Project 240SX Land Speed Racer: Better Living through Volumetric Efficiency
By: Chuck Johnson
“A big ass turbo with an engine strapped to it.” From under the hood, that’s how Project 240SX LSR is best described. When it comes down to it, our SR15VET 20V engine and all of its ancillary components exist for the sole purpose of propelling our turbo so that it can make boost. By packing as many air molecules into our 1.5 liter engine as possible, volumetric efficiency increases which ultimately equals more power. With drag increasing exponentially with speed, more power is exactly what we need to go faster.
Up until this point, we’ve only discussed the build of our SR15VET engine by 5523 Motorsports in San Diego, California. During that build, we boosted volumetric efficiency through the assembly of a high compression, long rod bottom end and a fully ported 20V head. All great mods, but in this game forced induction is the MVP.
At the center of Project 240SX LSR’s turbocharged universe, is a massive Borg Warner EFR 8374 turbo. We chose a Borg Warner EFR series turbo because it is far from the common repurposed diesel truck turbo; and instead, is specifically “Engineered For Racing.” (Hence the acronym E.F.R.) If there’s any doubt to that statement remaining in your head, check out an Indy Racing League engine for the last bit of reassurance that you’ll need. What you’ll find hung off the end of an IRL engine’s manifold will be either a single EFR 9158 or a pair of EFR 6758 turbos. Enough said.
When looking at a Borg Warner EFR turbo one can almost see a technology rich aura radiating off of it, but what specifically makes the EFR series so good? What it really comes down to is the all-inclusive packaging and technologically advanced features of Borg Warner’s EFR turbos.
On our EFR 8374 turbo, the all inclusive packaging starts with the incorporation of a boost control solenoid, speed sensor port for collecting impeller wheel speed data, and an integrated compressor bypass valve.
A closer look inside the compressor inlet reveals the attention to detail of Borg Warner’s engineers. Notice that the discharge slot of the integrated bypass valve aims right at the compressor wheel. This wasn’t an accident. During instances of closed throttle, the bypass valve opens to shoot high pressure air through this port and at the compressor wheel. This utilizes the recirculated air to help retain shaft speed as opposed to wasting it by venting it to atmosphere. Every little bit counts.
However, the Borg Warner EFR 8374 comes with an integrated bypass valve, we replaced ours with a Turbo Smart Kompact Dual Port. The Kompact dual port is manufactured from billet aluminum and has a piston type valve inside that eliminates the risk of a diaphragm rupturing and is able to easily handle 30+ PSI of boost pressure.
The Turbosmart Kompact earned its “dual port” name by having two ports which allow it to fully recirculate, vent to atmosphere, or a progressive combination of both. What’s cool about using a combination of the two, is that at low boost pressure the Kompact will recirculate up until 50% valve lift before venting to atmosphere. This keeps MAF sensor equipped cars like ours happy at idle and low RPM. At high RPM and boost pressures, the second port will open up to double the amount of available flow.
As demonstrated by our lovely resident hand model, the ratio of recirculation to venting to atmosphere can be adjusted on Turbosmart’s Kompact BOV by simply rotating the head. It sure smells like zombie ass up in here…
Getting back to the Borg Warner EFR 8374, the more significant finding that’ll result from a gander inside the 4″ ported shroud compressor inlet, is the aerodynamically efficient design of the compressor wheel. The compressor wheel inducer measures 62 mm in diameter and expands outwards to an 83 mm exducerer (or major diameter).
The compressor wheel is a “forged milled wheel.” During the forging process, an extruded aluminum bar is smashed into the general shape of the compressor wheel, optimally aligning the grain structure, and achieving far improved strength over a casting. The exotic, CFD birthed contours of the compressor wheel are then milled into the forging by a multi-axis CNC mill.
Disconnect the V-band clamp that holds on the compressor housing and take a closer look but please don’t drool on my fender. The compressor wheel of the EFR 8374 turbo could be mistaken for a work of art and could easily look at home as some blang-blang around Floyd Mayweather’s neck.
The center housing features four coolant ports. The four ports provide more flexibility in packaging the turbo inside the engine compartment.
The idea here is to configure the coolant lines in a manner to prevent an air pocket from forming inside the cooling passageways of the center housing. Asides from this feature, the center housing of the EFR 8374 turbo might seem rather unassuming.
