At low levels of boost, below 9 pounds, that is all. Since the fuel in American domestic models gives good pressure up to 6.5 psi in most cars, there is no need to do any modifications from 4 to 6 pounds.
Please read Dave Emaneul's book on Holley carbs. It's early 1981, and had some 1988 inclusions. It has a turbo section which covers what H.McInnes states. It also covers the ported vaccum the dissy needs to run off, and the control of a boost retard system if you want more boost. The fuel pressure is the issue, so follow there lead on that. You can't expect a 9 psi turbo boost to allow a 6 psi fuel load go into the carby at full boost.
There is onfo on boost referencing the adaptor plate you'd use on the Holley or Ford 2100/2150 carb you can use. This allows you to forget about teflon bushing or sealing the throttle, a pain of a job. The adive is worth every cent! The Holley~Weber 5200 can cope too, but its a little harder to calibrate as it doesn't like to have to take more than 3.5 psi of fuel pressure.
Remember, a turbo is there for boosting, and everyone ends up using all the boost they can. I'd follow Dave Emaneul's advice.
The latter big log heads found on the last 1977 onwards 3.3/4.1 engines is a stout piece of kit with big runners, big valves, and sits in a low compression engine which is just aching for some boost.
At 9 pounds of boost, there is over 1.5 times the power. If you have only 100 hp, you'll get 150 hp easily with no mods to the 1-bbl, just the carb altered per McInnes and Emanuel's advice. In practice, guys get close to 150 hp with just a small cam and some good 2-bbl carburation. A V8 spec Ford 2150 found on a 302/351/400 V8 truck is designed for 129/140/164 hp net, so it will liberate a lot of power. The best carb is possibly the 2V 351 C carb found in old 1972-1974 V8 Torinos and some Mustangs. Able to do about 216 hp net, from memory.
When its turboed, you get a proportional increase. A swap to the original spec that Jack Colins used on his 250 1-bbl before the cross flow six got dumped in was a good baseline. Just use the stock compression, and you will be fine. Don't go over 8:1.
The total amount of boost, say 9 psi, is diveded by two, and added to your compression ratio. It can't go over 11:1 with a stock cam (or 6 psi), not over 12.5:1 with a longer duration cam at the 270 degree (9 psi).
The stock 1-bbl carb emaculates the 200 or 250 past about 125 hp. With the later head, and a 2-bbl, you'll get up to 150 hp on a stock engine with 265 to 270 cam and a good exhast. With a turbo, the exhast can stay the same with just a j-tube, and you'll still get a great boost of up to 225 hp with 9 pounds of boost.
The big bell 200, or any 250, is the best to modify as it gives more room to fit the turbo and exhast plumbing with the low-mount V8-style starters they have.
