SC throttle body upgrade ?

[Supi]

Hi

I am putting " self-made" EFI setup to my SC3.0 during this spring.
Do you know whether there is any practise / method to somehow upgrade the single standard throttle bodys performance ? Flow or other parameters ?

If such exist I am keen on knowing some hints

Many thanks in advance

Br

[T77911S]

i just put the 3.0 throttle body on my 2.7, nice improvement. i would be curious if the 930's was bigger and would work on the 3.0

[euro911sc]

There are some guys who bore out the SC throttle body... I think that had been done more in the 80's, but IIRC it did not particularly do much on a CIS engine. I cannot remember where I read about it... For EFI you may find different results.

Let us know how it turns out and who did the work!

Best regards,

Michael

[cmonref]

For fuel-air tuning, the larger the throttle body the harder it is to get good off-idle transition tuning. A little bit of throttle opening equals a big increment of air. The SC already has some off-idle transition leanness that reduces the throttle response. The leanness is difficult to overcome in the CIS system.

[T77911S]

Originally Posted by Brian K. Haggard

For fuel-air tuning, the larger the throttle body the harder it is to get good off-idle transition tuning. A little bit of throttle opening equals a big increment of air. The SC already has some off-idle transition leanness that reduces the throttle response. The leanness is difficult to overcome in the CIS system.

I am not disagreeing with you, just trying to understand.
are you basing this on the way carbs work? i would not think the size of the throttle body would effect this because the AFR is not metered in the TB, like it is in carbs. if you open the TB to raise the RPM's to 1500 or 2k, the same amount of air is still being metered or passing thru the air flow meter just like it would be if the TB was smaller.
i put the bigger TB from a 3.0 on my 2.7 and have not noticed this. the throttle response seems to be better and i have better low end when i get on it. i would think the biggest improvemnet would be the upper RPM

my CIS has the vacuum enrichment circuit on the WUR. when i press the gas, the WUR quickly makes the AFR go rich for just a split second, like the accelerator pump on carbs. this helps in the leanness. the 80'sCIS did not have this and this may be the cause of the leannes you are talking about.

[cmonref]

The off-idle transition occurs when the throttle plate begins to move from the idle position. The bigger the throttle plate the more air is passed thru per unit of plate movement. As the plate begins to open, there is a rush of air thru it -- a lot of air in the first increment of movement. Reaction time of the measurements of the throttle movement and manifold pressure (as measures of air mass flow) and the resultant response of the fuel metering system become trickier and harder to tune (carbs, CIS, EFI all share in this effect.)

Beyond the off-idle transition, air is flowing smoothly and the rate of change of air flow per unit of throttle plate movement is much lower. Carbs, CIS, and EFI all handle throttle movement in that range, whether it be smooth movements or a stab at the throttle. CIS does well with its enrichment as you note, under these conditions.

[JohnJL]

If you decide its what you want I have a spare 3.2 Carrera throttle body for sale. Worked fine on my EFI's 3.0, its only spare because I needed a yet bigger bore for the supercharger.

[T77911S]

mine transitions fine. when i get the LM1 back, i may record the AFR's with the 2 TB's.

is the 3.2 TB than the 3.0? and will it fit the CIS air box? i have a 3.0 for my car, not ready to go in yet though.