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What's a budget way to increase cc's in an a12?
No life (a.k.a. DattoMaster)
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Hey guys. Legally here the biggest motor I can use is an A12. What combos of boring and pistons can I use to increase cc's and compression for a decent street engine? I don't want to go spending a lot on it, just find a balance of cost vs effectiveness. I may even just go a10 piston if it's not really too effective

Posted on: 2021/11/11 2:56
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Re: What's a budget way to increase cc's in an a12?
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Posted on: 2021/11/11 5:21
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Re: What's a budget way to increase cc's in an a12?
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Yeah an engine buildup is fun and can end up with more performance than a crank swap. On the other hand the larger CCs make for quieter and more relaxed acceleration


A10 pistons are same size as A12 at 73mm diameter so no CC increase there

The traditional way to increase CCs is to 'bore and stroke' the motor
* Bore the cylinder block +3 mm so larger 76mm pistons will fit (increase of 99cc)
* Use an A14 crank to gain the larger stroke (increase of 118cc)
Do both and the engine goes from 1171cc to 1397cc, an increase of 19%

for details see our tech article Bored and Stroked

Posted on: 2021/11/11 7:06
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Re: What's a budget way to increase cc's in an a12?
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A10 piston is a flat top , doesnt it have a higher comp ??

Posted on: 2021/11/11 8:15
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Re: What's a budget way to increase cc's in an a12?
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Wet sleeve it to 82 mm bore and fit modified A15 crank.

Posted on: 2021/11/11 11:39
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Re: What's a budget way to increase cc's in an a12?
No life (a.k.a. DattoMaster)
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Cheap is the operative word.

Fitting an A14 crank while not expensive is also not cheap.

Search for 76mm A14 pistons or the 75mm A12A pistons, then install whatever you find. Having the block bored is cheap enough.

Next port the head; you can do this yourself with nothing more than dremel. Concentrate on the bowl area of the ports and the valve seat. The seat actually protrudes into the port limiting flow.

After that find a used Weber 32/36 DGEV carb.

You can also use the GX head gasket to up the compression slightly.

All of the above will net you a out 12-15hp and set you back $450 - $500.

Posted on: 2021/11/12 2:21
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Re: What's a budget way to increase cc's in an a12?
No life (a.k.a. DattoMaster)
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Awesome info thanks. If I can find some cheap a10 pistons, I'll stay at stock bore. If not, I might go bigger bore. Is there any particular a12 bottom end that's better to use?

Posted on: 2021/11/12 2:32
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Re: What's a budget way to increase cc's in an a12?
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All A12 bottom ends are the same - tough and durable


Yeah A10 pistons are flattops. The later A10 pistons (the ones with the shorter skirt) were used in the Datsun 1200 GX engine. Going from the standard 9.0 compression ratio to 10.0 is good for 3% more power. To achieve that use the flattop pistons and the thin GX head gasket


On the other hand, fitting 3mm larger pistons will give the A12 about 8% more average power -- even if you keep the stock compression ratio

As they say, there is no replacement for increased displacement. It is more power for less money and less work to go with a larger engine

Taking that even further, ADR allows self-certified engine swaps up to what? 1360cc or so? And if engineered, up to 2 liter via the NCOP guidelines. In SA they have gone even larger
Quote:
We have been doing this for years in Adelaide with a few different very good engineers. Its not cheap, so dont think you can get it done for $500 or $1000, they normally charge $2500 upwards...
the problem is finding the right engineer, most decline to engineer anything outside the NCOP guidelines

Posted on: 2021/11/12 3:56
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Re: What's a budget way to increase cc's in an a12?
No life (a.k.a. DattoMaster)
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Proper running stock A12 is plenty sweet for a 1000 body, the torque increase alone is excellent but gearing
is not pleasant on the freeway vs an A10 which sings nicely at higher rpms due to motorbike like 59mm stroke.
I would stay the A10 if you have it, they last better than any other 3 bearing engines due to that stroke.

If you must modify an A12 I only recommend early A12 blocks as they seemed to have more beef round the bores
for A14 76mm pistons machined down to flat tops you will get an A13. Front dizzie helps with 1k mounts.

Theoretically A10 to A13 is 30% more everything providing you also up the compression a tad,
Singh lines usually reduce detonation/carbon build up dont increase hp but cleaner running engine that
allows higher compression ratios to make the extra hp. Small ports are underrated for cars.

Use an A15 flywheel or the heaviest flywheel you can get dont use the A10 flywheel and
stock exhaust for best running on the street.

Tom must be in a very cheap and diy friendly place for a14 crank and other mods but in Oz
A14 crank rebalance, suitable pistons, porting, dgv carb and the rest is 1000-1200aud.
In Oz electric dizzie, rejetted carb, machined pistons and head shave will cos $400-600 all up.
You will have an A13 with clean accelerator no hesitation and great fuel economy.

Here in Japan the manual Kei cars almost match the old vw beetles which were the most delightful
cars I have ever driven for torque in any gear, great economy and just feel good all the time
without any urge developing for wanting more of everything. The A12 stock is a nice engine but
going up to A14 and 15 the gearbox is the big price upgrade these days a 2k aud option.

After all that for a 1000 I would stay A10 all day, best economy, good revver, reliable and cheap.
For a street 1200 stock running like new is also nicer than most give them credit for.

Posted on: 2021/11/14 1:45
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Re: What's a budget way to increase cc's in an a12?
No life (a.k.a. DattoMaster)
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I'm pretty sure my diff center has been changed to a 120y one (old owner told me that). I am allowed to boost an A10 legally (has to be the original type motor so no a12+). I just dont think the 3 bearing mains would like it all too much?

Posted on: 2021/11/14 5:25
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