40IDA Carbs

[chris_seven]

Does anyone know the maximum Horsepower that we could expect from 40IDA carbs?.

I have been looking for a while and most of the published information seems to have them topping out at around 225BHP.

[Steve@Rennsport]

What size engine and main venturis?

Whats fascinating is that Eduardo Weber's original venturi graphs are remarkably accurate, even to this day. Head flow data can skew things a little, but thats pretty much it.

This is the one found in several Weber books, including the Weber factory manuals, the Hayne's Weber manual, & Volume 2 of the Passini books.

[chris_seven]

I have a pair of 40s and I wanted to fit them to an SC which we plan to modify to the limit of the carbs.

I don't mind what venturis to sue although I think 36mm in a 40 bore is a little to big.

If I can't make the horsepower we are looking for then I could bore the carbs to 45mm.

[Steve@Rennsport]

Originally Posted by chris_seven

I have a pair of 40s and I wanted to fit them to an SC which we plan to modify to the limit of the carbs.

I don't mind what venturis to sue although I think 36mm in a 40 bore is a little to big.

If I can't make the horsepower we are looking for then I could bore the carbs to 45mm.

36mm venturies in a 40mm carb is just fine for a 3.0, depending on cams.

If you plan on using "S" cams (or more), you'll need to modify the carbs to 42mm or 45mm for power above 6500.

[haasad]

Hi I have a little experience to add to this thread. My TP 2.8 with S cams and standeard ex 1975 CIS heads is making a genuine 190 hp at the wheels from a rolling road known not to flatter. I have bored chokes at 35 mm ( because I was worried about scrapping what for me is an expensive part) they are in 40's . I have used 1 5/8 headers.
The rolling road man with many years of experience was most impressed with the power but in particular how driveable the thing is. I wasn't paying for a full power and torque run since its not fully run in but its certainly got some grunt. It will safely let me have 7k but in reality never likely to get above 6-6500. He belives firmly that over carbed engines are pointless on the road and cited at least two 911 3.0's he had seen recently with 46's and only 34 mm chokes .....
I think my observation is that for most of us the driveability is more important than the outright power , unless of course one is building an out and out racer.

I have to admit I'm still scared of my 900 kg r car at present though

[burtm5]

I was interested in this years ago in putting together a hot rod small block ford. In looking at period ford racing from late 60s they put webers on small bock but made more power with 4 barrels instead of webers on the big blocks. Also said I 4 barrel made more power than three 2 barrels. Somewhere it said that webers could make a max of 70 hp per barrel so 70 x 6 could max out 420 hp. racing 5 liter v8 cobras made about 400, so realistically max per barrel in best of circumstances would be 50 hp for total of 300 hp for 6. Maybe an apples oranges comparison but gets in the ball park. best