Twin turbo Hemi build
Building a monster engine
Mark Ehlen - September 29, 2011 12:00 PM
Muscle Car Restorations
Indy Cylinder Heads
LSM Systems Engineering
(877) 334-8355 (Tech line)
1 Pistons are custom Diamond Racing parts designed for turbo applications. They are connected to K1 Technologies billet 7.100-inch H-beam rods with .200-inch tool steel pins.
2 A SpeedPro Hellfire ring set uses a stainless alloy top ring filed to .024-inch and a cast second ring set to .030-inch. The stainless alloy is better suited to handle the extra heat and pressure expected with the turbos.
3 Notice the difference in wall thickness between the Diamond piston on the left and the one that comes with the crate engine. The Diamond unit is designed to handle the increased stresses of a boosted engine.
4 The Diamond part, again on the left, is much closer to a pure flat top design than the one that ships from Mopar. This not only helps flame propagation but also improves detonation resistance while yielding a boost-friendly 9.0:1 compression ratio.
5 Swinging a stroke as long as 4.500-inches not only requires a careful check for the proper block clearance, it also needs some heavy metal on each end to bring this K1 crankshaft into balance. Using billet steel main caps for the three center journals will help prevent the crank and the block from distorting under max load.
6 The proper way to torque rod bolts is to measure bolt stretch — not with a torque wrench as frictional differences between the nuts and rod caps can lead to variations in clamping load. In this case, the manufacturer recommends .007-inch.
7 Ebert understands that making power at whatever desired level is all about balanced airflow through the engine. The stainless valves measure 2.25 and 1.94 inches and will use dual springs with a damper that yields 160 pounds on the seat and 450 pounds open for a max rpm of about 6,000. Keep in mind that this is being designed as a street motor.
8 This may seem like a pretty minor detail, but because of the small fillet around the inside edge of the spring contact area of the retainers, Ebert grinds a small chamfer around the inside edge of each spring to keep it from binding against the retainer.
9 Hydraulic roller lifters were chosen not just for their low maintenance but also for their ability to handle much more aggressive profiles than flat tappet lifters. They allow Ebert to specify much quicker opening and closing rates and thereby get more fuel into the chamber.
10 Likely an entire story could be written about the science that goes into the reasons for the cam specs Ebert selected for this engine. But the short story is that Brian specified 244 degrees of duration at .050-inch lift for both intake and exhaust because “this thing doesn’t need a lot of overlap” and he wanted to be sure that the intake charge “doesn’t get blown right out the exhaust” under boost. Again, keep in mind that this is a street engine so the power needs to be made at streetable rpm. Lift is .656-inch for the intake and .620-inch for the exhaust, but the real story is the 115-degree lobe separation angle (installed at +2 degrees for a 113 degree intake centerline) that Brian wanted. Seems no one made a cam blank to accommodate these specs so HiTech contacted LSM Engineering to produce and grind a custom steel billet for them. By the way, a bronze distributor gear is necessary with a steel cam as it will eat up an iron drive in a hurry.
11 One area that Ebert believes is often overlooked when building ultra-high performance engines is pushrod stability. He has seen data showing the amount that valve timing can be affected by pushrod flex in engines such as this that have the potential for very high cylinder pressures that work to increase the force necessary to open the exhaust valve in particular. The stock pushrods were 3/8-inch with a wall thickness of .080-inch. Brian ordered 7/16-inch custom length rods (intake 10.050 inches, exhaust 10.875 inches) from Trend Performance Products with a wall thickness of .165-inch.
12 In this case, both the heads and the block needed some material removed to provide adequate clearance for the fatter pushrods. Inspect each one as you rotate through a complete cycle.
13 This is going to sound like a pretty minor point but Brian insists that only about one thread of the rocker arm adjuster should be showing below the rocker tip. As the tip is extended, the rocker gets longer which slightly reduces the ratio but, more critically, it adds stress the adjuster tip. Because of the power levels we’re aiming for, you leave no advantage on the table. Of course, custom length pushrods are necessary to achieve this and one simply needs to take adjuster position into account when determining the proper length. Preload is set at 1 to 1½ turns or .030- to .050-inch.
14 The Indy rocker assemblies that come with the crate motors are perfectly acceptable at the rpm levels expected here.
15 Rather than use the oil slinger that is normally found on the crank snout to throw oil up onto the timing chain, Ebert likes to drill a .020-inch hole in the front oil galley plug to spray oil right at the back of the gear. This provides more positive lubrication and eliminates some parasitic power loss.
16 Airflow is controlled with a billet HiTechbuilt 90mm throttle body, based on the LS design. Attached to an ultra-low-profile throttle body elbow, it will flow about 1200cfm.
17 The Garrett turbos use ceramic ball bearings that are fed a trickle of oil through a .030-inch orifice. They are also water-cooled, though that plumbing wasn’t necessary for the limited time they were run on the dyno.
18 A pair of Tial Sport 44mm wastegates will control the boost level.
19 A pair of 50mm Tial pop-off valves are fitted to the intake side of the turbos to relieve excess pressure caused by quickly closing the throttle when under boost. Turbo systems really need these, as boost is not directly linked to rpm as the turbos spool down after the throttle is closed.
