With the new guides in place, the head is cut with a three-angle performance valve job. The valve seats are cut and blended for larger 1.94-inch intake and 1.50-inch exhaust valves. This increases the airflow through the port and allows the stroker to breathe much better than with the comparatively choked stock heads.
In addition to the performance valve job, Golen also back-cuts the valves to improve the flow a bit more. Here, the valve is installed on its seat, then a vacuum test is performed to ensure the valve seat is cut properly. A vacuum leak means the valve doesn't seal and the valve job doesn't pass muster. Ours all topped out well above acceptable levels.
The cylinder head is machined to provide a dead-straight gasket surface and to bring the combustion chambers to 62 cc. With the blended bowls, high-performance valve job, and new valve guides, the head will flow at least 155 cc and provide years of dependable service.
To achieve the correct 1.700-inch installed spring height for the Comp Cams valvesprings, the valvespring pockets in the cylinder heads are cut accordingly. Some shops will simply install hi-po springs without performing this step, but for these Jeep heads it's a crucial part of getting the right spring tension. Too much and you'll eat cam lobes. Too little and you'll get valve float at high rpm.
The entire rotating assembly is balanced to within 0.5 grams. That's pretty impressive. The pistons and 4.2L rods are weighed, then the crank is sent for a ride on the balancer.
The beauty of the Jeep six is that, unlike some high-end strokers, there's no need for expensive Mallory metal to bring the rotating assembly into balance. Just a little material is removed where necessary from the crank, and that's all that is needed.
Here, Chad Golen taps the Speed-Pro pistons home. The hypereutectic pistons will stand up to a decent-size shot of nitrous or supercharging. Once the machining was finished, Dan Eddins assembled the rest of the engine, including the Comp Cams bumpstick and lifters, and got our engine ready for the dyno. Tune in next month to see what it belts out and to follow as we install it into Project JR.
BUILD SHEET
| GOLEN ENGINE SERVICE 4.6L LONG-BLOCK |
Peak Horsepower:
| 260 at 5,000 rpm
|
Peak Torque:
| 295 at 4,000 rpm
|
Compression Ratio:
| 9.0:1
|
Cam Specs:
| Comp Cams Xtreme 4x4 hydraulic flat tappet
|
Duration:
| Intake 218 degrees at 0.050/ exhaust 226 degrees at 0.050
|
Lift:
| Intake 0.493 inch/exhaust 0.512
|
Lobe Separation:
| 111 degrees
|
Heads:
| '91-'95 Jeep H.O. factory iron, three-angle performance valve job, bowl ported, valves back-cut, new guides
|
Combustion Chamber:
| 62 cc
|
Intake Runner:
| 155 cc
|
Intake Valves:
| 1.94-inch SBI steel
|
Exhaust Valves:
| 1.50-inch SBI steel
|
Block-Machining Processes:
| Thermally cleaned and stainless-steel-shot; inspected by MPI process; decked, bored, honed with torque plates, and pressure-washed; Clevite cam bearings and Pioneer brass freeze plugs installed
|
Crank:
| Performance-ground 4.2L Jeep crankshaft; micro-polished and oil holes chamfered
|
Rods:
| 4.2L Jeep steel rods; shot-peened for strength, ends resized with new ARP rod bolts
|
Pistons:
| Speed-Pro hypereutectic
|
Rings:
| Speed-Pro plasma-moly
|
Bearings:
| Clevite main and rod
|
Core Plugs:
| Pioneer brass
|
Lifters:
| Comp Cams hydraulic
|
Pushrods:
| Comp Cams
|
Timing Set:
| Dynagear Performance
|
Oil System:
| Melling high-volume pump, pickup tube, HD drive
|
Gasket:
| Fel-Pro Performance
|
Head Bolts:
| SBI Performance
|