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Alunox Manifold with EFR 6258-G Twin scroll Turbo upgrade for the 4-cylinder Lotus Esprit

Mark Kassim

After some research into different turbo upgrades available on the market, I decided to go with the BorgWarner EFR 6258-G Twin Scroll unit supplied by Van Der Lee Turbo systems (Jaap), to replace the Esprit’s single scroll turbo charger. One of the biggest limitations of most factory single-scroll turbo system is the restrictive nature of its log or compact unequal-length exhaust manifold.

The design characteristics of both Manifold and Turbo were honed with collaboration between both Van Der Lee Turbo systems and Alunox engineers. Bringing the two companies together allowed me to get a twin-scroll (pulse) turbocharger system yielding maximum efficiency.

Divided or "twin-scroll" turbos and manifolds have emerged as the preferred design of many of the top tuners and even OEMs. To list some of advantages of the twin-scroll (or two-pulse) verses the Single-scroll (or constant pressure) turbo systems:

  • Superior scavenging effect

  • Better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbocharger's turbine

  • Allows for greater valve overlap

  • Increased turbine efficiency


The engineers in BorgWarner's Advanced Aftermarket Product group created a wish list of every notable design characteristic when designing the EFR (Engineered For Racing) Series. They used materials that had never been combined into an aftermarket turbocharger. They delivered quick boost response, powerful performance and reliable durability. 



The EFR 6258-G has an Aspect Ratio (A/R) of 0.8 and a low inertia 58mm Gamma-Ti (Titanium Aluminide) turbine wheel weighing 50% less than typical units. The turbine wheel is optimally matched with the FMW compressor wheel for maximum response and fast spool up.


So effectively we have a twin scroll manifold matched to our twin scroll turbo, designed for flow and pulse tuning. For the Esprit the firing sequence is 1-3-4-2 and the conventional single-turbo arrangement has all exhaust manifolds connected together at the exhaust turbine. The twin-scroll turbo splits into two separate paths and exhaust flows hit the turbine blades independently.



This prevents the two exhaust streams to interfere with each other.

I found many Video references on YouTube for Twin Scroll Turbocharging but this one seemed to explain the principle.



This is the resulting design shown on a 910-series engine block.


The manifold is made from 321 Stainless Steel, precision TIG welded in a dedicated jig giving a fracture proof construction. The flanges are now CNC machined cut out of Stainless Steel to give an accurate fit, the collector uses a burns double wall slip joint to allow movement during the heat cycle whilst and maintaining a seal to provide maximum pressure to the turbo. The system is also being protected against shock loading by the pivoting brace mounted at the back of the cam carriers.


This particular manifold has a further upgrade in terms of its T4 flange and larger collector


Other modifications include

  • Bosh Coil On Plug ignition system

  • 4 x 750cc Fivo Injectors sequentially fired – removed secondary injectors

  • Cam sensor using housing of old Charge Cooler water pump (Flux Capacitor)

  • Emerald K6 ECU

  • Electric Charge Cooler water pump

  • Upgraded Alunox radiator set – main rad, charge cooler, oil coolers, condenser.

  • Alunox 3” twin exit rear system


I was introduced to Emerald by a friend who knows Karl the designer of the K6 ECU, so I supplied information about the flywheel pattern from the Lotus manuals and oscilloscope traces. Karl then added an option in the software for the Esprit. This allowed me to re use the existing crank sensor.


 The car has been tuned at Emerald by John Lamsley and I have made a few trips over the years at various stages of modifications to the Esprit. It quickly became apparent he was on top of his game and has a lot of experience as he could quickly diagnose problems and provide solutions. Karl was also available for technical support when needed.


My first trip was in 2015 was after installing the K6 myself and base mapping it to run a bit rich with retarded timing.  It was a long journey to Watton in Norfolk from Wrexham at 50 MPH. It was enough to get there which we then spent a day on the dyno going through all the base mapping and boost tuning. My clutch started to slip so the full potential of the standard T3 and Alunox manifold wasn’t realised, the following results where obtained.



System 286 BHP / 291 lb/ft Torque


Since the clutch started to let go we had to leave it there but after speaking with John, more could have been gained with this setup. It would be interesting to compare results if anyone has dyno data on the T3.



So returning to the Dyno with an uprated clutch (after discussions with Dave Changes) and the new EFR setup, the car had to be completely re-mapped due to the dramatic change. Initially we tuned without any boost from the turbo to get the base map set up, the car made 170BHP with no boost which was about 30 BHP greater than the previous setup, which was mainly gained due to the larger collector ports of the T4 flange giving an overall increase in flow.



Dyno Run Video at Emerald in Watton




Torque and Power Figures on new BorgWarner EFR 6258-G  T4 Turbo


The graph show the figures for two maps overlaid, look at the orange line showing Torque, at 2000rpm it is double.


I was held back again this time the wastegate actuator failed to hold pressure at high RPM. But some impressive figures where achieved early on 270BHP was made on only 6 PSI boost. Also the Boost response is instant with this setup completely transforming the driving experience of the car.



This was my last dyno visit for now which yielded 340 BHP @ 1.2 bar, the graph was taken just before I got that figure. The Turbo is capable of 1.7 bar but due to the fact the car is running stock internals, and after further discussions and the sharing of data with Dave (Changes) on the limits of this I have held off turning it up for now.


Dave must have the most first-hand dyno data on an Esprit that I know of, and so after exchanging graphs and knowledge gained over the years through experience and Research and development, these two additional modifications were made for this dyno run

 

  • Turbo Smart dual port actuator and MAC 4 port wastegate solenoid

    The new actuator set up consists of a TurboSmart IWG75 Twin Port unit allows pressure to be applied to both sides of the diaphragm so it can be held shut as well as open. The MAC4 solenoid control takes the PWM signal from the ECU and translates it into a differential pressure control across the diaphragm.


  • PNM Plenum spacer 25mm



The Plenum spacer has helped at higher RPM allowing for a steady rise in Power /Torque, which is also noticeably smoother when you are driving over the 4.5K RPM.

 

The gains at Castle Combe Lotus Track day where noticeable this year with the instant throttle response with greatly reduced lag coupled with the new speed/Torque characteristic of the engine. This uplifted the track experience, the extra torque and where it was delivered made it possible to maintain 3rd gear as appose to 2nd in many corners.

Further development


I’m at the point now where I could just turn up the boost but again benefiting from Dave’s R&D I want to look at the valve timing with Vernier pulley wheels and some fine tuning of the intake system, so I can optimise the speed torque characteristic of this 2.2L lump.


Witten By Mark Kassim







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