Unless you’ve been living under a rock, as a reader of EngineLabs, you have more than likely heard us talk about Ben Strader of EFI University’s Spinal Tap project. What started as simply a discussion over beers turned into a three-year proof-of-concept project that resulted in an LS engine which functions and thrives at 11,000-plus rpm.
Of course, in addition to taking three years to complete, Spinal Tap uses a slew of custom, high-end parts that aren’t necessarily the parts that would be used by a mere mortal. And while that is cool, and proved the point, Strader isn’t in the business of just flexing on social media and having parts that no one else does. He’s in the business of sharing and imparting knowledge, and that’s difficult to do when your example is one-of-one in the world.
In order to bring the lessons learned during the Spinal Tap project into the realm of “actually attainable” by anyone on the street with the proper knowledge and resources (don’t expect to do this in your backyard shed with Harbor Freight tools after watching a couple of YouTube videos), Strader decided to build a new engine to become the focal point of EFI University’s Competition Engine Development class.
Let’s build a really neat package on readily available stuff, that’s not super-whammy custom, one-off, unobtanium. – Ben Strader, EFI University
“Part of the reason we built this engine was because of a challenge from Frankenstein Engine Dynamics to put together an engine for the CED class, with their cylinder head hardware, and then give away four seats in the CED class,” Strader explains. “From the beginning, the goal was that we were going to take the cylinder heads, and develop a combination around them that is in our wheelhouse (high-compression-ratio, high-RPM engines).”
While seemingly straightforward, Strader added a challenge into the mix for this new engine. “I thought, ‘let’s build a really neat package on readily available stuff, that’s not super-whammy custom, one-off, unobtanium,’” says Strader. “I wasn’t like, ‘Let’s build an Aussie Pro Stock or 500-inch Pro Stock deal,’ where we can certainly make crazy power numbers. Because, if everyone can’t replicate it then it’s not a great training tool.”
Making 2.7 HP-Per-Cube and 10,000 RPM Look Easy
Before we dive deeper into the engine, let’s give a breakdown of this new high-RPM, 350-cubic-inch LS test mule. The short-block starts with a Dart LSNext SHP block, machined for 55mm roller cam bearings, and .937-inch bushed lifter bores. The block has then been decked to a 9.235-inch deck height — .005-inch shorter than the nominal LS factory height. Strader also bored the iron block to its listed maximum bore size of 4.185 inches with EFI University’s in-house machines.
A Callies 3.185-inch-stroke Ultra-Billet crank, tipping the scales at only 37 pounds, is the heart of the rotating assembly. While that might sound like an extremely high-end part, it’s not unobtainable by the masses by any means, and Strader actually scored a sweet deal on it from someone who changed up their project before ever actually firing the engine.
Strader opted for a set of 2618 aluminum 4.185-inch slugs from Diamond Pistons. The custom pieces started with a 3D laser scan of the combustion chambers to ensure an exact dome shape for the perfect amount of piston-to-valve clearance with the Frankenstein heads. With a 1.383 piston compression height, the piston deck sits .0095 inch in the hole, with the 7cc domes.
Quick Calc: Compression Height
When calculating what compression height you need with a given stroke and rod length, the math is easy. For simplicity’s sake, we’ll assume you’re looking for a zero-deck solution (where the piston deck is even with the engine block deck).
You take half the stroke length, add the connecting rod length, and then subtract that number from the deck height. That will give you the compression height for a piston to sit flush with the deck. Now, using this engine as an example:
(3.185 ÷ 2) 6.250 = 7.8425
Now, remember that this block has been decked a little more than normal, and using the actual deck height is an important factor.
9.235 – 7.8425 = 1.3925
So a 1.3925 compression height would result in a zero deck situation. Strader needed the piston to sit in the hole slightly, so he simply subtracted the desired amount from the ideal and came up with a 1.383-inch compression height.
