larger updraft carbs?

[Ian Williams]

Jon if you use an H series rather than an HS, they don't look too out of place, with the H series you also then have the option of an 1 1/4", 1 1/8" or 1" choke bore. If you are using a decent cam, head and ported block I would strongly recommend you consider the looking at choke size and needle I suggested earlier as your starting point. The 1" OM is fine if you are using a std or mildly tuned engine, the problem with using an SU which is too large for the state of your engine tune is that you severely limit piston travel which in turn limits the mixture available from what ever needle is fitted to a very narrow range and subsequent reduction in performance. It is NOT enough to simply set the jet on an SU so that you apparently have a good cruising mixture, I can guarantee that following route will not give a good mixture through out the rev range and performance WILL suffer. To really make things work well you would be well advised to consider size/area of the entire inlet tract from Carb to piston; manifold, port, valve, valve lift and transfer port. Of course to complicate matters for you the exhaust path also has a bearing on how well the inlet path works, fortunately on an A7 most things have been tried, so match what you are doing in its entirety with a well proven set up not just repeated folk law from someone who has read something somewhere. Just because the fastest car on the track has successfully used a 1 1/2" SU with an OMG needle does not mean it will work for you if the rest of your set up is not matching the set up in the car you are copying. Going back to the manifold why not use steel tube as per an Un-Blown Ulster, possibly not the most efficient design that ever existed but period authentic if that matters to you and plenty good enough unless racing a a high level.