Skunk2 907-05-9001 Ultra Race Plenum Spacer +1 Liter Silver B-Series K-Series

Vehicle Fitment

Compatible with Skunk2 Ultra Race intake manifolds only. The 907-05-9001 fits the following Skunk2 Ultra Race manifolds for Honda B-Series and K-Series engines:

• 307-05-9000 - Ultra Race Intake Manifold, B-Series VTEC, Silver
• 307-05-9050 - Ultra Race Intake Manifold, B-Series VTEC, Black
• 307-05-9055 - Ultra Race Intake Manifold, B-Series VTEC, All Black
• 307-05-9200 - Ultra Race Intake Manifold, D-Series, Silver
• 307-05-8000 - Ultra Race Side-Feed Intake Manifold, K-Series (K20A2 Style), Silver
• 307-05-8050 - Ultra Race Side-Feed Intake Manifold, K-Series, Black
• 307-05-8055 - Ultra Race Side-Feed Intake Manifold, K-Series, Black variant

Fitment Notes

• Ultra Race manifolds ONLY - the 907-05-9001 is designed for Skunk2's Ultra Race manifold series, which uses a two-piece modular design with a removable plenum lid; it is NOT compatible with the Ultra Street manifold, the Pro Series manifold, or any other manufacturer's intake manifold; the Ultra Street manifold uses a different plenum architecture and its plenum lid is not removable in the same way as the Ultra Race design
• Adds exactly 1 liter to base plenum volume - the Skunk2 Ultra Race manifold starts with a 3.5L plenum at base configuration; installing the 907-05-9001 brings the total to 4.5L; installing the 907-05-9002 (+2L) brings the total to 5.5L; spacers of different increments cannot be stacked without engineering verification
• Replaces the stock longer hardware included - the spacer raises the plenum lid above the manifold base by the thickness of the spacer; the stock plenum mounting bolts are no longer long enough to reach through the lid and spacer into the manifold base; the 907-05-9001 kit includes longer socket head bolts of the correct length to replace the stock hardware
• Gaskets included - two new gaskets are required when installing the spacer: one between the manifold base and the spacer, and one between the spacer and the plenum lid; both are included in the kit

Features

• Purpose-built for Skunk2 Ultra Race manifold plenum volume tuning - the Ultra Race manifold's two-piece modular design was specifically engineered to accept these billet spacers; Skunk2 lists three discrete plenum volume configurations for the Ultra Race manifold and specifies target power levels for each: the base 3.5L plenum is recommended for high-performance naturally aspirated engines up to approximately 450hp and for forced induction applications from approximately 650hp; the 4.5L configuration achieved with the 907-05-9001 is recommended for 600-1,000hp forced induction builds; the 5.5L configuration (907-05-9002) targets builds above 1,000hp; the spacer system allows a single manifold to be re-configured as power output grows without purchasing an entirely new manifold
• Plenum volume and its effect on performance - the intake manifold plenum is the shared reservoir from which all intake runners draw air charge between each cylinder's intake event; at any given moment, only one or two cylinders are drawing air from the plenum while the others are in other phases of the combustion cycle; a larger plenum volume maintains a more stable pressure reserve for high-RPM or high-boost applications, where the individual intake events are happening more rapidly and the demand on the plenum is higher; a plenum that is too small for a given power level experiences significant pressure fluctuations between intake events, reducing peak airflow and creating inconsistent charge distribution between cylinders; adding plenum volume via the 907-05-9001 spacer increases the effective air reservoir without altering the runner length, taper, or throttle body interface of the existing manifold
• Billet aluminum construction - the spacer is machined from billet aluminum rather than cast; billet aluminum provides consistent density, tighter dimensional tolerances, and a cleaner surface finish than cast aluminum; for a plenum spacer that must create a sealed interface between the manifold base and the plenum lid, dimensional precision at the mating surfaces and the bolt hole positions is critical to prevent intake leaks and ensure proper gasket seating; the billet construction achieves the flatness and surface finish required at both mating faces
• Silver (natural/clear anodized) finish - the 907-05-9001 is the silver-finish version, matching the natural aluminum appearance of the silver-finish Ultra Race manifold variants; the black anodized version is 907-05-9051
• Complete installation kit - unlike sourcing individual components, the 907-05-9001 includes the spacer, longer bolts, and gaskets as a single package; all hardware required to complete the plenum volume increase is in the box

Specifications

• Part Number: 907-05-9001
• Brand: Skunk2 Racing
• Product: Ultra Race Plenum Spacer - +1 Liter, Silver
• Plenum Volume Added: +1 Liter (net plenum volume with base manifold: 4.5L)
• Compatible With: Skunk2 Ultra Race manifolds - B-Series (307-05-9000, 307-05-9050, 307-05-9055), D-Series (307-05-9200), K-Series Side-Feed (307-05-8000, 307-05-8050, 307-05-8055)
• Construction: Billet aluminum
• Finish: Silver (natural/clear anodized)
• Black +1L Version: 907-05-9051
• Silver +2L Version: 907-05-9002
• Black +2L Version: 907-05-9052
• Not CARB Legal - not for sale in California for street-registered vehicles

Included Components

• 1x Billet Aluminum Plenum Spacer (+1 Liter, Silver)
• Longer socket head hardware (replacement plenum mounting bolts)
• Gaskets (upper and lower plenum spacer sealing gaskets)

Product Description

The Skunk2 907-05-9001 is the Ultra Race Plenum Spacer in silver finish, adding 1 liter of plenum volume to any compatible Skunk2 Ultra Race intake manifold for Honda B-Series or K-Series engines. It is a purpose-built accessory for Skunk2's Ultra Race manifold series - which uses a modular two-piece design with a removable plenum lid precisely to enable this type of configuration - and takes the base manifold's 3.5L plenum to a 4.5L total, which Skunk2 specifies as the target configuration for forced induction builds in the 600-1,000hp range.

The practical value of the spacer system is that a builder investing in a Skunk2 Ultra Race manifold for a current build can upgrade plenum volume as the build evolves without replacing the entire manifold - the base manifold, fuel rails, throttle body, and sensor setup all remain in place; only the spacer and associated hardware changes. The 907-05-9001 is the 1L increment; the 907-05-9002 adds 2L for 1,000hp+ builds. Both are available in silver (this part and 907-05-9002) and black (907-05-9051 and 907-05-9052).

The kit includes the billet aluminum spacer, new longer socket head bolts required to bridge the added height, and the gaskets for both mating surfaces. For Ultra Race manifolds only - not for Ultra Street or Pro Series manifolds. Not CARB legal; not for sale in California for use on emissions-controlled vehicles.