Connecting the pistons to the crankshaft is a set of 6.250-inch GRP aluminum rods. The rods use the smaller 1.889-inch “Honda” rod journal diameter to reduce bearing speed at elevated RPM. The small end of the rod is special as well, with a .866-inch pin bore. The wrist pin is a corresponding .866-inch-diameter, .180-inch-wall tool steel wrist pin, measuring 2.25 inches long.
Bearing clearances have been set at .003 inch on all of the mains, save for the center thrust bearing, which is at .0035 inch. Rod bearing clearance is set at the same .0035 inch, and the crankshaft thrust clearance is set to .005 inch. For piston rings, thin is in for this behemoth, with the custom ring set coming from Total Seal. The top ring is a Diamond Finish tool steel piece measuring .0276 inch, while the second ring is a .0269-inch-thick steel Napier ring. A 2mm Hastings oil ring with a 4.175-inch expander handles oil-control duties.
Speaking of oiling, proper oiling at 10,000 rpm can be challenging, so the same setup as was run on Spinal Tap is used here. A Dailey Engineering six-stage dry-sump system, and a little bit of Strader’s secret sauce: Teflon-impregnated, ultra-low friction, high-vacuum tolerance GST Racing double-lipped front and rear main seals.
The focal point of the top end of this engine is the FED F-710 287cc square-port LS7 cylinder heads. The A357-T6 aluminum castings come with a 10-degree valve angle, titanium 2.260-inch intake, 1.610-inch titanium exhaust valves, and a .750-inch thick deck. Out-of-the-box, the heads flowed 427cfm at .800 inch of valve lift on the intake side, and 286cfm on the exhaust. The only modifications Strader made to them was to take .100 inch off of the deck to bring the combustion chamber volume down to 46.5cc.
Before you jump up and shout “The flow at .800 means nothing on an LS engine!” read on. The solid-roller camshaft for the engine was ground by COMP Cams with 276 degrees of duration on the intake, 294 degrees on the exhaust (both at .050-inch lift), with .821 inch of gross lift on both sides, on a 114-degree lobe separation angle.
Trend Performance one-piece double-taper 7/16-inch pushrods, with a .165-inch wall-thickness actuate the custom Jesel steel 1.8:1-ratio shaft rockers. Controlling the valves at such high speeds is a set of COMP P/N: 7245 dual conical valvesprings, with an installed height of 1.955 inches. The springs are surprisingly light on the seat at 205 pounds, and at .820 inch of lift, have 715 pounds of force.
Name one place on the planet where you can get real, live…hands-on access to a state of the art Spintron facility and get to work on a 10,000+ RPM engine???Go ahead…I’ll wait…When you’re done trying to find another place that will get you an All-Access Pass, just do yourself a favor and go sign up for the next Competition Engine Development class here:www.efi101.com/CED COMP CamsJesel Valvetrain InnovationTrend Performance ProductsDriven Racing OilTotal Seal Piston RingsFrankenstein Engine Dynamics LLC
Posted by EFI University on Tuesday, February 25, 2020
Obviously, one of the most important parts of making an engine live at elevated engine speeds is having a stable valvetrain. Here, Strader runs the engine on his in-house Spintron to validate the valvetrain components and demonstrate the system’s stability.
Running on VP Racing Fuels C45 race gas for the tuneup, Strader ended up with 31 degrees of timing advance, as he ran the engine to 10,500 rpm to validate the engine’s reliability. On the dyno, the engine power peaked at 9,420 rpm with 951 horsepower, and the 573 lb-ft torque peak occurred at 7,860 rpm. Doing the math, that comes in at 2.717 horsepower-per-cubic-inch, naturally aspirated.
While the engine’s purpose is to be a teaching tool, as opposed to powering someone to insane speeds on the land or in the water, there are no shortcuts taken in the name of it being a teaching tool. “The engine for the class is as legit as I would give a customer,” Strader asserts.
“With the caveat that we often reuse a lot of parts in the build, that wouldn’t normally be reused, like the ultra-low friction seals, rod and crank bearings, and on occasion, we’ve even reused head gaskets, especially since it only gets 3-10 runs on the dyno and taken apart. It’s not like there is a season of drag racing on the engine.”
