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Your Nissan A Engine is built for spritely power with maximum longevity. If you want to trade off reliability for wear-time, you can increase the horsepower significantly. The following applies to all Nissan A engines: A10, A12, A13, A14, A15 and A12A.
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Baseline Tuning
Tuning your car to factory specification -- without buying a hotrod parts -- can double the horsepower of your car. Even when relatively new, 1970s cars could be far out of tune. See Supertune.
Be sure to start here. Adding aftermarket "performance" parts won't help an engine that has basic tuning flaws in the first place.
Impact
Consider that the biggest acceleration gain is to be had by changing the rear axle ratio. Going from the stock 3.9 to 4.2 makes a stock A12 rev a lot faster, yes you'll have to shift sooner, but that's kinda the point, innit? And you can still do 75 mph (120 kph) top end. If you have taller-than-stock tires the need for a steeper rear gear is even more important.
First Upgrade
The biggest change you can make is to rev the engine up higher before shifting. The factory stock A12 can be run to 6000 RPM before it gets to the red zone. It will cruise (run all day) at 5000 RPM.
Then once you are used to running the engine at high RPMs, if you add a larger carburetor it will make more HP:
- It won't make the engine run better below 4,000 rpm
- From 5000 to 6000 RPM, hp will improve significantly
Adding a carburetor is relatively easy. The most popular swap is the Weber 32/36 DGV family. See Weber 32/36 Carburetor.
Of course at higher RPMs your engine will wear out faster. It is a trade-off you need to decide on.
Also see: RPM
Engine Swap
Before you go farther, decide whether you should swap in a larger engine. For example, going from an A12 to an 80HP A15 may cost around $500 for a good used engine, but will equal about $2000 worth of "buildup" for an A12.
A15 with larger carb: 85 hp. Cost: $ A12 build lots of work: 85 hp. Cost $$$
And the A15 will still have an acceleration advantage, having more average horsepower (25% more power at low RPMs).
The 80HP A15 is less expensive, easier to drive, and will last longer. On the other hand the 80 HP "built" A12 will be more exciting and sound gnarly when run at high RPM.
Stage One Buildup
Stage one is all about bolt-on induction improvements. This is relatively easy -- it doesn't involve removing the engine.
$
- Larger carburetor, e.g. Weber 32/36 (see Choosing A Carburetor)
- Exhaust headers (extractors)
- Stock 1.5 inch diameter exhaust
On an A12 engine, this might make, what? 75hp? (compared to 69hp stock). This is measured on an engine dyno (Factory specs are *not* measured by rear-wheel-horsepower -- see Performance).
Or: $$
- Sidedraft inlet manifold
- Twin sidedraft carburetors (see Choosing A Carburetor)
- Exhaust headers (extractors)
- 1.75 inch diameter exhaust (entire exhaust, including muffler)
On an A12 engine, this might make, what? 80hp?
Stage Two
Stage Two requires engine work on the inlet and exhaust side. It builds on Stage 1 by adding:
$$$
- Performance Camshaft, such as A12GX camshaft
- with mid-RPM dual valve springs, such as A12GX springs
- Cylinder head work:
- Head Porting and larger valves, or
- Oval-port head swap
On an A12 engine, this might make, what? 100hp?
Stage Three
Stage Two is a high-dollar option that includes new pistons. It makes power by revving higher. At 5000 RPM it may have less HP than stock, but at higher revs will have more HP than stock.
It builds on Stage 2 by adding:
$$$$
- Flattop pistons (for A12, use Datsun 1000 coupe pistons from KB10 model), or Forged dome-top high compression pistons
- High RPM (7000 RPM or more) camshaft
- High RPM dual valve springs (stiffer than GX springs)
- Big Valves: Larger valves than A14/A15 with Head Porting
High Compression pistons can add 3% horsepower, but you will need to buy premium fuel. Flattops will add 1% maximum horsepower.
COUP1200: My A14 makes 140hp & its not EFI or turbo. I have twin 40mm webers, good extractors the head flowes 141hp. All your power gain is in the head big valves extencive amounts of porting good spark ... I dont run roller rockers & have not had a problem.you dont need to go to big with the cam mine about 74deg ... Mine makes power to 7500rpm.
feral: COOPS 1200 SEDAN AFTER RUNNING A 2:11 AT PHILLIP ISLAND CIRCUIT ... The car sounded awesome and handled very well. In typical 1200 fashion showed alot of more exotic machinery including a Porsche 924 turbo and a lotus elite a clean pair of tailights :-)
Short Block
Upgrading parts to the block (rods, rod bolts, studs, forged crank, etc.) does not make more HP, although it may enable to engine to last longer. A totally factory-stock A12 short block can make 140 reliable HP with the right top-end parts.
- Forged pistons are generally called for at power levels in excess of 140 HP
- ARP rod bolts can be used for RPM usage above 8500 RPM
- Main studs will not increase the reliability -- the A12 already comes with the same tough main cap bolts as the L18 engine. It's overkill right from the factory.
- The stock crankshaft is plenty strong for 8500 RPM use
- For 10,000 RPM use forged pistons, custom rods, ARP bolts, and dry-sump lubrication
Forced Induction
Alternatively, adding a turbocharger or supercharger will make equivalent maximum horsepower but with more low-speed horsepower. It's generally less expensive than a traditional build-up too.
See main articles: * Turbo * Forced Induction
Example Builds
See Builds