thanks jmac i was planning on running 95 or 98 octane with the higher compression from the flat top pistons. But how else can i raise the compression to 10.5:1 or even 11:1? would that involve shaving the head, and decking the block? and the closed chamber oval port head your talking about is that from an a14/15? Head work is in the pipe line but just not yet. Ive already gone over budget on the first stages of this build and im getting all the machining at a discount, parts at trade and doing the work myself. I am a qualified mechanic im just new to modifications and have never really had the opportunity to do this sort of work.

With a cam like that (and I'm not suggesting it's 'the wrong cam spec' , but rather it's just a matter of getting the rest of the combo right to get it to work harmoniously) you're going to want to run enough compression to make it 'work' You'd certainly want to be over 10.5:1 (based on the assumption you'll run pump hi octane unleaded, not e85, or else you'd be able to go much high) probably as much as 11:1 given that it's the smaller bore a12 (which also helps avoid detonation vs a larger bore). Given that that is the case, I'd second the suggestion of going for a closed chamber oval port head. They'll outflow the round port head in std form, so if you didn't want to pay for porting at this time, it won't cost any more to reco an oval port head than an a12 round port head).

With such a rise in compression ratio you'll tend to 'get back' a lot of the part throttle crispness, throttle response and even fuel efficiency that is often seen to go hand in hand with modified engines. As long as you can source the various jets and chokes for the dellortos, and enough time is spent optimising the chokes, emulsions and jets/air correctors, you can actually get pretty decent economy out of the italian side draught carbs in general (don't forget they were fitted in various forms to a bunch of smaller Italian cars in the 60s and 70s, although outside of Italy most people only saw them used on race cars and factory high performance cars. A lot of that was also to do with price. But there's no reason you can't get good economy out of that style carb and an engine combo like you outlined. Obviously the other factor is a little harder to control (and I'm as guilty as the next person!) and that is the fact that this engine will outperform a factory a12 quite well, there's going to be a constant temptation to drive it to access that performance. So the fuel efficiency will also be strongly tied to whether or not it can be driven in a manner that will result in fuel economy in the first place :)

You'll be fine running a 2 inch exhaust system. they always tended to work on 998cc-1275cc minis even though on paper teh smaller 1 litre variants ought not to have needed quite that diameter exhaust, they just never lost any power, and for some reason the larger engines also similarly just 'clicked' with a 2" exhaust. The a12 isn't identical by any means, but in practice it also tends to show the same result. It's a handy size as most off the shelf extractors/headers come with a 2 inch main outlet past the final collector anyway.

thanks guys its going to be my daily driver as well, but i do eventually plan on doing head work. im not too fussed on fuel economy i mean how much more is it really going to use atm i drive about 20km everyday monday-friday and it costs me about $15 per week. I was expecting it to double would that be about right. And I will be ordering an electronic dizzy too. thanks for reminding me

had twin weber 38's on my a12. setup right will pull hard above 3000rpm.

Twin Dellorto's, Webers or Mikuni's would go very well on that engine. As mentioned you'd need to spend some time on the jetting.

I recommend an electronic ignition kit as well. A stock H89 head would go nice as well and bring the power up in the higher revs but you will sacrifice some bottom end power. It comes down to how you drive and what your fuel economy expectations are.

I'm not an expert at carbys but if you get the jets and chokes spot on it will be fine(this may take hours and may require a dyno). Twins will be harder to tune than a single dellorto, (once set up they will need a tune now and then) another option is a twin hitachi/su factory setup from a gx engine which uses a oval port head. I used a set of these for around 10 years and found tuning simple and they worked well. I'm my opinion you can't beat the sound of twin webers/dellortos

Hey guys im building up my A12 and was wondering if twin 40 dellorto are going to be too big for this build. I have .040" over flat top pistons, stock head with dual valve springs, 4.1 extractors with maybe a 2" exhaust (not sure if going to be too big aswell) and my cam specs are as follows
| Advance Ground on Cam: Lobe separation: 107 |
| .050 VALVE TIMING |
| Inlet opens: 13 BTDC Closes: 47 ABDC .050 Duration: 240 |
| Exhaust Opens: 47 BBDC Closes: 13 ATDC .050 Duration: 240 |
| ADVERTISED VALVE TIMING |
| Inlet opens: 40 BTDC Closes: 74 ABDC ADV Duration: 295 |
| Exhaust Opens: 74 BBDC Closes: 40 ATDC ADV Duration: 295 |
| Inlet lobe lift at TDC on the over lap:.084 |
| ----------------------------------------------------------------------|
| Valve lift Inlet: .4118 Inlet Rocker Ratio: 1.50 |
| Valve lift Exhaust: .4091 Exhaust Rocker Ratio: 1.50 |
| Valve Lash Inlet:.014 Valve Lash Exhaust: .014
Your help would be greatly appreciated because the carbs are the last thing left for me to order before i start rebuilding, so if you have a different carb setup you think would be better or think i should change anything in the build let me know. Im new to the datsun scene and need your help.
Thanks in advance