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Last Updated: 16 Jul 2003

Author: Dave Williams; dlwilliams=aristotle=net

Kemper Porter's 315 Stroker

As usual I didn't take nearly as many pictures as I thought I did, and some of the ones I did take didn't come out well. [sigh]
This combination doesn't offer a whole lot more displacement than stock, but it's simple to do and can be inexpensive. You offset grind a 302 crank to 3.075" stroke and 2300 Pinto rod bearing size. You use 2300 Pinto rods, which are 5.205" long, have 8mm bolts, and are generally beefier than the 302 rods. The pin ends have to be opened up from .912 to .927 for Chevy wristpins. The stock width Pinto rod bearings may work, though you may have to narrow or chamfer the crank cheek side depending on the crank radius. Note: 2300 rod bearings are now available only in *metric* undersizes! Pistons are 1.43" pin height for a Chevy 383 stroker with 5.7" rods. These are available in castings from various sources for around $125, or TRW forgings at $230. No block or crank clearancing is needed. The Chevy valve reliefs have been fine for Ford D0OE 351W heads with a .480 lift cam and Twisted Wedge heads with a .500 lift cam. Balancing is about the same as a stock 302. No clearancing of the crank or block is required - just bolt it all together and go!

Almost all the cost of the 315 is in the rod work. If you can get the machine work done at a reasonable price the 315 can be an inexpensive upgrade from a stock 302.


Kemper wanted TRW forgings in his engine, so that meant finding a block that would clean up at .030 over, as chances of finding one acceptable at stock bore were negligible and we felt .060 would be pushing it with the eventual twin turbo fangle. I went through eight (8) 289 and 302 short blocks before I found a '68 302 that would clean up; here's one coming out of the caustic tank.

Here's one on the boring stand... you can't tell if it'll clean up at .030 until you bore it and see.

This is the typical problem - what rebuild shops call a "fingernail mark", generated on the thrust side when a severely worn piston rocks at Top Dead Center. The thin lower line is the actual fingernail mark; the thick band at the top is Magic Marker. I put a top ring on one of the stroker pistons and turned the motor over so you could see how much higher the ring goes with those pistons and the longer stroke. The mark is only a few thousandths deep; the bore has already been honed to size. No joy here.

This is the '68 302 that finally made it. This was the scummiest, nastiest motor I'd ever come across in my life - the entire crankcase was solid with what looked like black Jell-O. It's already been pressure washed, boiled in caustic, and wire brushed in this picture.

Since it bored out clean I'm cleaning the head bolt threads. If you don't do this, particularly on a core that has been exposed to weather, the head bolt torque readings won't come out right and you'll blow head gaskets.

Here I'm heating a rod so I can install the wristpin. That's my homemade pin heater. Commercial rigs tape up a couple of feet of bench space and run on natural gas. Mine is just a strip of steel to hang the rod, a $15 barbecue grill propane regulator, a propane tank, and some air-assisted burner nozzles I made out of copper tubing. Works just fine and I can put it in a drawer or hang it on the wall when not using it. The piston fixture to the left was made out of wood scraps and a stove bolt; it holds the piston in position and has a stop for the wristpin. You have only a few seconds before the rod cools enough to bite the pin; after that you need a hydraulic press to get the rod and piston back apart. A fair amount of the time it'll bend or break the piston when you do it, so the fixture makes it faster and more accurate to slide the pin through.

The engine has a Crane cam, Ford Motorsport rockers, and TFS Twisted Wedge heads. That's how much longer the pushrods needed to be for the geometry to be correct.


Just a few shots of the heads and lifter valley...

These are early Wedgies. They use special TFS pushrod guide plates, and that's how far they were off side-to-side. Very ungood. TFS shipped a set of revised guideplates when I called to ask what was going on.

With the new guide plates everything lined up fine. Magic Marker is for inking the ends of the valve stems to check pushrod length.

Kemper contemplating the Zen of cleaning valve covers. Kemper and his friend Lance came up from Vicksburg to pick the engine up, complete with the dead 302 in the back of Lance's truck. They pulled the pan, valve covers, intake, and assorted bits from the dead motor while I finished putting the 315 together, then spent the rest of the day cleaning dirty parts. They missed out on the black Jell-O, though... 
===========================================================================
SPECIFICATIONS:

302 Ford stroked to .075", .030 overbore  (315 CID)

Crane 222/234 @.050 hydraulic cam, rated 2200/5200 powerband, 6500 valve float
  with 280# springs

(this cam turned out much lumpier than Kemper wanted.  I'd built a previous
 315 with a similar-duration cam that idled like a stocker, but that one had
 a 112 degree lobe center.  Kemper's is 108 degrees.)

TFS Twisted Wedge heads, cut for Loc-Wire gaskets


Compression:
          724cc   swept volume    (bore/stroke 4.030/3.075)

         61  cc   nominal chamber volume
          5.2cc   -.025 assembled height
          7.3cc   .035 gasket
          5  cc   valve trough (estimated)
        --------
         78.5cc   total clearance volume

         724/78.5 = 9.22:1 CR


===========================================================================
COMPONENTS ---------------------------------------------------------------

crankshaft:
        302, 2M casting, full counterweight
        stroked to 3.076"
        mains 302 -.020
        rods 2300 standard
        polished journals
        balanced  (drill only)

pistons:
        TRW forged 1.43 pin height  (for 5.7 rod 383 Chevy stroker)
        flat top with two valve reliefs
        4.030 diameter

rings:
        standard small block Chevy. 4.030, file fit, Speed Pro moly top
        side clearance .003 top and second
        ring gaps .011 second, .013 top  (Ford spec .010-.020)

rods:
        2300 Ford 5.205" D42E-AA forgings with oil squirt hole
        narrowed big ends (.835)
        pin ends opened to .925 (.002 press for .927 pins)
        bearings 2300 Ford  (narrowed .055 one side) (King)
        rod side clearances .010
        resized big ends (minimum size)
        chamfered sides of big ends
        oil holes in rods face cam

block:
        1968 302 C8 casting
        bored .030
        honed to .005 piston/wall clearance, spec for TRW forging
        honed to #600 finish (ultra smooth)
        2 piece rear main seal (blue silicone around edges)
        new core plugs (blue silicone sealer)
        painted  (Rust-Oleum Sail Blue)
        #80 (.030) hole drilled in 1/2" cup plug behind distributor shaft
        new cam bearings  (King)
        .040 hole drilled into oilway below distributor gear for oiling

heads:
        TFS Twisted Wedge

cam:
        Crane Powermax H-278-2, 222/234 @.050, .498/.527 lift, 110 LC
        Crane cam lube used for assembly lube
        firing order: 1-5-4-2-6-3-7-8

pushrods:
        7.2" (checked)  (stock 6.6")

rockers:
        Ford SVO 1.6 roller


timing set:
        double roller, Dynagear


oil pump:
        Melling high volume, used, disassembled & cleaned


===========================================================================

Stewart-Warner Model 2000 Industrial Balancer

balance:

        643  piston/pin
        165  pin end of rod
         55  rings
        ---
        863  grams reciprocating


        426  rod big end
         34  rod bearing
        ---
        460  rotating


        bob = 1x reciprocating + 2x rotating
            = 863  +  460*2
            = 863  +  920
            = 1784

        + 2 grams oil allowance

        bob = 1786 grams


critical speed 800 RPM
resonant speed 650 RPM

max front imbalance .025 oz/in
max rear imbalance .045 oz/in
(balance is 1/10 of standard spec; close to the machine's resolution limit)

balanced for 28oz damper and flywheel

============================================================================