Inside though, the technologically packed theme continues with the ball bearing assembly. The races of the ball bearing assembly are constructed from an M50 military grade steel while the ceramic ball bearings are encased in a silver coated metal cage to prevent galling.
On the turbine housing side, the EFR 8374 ascends to a whole new level of awesomeness. The housing itself is constructed from cast stainless steel, which with its low thermal conductivity, helps retain heat energy inside the gas stream. In fact, the overwhelming theme of the EFR 8374 series turbine housing revolves around optimizing exhaust flow efficiency to improve overall turbo response.
The twin scroll design cleans up the exhaust stream by separating and strategically timing the exhaust pulses, ultimately improving turbo response. This is done with a specifically designed Full Race Motorsports’ EFR turbo manifold, which properly pairs the cylinders by firing order into the two divided turbo housing scrolls.
Specifically, the Full Race Motorsports manifold merges cylinders one and four into one half of the turbine housing and cylinders two and three into the other half. This configuration ensures that the exhaust pulses have a clean, unimpeded pathway while the equal length runners strategically time the arrival of the exhaust pulses to promote exhaust scavenging.
Full Race Motorsports applied a thermal coating to the outside of the manifold in an attempt to keep engine compartment temperatures in check. In addition, 5523 Motorsports, swapped out all of our exhaust studs with Inconel studs from a Nissan GTR.
The key player behind the EFR turbo is the gamma-ti (titanium aluminide) turbine wheel. Your average run of the mill Inconel turbine wheel weighs about twice as much as Borg Warner’s gamma-ti wheel. It’s absolutely crazy to hold one of Borg Warner’s gamma-ti turbine wheels in your hands while holding an Iinconel wheel in the other. The difference in mass results in a large reduction in rotational inertia which equals kick ass spool response and overall power.
Originally we were planning to use an internally wastegated version of the EFR 8374 to maintain a tidy, easily serviceable package. The Borg Warner engineers spent a lot of time optimizing the internal wastegate set up of the EFR series turbos. In the diagram above, you can see how the wastegate port is split in two to ensure that excess exhaust from each scroll is diverted. This is to maintain equal balance on each side of the turbine wheel.
Unfortunately, when shoehorning such an enormous turbo into an engine compartment compromises sometimes have to be made. It turns out that the actuator canister and coolant neck of the SR20 reside in the same area. No problem that a pair of Turbo Smart’s Hypergate 45 wastegates won’t take care of.
Although one of Turbo Smart’s wastegates could have easily done the trick, we chose to go with two. So why two wastegates? Easy, using two Hyper Gates preserves the clean exhaust flow of the twin scroll configuration. Just as cylinders 1 and 4 as well 2 and 3 have their own dedicated turbine housing scrolls, they should each have their own wastegates. Full Race Motorsports has seen improvements in response of 400 -500 RPM by keeping the paired exhaust streams separate utilizing dual wastegates. Ultimately, we need all the boost response we can get since we only have 1.5L of displacement powering our enormous EFR 8374.
John Kuchta of Specialty Cars, constructed a wastegate dump tube for each of the Turbosmart Hyper Gates using 1.75″ stainless steel J-bends from Burn’s Stainless. Both dump tubes, exit through an unrestricted path right behind the driver’s side front wheel.
Installing fiberglass header wrap can be a real pain. To help prevent the fibers from getting embedded into the skin, 5523 Motorsports soaked the DEI header wrap in water before installing it. Once the dump tubes were wrapped and mounted, the header wrap was then safety wired in place every three to four inches.
The reason we went with the E Boost Street 40 was because of its simple interface and powerful features. The E Boost Street comes with two stages of boost control, a 40 PSI map sensor, and a programmable RPM or boost level auxiliary output. The programmable auxiliary output can be used to control a methanol injection system or the VVL mechanism on our SR15VET.
In addition, Turbosmart’s E Boost Street features an over boost shut down protection function where if the max boost setting is surpassed boost will automatically be cut to protect the engine. Lastly, a programmable boost correction factor can be set using the E Boost Street. This feature allows a tuner to combat boost drop at high RPM which results from a build-up of exhaust back pressure. By ramping up the solenoid’s duty cycle, the power band can typically be extended by another 1,000 RPM.
