Quick Fuel tech draw-through to blow-through?

[Paulmorris]

Hi all. I’ve got a draw-through Quick Fuel Technology 850 carb for a old school V8 turbo setup, but I’ve changed plans and want to go blow-through turbo. How can or can I change the carb to suit. Please bare in mind I’m no carb expert. Thanks. 😉

[djh61187]

If your not good with carburetors, I'd do yourself a huge favor and have one custom built by CSU, C&S, etc. I ran a blow-through carb for 16 years and learned a lot. But I already had a good understanding of building and modifying a carb for blow-through turbo setup. If you want to give it a try yourself, this is a good writeup to do a blow-through carb. This setup is good for around 600-650 HP. Above that, you'd be better off getting one built.
https://www.hangar18fabrication.com/blowthru.html

[Paulmorris]

What are the differences between a blow-through and draw-through turbo carb? Thanks.

[djh61187]

A draw-through is basically a N/A carb that has the power valve externally referenced so it can read manifold vacuum/pressure. They will usually have larger main well passages and PVCRs to get more fuel for the desired HP. A draw-through will be limited in HP by how much CFM the carb can flow just like a N/A carb. The bigger the carb the more power, but low speed driveability can be a problem with to big a carb. A blow-through carb can be smaller for good driveability and still make big power. A 750 blow-through carb can make over 1000 HP with ease. A 850 can make 1500 HP. They will have big annular boosters, main well passages along with boost referenced Power Valves and larger Power Valve Control Restrictors (PVCR). They also need the High & Low speed air bleeds reworked, Rear Jet extensions and Nitrophyl floats and larger needle & seat assemblies. Most Blow-through carbs will need atleast one 50cc accelerator pump on the secondaries and both the primary and secondary bowls if using E85.