I bet this has been answered, but I haven't found it yet. I was working on making an intake manifold to stick some sidedraft SU's on the car rather than the single downdraft but the more I read, the more it appeared that the later Datsun downdraft really is terrific for everything but performance: it starts well, idles well, accelerates well, has good economy. SU's appear to breathe better, but are a lot of work on all other points. Now I'm back to thinking about fuel injection, and making the SU intake adapters was kind of a pain even without FI bungs welded on. I was reading the page about fuel injection and saw the pic of the throttle body FI unit using the stock intake manifold, and hey wow that looks easy in comparison.
So if I were to go find a throttle body from some other car and machine an adapter plate, what size would it be? Roughly the same cross-sectional area as the combined area of both bores in the original Datsun carb?
Anyone else done this?
Still very much in the planning stage, but it'd be a neat addition, and sure make later boosting easier.

Yes, SUs start well, idle well, accelerate well, has good economy. And breathe better

Quote:Yes, that's a good starting point. For factory-like breathing of A12 use a 33mm throttle body, A14: 35mm, Weber 32/36: 37mm. SU: 38mm

The factory Nissan A14 throttle body

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Quote:Yes looks easy, but not great for performance. The engine will be limited by the flow characteristics of the stock manifold




* Stock manifold + A12 carburetor: good flexibility, limited power
* Stock manifold + Weber 32/36: poor flexibility, good power
* Stock manifold + EFI: excellent flexibility, good power
* Factory twin-SU manifold: excellent flexibility, better power

If you look at the turbo a series for under 1200 thread Simon's using a Hyundai Excel Throttle body (from memory). Being something I'm currently looking at myself I'm thinking a throttle body off a 1.5-1.8L motor, ideally one that also has an IAC stepper built into it to make cold start up easier. Something like the one on the GA16de engine. I'm planning on heading down to the wreckers just to see what there is.

This calculator is useful for comparison:
http://www.megamanual.com/v22manual/minj.htm#throttle

Ideally you want the minimum size to have zero restriction at WOT/ max power. Going too big makes it hard to drive. A progressive dual plate throttle gives you a little bit of both worlds, larger throttle area but good part throttle control.

Huh, maybe I should look at the SU's more if they do okay. I have a matched pair from a 1500cc MG. But in a lot of ways fuel injection sounds easier. (I'm more a software person than a hardware person, in a lot of ways.)
I'll reread through the turbo 1200 thread. There is SO MUCH MATERIAL in there I end up distracted by other neat subprojects.

Maybe I should go ahead and use the DIY A14-to-SU adapters, bolted onto the side of a plenum, with the injectors on the opposite side pointing down the mouths of the adapters, rather than try to figure out how to put them as close as possible to the valves. It's for a street car, anyway.

Hey that page says 38mm will do 83 HP -- exactly what the A12GX engine is rated at (and using 38mm SUs without plenum)

If you can find an injection throttle body at the wreckers that would be ideal (the Hundya one doesnt have an injector)

True, if you're in Aus there were some 90s astra/ pulsars that had central point injection, there was also a ford falcon (3.9L?). A trip to the wreckers might save you a bunch of work...

Nissan B12 and N12 had them too. They have the throttle, TPS, and fuel regulator together

Here's a Nissan throttle body from 1987 Pulsar G16I engine, almost a bolt-on compared to stock A-series carburetor -- and compatible with MegaSquirt

inludes
* 1200 style throttle linkage
* MAF (mass airflow sensor)
* TPS
* IACV (Idle air control valve)
* Fuel regulator
* Injector

Uses an air cleaner & filter the size of the 1200 air cleaner

Normally fitted with a electric heater-grid spacer between the manifold and the Throttle Body, but if used on a stock A12/A14 manifold (which is heated too), then that it not needed

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