Induction Puzzlers

30 05 2013

Here’s where it gets confusing. I’ve given loads of thought on the combination of inlet manifold, carburettor, ram pipes, filter etc etc and to be honest I think it’s going to be a case of trying everything on the rolling road and the track.

As far as I can see most of the Miglia runners use the same combination of a 3 1/2″ steel Maniflow inlet manifold. However, sometimes I’ve seen some alloy extensions of approx 1 1/2″ added between the manifold and the carburettor – which essentially is the same as having a 5″ manifold. Given that we know a longer inlet manifold generally gives more torque I’m assuming that is the reason for adding them. Why not just use a 5″ manifold? Maybe they are added for the twistier circuits, and removed for the flat out ones?

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Casey’s engine bay

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Peter Baldwin’s engine bay. Note alloy spacers

I’ve got 3 inlets to try. One is a 3 1/2″ alloy Minispares one that came with the carb from mini racing legend Richard Wager. I’d like to try this as Richard said it was at least as good as the Maniflow ones. I’ve also got 3 1/2″ and 4.75″ steel Maniflow ones. I’ll be trying them all to see which suits best. I’m also trying to sort out someone who can get them chromed for me, but for now they will be wrapped to keep them as protected as possible from the exhaust heat.

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Which inlet?

As for the carburettor I don’t know anyone who doesn’t use the Weber 45DCOE. There are several different types.  I bought mine from Richard Wager and I’ve noticed a few pretty trick modifications which I think i’ll keep quiet about for now…

One thing that has always puzzled me is why it is quite common to see mini se7ens and miglias without filters. Nowadays filter case design is so good there is no loss of power, and why risk that lovely expensive new engine by letting it ingest a stone or worse? It’s just common sense to me. The main filters on the market are the cotton gauze K&N’s and the foam ITG ones. I’ve heard one very well respected engine builder say that K&N’s are fantastic and ITG’s are rubbish, only for another very good engine builder to say the exact opposite. If I was being cynical I might say that being a dealer for these filters might play a part in their point of view… Anyway, Performance-wise I’ve had good results with both. In practical termsn, in my humble opinion the K&N has always been better for my previous discipline of Autograss – mainly due to them being a bit more hardy when cleaning and oiling. That said I’m using an ITG on the Miglia. It did help that you get one as part of the MBE DCR trumpet setup which I’m running. This is an interesting bit of kit which I read about a little while back. Developed by Mike Barratt of MBE, it is said to both increase power and have the effect of bringing the power in earlier on a race cam. A bit too good to be true? Maybe. I’m going to try some back to back tests and see for myself.

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4 3/4″ steel Maniflow inlet

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MBE DCR trumpet kit. Will it work…?

And then there is the decision on whether to run a cold air system. The theory is that cold air is denser with oxygen than hot air, and so more oxygen = more fuel = more power. Some top runners run them, and some don’t. Some only use them in hot conditions. Half the problem is that it is quite difficult to test how effective these systems are as it’s almost impossible to simulate the amount of cold air going in at 120mph.  I have acquired a carbon fibre kit – again from Mr Wager, so we will give it a try. I plan to run the filter inside the air box which may or may not work. I have seen miglia runners put a filter at the opening of the air scoop behind the front grille which I’m not sure would work as well. Again, we will see…

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