In one of those “no one has ever done it, so let’s try it!” projects, engine builder Barry Rabotnick of Survival Motorsports literally stuffed a 4.750-inch-stroke crankshaft into a FE block to create one of the largest SOHC motors to pound the asphalt.
“As far as I know, it’s the largest stroke ever put into an FE motor,” surmises Rabotnick, noting that larger displacement SOHC engines have been built using offset cylinder liners that allow a massive 4.600 bore. “Everything was a clearance issue on that engine.”
Combined with a 4.280-inch bore, the displacement is a shade under 547 ci—certainly more colossal than what Ford engineers had in mind in the late ‘50s when they created the iconic big-block platform with its 4.63-inch bore spacing.
Going with the overhead cam heads actually paved the way for the long arms on the crankshaft. Since there’s no camshaft in the block, there was no potential interference with the crankshaft or rods hitting the cam lobes.
“You can’t even dream about having that kind of stroke in a wedge engine,” says Rabotnick.
The owner wanted a SOHC from the start for his Pro Street-style Mustang build. When discussing components, the owner asked about the biggest stroke possible. A call to Scat Crankshafts revealed that a custom billet could be machined with a 4.750-inch stroke and 2.200-inch BBC rod journals. Most stroker motors out of Survival sport a 4.25-inch stroke crankshaft.
“It’s a counter intuitive move from a combination standpoint,” admits Rabotnick. “But the owner thought it would be cool, so we did it.”
That expensive bespoke crankshaft was soon on the Bridgeport With machinist William Blair giving the counterweights a crazy haircut. Even after clearancing the Robert Pond aluminum block, the crankshaft was hitting the custom Diamond pistons.
“We put the short block together and slowly rotated the piston down until it touched the counterweight,” remembers Rabotnick. “We marked it and machined off the metal. We kept turning until we ran out of parts that were hitting.”
With the peculiar shaped counterweights and the weight of the pistons, the crank had to be balanced again, this time using “at least 10 pieces of mallory.”
Custom-length billet steel connecting rods were ordered from R&R Racing Products.
“There’s certainly no room to put an aluminum rod,” says Rabotnick. “With a cammer piston, the valve reliefs force the piston rings far down the side compared to a normal motor. Even with a support rail for the oil ring, you run out of room.”
Normal rod length for a stroker FE motor is 6.700-inch. The tall compression height forced Survival to order a 6.530-inch rod. Securing the 9:1 pistons are H14 tool-steel pins.
“We wanted enough compression so it wasn’t soggy driving on the street,” says Rabotnick.
Since the stance of the Pro Street Mustang would be low up front, a road-racing style oil pan from Moroso is used, although there was no room for a windage tray.
“While it may have been advantageous to have one, this is one of the those cases where the vehicle wasn’t going to let it happen,” says Rabotnick.
The Bill Coons cylinder heads were treated to a mild porting, port matching to the intake and a “nice” valve job. Survival tried two different sets of camshafts before settling on a Crane model supplied by the owner. The Coons front drive hardware is rather standard for a modern SOHC build, although Survival upgrades to studs on the idler and tensioner to support the iconic 6-foot chain. There’s always been some mystery to the timing strategy with a SOHC engine The legendary Ed Pink used special bushings to offset the difference between the “driven” cam and the “lagging” cam.
“We degree the cams independent of each other,” says Rabotnick. “We degree the driver’s side first, the one that gets pulled first. Once that gets set, we do the same thing on the passenger side.”
So far there have been no harmonic side effects to the timing set from the long-stroke crankshaft.
“Honestly, we don’t know,” adds Rabotnick. “This is the first time anything like this has run. We haven’t observed any problems. The chain has stayed tight. I honestly can’t tell you how it’s going to behave in the long term.”
Rabotnick may have helped solved any early problem that contributed to many of the early myths surrounding the chain drive. Rabotnick worked with Billy Godbold and Chris Padgett at Comp Cams and SOHC racer Jay Brown to study the valvetrain setup and came up with a revealing observation.
“On one side of the motor the cam is essentially pushing the rocker arm and on the other side it’s being dragged behind the rocker arm,” explains Rabotnick. “The attack on the fulcrum of the arm is different on each side.”
“If you grind the same lobe for each side, you end up with two completely different cams, as far as the valve action is concerned,” continues Rabotnick. “Comp took data that Jay and I came up with and reversed engineered to get identical valve motion on both sides of the motor. If you use those cams, I think it takes a lot of variables out of it, and I suspect it addresses the reasons that people were making changes left to right.”
The camshafts are rather mild at just over .700-inch lift. Unlike a big-block pushrod engines, a SOHC engine doesn’t have the same rocker-arm ratio options.
“You can’t get a ton of lift with a SOHC engine,” says Rabotnick. “Our working rocker ratio drifts between 1.28:1 and 1.32:1.”
The current Crane cams in the engine were custom ordered by the owner with a different base circle in hopes of a more aggressive lobe profile.
On top the engine sports a multi-piece Dove intake manifold with a top that supports a Dyers 8-71 supercharger. The blower runs only at five percent overdrive right now and isn’t stripped for maximum efficiency.
“It’s a street motor,” reminds Rabotnick. “Right now it’s around only seven pounds of boost.”
Fuel is fed through 16 injectors: eight 24-pound injectors under the Enderle bug catcher and eight 100-pound Moran injectors in the intake manifold. Limited time on the dyno was run with a FAST XFI controller but using only the manifold injectors.
“We used the big injectors on the engine to keep things safe,” adds Rabotnick. “The idea is that the motor will cruise down the road on the small injectors, also keeping the blower cool. Then he’ll use the big injectors on the power end.”
As you can see from the dyno chart, the engine pulled over 880 horsepower at 6,600 rpm and was still climbing.
“This engine has much higher potential that what the dyno sheet reflects,” sums up Rabotnick.