This is the standard Esprit V8 Lotus Type
918
3.5 litre, Twin turbo, Quad cam, 32
valve V8
90 degree
cylinder bank angle, single-plane crankshaft.
Bore: 83 mm
Stroke: 81mm
Capacity: 3506 cc
Head Chamber Aluminum alloy, four-valve pent-roof
Valvegear: Dual overhead camshafts with one toothed belt per
bank, hydraulic tappets
Inlet valves: 33.5 mm
Exhaust valves: 30.0 mm
Block: LM25TF aluminum alloy , cast iron "wet" lines,
spheroidal graphite cast iron cross-bolted main bearing caps
Weight: 485 lb
with ancillaries
This is the
Project M71 engine - the same Type 918 unit with
uprated and Keronite coated Mahle forged pistons,
gas flowed and ported cylinder heads and the
inlet plenum assembly from the GT1 racing program
Pistons are very important in high boost applications, with the
associated heat soak, even when running lower compression ratios
Mahle pistons are about as good as you can get and
are ideal for this engine and the Keronite coating is extremely
hard and has a very high degree of thermal insulation
Plasma
Electrolytic Oxidation (PEO) surface treatment technology is
used to deposit the coating
The standard 918
uses two Garrett T25 water-cooled, oil lubricated
turbochargers without intercooling
The cast exhasut manifolds have built up a great deal of heat in
this test and this imparts heating into the high pressure air path
from the compressor, reducing its density
The Project M71 engine uses
Garrett GT28RS turbochargers, which are considerably larger than
the T25s, with a much greater potential for power output, whilst
maintaining short spool periods with their dual ball bearing
construction
Their fitment requires facbrication of specialised
tubular exhaust manifolds - click here for more details on the
GT28RS and fitting
Click the image for the full details of the
difficulties with using these turbos
This photo on the left shows the "boost piping", high pressure
inlet from the turbos into the throttle bodies and standard plenum
- the plenum is quite restricive and the throttle bodies, below,
are fairly small diameter
The GT1 plenum used on the Project M71
engine is grater in volume and much less restrictive, allowing
the equalisation of boost pressure across all cylinders
It also used much larger
throttle bodies, from the Lotus Carlton
With the lack of inercooling, or chargecooling as its called when
an air-water intercooler is employed in conjunction with a water
radiator in a pumped cooling circuit, many attempts have been made
to use twin smaller chargecoolers on the 918 engine, as in the
photo below
I was looking to use the twin Lotus chargecoolers on the left,
from the Lotus 910 four cylinder turbo engine
This would line up perfectly
with the GT1 plenum throttle bodies, all keeping the path from
turbo compressor as short as possible - this helps to keep boost
lag to a minimum
The result is here on the engine, with the final touch of the name
plate on the chargecooler
A lot the design thought here was from basic
turbocharging principle but also inspiration from the Esprit V8
GT1 racing cars and the similarly engined Elise GT1 racer
The works V8s used 1 bar of
boost when they used a single large turbo and 1.2 bar of boost
with twin turbos - class regulations meant that they had to run
with 33mm air restrictors but with mildly fettled heads, the end
result was 540 bhp!
Click the image on the left for a full
set engine build photos
This photo shows the
chargecooler and plenum on the GT1 Esprit
V8 and below shows the comparison with the Project M71 engine
- click here for more on
the Esprit GT1
Further developments on the turbo positioning
and associated plumbing are in the Progress
Section
Cutaway drawing of the Lotus 918 engine
Click on the images below for enlargements of the V8
engine drawings from the Lotos workshop manual
Lotus Type 918 Engine Specifications -
click for pdf
Lotus Type Twin Turbo
Engine Technical Specification - click for pdf