As the 2010 Monoposto rules are allowing fuel injection, we are evaluating making the change. Whilst the carburettor rules allowed any size of throttle butterfly, throttle bodies are limited to 40mm diameter. In 2009 we were using 48mm bodies with 41mm chokes, so it was going to be close whether injection would be an improvement.
To determine this, we’ve used a spare “donor” head, some old valves, some plasticine, our 48mm carbs, and a set of throttle bodies, all mounted, in various configurations, on a flow testing bench. The results are, obviously, not the whole story, as air flow in a real engine is not steady state. In principle though, the air flow tests give an indication of potential power and torque outputs.
So, what did it tell us? Well, as we predicted the results are very close, but we believe that on our engine, with our manifold, that throttle bodies will give equal or marginally better performance, particularly in terms of “mid-range torque”, which is where our Toyota engine seemed to be lacking compared to the Vauxhall XE engines used by our competitors. The other benefit of injection is that they are immune to lateral-G influences. Carburettors (or, at least, our carburettors) didn’t like very high-G cornering @2.5G, and at the beginning of the season they went rich above 2.0G. Having reliable power in high speed curves will not only improve tractive effort in said corners, but bring about an improvement in balance as well.
The actual benefits (or otherwise) won’t be known until (unless) we commit to injection, map the fuelling and ignition, and get a torque output curve, which is probably the next thing to worry about.
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