To finish the install of our turbo system, 5523 Motorsports constructed the oil delivery line using Earl’s Performance Plumbing -3 AN Speed-Flex stainless steel outer braid, PTFE lined hose and stainless steel Speed-Seal hose ends. Note, with the EFR series turbos an oil pressure restrictor is not needed.
To drain the oil back to the block, 5523 Motorsports constructed the oil drain line from Earl’s Performance Plumbing -10AN Perform-O-Flex with swivel seal hose ends. Earl’s Swivel-Seal fitting are anodized, reusable fittings which can be swiveled for easy orientation after assembly. The ability to clock the hose ends in relationship to the hose makes working with AN fittings and steel braided lines much easier and is worth the extra few bucks.
5523 Motorsports then constructed the coolant lines from -6 AN Perform-O-Flex again using Swivel-Seal hose ends. The coolant inlet is fed from the stock location on the front of the SR20 block, while the coolant outlet is fed back into the coolant neck. Earl’s Performance Plumbing 14 MM x 1.5 mm to -6 AN adapter in combination with OEM Nissan crush washers were used on the coolant port of the turbo, coolant neck, and block.
All of the oil and coolant for the turbo as well as any additional rubber vacuum lines in the vicinity were then wrapped in Earl’s Flame Guard sleeve. It’s important to use Flame Guard that is the next size up from the line its covering. For example, a -12 size Flame Guard would be used to cover a -10 line.
Earl’s Flame Guard is a rubber jacket with an inner fiber glass sleeve that is a self extinguishing heat barrier. With the extended stints of wide open throttle associated with land speed racing, heat management in the engine compartment is a must. Note the DEI turbine housing blanket, master cylinder heat shield wrapped in heat reflective gold foil, and thermal wrap around the brake fluid reservoir.
With all of the components of our turbo system covered, let’s spend a little bit of time covering how we chose our turbo. To figure out which turbo would best suit our rather unorthodox application, we used Borg Warner’s online turbo matching tool called MatchBot. At first look, the MatchBot application is intimidating as hell… even with that friendly little robot logo. The good thing is Borg Warner has a series of YouTube videos that give you a step by step explanation of how to work Match Bot. If you have the patience and perseverance, Borg Warner’s online tool is an invaluable tool which will reward you with a properly sized and performing turbo in the end.
One of the main hurdles for me was figuring out information like volumetric efficiency on a motor that didn’t exist yet. So we used the closest thing to an SR15VET that we could and applied numbers typical of a Honda B16A3. With its 1.6 L of displacement, high flowing head, and variable valve lift system we felt that the Honda B16A3 engine was a good match to our SR15VET 20V.
From talking to Geoff Raicer at Full Race Motorsports, we had a good idea that the best turbo for our application would either be an EFR 8374 or EFR 7670. We started out by plotting the 7670. Reviewing the compressor map, it looks like we’d be pushing the smaller 7670 out of its efficiency range at higher RPMS with our desired boost levels.
We tried the 8374 next, which showed the compressor working in a better efficiency range at high RPM. What made us nervous though, was how close we were to the surge line below 6,000 RPM.
The gamble came down between operating the 7670 out of its efficiency range at our 35 psi boost target. On the other hand, the EFR 8374 could be plagued with surge issues. In the end, we decided to go with the EFR 8374 knowing that we could always get creative with anti lag system to get us off the starting line.
The last step in Borg Warner’s MatchBot tool was to use the turbine sizing selector to help select a turbine housing size for the EFR 8374. There are three choices of turbine housings available for the EFR 8374, .83, .92, or 1.05 A/R. The smaller A/R housing would be more responsive at lower RPMS but would begin choking flow at high RPM. Since Project 240SX LSR is not in the business of getting groceries or even hot lapping Button Raceway for that matter, our concern wasn’t with making power at low RPM. Hence, the boost curve entered with a mere 4 psi at 4,000 RPM. Instead, we were solely concerned with producing the 30-35 PSI of boost, which we estimated was needed to achieve 500 plus horsepower. With this in mind, we chose the largest 1.05 A/R housing.
Before Project 240SX LSR hit the dyno, there were a lot of people that were skeptical that such a small engine could spool such a large turbo. In the end, there are two land speed records in the books that say otherwise and validate the value of Borg Warner’s MatchBot turbo matching program.