Cosworth’s XH LMP1 Sportscar Engine
© Alan Lis
Cosworth, the Northampton, UK-based race engine manufacturer, has
been developing a turbocharged V8 power unit aimed the LMP1 sportscar
racing market. Alan Lis spoke with
Bruce Wood, Cosworth’s American racing
chief engineer about the project.
was the motivation for producing a Cosworth sportscar racing engine?
“I have always wanted to do Le Mans and Sebring. Cosworth
has never been very well represented in sportscar racing. In the
1970s there were teams using de-tuned Formula One DFVs and in the
1980s there were lots of DFLs and DFVs around but none were that
successful. It’s a discipline where Cosworth hasn’t
really been represented and should be, but under the current climate
it’s a difficult market to get into.
“For the last few years I had personally felt
that Cosworth should be involved in sports prototype racing. It
was something that we had discussed as a company and we decided
that it if we wanted to be in it, we probably needed to have a product
to sell rather than to try and persuade someone to put up the money
to develop a product. That’s seems to be the way that sportscar
racing works at the customer level. At the end of 2004 it became
clear that our IRL programme with Chevrolet would be finishing after
the 2005 season. The Champcar programme would continue, but from
an engineering point of view that programme doesn’t require
a lot of work. So it was a desire to be back in sportscar and the
coinciding fact that we were losing one of our major programmes
that led us to seriously look at doing this engine.
“We had also seen a window of opportunity
demonstrated by race results in 2005, which suggested that whilst
the Audi R8 had been a fantastic car, it had begun to show its age.
It was also clear that it was not going to be modified to fit the
new ACO regulations. The Pescarolo Judd won the 2005 LMES title
and showed that the Audi, with the restrictions placed on it, wasn’t
necessarily the ideal tool to win race that it had been in previous
years. At that point, when we started looking at the design of a
sportscar engine at the end of 2004, there had been no word from
Audi as to what they would do in the future. We saw an opportunity
for a good engine packaged in a Lola, Courage or other customer
chassis and felt that the availability of customer engines had not
kept up with the availability of chassis. So we decided to go ahead
with and produce what we thought would be a top line P1 engine.
At the same time we of course had to recognise that in sportscar
racing, outside of the manufacturer teams, there was not tens of
millions of dollars floating around, so we were going to have to
do it from our own budget.
meant that it wasn’t going to be sensible to start completely
from scratch. So we looked at what was available to us and the IRL
engine seemed to be the perfect base for a sportscar racing engine.
They need to be durable rather than lightweight flyers and the IRL
engine had been built to rules specifying a minimum weight limit
and certain minimum dimensions. It wasn’t going to be a case
of trying to get an F1 engine to run for 24 hours (as Cosworth did
with its DFV-derivative sportscar racing engines in the 1970s and
the IRL engine (above) as a base for a sportscar power unit?
“The IRL engine is a substantial beast and would fit pretty
well in the chassis that are available. So we took that as the basis
for the XH and bored it out from 3-litres to 3.6-litres and added
twin turbochargers. From the outset our intention was to take on
Audi and so, recognising that there was a potential fuel economy
benefit to be had from direct injection, we decided that from the
start of the project the XH would be available with conventional
port injection or direct injection. Rather than trying to reinvent
the wheel by developing our own system, we chose to partner with
Bosch who had provided the direct injection system that Audi used:
in 2005 they made that system available on a commercial basis for
the first time. Obviously the injector nozzle configuration and
the spray arrangement are tailored to specific engine designs, but
the fundamental mechanics of the system are the same as those for
the Audi FSI system.
“The direction injection system was a very
big investment for Cosworth, that technology doesn’t come
cheap. It isn’t just a case of asking Bosch to send a system,
you sign a deal with them where they provide the engineering support.
The cost is why we offer the engine in two versions, with DI if
you can afford it, with port injection if you can’t.
In the IRL,
engines are rev-limited to 10,500rpm, with a turbocharged sportscar
power unit you were presumably running slower than that?
“Yes, the LMP1 rules have an air restrictor so there is no
point in running at high revs. From memory the engine became choked
at around 6500-6800rpm and at that point the power curve flattens.
We ran on to 7500rpm to give the driver somewhere to go before gear
shifting, and set the limit there. Beyond 7500 the power begins
to fall away. In endurance racing the slower you can run the engine
were made to the IRL engine to turn it into a sportscar racing engine?
“Having been designed to run flat out for 500 miles in IRL
races we knew that the XG was a durable engine. The experience we
gained from the XF-E Champcar programme, where we turned that engine
from a 550-mile sprint engine to a 1200-mile endurance spec. engine,
was also very useful. We knew which bits to look at within the auxiliaries
and drive systems to make them last longer.
