Peter recalls a product test from 35 years ago, the ramifications of which are still rippling around.
One of my most memorable stories as a motoring writer was back in 1989 when I was on the staff of Practical Classics and colleague Chris Graham and I tested a tin-based ‘device’ which, apparently, had been developed during WW2 and would, the makers claimed, allow any leaded-only car to use unleaded petrol without further modification. It was also said to deliver significant economy and emission benefits. The product was called Carbonflo.
Testing Carbonflo was Chris’s idea, and it was certainly topical. Unleaded petrol had just gone on sale, and while leaded four-star was still widely available, classic enthusiasts realised that it would eventually disappear. A drop-in-the-tank solution like Carbonflo was therefore potentially the answer to classic car enthusiast’s prayers – if it worked. And that is what we set out to prove.
I said ‘prove’ intentionally, because while we were certainly going to test Carbonflo’s claims fully and robustly, I think we both hoped for a successful result. If it worked, Carbonflo would have been the biggest good-news story for classic owners of the decade. It would have given the hobby a massive boost, and as the first magazine to have tested it successfully, Practical Classics would have been at the forefront of something hugely significant.
Anyway, I sourced a BMC 1800 from Ashford Motor Auctions. We chose this as the B-Series engine was definitely leaded-only but a ‘Landcrab’ would be spacious and suitable for motorway cruising, and the test was going to involve a fair amount of motorway work.
Motorway driving was crucial for two reasons. Firstly, we needed to cover a lot of miles in a relatively short time. Secondly, we already knew that valve seat recession from use of unleaded fuel was an issue mostly at higher speeds.
We started by having the cylinder-head removed, decoked and the valve positions, etc., measured. This also, of course, removed all trace of ‘leaded memory’ from the head. Then, after reassembling the car and running it for a week or so to ensure all was well and measuring power output on a rolling road, we put the Carbonflo unit in the tank. Then, after running for 500 miles on leaded as recommended by Carbonflo, we switched to unleaded.
The 1800 was driven extensively – we used it for all long trips out of the office, and I also used it for my daily 80-mile round-trip commute. At first, all seemed fine; and our initial report said that.
Then, at 2566 miles, and just as we were about to go to press with Part 1, a misfire developed. Investigation showed significantly reduced clearances on all exhaust valves, to the extent that one was permanently open. We weren’t, though, going to condemn Carbonflo on this evidence alone and thought it fairest not to mention it