20 120-lb injectors handled the fuel demand with a max duty cycle of just over 70 percent, which is right where you want it.
21 The craftsmen at MCR did a fabulous job of creating the stainless turbo headers and the rest of the exhaust and intake and intercooler plumbing. There is obviously no kit for this; it all must be made from scratch. There may be a lot of room in the front of a ’68 Charger, but a twin turbo intercooled Hemi takes up a lot of space. MCR routinely mocks up entire assemblies like this when it is still relatively easy to make changes and move things.John Balow
22 What really makes an engine like this practical is a complete electronic management system like the F.A.S.T. XFI that can precisely control fuel and spark at every load and rpm possible. Every engine parameter can be optimized for every engine condition. Chris will be able to cruise around town all night long with no driveability issues and then, without any warning, show anyone riding with him what scary really is.
23 One option that’s not a bad idea is using a cam sync distributor. The top magnet (green stripe) tells the computer when the number one cylinder is firing, so the injectors can be run sequentially instead of batch firing. This also allows adjusting fuel and spark for individual cylinders should that become necessary.
24 Initial dyno runs aren’t meant to be pretty but to be sure everything is working properly. The F.A.S.T. XFI system is an awesome tool for controlling a beast like this, but it needs to be given safe spark and fuel parameters before you light it up for the first time. HiTech has lots of experience tuning EFI systems, so Ebert knows from experience how to set it up so it won’t melt down on the first pull. Don’t try this on your own. Get expert help.
25 Tuning the F.A.S.T. system involves monitoring all of the telemetry coming from the XFI ECU during each phase of the tune. Most critical is ensuring that initial air/fuel ratios are safe and that spark timing is on the conservative side. Since everything is monitored in real time and can be immediately reviewed by checking the data logs, Brian is able to easily see what adjustments are needed for each section of the power curve. These first runs are not about tuning for max power but rather for learning exactly what this particular engine needs under different operating conditions.
26 This is one of the first full power pulls on the dyno. The flat spot in the torque curve was caused by HiTech leaving the dyno set to its low range, which maxs out at 1,000 pounds. Brian left the springs out of the wastegates and wasn’t expecting it to make this much power. Even with the gates full open, this thing managed about 10 pounds of boost and made 1,108hp at 5,900 rpm.
27 This obviously aborted run is trying to show how frightfully powerful this creation really is. With 13-pound wastegate springs, HiTech’s dyno couldn’t hold onto this beast to measure peak torque. It simply couldn’t pull it down to less than 4,600 rpm and even though the water temp entering the dyno was in the 40s (thanks to Minnesota in February), it was coming out as steam and creating a huge cloud in the dyno room. Brian did measure 1,208hp at 5,000 rpm and 1,313 lbs-ft of torque at 4,600 rpm with 15 pounds of boost, but the torque was already falling by this point, leading him to believe that peak torque could be in the 1,400-plus pound range (peaking probably in the low 4,000s). And this was before Brian had much of a chance to optimize fuel and timing. It was always part of the plan to do the final tuning on MCR’s Mustang chassis dyno where the effects of air cleaners and the full exhaust system can be taken into account. It now that looks like that’s the only way we’ll get to really know just how strong a monster HiTech has created.
As a young boy, Chris Perna discovered that he had a gift for drawing. He also had a vivid imagination for, of all things, creating monsters.
His ultimate dream was to be a part of creating monster movies so he spent countless hours (often neglecting homework) drawing all kinds of scary creatures. While most kids grow out of their childhood fantasies, Chris continued to pursue his despite repeated warnings that, “You can’t make any money doing that” and eventually landed a job in the video gaming industry.
Since one of his influences was Ed “Big Daddy” Roth, a love for fast fantasy cars also found its way into the mix and to Chris, the ultimate monster car would be a completely over-the-top, Hemi-powered ’68 Charger. As it turns out, Chris was able to make some money doing what he loved and is now an art director for Epic Games (ever heard of Gears of War?).
And even though he is currently driving a 470 rwhp 2007 6.1L Hemi Charger SRT8, that monster Charger was still lurking around in his imagination. So he contacted John Balow and his crew at Muscle Car Restorations in Chippewa Falls, Wisconsin, to turn his dream into a reality.
While MCR was building the car and all of the turbo intake and exhaust plumbing, HiTech Motorsport in Elk River, Minnesota, was charged with the task of building a really scary Hemi that could still be easily driven on the street. HiTech’s Brian Ebert is not only an expert engine builder, but also a genius EFI tuner. The goal is 1,200-plus streetable horsepower on pump gas.
The basis for this beast is a crate Hemi block that ends up with a 4.530-inch bore and a 4.500-inch stroke, for a total of 580 cubes. Feeding this monster through a HiTech-designed 90mm billet throttle body will be a pair of Garrett GT4094 68mm liquid-cooled ball-bearing turbos.
Granted, this isn’t the average engine build, but we thought you’d like to see what’s possible with the latest in turbo and EFI technology. Besides, sometimes it’s just fun to let your imagination run wild for a while.