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MSVA for a Small Block Guzzi and Other Weighty Matters

by

Philip Waring

After much helpful guidance from Mike Meakin and others, he tells me that I might be the first Pembleton builder to get a small-block Guzzi-powered Pembleton through the MSVA as a heavy quad, it was in November last year (2016). Whether or not this is the case, the process of complying with the rules for the power to weight ratio by reducing the horsepower of the engine caused a certain amount of head scratching and I offer the following, with no guarantees of course.

The primary method was the introduction of restrictors into the induction tubes between the carburettors, Dellorto PHBH 30s, and the cylinders (see photograph). These were turned by a neighbour, Simon Barley of Barleycorn Engineering who makes parts for British motorbikes, BSA and others. There is a shoulder in the rubber part of the tube and the flange on the restrictor sits on the carburettor side of it, there is enough room then to push the carburettor onto the tube and secure Iraq with a clip. There is another clip on the cylinder side to secure the rubber tube to the short length of cranked tube which is attached to the cylinder.

There were two other elements to horsepower reduction. From Phil Hardcastle, via the forum, I obtained a pair of ex VW beetle exhaust inserts which I secured with a self tapping screw at the back end of the PMC stainless exhaust pipes, immediately in front of the Brooklands cans. Though their main function is noise suppression, there is anecdotal evidence that by restricting the flow of exhaust gases they also bring down the horsepower. I say anecdotal because the car had only one dynamometer test, at Scole Engineering, so I do not know the proportion of the horsepower reduction which can be attributed to each measure.

Thirdly, I simply put an M6 stainless bolt, with a couple of plain nuts underneath the head, through a hole in the forward bulkhead so that the lowest bend in the throttle pedal stem could not reach the aluminium. This restricted the horsepower by restricting the revs, I was concerned that the MSVA examiner might not like this, it was the only obvious element in the whole exercise, but he made no comment on it. The dynamometer test at Scole showed 18 horsepower and this was accepted at the test station.

The other qualifying criterion in order to be eligible for MSVA is, of course, the weight of the whole car. Martin Cartwright warned me that our local public weighbridge claimed an accuracy of plus or minus 20 kilos. This seemed like a rather wide margin of error, so I followed up the possibility of weighing in at the VOSA station, and a couple of weeks before the test we again inserted my car into Martin Cartwright's trailer and went up to Norwich. A call to the examiner there had fixed the date and he asked me to make sure that the petrol tank was full. This seemed slightly odd, I assumed that the weight of the petrol would then be deducted from the overall figure, but unless he took external measurements and estimated, the examiner would still have to take my word for the (bespoke) tank capacity. Anyhow, we were well overweight, 460 kilos. I knew that the large PMC, MGA sized wheels, tyres and adapters were much heavier than 2CV ones, so another friend, Jon Fraser, a Citroen guru, in a typical act of generosity, took the wheels off his Dyane and lent them to me. I removed the spare wheel altogether. The examiner also said that I didn't need mudguards for the test so they were also removed. In the end I got rid of 101 kilos, added 48, taking off a further 24 for the 33 litres of petrol left me with a calculated weight of 383.91 kilos. The weighbridge said 381. Reader, she passed, but that's another story.


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