Drag racers go for sexy, thin-waisted...
Drag racers go for sexy, thin-waisted piston pins, but road racers are in for the long haul and prefer a more voluptuous slathering of material in the pin wall. To better package the oil ring, these suitably thick units measure 0.912 inch in diameter rather than the common 0.927-inch option. Griggs wants the pin out of the oil-ring groove.
Besides building torque, the savvy American Iron engine builder is looking for ways to restrict horsepower. That way, an engine can be built with plenty of torque and a little too much horsepower, then the horsepower can be squelched somehow. Initial attempts at this by AI competitors were fairly lame, including pinching the exhaust-pipe tips (doesn't help) and fitting cheap, low-profile air filters (kills 20 hp). Now the wet rag is applied electronically by tuning the engine management to pull timing at higher rpm. This is more accurate, allowing maximum torque and allowable horsepower in a broad, flat powerband.
Obviously, the facts point to EFI as the logical American Iron induction solution, so Griggs Racing has gone the EEC IV route. The company has also done the displacement thing, using a stock 4.00-inch bore and a 3.250-inch stroker crank to arrive at 327 cubic inches. That's a nice compromise between working area and revability.
Plenty of compression is another definite attribute of the Griggs' AI engine, although exactly what the compression ratio is was not divulged. Bruce's only comment on compression is, "People wouldn't believe what we run in these things." We'd guess something near 13:1.
Big compression mandates small combustion chambers and pop-up piston domes, thus driving head and piston design. Griggs takes care of this by milling the heads and specifying a custom dome on its Ross pistons.
There are no tricks in the...
There are no tricks in the Griggs AI engines' "packaged parts," such as rings and bearings. These Childs & Albert plasma-moly rings are the standard fitment (Griggs has run Total Seal but doesn't insist on them). Naturally, they are file fit. Bearings are Clevite HP bearings, occasionally with extra clearance on the mains, depending on how the crankshaft measures.
Of course, the camshaft, the intake, and the porting combination has to be torque-friendly. Griggs camming specs are secret, but they must be barely in the low-0.500-inch lift range, combined with short duration, as there just isn't that much power being made here. Word was that Griggs was playing with moving the lobe centers around, but then, racers are always moving everything around.
And speaking of playing around, at press time an induction experiment was being built from a hermaphrodite Trick Flow intake pairing (see the photos).
The good news is, there is only so much power of any kind that can be made with a 9.5:1 power-to-weight rule. Thus, stress builders such as high rpm and excessive heat aren't overpowering considerations, so the durability requirements are not excessive (this is somewhat offset by the brutal on-and-off duty cycle road-racing engines must endure). Aside from a strong Ford Racing Performance Parts R block-the stock 5.0 engine case won't last too many races before splitting through the number-two main bearing web-going wild on exotic materials or extra beefy parts isn't necessary.
Furthermore, exotic cylinder heads, zoomie exhaust, and all that aren't what make torque. That means more affordable, mainly streetable hardware is all that's required. This is especially helpful in the simple roller-rocker valvetrains, and well illustrated by Griggs' use of Air Flow Research 185 or Trick Flow Track Heat heads at most-not race stuff.
In fact, Bruce jokes that this is Griggs' "Summit engine" because it uses Summit gear for the heads, the valvetrain, and much of the rotating assembly. So, if not cheap, at least the basic engine bits are reasonably priced.
 Griggs' standard cylinder...  Griggs' standard cylinder head is the Trick Flow Track Heat. This head has little trouble spooling up 400 hp, so it needs minimal preparation from Griggs. This includes running Trick Flow swirl-polished, stainless-steel valves and 10-degree locks, Trick Flow chrome-moly retainers, and Trick Flow springs. The spring pressures are checked, of course, and occasional adjustments are made. Bruce says they check their valvesprings after every race, but find they're typically good for one season. |  While the Track Heat already...  While the Track Heat already has a compact combustion chamber, Griggs mills the heads to raise the compression ratio. Bruce is also considering cutting a small eyebrow in the deck face to provide a steam bleed in the cooling system. That passage, which is present in some aftermarket aluminum heads, seems to deliver slightly cooler water temperatures. |  What Griggs does chase on...  What Griggs does chase on its heads is core shift and how the bowl/valve seat relationship works out. Some heads need little work, while others require a defi-nite touch with the cutter to align the bowl/seat interface. Naturally, while we were visiting, all the heads in the shop had little core shift. Although we don't have much to show you in this as-cast example, the eyebrow of material at one o'clock to the seat in this photo, and the area just to the left of it, are where the action occurs.A quick port match and knocking off any obvious casting imperfections completes the minor Griggs AI engine port job. |