Quote: A worked GX head is not the sort of thing that one normally associates with the word 'economy'
Like I said, you need to figure out just what you want, just what kind of fuel consumption is regarded as 'economical' by you, & how much performance is regarded as a minimum. Once you get it clear just what you want, you can move forward.

Just remember that new car engines have things like, four valves per cylinder, dual overhead cams, variable cam timing, EFI, & computers that are trying to 'tune' the engine while it's driving. If we could engineer all these things into a 1200 engine, we could very likely duplicate the performance of a new car engine.
What we are working with is a technological Dinosour, yet a very loveable one. We can only do the best we can with what we have to work with.

My big bore 1200 GX & five speed in my 1000 sedan gave quite 'spirited' performance, enough to impress a few unbelievers in its day, yet when driven for economy, it returned better than 50 mpg, Ummmmm, thats 17.7777 kpl or five point six two five litres per hundred kilometers.

This was with a mild cam & an otherwise stock GX engine but with a 76.5mm bore size. [1286cc]

If you want to run a bigger engine, with more power, then you can still get good mileage, just not quite as good, & probably not as often. [Then again, with the right gearing,...]

Do you have an aftermarket manifold with twin SU's or a GX manifold with twin GX Hitachi's?

Oh yeah, what do you bore out in an A14 to make it suit an A15 crank?

Quote: YOU LIE, ... you're not sorry at all.

Quote:
Yeh i know between work and the the wife time just drifts away.

I would have thought that if you want more power & reasonable economy, more capacity would be the best way to go. I reckon that a mildly worked A15 would be just as quick on the street as a heavily worked A12. Also the build costs should be less, the engine more reliable & the car easier to drive. Has anyone tried both?

it's partially about how and where you drive, i had a little 1.8L 4 cyl MPFI car, we'll call it a subahashi. on one particular drive the ambient temp was 105F it was running about 5500 rpm wound out in 3rd gear making about 105 mph. doing this for 1 hour resulted in a fuel usage of 10 MPG! it had very bad aerodynamics and not really much of an IC.

I nearly didn't make it to the fuel stop, had to drop down to 55mph and draft people till fuel was located.

point?

aerodynamics can help make or break your MPG at speeds above 55, and our datsuns aren't from the age where people drive 80+ mph daily / i do an mine can still get 30+ on the highway.

if you want to learn to drive more economically, get a vacuum gauge and learn to watch it and only give the car the minimum fuel it needs to maintain speed. that can gain a decent bit and you get a useful diagnostic tool.


strangely about 2 years later the same company released the most aerodynamic car of it's MY - the Alcyclone. hehe who has driven the flat 6 3.0l awd one? the 1.8t fwd one was pretty fun.

oh! other things that can be done to our engines... better EMS. ( i think i said that before )

even if you just get a aftermaket ignition box, that will help too, add a lambda 02 system.

funny thing is, some of this is harder to implement on a petrol car.

it's really easy to add a lambda system with TPS to an LPG vehicle, with a petrol carb vehicle, it depends on he carburetor.


what about things like roller rockers? shouldn't the reduced friction help some? mybe not enough to matter, but you'd still have roller rockers.