The "diff" is the rear axle assembly, which includes the differential.

You can make perhaps 75 HP with the mods you listed, which is more than the 65 RWHP which the A15 makes stock. Instead of a mild cam (which is what the A15 comes with stock), use a 7000 RPM cam with mild head porting for 90 HP.

Using the lighter A12 flywheel will make the engine run less smooth as low RPMs, such as when creeping along in traffic. But reducing the flywheel weight lets you accelerate a little bit faster.

I'll give a list of some things I just did as I'm put an A15 in my coupe: I'll leave out the costs for things that needed to be rectified because the engine sat.

Forged flat top pistons with rings were $550, the machine shop bill was $920 (boring, balance,bearings, new guides and seats) bigger valves were $125, Gaskets etc $100, i bought a cam from another forum member $125..........so near $1900.

Now add in I had an existing GX head, Dual Valve springs, flat slide carbs and header, I got a smoking deal on the parts and still had $750.

$600 for a 4 speed close ratio box and I'll have $1300 invested in a upgraded rear end


So I'm pushing 5K pretty quickly, I'm expecting to be around 110 at the wheels, the motor idles OK and should make power from 3500-7500 rpms.


The A12 I had made 80HP at the wheels (this is probably around 92-95 at the flywheel and needed to be kept above 4500 RPMs..............I had about $1300 in it.

Tom

I think you'd find yourself quite happy with about 100 flywheel horsepower from the A15. It could be done with a change of camshaft, fitting of a downdraught twin barrel weber, a slight increase in the compression ratio & the fitting of a good set of extractors & exhaust. You wouldn't have to overbore the motor, though a clean up of the bores 0.5mm may be necessary. This is the recipe I have for my Sunny wagon with an A15. It has 300,000 k's on it, & when I finish putting the L20B into my Sunny coupe, I'll probably pull the engine out & get it rebuilt. The car is already quite nippy with the A15, surprisingly more so than the A12 powered Sunnys I've had. So, a factory 70 degree cam with GX valve springs, 76.5 mm stock replacement pistons, a 32DGV or 32/36DGV Weber, a factory GX exhaust header or aftermarket extractors, a larger exhaust, an N12 Pulsar electronic distributor & a HEC715 coil to suit is what I want. If you still want more power, twin sidedraught carbies, larger camshaft , bigger pistons etc,can be fitted. I'd recommend you fit the A15 first, to see how much more you need after that. Remember, the A15 is already 86HP, with a lot more torque. A bit of fine tuning & you could be very happy with the result. My second 1200 sedan had 100 HP at the flywheel, & it was a rocket, so 90-95 might be just what your looking for. Good luck as always with what you do, let us know how you're getting on, too. Too many times I've never heard from somebody again, I always wonder was what I said any use. So I hope this is useful to you.

thx so much everyone! :D this has been a lot of help! i will try to start my project as soon as i finish the exams which i'm doing right now, so soon hopefully :) i will definitely use the advice and suggestions you gave me :)

Thank a lot for you advice dude :) it is very useful! :D i have another problem though, its about the gearbox. With the a 12 at 130-140km/h i'm in 4th gear and its revving the balls out of it! Lol would i have the same problem if i modify an a15 with the 4speed gearbox of the a15?

If you use the A14 4 speed, it'll have the same gearing as the A12. Interestingly the extra torque means you can use less throttle to get the same speed, so it seems easier. The only way is to find an overdrive 5 speed to suit the A15, which are quite rare over here in Australia. They are easier to come by in South Africa, being used in the Baky ute until they stopped making it. It does make a difference fitting the 5 speed, & you never know where they'll be. You can only look, I suppose.

Mmm ok :/ the thing is i'm in malta so i definitely won't find that gearbox :( do you know any alternatives? Can i install a different gearbox? Or if i stick with a15 gearbox would it be ok?

The A15 can run at 5000 RPM all day long. Don't worry about it.

I think i dind't ask correctly. What i want to know is: if i modify an a15 engine and use the 4 speed gearbox of the a15 wouldn't it stop making power on 4th gear pretty quickly since the engine has more power and therefore it goes through gears faster? I mean with my stock a12 it feels that at 140km/h (the engine now is revving hard on 4th gear) stops making power, it feels like it needs a 5th gear. Would that not be a problem?

The A15 makes more power at 5000 RPM than it does at lower RPM. If you shift it up to another gear, the RPMs go down and so does the power.

A 5-speed is good for fuel-economy, but is slightly worse for acceleration. A 5-speed does not increase the top speed -- more HP does. Highest top speed with a 5-speed is achieved in 4th gear.