One thing we’ve published articles on quite a bit recently is piston speed. So naturally, we asked Strader about piston speeds in this engine. “In this engine, piston speed is not a limiting factor, because the stroke is so short. However, that is part of why we build the engines the way we do. We knew going into it, that we’d be turning the engine pretty hard,” Strader explains.
“I kind of think the 6,000 feet-per-minute measurement (that’s about 30.5 meters per second, if you’re comparing it to the metric measurement) is an average rule of thumb. If you’re taking this engine to 10,250 rpm, we’re only at 5,400 fpm. As with anything, there are other contributing factors, but that 6,000 fpm is where you start to run into sonic choke in the port. So if you can stay below that, you can avoid a lot of issues.”
What is Sonic Choke
The subject of sonic choke can (and very well might) be a tech article all on its own. But since Strader mentioned it, we’ll go over it quickly. “Why does air move from the intake manifold to the cylinder?” Strader asks, rhetorically. “Whenever there is a differential pressure, specifically across the intake valve, the air moves in that direction. The greater that differential becomes, the more likely you are to get air to move.”
“The motion of the piston is what creates that pressure differential in the cylinder — by changing the volume — and the faster it does that, the greater the pressure differential. At some point, when your piston speed gets too high, it causes the air to go supersonic while trying to fill the cylinder. At that point, you can actually have a reversal of flow.”
Strader also notes that the 6,000 fpm mean piston speed isn’t a hard and fast rule, because you can work around it in specific circumstances.
Once the students have rebuilt the engine in the CED course, it goes onto the dyno. While it may be a teaching tool, it is still a completely legitimate and functional engine, which has to put up the expected numbers.
While this is a teaching tool, that doesn’t mean the project is over, and the engine relegated to a life of disassembly and reassembly. Quite the opposite actually, as Strader has several rounds of upgrades planned. “I think I’m going to take the cylinder heads off of the engine and put them back on the Spintron to see if I can’t stand the spring up a little bit with a different retainer and lock combination, and different amount of shims, and see if I can go from a 1.8:1 rocker arm to a 1.9 or 1.95, or maybe even 2.0:1,” Strader says.
“We have a very dynamically stable, smooth system right now, so I want to keep working on that. Basically, I’m going to try and find the limit between how much valve lift I can get and how much seat load I can produce — as I stand the spring up taller — without getting into coil-bind. Right now we’re at .800 lift, my goal would be to get to .900 with the same valvespring, so I’d be down around 130 pounds or so on the seat.”
Of course, if you remember the section of the article on the cylinder heads, you remember the term “out-of-the-box” being used. “What’s really incredible about this engine is that these are FED’s off the shelf F-710 cylinder head. We didn’t modify the port, we didn’t modify the valve seat or valve job. The only thing I did was deck the head a bunch,” reveals Strader.
“With these really, really-high-RPM engines, we want [a high] compression ratio, but we need to be able to do it without a big dome. The dome can get in the way of the flame front and we have to alter timing to overcome that. Then we start the spark timing too early and lose too much heat into the cylinder walls and lose compression, yadda yadda, yadda. The point being, there’s still a lot left in the head.”
Strader explains that there is a significant amount of work to perform on the valve seats, as the F-710 head is designed to work on the street, and as such there are some tradeoffs that have been made by Frankenstein to increase reliability at the cost of absolute performance. “They still have a standard 45-degree valve seat that is pretty wide, because they sell these heads to guys who are doing street car stuff. We’re thinking about going back and modifying all that a little bit, and making everything into a little more racey version of the head,” says Strader.
“This engine is currently at 2.7 horsepower per cubic-inch, I think we can get it to 2.8, 2.85. Maybe even 2.9. I would not be surprised to see us make 1,000-1,030 horsepower with the same short-block. I feel like there is 50-100 more horsepower in the engine, without changing the camshaft or short-block at all, just more valve lift and cylinder head work.”