Anything and everything Spitfire.

Help,
i have the one and a half inch SU set up on a stage three head, do i need to connect the carbs up to the engine breather with the t-piece or not, if not, what do i do with the breather in the top?
Thanks Calvin.

Hi Calvin I think there has been a fair amount of debate on this. Normally the breather goes to the T-piece and fumes go into the carbes to get burnt. In theory you should get a more efficient engine if these fumes and general crud are fed to a catch tank instead. The feeds into each carb should be capped off. The racers do this and run with (2 Litre) catch tanks so there is only petrol and clean air being burnt. You can vent the rocker cover to atmosphere via a pipe under the engine but that is not particularly environmentally friendly.

There is supposed to be a small gain in power going via this route but I don't think it will be too much or particularly noticeable. Others may tell you it is well worthwhile. You can buy catchtanks from various suppliers. They are usually fed via a long length of rubber tubing and have a small filter to vent to the outside world.

I have not gone down this route myself so am unsure of the emrit of doing all this. Some of the catchtanks look quite cool inside the engine compartment bur I think the jury is out as to whether it is all really worth the effort or money! I think you can rig up something very cheap and cheerful to see how you go and can always go back to the standard setup if it makes little difference. Maybe it is only really noticeable at higher revs where racers tend to sit for prolonged periods.

Get back to us all if youn decide to go down this route won't you with any of your findings.

best of luck, Neil

I can confirm that having the breather venting to the open air (under the car and out the back) does release a lot of smoke on a tired old engine like mine, although I daresay it's better on a less b*ggered engine! In the end I got fed up with people looking away from my car in horror, and I reconnected the breather to the carbs, and suffered no noticeable ill effects with normal road driving, although I did have to re-adjust the carbs, which is understandable.

Sam

Hi, I too have bypassed the breather system, using a home made catch tank with baffles from a stainless steel kitchen container! - looks quite like the real thing. The reason I have done this is not for performance (there may be some gain) but to stop all the oily carbon containing pollution being fed into my engine. As engines get older they blow by more and more - if the inside of your inlet manifold beyond the breather inlet looks like the Torrey Canyon, then imagine how caked up with gloop the inside of your cylinder head /valves will be.

Thanks all for your advice, my set up will probably go to the catch tank system as the engine has never been run after a comprehensive modification/rebuild programme. Will inform at a later date if i think it works, but i really have nothing to compare it to,
cheers all
Calvin

Section : Carburettors

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