TLF member David Lisle gives us the last and for some, the most interesting part of the serialisation of the ‘Changes’ he’s made to his Lotus Esprit Turbo SE.
Contrary to thoughts this engine was not built to see how much BHP could be gained but built to be the best it could be. The aim was smooth driveable power, BHP was a by-product of the systems and engineering implemented to achieve this. The results were staggering. What follows is a brief outline of the developments carried out and some of the changes made.
In keeping with the rest of the project, staying as close as possible to standard design parameters was important. However I still had to make quite a few changes. The main areas for improvement were the induction air flow and exhaust; these had far too many restrictions which drastically affected the volumetric efficiency (VE). Improving this would influence the mass air velocity which in turn will affect the fuel air mixing so maintaining a balance while changing the flow dynamics was key. The direction I took was to concentrate on getting the best flow volume within the confines of the original intake manifold system and then exhaust it in a way that was complimentary via the turbo. The calculations showed a massive improvement could be made but up to date technology on the fuelling /management systems would be essential to gain all the benefits from the developments introduced. The preliminary calculation did show that 400 BHP was a possibility so the bottom end needed to be built very carefully with this in mind.
I started with the original SE engine, this was systematically stripped and every part meticulously inspected. As this engine had covered circa 45k miles there were small signs of wear on all friction surfaces, although they were only slight I decided to change the lot with the exceptions of the castings and camshafts.
The block assembly
The crankshaft was changed for a new later model with the in-built oil thrower, this is slightly stronger and more suited to the application. The pistons and chromium alloy liners were replaced with new Lotus original spec. parts, con rods were retained but fitted with new bearings. The flywheel was changed for a new Esprit Sport300 version with a cerametallic paddle clutch in anticipation of increased torque. With the exception of the liners these parts along with the front pulleys were sent to a specialist for super dynamic balancing with a very tight tolerance.
All of the castings were cleaned bead blasted and crack tested, except the cylinder head which was rejected as out of spec on combustion chamber alignment. A new head of same SE spec was obtained.
Once I knew the castings were good the block was prepped for the new chromium plated alloy liners. The fitting of the liners is most crucial to get correct. I first dry fitted them to the block to ensure the nip was spot on. Only when 100% happy with the fit were they put into position using Loctite 572.
Although the Loctite stays elastic for a time the liners grip too tight to rotate within 30 seconds, so to ensure alignment was correct I used a datum mark on each liner and the block to insure each were in the correct orientation. When all positioned the cylinder head with the original pre compressed gasket were fitted and torqued down. This was left overnight to cure as it ensures the liners were in the perfect position and will not move when pistons are fitted.
The next job was to lay the crank; this was done with all new Lotus bearings and copious amounts of Graphogen. The main bearing housing was sealed using Permabond A136. The pistons could now be fitted along with the all the other ancillaries to the block.
The first area to look at was the air intake. I chose to go the same way as Dermot O’Hare on this, adopting his ram air principal and increasing the inlet to 100mm also using the Viper Evolution air filter. This would provide the flow volume I required.
Working with Turbo Technics we eventually came up with the T38 hybrid turbo; this has a compressor intake and outlet with surface areas over 50% larger than the standard T34. This design will allow & produce the greater volume of air I required at a lower boost level. It was a bit of a squeeze to get it all in but eventually it fitted quite snugly after a few minor mods.
The next area to be addressed was the chargecooler. I designed a new unit which would be able to handle the new air flow volume without restriction and at the same time provide a greater cooling capacity than the original. This was achieved by using the latest high efficiency cores with longer stall time and 80 ltr/min recirculation pump through 1’’ bore pipes. A few more changes had to be made to allow the larger diameter pipes which could not travel through the chassis to be fitted externally. The front cooling radiator for the system was the same high quality alloy core, but as big as possible to fit into the space available in front of the a/c rad.
