i am looking at putting twin 40's onto my engine, what would i need for them to jet them down for a 1.3?

Take if to a rolling road. You will never get them set the best without it

http://www.pumaracing.co.uk/Chokes.htm

have a read of that,, also worth reading pretty much everything else the guy has written as well, you will need to sort your choke size before visiting the rolling road as its unlikely they will have them small enough for a 1.3. you will also need to do all the other mods you are going to do to the engine i/e exhaust, cam, etc before your rolling road tune up, you will need a low pressure high volume fuel pump, a pressure regulator, and ideally pressure gauge, once you have all these bits done find a rolling road who know about tuning webers and be prepared for a couple of hrs plus parts,,

i'm hoping to get mine on in a month or so, on my coupe, with 4 branch, gt cam, g40 exhaust etc and will post in the weber thread in the faq's my full jet and choke setup. i will also be making some super short intake trumpets so as to clear the brake master cylinder. if these work i would be up for making more.

good luck . dan.

i'm hoping to get mine on in a month or so, on my coupe, with 4 branch, gt cam, g40 exhaust etc and will post in the weber thread in the faq's my full jet and choke setup. i will also be making some super short intake trumpets so as to clear the brake master cylinder. if these work i would be up for making more.

good luck . dan.

Hi Dan - did you get this all set up? How did you get on with the short trumpets?

I've got reasonably hefty ones on mine and was looking to relocate or change the master cylinder to compensate.

I had assumed that shortening the trumpets would have some bearing on performance (as I'm sure someone told me that once), but to be honest have no idea how.

Would be good to see what you've done to yours.

The length of the inlet can have both positive and negative effects. Basically a sound wave is produced at the inlet and moves out of the inlet tract (inlet mani, carb and trumpet) and then returns once it reaches the end of the trumpet. This acts as forced induction (v.low amounts of) but can improve performance. However, what god giveth with one hand, he takes with the other meaning that at a certain rev range, the air will move out of the carb, taking a little fuel with it,reducing performance at those revs. The trick is to get the length so the induction comes within the operating rev range, but the flat spot comes outside of the usable range.

So yeah, inlet length can have an effect. Whether it's noticeable is another question

The length of the inlet can have both positive and negative effects. Basically a sound wave is produced at the inlet and moves out of the inlet tract (inlet mani, carb and trumpet) and then returns once it reaches the end of the trumpet. This acts as forced induction (v.low amounts of) but can improve performance. However, what god giveth with one hand, he takes with the other meaning that at a certain rev range, the air will move out of the carb, taking a little fuel with it,reducing performance at those revs. The trick is to get the length so the induction comes within the operating rev range, but the flat spot comes outside of the usable range.

So yeah, inlet length can have an effect. Whether it's noticeable is another question

Hmm - interesting.

Wondering if I can save myself a lot of hassle by buying extra-short trumpets :)