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Hello all


 I’m going to get some Weber’s for my 1500 engine. The head is standard and in time that will change. And the cam is standard and in time I will change the cam to a fast road cam. Now I want some Weber’s for the car but not sure weather to get twin40’s or one 45 or one 40?  

What’s the best choice for most power. 

now this isn’t a track car but I want to make it quick so please don’t bombard me with keep the su carbs or change it for a 1300 or anything like that I want a fast road classic with classic parts. I would just like to know what’s best twin 40 or one 45. Now obviously it mite be different depending on valve sizes so what do people think is best. 

I read something that a bloke had a 1500 spitfire 120bhp that he used everyday for his daily  I’m not going to use it everyday but bhp120 is something I’m looking for with out changing the engine  

What are peoples thoughts.

many thanks 


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To get 120hp from a 1500 you will be extensively modifying the engine. The head, cam, exhaust, etc. will all have to be done carefully to get there.

Dual 40 DCOEs is probably the way to go. Don't bother with a single. The mixture distribution will never be as even as you need to get the power you are aiming for with a single.

Weber carbs aren't magic, they take careful setting up to get the best from them. Once set they are stable. The setting up process will include trying different jets for several functions. Each jet will change what is needed for some of the others.

To start the process with the Webers will mean setting them up again each time something else is upgraded. New cam? Reset the Webers. Ported head? Reset the Webers.

Sticking to the SUs will reduce the carb trouble to changing needles each time and tuning to suit.

Once the final modifications are made the Webers can be set up once and checked on a rolling road.

Good luck,


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Hi George, twin 40's as Paul said need to be set up on a rolling road, please dont be put off by this, iv'e just had my GT6 set up by Airey Tuning ( http://www.aireytuning.com/#home ) in Hampshire, I think a 45 will be to big, you will be amazed on how close you can set them up yourself with a colour tune plug, and a carb balencer unless i was very lucky,                              after the guys at Airey Tuning had finished it was like driving home in a different car,              you just need the correct manifold in my case the front carb sits lower than the other two,              this is to clear the bonnet, I had head work and all engine machining by done http://www.ocservice.co.uk and run a Newman Cam "TR16/280/405Fast Road/Rally Cam PH2   I find it easy to drive in town no lumpy tick over and instant get up and go

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I have around 100 hp on my Spitfire with SU`s, Newman cam,vernier twin chain timing gear ,electronic timing etc etc and that to me is `fast` enough. Keeps up with the big sixes on most events. Webers OK with a six pot but with a four pot Spit?. I think you would be wasting time on `just` fitting Webers . My Spit has been around Cadwell and Donnington (Nurburg/ Le mans etc) ...and I found it fast enough. My Westfield track car had  40s Webers and found they were ok on a Cosworth set up ....but I personally wouldnt fit to a Spitfire   

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