Our Cars and Projects

250 OHC - Stage 1.

Primatech Motorsports is building, testing and dyno tuning a 250 CID Stage 1 crate motor.  A long-time Pontiac enthusiast in the metro NYC area contacted Primatech with a desire to put a well-built 250 into his Firebird. For a dedicated OHC-6 fan with more than one Sprint powered car in his garage, Primatech jumped at the chance.

The 250 short block was treated to forged .040” over flat-top pistons and rebuilt factory forged rods (with ARP bolts). The crank was magnafluxed, ground and all oil holes were chamfered. The block was zero decked.

The cylinder head is a Primatech-built 1967 1-BBl head with a Stage 2 valve train kit. The head was prepared with all new hardware, new venturi oil regulator and a three-angle valve job. In keeping with our intention to increase the performance potential of everything we build, the valve angles were all changed to 45° to better match the forged stainless undercut valves that are featured in our stage 2 valve train kits.

Induction is handled by a port-matched 1966 Sprint intake with a factory 1968 OHC Quadrajet. The exhaust system is Primatech’s Sigma6 header. The intake and exhaust system are a perfect match to the Stage 1 camshaft and are mated to the head through a Flatout composite gasket.

The motor will be going into an original 1967 Firebird Sprint convertible replacing the original 3.8L 4 bbl OHC6.  The original 3 speed has already been replaced with a Saginaw 4 speed but will be changed over to a Keisler modified Tremec 5 speed in front of the factory 3.55 rear.

Braking has been upgraded with power 1969 single caliper front disc brakes. This car was restored in 1997, though additional updates are planned.

This very same long-time Pontiac enthusiast in NYC is also building another OHC motor, this one a 230 (3.8L). This motor is under construction locally by Westchester Automotive using Primatech parts. This motor will be a 230 bored .060” over and wears a 1bbl head for a streetable 9:1 compression. This engine also features factory 4bbl Sprint intake and exhaust. 

Plans are for his second engine to go into what was originally a "plain-Jane" 1967 OHC Firebird convertible (1-Bbl with a 2 speed automatic) converted over to a Saginaw 4 speed  (with 3.11 first gear) in front of a 3.08 rear. This is a long term project that may see a change over to a NEW tub if they become available (given the rather rusted condition of the original NE car which survived more than a few college winters in the late 1970's - and has been parked for 25 years). We will feature both cars in upcoming photo spreads. Check back for more information.

CM Stroker 271.

Capt. Nathe Martin - a fervent OHC enthusiast - is serving in the US military on active combat duty in Iraq.  Primatech Motorsports has taken on one of our more interesting projects in his absence:  Primatech’s first long-rod, Stage 2, 271 cubic inch stroker OHC.

Primatech’s stroker 271 is a 250 bored and stroked to 271 CID. We start with a 250 block, bore it .040” over, then offset-grind the crank to 3.75 inches stroke. (Almost ¼” longer stroke than the factory) We install a 5.90 inch forged H-beam rod and custom forged lightweight pistons, and add a custom dual-mass harmonic dampener.

Capt. Martin basically allowed us to do whatever we wanted with his stroker.

We decided to start with the base stroker kit and focus first on a naturally aspirated, pump-gas friendly “torquey” motor. (Although we’ll certainly leave the door open for the turbo … stay tuned.) The pistons are light weight (tipping the scale at just under 490 grams) custom forged with moly-coated skirts and ceramic-coated domes.  The 5.9 inch forged H-beam rods are bronze-bushed for floating pins, EDM drilled for pin oiling and weight matched to ±1 gram.

Roller Followers.

Always innovating, Primatech Motorsports embarked on a project to create a roller-follower design that would permit the use of factory camshafts. The resulting lift would be considerable higher than the factory rating, which would require some cylinder head modification.  Dyno testing with a cylinder head built to handle the extra lift will continue throughout the year, culminating in a follower package becoming available early in 2006.

Conical (Beehive) springs.

Conical valve springs – also known as “Beehive” valve springs - offer several advantages over the rather large single and dual springs that were designed into the OHC motor.

Technology marches on and Primatech is capitalizing on modern technology to bring out the best possible performance from the factory OHC cylinder head. Primatech has sourced conical valve springs with correct factory installed heights and seat pressures that will increase the red-line by at least 500-800 RPM without valve float.   This spring design will not require machining of the factory spring pad and can be installed with factory valves or high-performance Primatech valves and factory followers and lash adjusters. Kits will be available early in  the new year!

Oil Metering Tubes.

More innovation from Primatech! After several cylinder head tests, Primatech has designed and is testing a lash-adjuster oil pressure metering design that will replace the factory oil metering tube with a venturi design that offers 98% pressure recovery on the top end while better regulating pressure in the lash adjuster gallery!

The oil pressure in the lash adjuster gallery is the most critical facet of the OHC motor. Changes in oil pump pressure, oil flow through the camshaft and bearings and increased leakage in the cam bearings all contribute to variations in oil pressure to the lash adjusters. Primatech’s new metering tube will increase the oil flow and pressure to the top end while improving the pressure stability in the lash adjuster gallery.