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300BHP lump seen at Caterham?

Paul Drawmer

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I was lucky enough to be shown round the build area at Dartford last week.


In the far left corner is a customer's car which has a VX(?) based engine which is reputed to be 300bhp!!! it does not appear to have forced induction - but I didn't get a chance have a really close look.


I couldn't see any distinguishing marks on the engine, but the cam covers look to pretty angular, as if they have been machined out of solid, or constructed from plate.


Anyone know what it is, and is it really 300 bhp?

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That's the one - 'a bit peaky in delivery' I would be surprised if it isn't! I had a crawl over a VX touring car engine from a few years ago, and the builder had incorporated two sets of injectors; one in the airbox, and the other at the ports. Programmed to run on air box at low speed, ports at high speed, and both for maxxxxx.


If you put a 300+ bhp lump in a Caterham, what do you use for a gearbox and diff? Or are the sierra things that strong?

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How do twin injector set ups work?


Obviously extra injectors don't get more air into the cylinder, so if there is any extra power to be had it comes from fuelling the mixture more effectively.


At low power/low fuel requirements, if you inject on the port side of the throttle butterfly the fuel gets a chance to hit the back of the hot valve; a lot of the fuel wets the walls of the inlet tract and evaporates from there into the air stream; some fuel atomises directly into the shear of the airflow. Now these modes of fuel progressing into the mixture have different characteristics. The fuel that evaporates directly does so most efficiently when small droplets are injected and the air speed is fast and turbulent. The hot valve path is pretty much independent of droplet size, but is dependent on timing of the injection pulse. The wetted-wall process is independent of droplet size, but depends on how much wall surface area is wetted.


The wetted wall mode is what is so important for a dual injector setup.


The wall of the inlet tract is of varying temperature, hottest closest to the valve. The fuel wetting the wall close to the valve evaporates into the airflow pretty quickly. If the fuel wetting the wall further up the tract doesn't evaporate on the cyle it is injected, the airflow starts dragging it down to the hotter parts of the inlet tract. In any steady state condition of revs and fuelling, there is a boundary on the wall of the inlet tract between where the wall stays wetted and where the wall evaporates all the fuel each cycle. As the fuel demands of the engine increase, the boundary moves closer and closer to the valve. As the fuel demands decrease, the boundary moves away from the valve. When the boundary reaches the valve itself, squirting more fuel in does not result in more atomised fuel getting into the fuel/air mixture, it just results in more depth of wet fuel in the tract and large droplets getting into the combustion chamber. The poorly prepared mixture does not burn as well and less than optimum power is released from the combustion. This is when you have to start looking at dual injectors.


At this point, the only way to get more atomised fuel into the mixture is to give it more time to do so. For this reason you start injecting fuel from further away up the inlet tract. Injectors in the airbox or in the trumpets are injecting against colder surfaces, so injected fuel will need to be spread over a much larger area to get into the mixture. This is why the secondary injectors get mounted so far up the inlet tract. This also means that fuel from an injection event hangs around wetting the walls and getting dragged down the inlet tract for several engine cycles - there is a lot of fuel just hanging around and when you stop injecting that previously injected fuel still has a chance to evaporate into the mixture; transient control of the fuelling is not good. The transients can be made better if the direct evaporation from droplets can be encouraged. This means that the secondary injectors should only be used at full throttle and high rpm, where the air shear is greatest; secondary injectors can be sized to be very small with a very good droplet size because they are only ever used to top up the fuelling you are getting from the primary injectors.


The trick with twin injector set ups is all to do with phasing in the secondary injectors appropriately. The extra power comes from fuelling the mixture more effectively. If your injector position is not already compromising the fuelling, there is no more power to be had from twin injectors. For a k-series with QED DTH throttle bodies, that means you need to get the power potential up to ~240bhp before there is any possibility that twin injectors are required.

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Peter - this sort of stuff is getting in the way of work! Thanks for the info.


ISTR in the explanation I was given of the dual injector set up (bearing in mind that I have already demonstrated a 'senior moment' in respect of remembering what was said) that the second set of injectors are controlled by a separate control system. Or maybe that was just for initial set up in the test cell.

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How they are controlled depends on the capability of the ECU. You need extra output amplifiers for the injection events and you need a separate map. You need all the usual corrections and timing information. This can get very close to being a separate ECU, depending on how primitive the principal ECU is. This is less than ideal though as it means splicing the loom to get all the sensor information to the second ECU or running multiple sensors.


The easiest, simplest way is to have an ECU that handles two sets of injectors and has a control strategy for phasing the outer injectors into play, because then the single brain can make all the appropriate decisions and the mapping software will be easier to use.

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The Emerald ECU has been set up for twin injectors before now , the outer injectors are set up to switch on at the upper most load sites above a set rpm point - where the air speed is sufficient to carry the fuel, and halve the fuel number or duration at the same time . The ecu actions this at a set rpm point using a second driver already within the emerald ecu .

the cost of upgrading the Mk3 box is around £80 inc .

Plus of course around £200 inc for twin injector trumpets .



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I saw's Stan's engine at Caterham's and it looked to me like it was only running one set of injectors on an interestingly designed carbon intake.

The fact Stan's engine is 10% larger than the standard 2lt displacement would indicate to me that Stan's deliberately not gone the peaky 2lt touring car route and instead got an engine with a wider more usable power band.

Re 8 injectors - Peter's right in that they are the optimum solution although suit some applications better than others. I considered having 8 injectors on my BD but the original positioning of the single injector had already been optimised for racing applications and hence would have proved difficult to improve upon - plus space was a consideration. At the other end of the spectrum is the original 4 cylinder BMW M3 engine where 8 injectors are worth investing in because the standard injectors are so much closer to the valves.


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> Chelspeed runs twin injectors in his 7. I don't know how much pwer his engine > puts out


Last years engine was 274bhp on Griffins dyno at the beginning of the season and 260bhp at the end of the season on Emeralds (seemingly anti-Vauxhall???) rollers. This years engine isn't built yet so who knows.


The twin injector set-up was supposed to liberate more peak power but only increased it by a couple of bhp over the previous year (but torque was increased when it shouldn't have been so not bad really). The conclusion was that it was being held back by the head, standard diameter valves, waisted stem, in a later Vauxhall casting head. This years big valve, 5mm stem, coscast based head will see if this was the case.


About 11 weeks to Curborough isn't it? When are regs out?

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Yep, presume so. Plus speed round Fradley, traction, weight....


I've been pushing for a fastest thro the finish award for the last two years but it seems I'm the only one interested. Wonder why?


The Peter / Arnie speeds across the finish line will be equally interesting in May.


Mr Edmands - Are you coming out to play in May too?

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If this is the engine that I think it is, then it is a Swindon Vauxhall. This has been bored & stroked to 2200cc and produces about 296 bhp @ 8750 & 205 ft/lb @6500. It is not at all peaky - torque is above 175 lb/ft from 4750 to 8750rpm and is still 154 ft/lb at 3000rpm. Very good spec from probably the best & most experienced engine company in the country. I've used their engines for years and the service and quality is superb. Of course, there is a down side, as a 2.2 to the above spec doesn't leave much change from £25000 - maybe one day....
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