For engine geeks, a peek inside a Pro Stock engine might be like gazing on the inner workings of an electron particle accelerator – it won’t mean much unless you are given some kind of personally guided tour. So imagine if David Reher, Warren Johnson, or Greg Anderson walked you through a guided tour of a state-of-the-art Pro Stock engine. Would that make your inner-gearhead-self do back flips? Getting close to that level of internal combustion engine science is actually attainable. This is what Ben Strader does on a monthly basis with EFI University’s class on Competition Engine Development (CED).
In NHRA drag racing there is probably no more secretive clan of racers than the Pro Stock guys. In 1986 Bob Glidden barrel-rolled his Pro Stock Fairmont several times at the Southern Nationals. After emerging from the car unhurt, he had the presence of mind to immediately cover the now-exposed intake manifold with a jacket to protect its inner secrets.
Strader enjoyed a unique opportunity a few years ago when he was asked to help a couple of Pro Stock teams with EFI design and tuning after they were challenged to quickly convert to EFI when the NHRA made carburetors obsolete. Ben offered his expertise on EFI and at the same time learned much from these Pro Stock teams. Using what he has learned, he now passes it along to students in his CED class.
Strader is quick to acknowledge that while this information can be incredibly useful and valuable, it will not instantly make you a competitive racer in Pro Stock or even in Competition Eliminator. But what this will do is enlighten you as to how meticulously these engines are assembled, tuned, and massaged to coax the maximum amount of horsepower to the flywheel. So signing up for a three-day course at EFI University’s Lake Havasu, Arizona site is the quickest way to do a full immersion into the world of building race engines, which is much more than just class work, thanks to all of the hands-on teaching.
For some, knowledge unto itself is the end game. But for Strader, it’s much more fun to apply that knowledge to a spinning internal combustion race engine. So for roughly the past two years, Strader and Comp Cams’ chief cam designer Billy Godbold have collaborated on an engine they call Project Spinal Tap. If you’re familiar with the movie, there’s a scene where a band member proudly points out that his amp goes not to 10 – but to 11. A couple of earlier EngineLabs stories have touched on this quest. The idea was to build an LS small-block targeted with the goal of making 950 to 1,000 horsepower at 11,000 rpm – and survive.
You may have seen Strader’s Facebook video adventures filmed in Comp Cams’ R&D area where he and Godbold successfully ventured past 11,000 rpm with Comp Cams’ Chris Potter at the Spintron controls. The most impressive part was that the valvetrain didn’t achieve this goal just once but eventually survived 30 successive simulated drag strip passes spinning to 11,300 rpm. That may be the cream filling in the chocolate Ho-Ho, but the real story is all the geeky-engine details where all the rib-sticking protein is found.
We spent a day and a half with Strader at his EFI University shop where he revealed how they intend to apply this hard-won Spintron knowledge into the construction of a 4.185-inch bore, 3.52-inch stroke, 387ci LS engine that will eventually go in the school’s test mule Mustang and make passes.
The art of pulling off 11,000 rpm with a pushrod engine demands serious preparation to ensure this is more than just a Hail Mary attempt into the stratosphere. The achievement is ensuring the engine will survive. The engine builder becomes immersed in a literal sea of minutia. He must become obsessed with assuming nothing. This may sound more like a clinical description of obsessive-compulsive disorder–and that may not be far off the mark–but it’s this attention to detail that prevents calamity at this rarified engine speed.
Our story starts with a proper foundation. Strader chose Dart’s iron LSNext block for several reasons. Yes, its heavy with a 114-pound tariff but stability and strength are just two of many good reasons for this decision. Strader says the SHP block would have also worked, but when this project started, the SHP was not yet available. The LSNext block was configured as an LS with a 60 mm cam bore, which is current Competition Eliminator cam core territory. Current Pro Stock cam cores went to 82 mm roughly five years ago, but before that the typical cam size was also 60 mm.
There’s much work yet to be done on the block. Strader has plans to fabricate a complete tunnel cover for the camshaft to isolate it from windage issues. He also plans to add a sixth dry sump scavenge stage that will pull from the lifter valley to attempt to minimize oil that can leak past the cam, hit the crank, and add to the windage issue. At 11,000 rpm, ounces have a bad habit of quickly becoming pounds of drag that can cost horsepower.
