Maybe we should've had Coast High Performance build us a 7.3 diesel. Our oil-burning F-350 shop truck broke down on the way to pick up the 347.
We've always maintained there are worthwhile tuning differences between a 302 and a 347 small-block. While both engines are built using the same block, use the same heads and intake, bolt on the same exhaust, and are often dressed using the same camshafts, the increased displacement and piston speed of the 347 no doubt means the head, intake, and cam package will respond differently in the stroker than in the stocker. Given the land-rush popularity of 347s these days, we're aiming to find out.
Naturally, the best way to pry secrets from engines is to strap them to an engine dyno. And while we have a 302 dedicated to dyno duty at magazine dyno specialist shop Westech, we didn't have a 347 on the shelf next to it-until now.
Our new dyno engine uses a...
Our new dyno engine uses a Coast High Performance 347 Street Fighter short-block, which is assembled from all-new parts, including a standard Ford 5.0 service block. A regular replacement unit, the block is sourced from a large supply of Ford service parts CHP bought before 5.0 engine production was shut down.
Having to do little more than ask, we convinced Coast High Performance to assemble one of its many 347 short-blocks for dyno mule duty using its $2,299.99 Street Fighter short-block as a base. The idea was to have a 347 that could accept many different cylinder heads and cams, and an engine capable of running fuel injected or carbureted-one we could put up against our 302 from time to time just to see what the difference would be.
Given those intentions, all Coast High Performance had to do was build one of its 347 Street Fighters. This is mainly due to CHP's use of its in-house Probe pistons. These feature dual valve reliefs, so they'll accommodate anything from a stock E7TE iron head to a Twisted Wedge without any piston-to-valve interference problems. As forgings, these pistons are good and strong to withstand the occasional "lean and rattle" that is so easy to do when fiddling around with new combinations. With moderate compression they'll work with real-world pump gas and cylinder-head volumes.
Stout describes the bottom end. A cast-steel stroker crank provides the extra 0.400-inch stroke, along with the sort of physical durability required to live through a thousand dyno pulls. The block is a new 5.0 service unit, with stock cylinder bore diameters. That means our engine is really a 342, but as "347" is the popular designation for a 3.40-inch stroker 302, that's what we'll call it. The heavy-beamed connecting rods are another high-durability Probe item. For much of our dyno testing, a prepped stock rod with good bolts would likely do, but when pushing things, it'll be nice to know the stronger Probe rods are on hand.
Oiling is via a high-volume pump and Pro Mustang oil-pump drive. This $41.99 pump provides greater oil-flow volume to ensure the increased bearing loads and rpm are safely supported. The $19.99 heavy-duty oil-pump drive won't twist or break as would the totally limp-wristed stocker.
The combination of "tin" on our 347 differs slightly from standard 5.0 H.O. practice. The front cover is one of Ford's standard late-model replacement pieces. It's exactly what you'd expect on a modern crate engine. This aluminum cover supports all late-model, fuel-injected front engine dress, but it also has a dipstick hole and a mechanical fuel-pump boss. This allows the cover to be used on an early-model Mustang or Ford in addition to a late-model. About the only consideration you'll need to address in a late-model is installing a fuel-pump boss block-off plate, and deciding to use either the stock-block's pan-rail dipstick or the front cover's dipstick.
The oil pan is a Pro Mustang Street Fighter unit with 7-quart capacity and gold-irridite finish. We ended up with a $159.99 front sump unit because this engine may eventually be installed in an early-model Mustang (we have early and late projects around the shop), CHP had one quickly available the day the engine was buttoned up, it makes no difference on the engine dyno, and as the engine will come apart for freshening anyway, the pan is one of those things that can be easily changed. The pan has no dipstick provision, and it isn't needed thanks to the front cover.
CHP uses several sources for...
CHP uses several sources for stroker crankshafts, but all are cast-steel pieces from Chinese foundries. Ours happened to be a Scat unit. All such cranks are far stronger than the somewhat wimpy stock 5.0 unit, and they have all the necessary strengthening for stroker duty built right in. We might lift head gaskets and black-death cylinder walls if we get carried away while dyno'ing, but it's highly unlikely we'll hurt this crank. Besides, in short-blocks, CHP often sells these cranks as part of its $1,299.99 Street Fighter engine kit, which includes the crankshaft, forged rods, forged Probe pistons, Total Seal rings, and Clevite rod and main bearings. By itself the crank is $249.99.
While off-shore H-beam connecting...
While off-shore H-beam connecting rods are popular these days, they really are overkill in many applications. To bridge the gap between a prepped stock rod and an H-beam, CHP offers these 4340 lightweight, machined-beam, forged-steel rods. They can easily handle the 400-plus horsepower we might generate while trying out the latest bolt-ons. It's also worth noting Probe pistons use an offset piston pin bore, which makes the rods act as though they're a bit longer than their 5.400-inch, center-to-center length from a rod-ratio standpoint.
Probe is rapidly becoming...
Probe is rapidly becoming a major force in the aftermarket and replacement piston business-in part because its pistons are available in a large variety of diameters, dome shapes, and weights. Here in Probe's Sportsman Race Series (SRS) are two high-compression versions and the more pump-gas-friendly flat-top we're running. All have antidetonation grooves, are made of high-quality aluminum, and are nitrous and blower ready. The pistons' trick, elliptically machined and diamond-faced thrust faces and skirts allow tight, quiet-running clearances. The pistons are $459.99 per set.