Ok this week I landed an 81 A15 powered wrecked Datsun for a whooping $60 so at that price I figured time to upgrade from the modded A12 that's pumping out 85HP

The goal is a 100HP A15 (I've been racing the A12 for 16 seasons)

So here are my questions;


My current A12 uses the so called H-production head (Kidney shaped chambers with round ports) , the head has A14 swirl polished valves with a very good port job , header and a single side draft Dell Orto. (I believe this year A15 in the USA had a smogger head.) So use the worked A12 head or work the A15 econo head?

oil pump should swap straight accross correct? (the one in the A12 has been modded)

A12 flywheel should also bolt on (car has an Auto Box) plus A12 flywheel is lighter , correct?

Finally cam spec: I wish to keep a non interferance fit motor. I instruct at a ton of track days and have been distracted with a student in the car and floated the valves once (8100RPM's) So I am thinking of using the GX spec cam.

So to sum things up I'm looking for 100 HP using an A15 with worked A12 round port head , A14 valves and dual springs , single side draft Dell Orto (LF hand drive car dual carbies foul the master cylinder) , Header ,2" exhaust, A12 Flywheel and a GX spec cam.

Thanks in advance , Tom

Note; I use a 4 speed box with an H145 LSD and the 530KG pressure plate

Don't know if 100 is achieveable but as for the questions

1. I'd try the A12 head first
2. A12 flywheel will be fine on the A15. I use one.


Thats all I have

100 Brake, or at the wheels?
No way in hell are you going to get within a bulls roar of 100 Brake horsepower with a GX cam. They are a prodution grind (Read tame) that is bugger all better that a stock one.
I'd pull the head off the A15 and check out what chamber it has before making any decisions on which one to use.

Thanks guys keep the opinions coming

Talking brake HP

OK on the Cam anyone have a rough spec on something more aggressive than the GX but will still allow non interferance fit??

The 100HP is a "goal" regardless the A15 will still have more go than the A12 for sure.

Tom

My cam specs

I run 1.65:1 roller rockers
So its probably abit big for your requirements of non interference

Thanks for the info , with the A15 it's not likely I will have to buzz the motor to 8000 to keep the car moving forward.
Basiclly I'm lazy , I like to drive the 1200 not work on it so I'll give up horsepower for bullet proof reliablity.

Tom

Tom,
Contact Elgin Cams ( http://www.elgincams.com/ ) in Redwood City, CA. Tell him about the engine, gearing, etc. and he should be able to grind a cam that will work (make sure you send him a A14/A15 cam core)
Bruce

use the lightest flywheel, really makes a noticeable improvement in acceleration light crank pulley will help too. I don't even have double valve springs and the engine is really responsive ( spools quick ) and I never go over 6250 rpm ( soft rev limiter )

I'd go with roller rockers in any case where you have $$ as it reduces valve train friction and makes more power go to the wheels.

the A15 isn't a rev monster, but you won't need to rev it as much. Having a lighter valve train makes downshifting more fun.

Bruce I called Elgin and will be sending him a core. They were asking about how much the head flowed , as if I had a clue , but said provide as much detail as possible. Anybody know the rod length center to center?? I can give him valve sizes , carb size , RPM range and most of the stuff including my desire to have a non interferance fit. This sould make the "pokey" not so Pokey anymore.

Tom

Rod length on A14's and A15s is 133mm centre to centre +/- 0.05mm.

Watch your compression on the smaller a12 chambers. You can actually go for quite a big cam with an a15 and still achieve 0.060" clearance between piston and valves.

I have a simulator which can give very accurate results with all this type of thing. Its very useful in designing engines. When you have a good idea of what you are planning to do, then I'm only too happy to run your specs through it.

Things I'll need to know are bore, piston brand and type, cam specs (or let me figure out the biggest), chamber volume and depth the valves sit above the head/gasket interface. If you give me head flow figures, inlet manifold dimenions, header dimensions as well then I can also give you a rough idea of flywheel HP.

Daniel