Ok, I know what your thinking. Bill you idiot, you can't put 55psi to a carb! It'll blow right past the needle and seat. Ah, young grasshopper, read on and learn.
When building a blow-thru you end up either modifying a mechacnical pump for boost reference (adding boost to the atmospheric vent on the pump to increase the fuel pressure as boost rises) or using a Fuel Injection style pump with a boost referenced regulator.
The reason for this is when you put boost to the carb you are pushing back on the incoming fuel at a 1:1 with boost...so if you are running 10 lbs boost, 6 lbs fuel pressure and had 5 lbs for line-loss..you are looking at 10psi + 6psi + 5psi = 21psi...even the healthiest of carb pumps like a $200 Holley HP can't handle that! (it only puts out 16psi max) ...and if you are using a dead-head regulator add another 10-15 lbs for adjustment. So, from a pressure standpoint you got to run a bunch and regulate it down.
Then we have to think about feeding the beast. How much fuel does it take to feed a turbo small block. Well it goes a little something like this:
BSFC - Brake Specific Fuel Consupmtion. This is the amount of fuel it takes to support 1 horsepower for 1 hour. For a normally aspirated engine this is around .5(lbs/hr)/Hp for a turbo it is about .6(lbs/hr)/Hp (as a side note: superchared is even higher - around .65 - as it takes crank energy to spin the blower). So to figure your needs you take your target horsepower (in my case 425ish) and multiply it by this number:
425Hp * .6(lbs/hr)/Hp = 255 lbs per hour. This pump flows 360 so it would be good up to 600 horsepower! Nice.
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