Does anyone know if it's possible to use a carb with vacuum secondaries in a blow through carb application?

I'm considering the Vortech S-trim centrifugal blower for my car. The carb box that they supply is usable with 4150/demon style carbs. I believe my 4160 will fit the box physically(correct me if I'm wrong). I'm just not sure if vacuum secondaries will work under boost??? http://www.camaros.net/forum/confused.gif

It would kinda suck to have to buy a $600 carb on top of the $2300 blower kit.

Thanks, Joe.

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79' Z28 4-spd- built 355, TRW 10:1 forged flat tops, WP SportsmanII heads, Crane Energizer 228* duration .480" lift, Edelbrock Victor Jr., Holley 750cfm, Dynomax headers, dual 3" flowmasters :) 3.73 Posi 10-bolt

Joe,

I've only used mechanical secondary carbs for blow through applications. However, I have been told by someone whom I trust that the vacuum secondary ones will work also. You will need to send your carb in for mods to make it run correctly. This is the most critical area of advice I can give you; don't try to just re-jet it, it needs metering block and air bleed work, etc. to work right. When set-up correctly the blow through carb deal works very well.

I used Scott at SD Concept Engineering to mod the last two I used. I believe he gets about $300 to fully mod the carb, including removeable air bleeds, modified metering blocks, milled air horn, etc. His number is (401) 732-4047. He is also the guy I'd ask about the vacuum secondary deal.

Jody

Thankyou Jody. The project will be much more managable if I just have to send my carb off for a $300 mod run, instead of a $600 4150, + the $300 to mod it.

I'll keep his number handy.

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79' Z28 4-spd- built 355, TRW 10:1 forged flat tops, WP SportsmanII heads, Crane Energizer 228* duration .480" lift, Edelbrock Victor Jr., Holley 750cfm, Dynomax headers, dual 3" flowmasters :) 3.73 Posi 10-bolt

You're welcome. Actually, I bought a new 4779 750 mechanical secondary carb with all the mods from him for $600. That's a new carb with mods.

Jody

The Carburetor Shop also sells modified carbs for blow thru applications. Their Stage II blow thru mod package is $500. It includes the same stuff Jody mentioned and also includes a balance tube between the front and rear float bowls to equalize pressure in the bowls. I don't know if that is as critical in a box application. It's pretty much mandatory with a blower hat.

at what psi boost can you run with 9.5:1 compression? i've been reading alot about s/c's and am thinking its cheaper in the long run. (no bottle to fill) Also is it worth the gains? (at low boost)

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My '68 Camaro (http://hometown.aol.com/Dougs68Camaro/index.html)
Doug G.
68 Camaro
406 ci.
13.5@102 W/ 2.73POSI.

[This message has been edited by DOUG G (edited 03-26-2002).]

Doug,

With a centrifugal and 9.5-1 compression you can run 8 psi of boost pretty safely, depending on the rest of the engine components. If you add an intercooler, you can run 10-12 psi of boost. This is on pump gas. Race gas will allow more. I'm running 10 psi of boost with 9.7-1 compression and 91 octane pump gas. However, I have EFI, all aluminum engine, and ceramic barrier coating on the valves and pistons. All of this controls the heat very well. When I add an intercooler, I'll be able to run more boost.

I know ProCharger recommends 9-1 compression or so. 9.5 isn't a bog difference. And yes, you'll NOTICE 8 psi of boost!!!!! http://www.camaros.net/forum/eek.gif

Jody

So you think 9.8:1 with iron heads, would be safe with 6-8psi using a Vortech S-trim? Using 94 octane Sunoco. Just curious, as that's the blower I'm considering. I know my buddy with a 2000 Rustang GT is running 14lbs on pump gas with the same blower...

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79' Z28 4-spd- built 355, TRW 10:1 forged flat tops, WP SportsmanII heads, Crane Energizer 228* duration .480" lift, Edelbrock Victor Jr., Holley 750cfm, Dynomax headers, dual 3" flowmasters :) 3.73 Posi 10-bolt