Given the recent news surrounding this horse meat kerfuffle I thought it best to check on my horses. Matt was already dropping his Westfield off at BTec racing for his carbs to be rebuilt and Stu was getting a go on the rollers to check his air fuel ratio – it only seemed natural to tag along. Since I’ve built it I’ve not been massively impressed with the speed of my Westfield.
After wrapping up like the Michelin man I met with the above Swindonites and we convoy’d off. It was a bit foggy made worse with it condensing on the windscreen. Curse my decision not to bother with the intermittent setting for the wipers! Still we arrived there safe and sound and Stu put his loud and proud VX effort on first. That’s a really impressive engine that just doesn’t stop making power.
And then it was time for my much more sedate version. Two runs were done, one with the AFR probe in and one without. Interestingly it made slightly more torque with the probe in but with figures that small and close I don’t think you could confidently say that my car runs better with an ever so slightly more restricted exhaust!
Standard MX5 power is 133, so only one of mine has become lasagne. That’s not bad, and a shame really. I was all set to replace the engine to save fixing the coolant leak but as it’s giving good power I don’t think I should write it off, even after 144,000 miles! So at some point, assuming I ever get around to it I’ve got to pull the engine and get the block skimmed. A Westfield manifold will make an appearance some time soon and I’m tempted to fit an induction kit to replace the standard air box. It’d be interesting to see what kind of difference that makes.
Later on, after studying the graph in more detail I came up with the following thoughts:
The scale of the graph amplifies the dips in torque a bit, but they’re still a touch longer than expected. For instance at the start of my dip around 3,450, torque doesn’t come back to the same level until 4,600. Where as a 1.6 graph posted on WSCC lasts for 600rpm or so.
Putting my head in the sand, I’d quite like to blame it all on the intake track that you get with fitting the standard airbox (complete with pattern filter). I designed pipework to have an induction kit sitting just behind one of the FW intakes, but it was coming in at over £200 so I dropped it from the build in the end.
It’d be nice to blame my dissatisfaction on performance on this flatspot. I generally start overtakes at 3.5k rpm and that’s what I’m most disappointed in. Torque only drops off a couple of lb/ft though and to be honest I can’t see the bum dyno picking that one up.
Hearing Stu’s VX on throttle bodies screaming at the rollers has certainly kept superchargers off the radar!
However, if you change the axis of the chart to start from 0 lb/ft it looks a lot better:
Maybe I’m just reading too much into the small fluctuations! The above is a pretty good torque curve to me.