Larger Venturies for my Webers?

[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

[Tyson Schmidt]

What size ports? I think a '77, assuming they are '77 heads, should have 35mm ports.

I'd use 34mm venturis. You'll need to rejet after the change. Slightly larger idles and mains.

[jgparker]

For 90% track, I'd go as large as you can stand on the venturies. I found 36mm venturies on my 2.8 to be a good compromise for max high RPM track power but with adequate street drivability. Talk to an expert, like Richard Parr at PMO to get a recommended starting point for your set-up, but you'll need to know the internal details of your engine.

Good luck,

JP

[iobound]

If you are interested in selling the 32mm venturis I'll buy them.

Daryl

[cstreit]

Larger venturi's will give you a bit more flow (assuming the jetting and port sizes will accomondate, as Tyson and others mentioned) but will also reduce your low RPM throttle response.