“The 3.6 litre displacement of the XH was
achieved by increasing the bore and stroke of the XG, by the fitting
of new liners and the crankshaft from the 3.5-litre version of the
“Part of the deal with Bosch for use of their
DI system is that they specify the injector location and design
bespoke versions of the injector to suit a particular engine. It’s
definitely better to retain the ignition source in the centre of
the combustion chamber, between the valves, and introduce the fuel
underneath the inlet valves. That meant designing all new cylinder
heads to fit the injectors in, but not a fundamental tear up like
having to move the camshafts around.”
“From talking to a lot of sportscar teams
and manufacturers it became apparent that we needed to move our
alternator. On the IRL version of the engine it was down on left
side, which is quite a common location for a single seater. In endurance
racing, the teams want to be able to change the alternator at a
pit stop if it’s failed, so we did some engineering to move
it into the centre of the of the vee, and make it a quick release
far was the sportscar engine developed?
“We took it to the point where, from all the information we
could glean, it was a bit better than the Audi V8. We measured 617
bhp and 730Nm of torque, while from our information the Audi engine
made around 610bhp and 700Nm.
figures led us to believe that we had an engine that was a bit better
than the benchmark LMP1 engine, in terms of performance, at that
time. With regard to durability, we ran Cosworth’s first ever
24-hour endurance test using data from a qualifying lap at Le Mans,
and ran a full race simulation at that pace on the dyno. We ran
the equivalent of 14-15 lap stints, what we were expecting from
a tank of fuel: at the end of each stint we simulated an in-lap,
after which we stopped the engine for around a minute to simulate
refuelling, before restarting it and doing another stint.
“We stopped the test after 24 hours, ticked
that box on the engine test sheet and then ran it for another six
hours to make sure that we had some ‘headroom’. We didn’t
have a single problem throughout the test, which was very rewarding.
That engine was running on port injection, so we felt that we had
an engine that was probably better than any out there in terms of
performance and durability.
Did the direct injection version of the engine get onto the
“A limited amount of dyno testing was carried out with the
direct injection system. We probably gave it only half a dozen power
tests to feel our way around before we decided to stop the programme.
I’m entirely confident that it would work very well, although
it would probably require some fine tuning of the combustion chamber
“Performance and endurance development on
the XH was initially done with port injection because that’s
what we knew. Direct injection was a complete departure for Cosworth
and the cost of it was going to have to be passed on to the customer,
and at that point we weren’t at all sure that many would be
able to afford it.
“By that time we knew we’d got the performance
from the port injection version. We felt that there would be some
economy to come from using direct injection, but we decided that
we really needed to wait and see if we were going to get a customer
before we invested any more money: that’s where the project
stands at the moment. We approached pretty much every sportscar
racing team you could care to mention, we had several people come
and visit and have the engine demonstrated to them, and there was
a lot of interest, but we are still at the same point of waiting
for a customer. There was another flurry of interest at the beginning
of 2006, but that hasn’t gone anywhere either.
“We did also consider an LMP2 engine. The
way the rules are for that class it would be a naturally aspirated
3.4-litre engine and the IRL engine would lend itself pretty well
to that use too. What made us decide against it was that we knew
we were going to be at the expensive end of the customer scale,
so if the teams couldn’t afford a P1 Cosworth engine they
certainly would be able to afford us in P2. If the P1 engine had
gone ahead and met with good take up and success, it was in the
back of our minds to do a P2 engine.
customer buy engines outright?
“The deal for the XH would be the same as all of our customer
programmes, a lease arrangement with full technical support from
Cosworth. We approached several manufacturers to see if anyone was
interested in badging the engine and turning it into a semi-works
deal. Obviously we could make it available to customers at a more
attractive price if that happened. Again we had several conversations
in that direction, but none that came to anything.
the project stand now?
“After the dyno tests with the direct injection system we
put the project on hold: we’d spent a lot of money on it and
during the months of development we’d been looking for customers,
but circumstances meant that we were not able find any. Within that
period Porsche launched its LMP2 car, Peugeot committed to a diesel
Le Mans programme and Audi announced that they would have new car
in 2006, which turned out to be the R10. A lot of the teams that
might have been potential customers were either holding out for
works deals, which is perfectly reasonable, or perceived that with
Audi, Peugeot and Porsche coming back, it was going to be difficult
for customer teams. It seemed to us that they were thinking that
without a works deal they weren’t going to win anyway, so
they might as well go for the cheapest customer engine deal. We
made no bones about the fact that the XH was the most expensive
customer engine. At Cosworth we have a big overhead and the reason
for that is that we have things like a metallurgy department with
six staff, and equipment like scanning electron microscopes and
all the other things you need to build Formula One engines, as well
as engines for other classes, and that all has to be paid for.
“Although it comes with a price tag attached
that is probably more than any of the other customer engines available,
we feel that we were offering the best product available in terms