550 HOLLEY TUNNEL RAM CARBURETORS. This is an unique set of custom 550 cfm mechanical secondary. These are only available here. These highly developed carbs are also the hottest set of tunnel ram carbs to date. Because of the design and claibrations the quick throttle response will throw you into your seat. Also they have a Very clean idle quality. YES they are MECHANICAL SECONDARY carbs. They are similar to the Holley 9776. Choose your finish from the drop-down menu. ACFI Polished finish as shown or the classic Holley Gold. All Non-stick gaskets and .110 adjustable needle and seats. Also featured in this set of carburetors are custom secondary metering plates. Because of this the secondary main jets are removable as well as the primary. Thus making these more tunable to your engine.