This is a basic 4bbl carburetor based on a 460 CFM Impco 425 mixer and a square-bore 4bbl throttle body. It can be installed on a spread-bore intake manifold with a square-bore to spread-bore adapter. This carburetor is assembled from the following components:

  • 1 x Impco CT425M-2, Model 425 Mixer, Silicone
  • 1 x Impco G1-65, Gasket, Model 425 base
  • 4 x Impco S1-39, Screw, 12-24x 7/8"
  • 1 x Gann TB9-8, Throttle Body, Holley Square Bore
  • 1 x Gann 11SB, Vacuum Straight Brass, ¼” Hose x 1/8” MNPT
  • 1 x Gann 88EN, Vapour Elbow, Nylon, 1" Hose x 1" MNPT

To make an underhood conversion kit, you must add either the BCP-EE or theBCP-EV Basic Components kits.

While you can use a Holley throttle body from a parts gasoline carburetor, the Gann throttle body (the plate containing the throttle valves) is designed for propane applications and does not have the surplus mounting hole of the gasoline carburetor throttle body.  This carburetor includes Gann 11SB, which is for your distributor's 1/4" vacuum advance hose.

The Model 425 mixer has a 5-1/8" diameter airhorn, which allows it to use your OEM 4bbl air cleaner.  However, if the distance between your air cleaner's mounting flange and the bottom of the air cleaner's lid is less than 3-1/4", you will need to use 1/2" high spacer adapter (PN A2-73) for clearance.  Measure your air cleaner before ordering!

Propane carburetors are not over-sized like gasoline carburetors. This carburetor will properly meter fuel to a 350 CID (5.7L) engine up to 5344 RPM. On a 454 CID (7.4L) engine, this carburetor is good to 4120 RPM. Above these RPMs, these engines will simply gradually lose power. For stock V8 engine applications, this carburetor will work well.

For open-loop engine applications above 390 CID (or for generally better fuel economy), we recommend replacing the air-gas valve with PN AV1-1644-2.

Model 425 Square Bore Carburetor

  • Brand: Impco
  • Product Code: LPGCARB-425-SQ
  • Availability: Pre-Order
  • $479.36


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