Most camshafts look indistinguishable from one another—even custom camshafts. “Not mine,” declares blown alcohol pulling tractor champion Mike Wilhite. “Mine are 2.5-inches in diameter.”
Wilhite, who runs an engine shop in Bardstown, KY, thirty miles south of Louisville, purchases a 12-foot length of 2.5-inch case-hardened 8620 alloy steel or S7 tool steel bar stock. He then takes the long length of round bar to Russ Yoder at Erson Cams, who makes four camshafts from it. When finish-ground and heat treated, Wilhite installs the custom-made billet camshafts in the engines of his alcohol pulling-tractor customers.
Six-cylinder inline engines adapted for pulling tractor competitions begin life as 200 horsepower diesels revving to 1,500 rpm, but when increased to 505 cubic inches (Light Super Stock) and converted to alcohol and assisted by three turbochargers they generate close to 4,000 horsepower and 7,000 rpm.
On the topic of pulling tractors, Yoder says, “We’ve made camshafts for 7.8-liter Ford diesels to an A22 International, from Cummins to Walkinshaw, Oliver to Massey Ferguson, Allis Chalmers to antique pulling tractors with engines originating from the 1920s.”
Why no shelf stock for the extreme categories?
“It’s common practice for competition engine builders to increase cam bearing sizes, and our shelf-stock materials accommodate increases of up to 60mm for big-block Chevrolets and also big-block Fords and for some Hemi engines,” says Yoder. “But, beyond this it just isn’t practical to inventory cam cores of such diversity.” Hence, in this regard, Erson identifies the optimum grade of steel required, the customer brings them the appropriate round bar stock (some measuring 70mm), and they grind the camshaft.
“We’ve experienced good luck with 8620,” says Yoder. “It’s exceedingly tough and hard and durable.” But on vehicles with extreme engine power that have encountered cam lobe damage, he advises them to switch to S7 tool steel. “Though it’s three times more expensive than 8620,” he cautions, “its hardened boundary layer penetrates deeper than 8620.”
How are custom cams created and who determines the grind?
As you’d predict, Erson needs access to an original equipment camshaft in order to establish the lobe centers, as they have to be aligned with the lifter bores. The grind, however, is usually determined by Yoder and, on pulling tractors, is influenced by the number of turbochargers used (one or three), the fuel (alcohol or diesel), and engine displacement.
“A lot of these tractor guys convert the engines from diesel to alcohol and run multiple turbochargers—they actually compress air from one turbo into another, which necessitates running over 100lbs of manifold boost. As a result their cylinder pressure is about as extreme as a top fuel car.”
Yoder continues, “Some of the 650ci Heavy Super Stock tractors produce 5,000-plus horsepower.”
So the cylinder pressure is so high the exhaust valve has trouble opening, exerting excessive pressure on the exhaust lobes—as they have to push the lifters up.
“To survive, the cam lobes must demonstrate 64C (Rockwell C scale) or harder, which is where the S7 tool steel camshaft has the advantage with its deeper hard surface. Its core, the center of the material, starts out at 16 points harder than the 8620.” Because its hard boundary layer is deeper, it succeeds in combating the high spring loads better.”
On Heat Treating
The 8620 material is carburized while S7 tool steel is induction hardened; it does not absorb carbon. The process for tool steel camshafts involves an induction furnace and electric coils that bring the cams to the required temperature at which point they are quenched in alcohol.
On the other hand, the 8620 camshafts are placed in a carbon furnace that exposes them to a temperature of 1,960 degrees for 40 hours.
When would you wish to change the profile and how would you know what profile to change it to?
Recently, Erson encountered a customer who had suffered multiple engine failures. Running blown alcohol, he mentioned he’d acquired a newly designed cylinder head and a camshaft made to match the head. But it turned out to be an expensive mismatch. Confused and dispirited, he sought help.
We asked him if he knew the percentage of his flow figures, exhaust to intake. His answer immediately revealed the problem: his exhaust flowed 90-percent of his intake—which is wildly excessive.
“You have to trap the intake charge of alcohol in the cylinders,” insists Yoder; “you cannot allow it to be blown out the exhaust, as the engine will turn lean and destroy itself.
“Let’s say you’re running gasoline with the exhaust flowing 70 percent, you might consider adding 10 or 12 or 15 degrees more duration to the exhaust than the intake. But if you consider a blown alcohol engine that’s flowing 70 percent on the exhaust, we would typically suggest a standard straight-pattern cam or a reverse-pattern cam because the intake charge is under pressure; so on the overlap stroke, when both valves are open, this formula prevents premature ejection of the charge from the combustion chamber.
“As this camshaft was 4 degrees greater on the exhaust than the intake, we reduced its duration, making its intake period longer than the exhaust and reduced its lift capability by 0.050-inch. That fixed it!”
By: Bertie S. Brown