so who has experience in doing blow thru turbo conversions on A12 engines? ... cheers ryan

What would you like to know?

is it such a costly project to have an affective turbo in the a12

Look I've done a few small engines, and a fair few blowthrough in general. It's not that hard, or expensive, it's just a matter of patience sometimes.

theoretically you could get a 1200 with a12 to run in the 14s (I did it in a much inferior 3K powered corolla, with small port head and an abortion of an exhaust hookup).

Holley 350 is far and away the easiest carb to prep for blowtrhough. As long as the throttle shaft seals are reasonable, it won't seep fuel out of them. Then you just run a nitrophyll float (reinforced off the shelf float for a holley, has been pressure tested above 60psi and won't collapse, by people on the old blowthrough turbo list, they put it in a chamber and ramped it up that high and left for hours). You might find the powervalve works a little inconsistently, so you can run a power valve blockoff plug. To get the right full power mixture back, you run slightly richer jets than you would for an NA holley on 1200 and reduce the high speed air bleed area by about 50% which will make it go progressively richer as flow/boost ramps up. That method should be enough to get you to the limit of safe boost for a stock engine anyway. Stay _well_ away from holley 320s. They are a heavily reworked 350, with different booster venturis and a much altered metering block, setup for high signal strength and fine metering, for _emissions_ purposes, they aren't the go for performance,

You''ll need an electric fuel pump, rising rate regulator (malpassi do make them for carb spec, or you can get an efi spec one and replace the spring with a much lighter one - and this is about the only size engine a malpassie would be recommended for, they aren't great for higher flow rates / needs) and of course a modified tank for new pickup/feed line (needs to be bigger than std) and a new return line from the regulator (and the stock fuel line will be too small and likely act as a restriction - if used as a return line, and cause the fuel pressure to ramp up.)

I used holley pumps, and disabled the integrated bypass/regulator. They pop off around 10-12psi, and recirc the fuel in the tiny amount around the pump itself and cause it to overheat, and also limit output pressure. They are often used with deadhead regulators. With a BYPASS regulator, like the malpassi (and only with this type of reg) you can disable the internal spring/valve and the fuel pump will work (transiently) up above 20psi. It doesn't have to do that for long, because at that much boost, you are at the end of the strip before long. All other running around, the regulator bypasses all the fuel, so there's no real load for the pump, it runs cool with no load, and cooler still because the fuel is recirculating in a huge loop to the enginebay and back, and cooling it.

If you are really on a tight budget, you can find an old fire extinguisher, there's a standardised size that just happens to be able to be cut open and will fit perfectly as a carb hat, just needs an inlet pipe welded in. They are thick steel - probably more than 3mm, so won't flex or leak. Can be a bastard to cut straight through. Best advice there is to use a band saw and plenty of lubricant for the initial cut, then mount in a lathe, and true it up using a stone cutter if needed. The size of the jaws of the lathe would have to be big, so you'd have to farm that out. Still heaps cheaper than a commerically bought one. Other option is to use the 'lego' type pieces of the lpg conversion snorkels to make a carb hat. One word of caution, make the air inlet to the carb hat a good 2 inches above the choke horn (even if the choke horn is machined down) because any closer than that and air rushing across the top of it can depressurise the fuel bowls and interupt fuel flow into the engine.

The rest is fairly simple stuff, less total timing (posssibly even a locked dizzy).

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Having said all that., I'd STRONGLY suggest finding an a14 or a15. The extra capacity means you need less boost to get the same output, and that extra stroke also tends to mean a wider powerband, more flexible engine. Or if you run the same boost, it's a going to run a lot harder than an a12. Consider also the oval port heads on most a14/15s will be better than the round port on an a12 (unless you find a GX head)

^thats a pretty good write up

wow that was a good read nice work. . .