Interesting thoughts here. With one of my customers we seriously evaluated using a 172/182 for the Castle Combe Saloons; but the bug bear was the engine. I'm developing an F4R race engine for a friend now, but it's a very difficult one compared to some others, they all have their advantages/disadvantages.
Peugeot engines are among the best for race builds, I know that'll get some spiky reaction here, but you have three basically really good 16v engine designs (TU, XU, EW) that are well suited to 14-1600cc (TU), 16-2300cc Iron or alloy block. They have wonderfully simple and reliable valve trains, a good range of strong standard cranks and the head castings allow you to build small port or big port engines as you wish to get pretty much any power delivery you like. The latest EW engines have a block ladder design that makes it as strong and lighter than the Japanese rivals. The chassis' are light and very effective too, not to be ignored for this kind of use!
Ford engines of late aren't quite as great as they're made out to be. I've done alot of development with these and had a great deal of championship success with the Sigma/ZETEC-SE 1400, but it's a fragile and expensive engine to build compared to the equivalent Peugeots. The Duratec 1.8-2 litre engine can make impressive numbers in the right hands, but the breadth of the delivery can't match Peugeot/Vauxhall equivalents and although it seems like alot of parts are available, you have to junk so much of the standard engine to make it reliable, that there's not really any middle ground between the road engine and a race one. Also the apparent appeal of the Fiesta ST150, is curbed by the chocolate gearbox, even a Gucci gearkit can solve the problems with the selector design.
Old school Honda engines I prefer to be honest. The B and H series were born race engines and although you don't really have the option of building a small port grunt engine, they can be made to work very well and have the best parts availability of all. The gearboxes are good to and the older Honda Chassis' are easily made good. I've not got quite so much love for the latest F20C and K20 engines. I've done alot of work with them and like the "Duratec", they can make impressive numbers, but the delivery always seems to lack punch somehow. Naturally I blame the huge ports! For a race engine with close ratios, that's maybe not a major, but don't just look at the numbers and think they're the best. Also although parts availability is excellent, there's alot of bull***t too, it's the biggest aftermarket darling and attracts all the attention good and bad. Bear in mind that the K20, although ultra-reliable in standard form (as long as the oil's topped up), is not reliable in race form past 8500rpm with standard valve gear. To overcome that issue is HUGELY expensive. as had been said, "fast road" spec with the right ITB design can be very cost effective though and can't be ignored.
Vauxhall engines are very effective and well supported, particularly the older C20 and X14-X16 series. The Corsa B and C can be made to work well. I'm not really a vain person, but not sure I could race a Corsa!
Be wary of wild-card engine choices. Parts will be difficult to get (you might have to get into designing custom parts, which is a risky business) and getting good support at reasonable cost, from a good engine builder may be difficult. I use to thrive on the challenge of making a quirky engine work, but that's gradually worn off as I realise how much it really costs me to do! If an engine builder tries to talk you out of something, ask yourself why?! It may be because he's a dull, stuck in mud or profiteer; or perhaps he can see the problems you don't.
Regards the Combe series... I get alot of people from outside trying to play it down, saying it's a one circuit series with specifically developed cars etc. Well to some extent that's probably true. But it's regularly shown in the motorsport press as one of the toughest series, with 30-40 car grids at every round, when some others struggle to get 20 cars. Also it has the challenge of running on road tyres, list 1A, R888s/A048s etc are not allowed, which presents a unique challenge of preserving the tyres for the length of a 20 minute race; I'm sure those of you who've done a trackday on road tyres will appreciate what that means! Will DiClaudio's 1:14 time mentioned above, was on 2nd hand slicks, but he's done 1:15.9 on Yoko AD08s, the current series lap record and when the CSCC tip tops came to Combe (perfect dry weather BTW!), only Mike Jordan did better with 1:14.557 on slicks, the best of the rest was Nigel Tongue's 306 with 1:17.991, the rest of the field 1:18.8 upwards. That's most of the field running 2 seconds or more slower on slicks compared to road tyres! Also Jason Cooper, who I won the 2009 Combe Saloons championship with (1400 Fiesta), was being touted as a Combe specialist, wouldn't work elsewhere; he's just won the 2012 Fiesta ST championship by a useful margin, touring the top UK circuits.
