38 degrees at full advance (no vacuum advance) modified stock oil pump (gives 60 psi pressure) I got some smoking deals on some of the parts so I only have about $2500 in it.
The power is in the cylinder head:
You'll want the GX cylinder head, these will cost between $400 and $700 depending on what's been done to them.
Porting them isn't a huge deal, I actually did mine using a dremel. The biggest issue is the valve seat actually protrude into the port by 1mm all the way around, meaning you have a 2mm smaller port at the valve seat. Just getting rid of that makes a huge difference. Look at the pictures on Datsun1200.com of what is done around the guide / bowl area. After that match the manifold and gasket to the head. Also CC the combustion chambers so they are all the same (you can look this up) I use a piece of lexan and a basting syringe (get it in the kitchen utensils section of Walmart/Kmart etc.)
For valves use one of the Nissan prep manuals specs 38/32mm intake exhaust (as noted above you can use SI brand as the the stems are narrowed so they flow a bit more) the SI valves are 37/30. I do not remember the exact cost but I want to say they were around $150 for the set.
Delta Cams in Tacoma will do regrinds for around $100 (you'll need new lifters) as well as dual valve springs Isky sells them for a-series engines, I think they around $150
Custom JE Pistons with rings wil be around $600; you can go the Subaru Justy route for 79mm in a A15 but by the time you order up two sets have the block decked etc. it's almost as much as just buying custom pistons. Note on an A12 76mm is as large as you can go.
I prefer the Flatslide carbs but I got the deal of a lifetime $250 for the carbs and the custom intake manifold. You can price out 40-44mm DCOE carbs and compare that to having an intake fabricated and using 4 cylinder bike carbs.
For for headers / extractors you can buy the works of art Tomei ones that are a mere $3000 or generic types for $200 used. For a street car it likely won't matter. Use 2" exhaust out the back.
The one part of the equation rarely talked about are the gear ratios; the harder the motor is tuned the more it needs close ratios; a mid close box will do the job for a street car. I have both a mid close and an ultra close ratio 4 speed 56 series gearbox, these are fine for an A12 but the built A15 will eventually break them. I currently use a stock 60 series 5 speed, while I whine about the horrible rpm drop from 2nd to 3rd I recently turned my fastest laps ever with this gear box. The stock box is annoying but apparently not as bad as I thought, my motor is moderately tuned by race standards so I can get away with it.
Last is the rear end; I can't remember what is in the long wheelbase Utes, H165 or Borg Warner. If you're using a 5 speed then using a 4.11 or 4.38 ring and pinion is not a huge deal. A series motors will turn 5000 RPMs for hours on end so the lack of an overdrive won't matter to the motor but the passengers will get tired of it. Limited slips can be found but they are not cheap figure $1000-$1500. I paid $1300 for H190 LSD diff in my coupe.