Look on page four of my htread "another turbo 200 nears completion"
I had this to say to Drag 200 stang:
"you don't want to run a carb too large. I think a blowthrough works way better with a carb too small than too large (and speaking from experience here, I have more potential yet to tap from my 1 bbl)
I have read a lot of scary stories on turbomustangs about guys trying to blow through a carb that is too large. The fuel/air mixture ratio just goes everywhere. Smaller is better in this case."
and :
"The only guys running 750 carbs on 350ish cube motors are running over 1000 HP., and those carbs are super well prepped by specialty shops for about $800 (not including price of carb).
I figure if a 350 chevy with a stock re-jetted 650 DP Holley can run 8's in the quarter, then my 200 won't ever need anything larger than about 250-300-350 cfm. I am going to try a 1.08 motorcraft 2 bbl and probably also a 1.21 motorcraft 2 bbl. I already have both. According to info from here, a 1.21 is about the same as a Holley 350.
3) The carb set-up running OK on a N/A car, if a little too large, will get super crazy over 8-10 psi.
It has something to do with the pressure drop through the venturis.....or lack of it.
I think it is like this: If the carb is too large, boost builds up in the intake, and above the carb, and even though pressure is high, flow through the venturis is (relatively) low. High pressure but low flow and the metering goes away at the venturi.
One guy (actually running a chevy, lots of them on turbomustangs) on the turbo mustangs board was trying to get (I.I.R.C....) a Holley 850 HP series carb that ran great on his N/A 350 to run under boost. He didn't have the $$$$$ to buy a new carb, so he was trying to use the one he already had.
He kept going WAAAY lean under boost, even with the largest jets in it that Holley makes (I think 120's).
The way he fixed it was to have it sent off to....I think CSU? carb shop, and they installed custom downleg annular venturis that were VERY thick, and brought the CFM's down to around 700. That fixed the problem.
I think it also helps to have more consistent metering when the pressure drop through the venturi is very high.....it makes a lot of suction between the venturi and the float bowl. That extra suction helps cover up any flow inadequacies in the metering circuit.
The venturi in my 1 bbl is I think 1-1/8" at the smallest point. I think I can honestly run a 12.99......through a single 1-1/8" venturi!! "
Like I said, you may be the first. Just use lots of cuation while tuning it.