Spinning this fast also means the crankshaft must be nothing short of the best, which is why Strader ordered a billet 4330V-steel piece from Winberg crankshafts. This is a slightly stronger material than 4340 with the addition of vanadium in the alloy, which improves fatigue strength and toughness. This is a 3.52-inch stroke piece using standard LS main 2.559-inch journals, matched with Indy car rod journals measuring barely 1.850-inch. These are the next step down from the popular Honda bearing size of 1.880-inch. Compared to the 2.100-inch stock journal size, the smaller diameter reduces bearing speed. They are also narrower, at 0.770- versus 0.818-inch, to reduce friction. Strader retained the main journal size to help the journal overlap between the rods and mains because the rods are so much smaller.
We did some quick calculations comparing a 1.850-inch rod bearing to the standard LS 2.100-inch diameter. The speed numbers in inches per minute are huge (72,567 inches per minute at 11,000 rpm for a 2.100 journal) but not necessarily meaningful until you compare the difference in percentage. The undersized journal reduces speed by 12-percent. As a sliding motion, this represents a measurable decrease in potential friction.
Clearances are also critical. The slower bearing speed means Strader can run a lower viscosity oil to match the 0.0018-inch rod and main bearing clearances. This is somewhat tighter than normal for a 2.559 main journal, but with a more stable iron block and a crank that will not deflect, these are reasonable clearances that tend to improve and extend the contact point of load on the bearings. Strader will start with a zero viscosity XPO 0w race oil from Driven. The bearings are Clevite for the rods with Daido Metal for the mains.
Moving to the pistons, The Gibtec billet pistons are under constant development, so there weren’t any finished pieces for us to photograph. Strader says he is shooting for a 16.5:1 compression ratio. His CED class has tested ratios as high as 17.8:1 but found the small power increase was offset by a combination of sensitivity to ignition timing with even minor changes in atmospheric conditions, as well as increased maintenance issues. In essence, it was living too close to the edge.
For piston rings, Strader worked closely with Keith Jones at Total Seal. The current package uses a 0.6 mm x 0.102-inch radial-width stainless steel top ring with a barrel face, which is titanium-coated to reduce friction. The second ring is also a 0.6 mm with a Napier design, but is slightly narrower at 0.101-inch, that is also stainless. The oil rings are a low drag 2 mm package, measuring 0.078 x 0.135-inch. How thin is a 0.6 mm ring? At 0.0236-inch, it measures less than a third the thickness of a 5/64-inch ring.
Any friction developed by the pistons and rings is amplified when spinning an engine to 11,000 rpm. By reducing ring thickness, this reduces friction while likely improving ring seal. As the contact area of the ring is reduced, this allows the designer to also reduce the static radial load applied to the cylinder wall. As an example, if reducing friction reduces the amount torque required to turn the rotating assembly by 5 lb-ft, that would theoretically improve horsepower at 11,000 rpm by 10.4 hp.
The connection between the pistons and that jewel-like Wynberg crank is the responsibility of a set of Carrillo H-beam rods that measure 6.480 inches, center-to-center, which puts the rod-to-stroke ratio at 1.84:1. The rods are made in the USA from Carrillo’s 4330M steel forgings, which enable proper grain flow and guarantee removal of any surface inclusions.
Besides the valvetrain, the highest stressed components in an engine are the rod bolts, so Strader elected to use M10 CARR bolts with a 285,000 psi rating. Each bolt is serialized and measured for free length so that later testing can ensure each bolt has not exceeded its yield strength.
Moving back to the valvetrain, a big reason for the larger, 60 mm cam core is valvetrain stability. Strader’s early testing revealed that the smaller, stock 55 mm cam core combined with an 0.842-inch diameter lifter was not capable of withstanding the spring loads that were evolving with the valvetrain. As an example, with a mere 0.008-inch of deflection in the cam core alone, that equates to a loss of 0.015-inch of lift at the valve.
Strader found that adding the larger diameter cam core and wheel-guided lifter along with the pushrods and Jesel shaft system, he minimized the deflection to a mere 0.046-inch of lift at the valve at maximum lift. That may seem like quite a bit, but with over 1,200 pounds of spring load at a maximum valve lift of over 1-inch, 0.046-inch is a major achievement.
There’s a much more detailed story around this, but a larger core allows a larger and more stable base circle, which then offers opportunity for additional lobe lift, which can take advantage of a larger lifter wheel. All of this is aimed at improving stability at all engine speeds. Strader took this notion and applied it in order to generate the largest wheel possible, which reduces the pressure angle on the lifter. This led to a set of Jesel roller lifters with a wheel larger than the lifter body itself. This is called a wheel-located lifter, which eliminates the traditional lifter tie-bars, thus reducing weight. The larger-diameter wheel slips into slots cut into the lifter bore bushings that guide the wheel and prevent the lifter from spinning in the bore.