After the charge cooler was the plenum nose, this was very poor and needed extensive gas flow work to function effectively. The opening through the plenum back plate was also increased in size to maintain the improved flow characteristics into the plenum chamber. A spacer plate was fitted to the plenum increasing the volume by 60 cubic inches. This was done to provide a larger reservoir of air for the inlet ports increasing flow efficiency and reducing mass air velocity, this insured each port could receive the same air flow throughout the full rev range without boost drop off.
The change of the flow dynamics into the plenum was not ideal for the secondary injectors which required a more turbulent higher velocity air flow in that area. However with the new injection system that would be fitted they were not required so blanked out. This in turn opened the door for gas flow work in the inlet manifold ports. The natural finish had no machining and was very undulating and coarse. I was able to smooth out the ports considerably reducing the laminar layers and again increasing the flow volume.
The flange joint between the inlet manifold and cylinder head was a joke and this misalignment was creating a step effect preventing the continuous smooth air flow into the cylinder head. This massive disruption in flow would increase the mass velocity greatly which is preferable with injectors producing poor spray patterns to assist the fuel air mixture. The top end injectors I intended to fit would not benefit from this, plus the reduction in flow volume in this area would undermine all the previous work so the inlet manifold was ported as part of the cylinder head to insure a smooth transition from one to the other. The gasket was also in place as part of the process because the port size was increased. To ensure on final assembly they realigned perfect the two were drilled and doweled before dismantling. The head ports were slightly modified giving a more direct flow to the valves and carefully balanced to give uniformity across the whole induction and exhaust ranges. The valve sizes were left original. The combustion chambers were machined and polished to make sure sizes and compression ratios on all four were identical, this also aided exhaust flow which is equally as important as the induction.
The exhaust ports were highly polished as were the valves. The exit to the exhaust manifold was also machined to perfectly match the new manifold which was a specially made pulse tuned high flow stainless steel unit, this was important to maintain the flow efficiency that had been built in throughout. The original cast unit could not provide the flow required. All of these changes in the flow dynamics which had increased VE, provided a more balanced higher volume and smooth airflow to the turbo turbine, this in turn had been manufactured with this flow information. Being now slightly larger it was more effective at driving the larger compressor and because of the flow volume had none of the old familiar turbo lag. The turbine exhaust outlet was increased by 45% also incorporating a larger waste gate. The rest of the exhaust was a 3.5” stainless straight through system.
For all of the aforementioned work to be effective the fuel system needed to be improved to compliment it. This I did by adopting only large primary injectors (860) which would work sequentially as opposed to the wasted system. I was able to use the now redundant mechanical charge cooler pump which was re-engineered into a trigger/sensor device for injector timing.
All of the systems were now being controlled by the new Omex ECU, this provided far better control and tuning parameters over the complete ignition and fuel range with 3D mapping. This did however require a compatible trigger wheel which the 910 engine does not have. I overcame this by fitting a specially made 36-1 trigger wheel to the back of the front pulley.
During the dyno tuning process it became evident that the fuel lines were too small in the tank. They could not supply the volume of fuel required at higher RPM. This was overcome with a larger secondary fuel set up supplied from the original with a 1.5 ltr swirl pot as the bank for the high RPM requirement.
A few other parts such as the idle control valve and fuel pressure valve were no longer compatible with the new system and were subject to more changes. Once all was complete a starting problem from cold became apparent. This was caused by the new trigger sensor not getting a clear even signal due to the starter motor pulsing action during turn over. Another change in the way of a high torque geared starter motor solved that one.
After many hours of patient tuning and balancing of all the new developments on the dyno at Northampton Motorsport we broke through the 400 BHP mark with 412. We later after a few refinements settled for a dyno run average of smooth drivable 422 BHP at the flywheel, 391 BHP at the wheels with 370 lb-ft torque at 5200 rpm and 1.52 bar map.
The red lines show the first 412 run and the black the 422 run after the refinement on fuel and spark
Click dyno print-out to enlarge.Thank you for your interest, I look forward to any comments you may have.