Larger chokes (venturies) on my Webers? Options

[Eddie914]

I have removed the Weber 40IDC 3A carbs for a rebuild.

They currently have 32mm venturies.

Will larger venturies give more top end power?

The engine is 2.7 from a '77 911. Internals (P/Cs, compression ratio, Cams) are unknown. Bursch Headers with megaphones (with removable baffles).

The car is 90% track. Weighs less than 2100lbs.


Thanks

Eddie

[Root_Werks]

For something cammed like a 2.7S engine you will want to stick with about an 8mm difference between the carb and venturi size. You will loose velocity if you go any larger. Examples:

Have a customer with a 914-6 2.7 that had 40/36's and 208rwhp on the dyno. He is also running 39mm intake ports and R cams. The car didn't have much of anything on the bottom end, but didn't like to turn much past 6600rpm's either.

We tried a fresh set of 46's with 38 venturies, dailed stuff in. No huge HP gaines, but oh man! The power comes on much, much sooner and the 914 pulles like a raped ape to 7500rpm now! (IMG:style_emoticons/default/driving.gif)

Bigger is not always better.

For fun, I threw his old 40/36's on my 2.2, ran great, but when I put my 40/27.5's back on, now my 2.2 has gobs more torgue, but doesn't pull in the upper RPM's like it did with the 40/36's. You will loose torque as you increase the venturi size. I would stick with the 40/32 set you have. (IMG:style_emoticons/default/wink.gif)