These details underscore why the cam core had to be a 60 mm chunk of steel. Godbold progressed through several lobe designs before landing on one that would not devour parts after just one 11,000 rpm venture. The plan was to have a package that would last for a reasonable number of passes. Lobe design is much more than just establishing lift and duration. It’s a complicated formula of creating a critical lifter acceleration rate both on the opening and especially on the closing side as the valve approaches the seat. The term “asymmetrical lobes” applies here, so that the closing side accelerations are not the same as the opening side.
Another advantage to the lifter bushings is they can be customized to restrict oil flow. The stock lifter oil passages in the LS block are 5/8-inch but these new bushings reduce that diameter to a much more manageable 0.125-inch. Much of this effort is aimed at reducing the oil flow across the entire engine including the use of restricted pushrod passages. However, oil is still important for cooling the valvesprings, so Strader has also added spray bars in the billet valvecovers to spray a cooling mist of oil on the springs.
Reducing internal oil leakage in the engine is a major concern with any LS engine, so Strader paid attention to also reducing the total oil flow through the engine. Stock LS engines use a crank-driven oil pump, which means it spins at engine speed. However, Spinal Tap will use an externally-driven dry sump pump that will run much slower than engine speed. According to Strader, his tests point to a stock LS oil pump moving between 18 and 20 gallons per minute (gpm). Employing a highly accurate flow meter to measure current flow rates, an EFI University CED class 358ci LS engine reduced this flow to 9 gpm – half of the stock LS. His projections for Spinal Tap aim at closer to 6 gpm. While this is a way to increase power by reducing parasitic pumping losses, it’s a double-win since less oil slinging around the inside of the engine reduces windage losses.
The heads for this high-RPM adventure are a set of RHS LS7 castings with Victory 1 titanium 2.250-inch intake and 1.615-inch exhaust valves. The as-delivered RHS heads were originally designed for serious street use and within that arena offer some significant flow advantages with a 12-degree valve angle, .220-inch raised intake ports, and a 6-bolt head pattern to stabilize the clamp load. Strader admits these heads are not ideal for this application, but he has plans for improving flow.
Both the intake and exhaust valves will be DLC (diamond-like carbon) coated for durability while working within the 47cc chamber. The RHS heads were originally developed to improve port flow, peaking at around 0.650- to 0.700-inch lift. Strader commissioned Slick Rick Racing Heads in Magnolia, Texas to rework the heads to push flow beyond 0.850-inch lift, which is still far short of the camshaft’s one-inch lift capability. The current RHS heads flow around 410 cfm on the intake side, with new numbers that will likely be nearer to 450 cfm.
Future improvements will include changing to a 55-degree intake valve seat, which will widen the short-side radius to allow the air to remain adhered to port floor and improve overall flow. Eventually, a different, higher flow capability head will be added to the program.
While carburetors are generally a safe bet, with a school named EFI University, it’s pretty obvious which track the Spinal Tap engine will take. The current intake system is based on a pair of 4150-style FAST four-barrel throttle bodies. Each throttle body is fitted with four, 85 lb-hr injectors. One reason that carburetors sometimes produce more power than EFI is because the fuel is introduced at the very beginning of the induction system where the fuel’s latent heat of vaporization can reduce inlet air temperature. This is why Strader chose the throttle body, wet manifold approach as opposed to locating injectors in each runner.
Strader chose an Emtron KV8 EFI management system to keep track of the myriad commands necessary to feed fuel and spark to this engine. This system can manage up to 8 low-impedance injectors while controlling the spark along with dozens of other features including data logging. Emtron is a relatively new Australian EFI company that is quickly building a worldwide reputation as a quality EFI controller.
We don’t have any photos of the completed engine as it was in dozens of pieces when we photographed this story. Strader plans to have the engine fully assembled very soon and we will be there to watch it spin its 11,000 rpm magic. It promises to be a scream!
Listen to what 11,300 rpm sounds like on the Spintron:
Last dynamics pass on Spinal Tap to check exhaust dynamics to 11,300 RPM. Anyone want to guess the total number of "crankshaft" revolutions on this set of valve springs during durability including warmups? (question edited for a good friend so we could all clear up if we were talking crank, cam or valve spring revolutions)
Posted by Billy Godbold on Friday, April 6, 2018