CIS performance -- throttle body mods/swap???

[Rich911E]

I have a CIS 2.7 liter engine and would like to improve the performance. I have been looking around the internet to learn about this system the net and see that a lot of people who have CIS injected cars (VW, Audi, etc.) opt for larger throttle bodies to improve the airflow as this is seen as the restriction in the intake system. Additionally, the book (How to Tune and Modify Bosch Fuel Injection) suggested that enlarging the throttle body would increase airflow and power.

However, I have been unable to find information regarding the dimensions of throttle bodies used in 911's. Does anyone know if the throttle body for a 3.0 SC or turbo has larger dimensions than the one for the 2.7 S (1975)? Has anyone tried a different throttle body and gotten increased power?

Thanks in advance for your input.

Rich

[Jim T]

With the stock exhaust and stock heads, a larger tbody won't help. The restrictions are downstream of the tbody.

It may help you lose torque, though.

Bored out tbodies were big in the '80s, esp. in the VW watercooled scene. But they ended up figuring out that the larger tbodies, on an otherwise stock engine, doesn't really do anything. Was just a way for people to make money.

[Rich911E]

I guess I should have mentioned that I have a set of 1 5/8 primary headers that will be installed as well along with an early muffler to improve the exhaust side of the equation. I think these modifications will significantly increase exhaust flow over the stock system.

I am still looking for actual numbers on the size of the throttle bodies. I have found many people who have bored out the throttle body on 930 turbos for better performance. What are the dimensions on the 930 throttle body? What are the dimensions of the 3.0SC throttle body?

Rich