Rolling road tune

With the engine finally running without tearing itself apart, we took the Mini to Hitech Motorsport in Drury to have it tuned on the dyno.

I was under the impression that they had a stock of SU carburettor needles and would be able to finalise the tuning, but I was wrong.

They identified an airflow restriction in the airbox at high load and got the ignition timing dialled in, but didn’t change the needles. “It’s a bit lean at the top end,” they said, “try fitting some AF needles and bring it back.”

Maybe I’m out of touch with the cost of dyno tuning, but I imagined I would get a bit more for my $800. If you want something done right, do it yourself. So we bought an Innovate Motorsports Wideband Air/Fuel Ratio gauge, cable tied it to the dashboard and fitted the sensor into the exhaust, and began to figure out the ideal needles for this engine.

But first, the airbox restriction: easily solved by cutting a big hole in the top of my airbox. It still has cold air forced into the area from the intake duct, but it’s free to take as much air from the engine bay as it needs. The lean condition at top revs disappeared instantly.

Airbox1

Airbox2

Update from June 2016: Eventually we’ve ended up with AF needles (as recommended by the lads at Hitech), but modified to enrich the idle. Now we’re reliably showing a 13.5:1 mixture at idle, 14.5:1 mixture at a very light cruise, and 11 to 12:1 under acceleration. I thoroughly recommend getting a wideband air/fuel ratio gauge- it makes tuning amazingly easy.

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