Unmatched performance & durability since 1983.

J Precision specializes in high performance machining of engines components. We let your local qualified mechanics to do the final assembly. Contact your local dealer for more details.



It only takes one pass on a dyno or a quick ride on an open road to fully appreciate the exceptional performance offered by J Precision heads.  Cylinder heads modified and upgraded by J Precision are simply the most powerful and reliable that money can buy.



STAGE II    (For stock castings)

This Stage features our upgraded intake and exhaust port design and is CNC ported for optimal precision and repeatability. We use only top quality components from the company AV&V for oustanding reliability. This is a perfect performance upgrade for your street performance needs.

It features a 1.700 inlet opening, and the chamber is left in its natural state; making this head a perfect fit for any motor combination from 88” to  107”.



High Torque Heads

STAGE II    (For stock & aftermarket castings)

Same as Stage II except  for the intake port which is redesigned and raised by welding to increase velocity; allowing for a crisper throttle response.

The chamber is CNC contoured and finished by hand to a satin finish.

Great upgrade for all TC heads

including SE, S&S and other aftermarket heads.


STAGE IIIB    (For stock castings)

Same as stage II plus we install 1.940" intake valves
& oversize seats and increase the  intake port area,
resulting in peak horspower increase.


STAGE IVB    (For stock castings)

Ultimate modification for your factory casting.
We install 2.000" intake & 1.580" exhaust valves and
modify the ports accordingly. Makes the most power
from bigger throttle body or carbs. We recommend a
manifold/ throttle body with 1.800" runners to take full
advantage of these heads.


STAGE V    (For stock castings)

Designed for 131'' / 4,250'' bore engines

We install 2.150" intake & 1.650" exhaust valves and modify the ports accordingly. Intake valve angle is modified and rocker arm geometry is corrected

Must be used with SE 120R Hurricane oval port manifold

Up to 175 rear wheel HP potentiel.




We port the manifold to optimize the airflow and to achieve a better fuel atomization through our proprietary finishing process.







We machine the heads to install the compression release valves in line with the spark plug for an easier access  and a better look.

We also machine heads for automatic compression release valves.






We machine the pistons to re-establish a correct  valves to piston clearance after installation of higher lift cams, larger valves or head shaving. (Usually, all TC cast pistons require clearancing)






To give that CNC finish on heads and cylinders.






To download our Twin Cam machining services catalog or our head work sheet , click here:

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