Ever since hot rodders in the ‘50s started swapping “3/4-race cams” into their engines, the search for the ultimate street cam has been an ongoing and highly debatable issue. The introduction of Lunati’s new Bootlegger hydraulic series – with its wicked 108-degree lobe-separation angle, fast opening profile and plenty of area under the lift curve – will serve only to fuel the flames on this heated bench-racing topic.
According to legend, the first 3/4 cam was developed by Ed Winfield when he matched the intake lobe from a full race cam with the exhaust lobe from his 1/2-race series – hence the 3/4 designation that has evolved into hot rod vernacular for a hot street cam. Lunati, however, took a radically different approach.
“On the design, the Bootlegger is more like a race cam on the exhaust opening with just a little less overlap to allow some street manners,” explains Lunati engineer David Chamberlain. “The intake closing is more tucked in for the street RPM.”
Lunati set the intake centerline at 104 degrees for the entire series, which covers the traditional Ford and Chevy small-blocks along with the Chevy big-block. The cams are offered in hydraulic flat-tappet and hydraulic roller versions, including retro-fit hydraulic roller kits. For each application there are hot, hotter and hottest grind options to give builders more flexibility in matching the cam to the engine’s compression ratio and head flow. Some of the applications offer complete kits with cam, lifters, valve springs, retainers, locks and a timing set. Lunati representatives will also discuss options for custom grinds, including Chrysler applications.
Leveraging Voodoo DNA
Basically, Lunati engineers leveraged design features from the popular Voodoo series, including the fast-open/controlled closing ramp and fat lobe nose, to develop the Bootlegger series. Obviously the primary goal is to make more power than a stock cam without sacrificing necessary street-performance characteristics, such as easy starting. But engine builders will look at that 108-degree lobe-separation angle and wonder about potential loss of vacuum, harder cranking compression and the chance for piston-to-valve interference – all possible consequences when narrowing the LSA.
“The quicker lobes really help on vacuum loss,” counters Chamberlain. “Think of how many engine builders used Lunati’s older series (Street Master and Bracket Master) and other tight 106-108 LSA race cams on the street. There is some vacuum loss compared to a more conventional 110 to 112 LSA street grind, but the power and sound of the Bootlegger cannot be matched on a wider LSA. Also, the loss of vacuum is not nearly as severe as with the large duration 106 LSA cams that used to be required for this type performance and sound.”
Vehicles that run into a problem with low vacuum for power brakes or to run retracting headlights can always be equipped with a vacuum canister or electric pump.
As mentioned, one of the glorious side effects of manipulating the LSA and giving the exhaust valve a race-like profile is the sound that comes out the tailpipe. Engines get their street cred from a nasty exhaust note that boasts just the right amount of cackle and rumble. Other cam manufacturers have tried taking street cams and tweaking them to sound like race cams. Again, Lunati rolls its own way.
Understanding the intake closing event
“Bootlegger would be more like a race cam with the intake closing earlier to work in the street rpm range,” says Chamberlain. “Imagine the four valve events of a typical mid-250 @ 0.050 duration race cam on a 106 LSA. Now, how can we get that type power and not be a pig at low rpm or lose throttle response?
“The key is to move the event that most directly changes cylinder pressure in that critical low- to mid-range part of the curve, being the intake closing. The Bootlegger closely mimics the intake closing of popular Voodoo grinds while the exhaust opening is more like the Bracket Master or other race grinds, and the overlap is somewhere in between race and street,” continues Chamberlain. “Altogether, this gives outstanding power through the middle and high part of the engine’s range without destroying the low-end response so critical to the ‘fun factor’ of any great street machine.”
Performance is the final determining factor in cam selection. Lunati baselined a ZZ4 crate engine from Chevy Performance and made just under 350 horsepower. The engine featured an Edelbrock RPM Air-gap dual-plane intake, 650 Holley HP carb, 1.6:1 Lunati rocker arms and aftermarket heads with “as cast” 180cc intake runners. A Bootlegger cam (PN XXX08240HR) was installed. It features .554/.554 valve lift and 240/252 @ .050 duration specs along with the 108 LSA and 104 ICL. The engine picked up more than 40 peak horsepower with a noticeable overall increase in the torque curve.
“The 40 peak-to-peak increase is cool, but the middle of the graph shows a solid 30-plus all though the heart of the curve,” sums up Chamberlain. “By the rev limit you will see improvements in the 50-70 range. It really is a monstrous change in the engine’s characteristics when compared to the popular ZZ4 camshaft. It’s as if someone stole the mule and left a race horse!”