Throttle body size

[Dale M.]

When doing EFI think of ITB as same size an carburetor venturies Example if you had 44 idf's with 36 mm venturies and car runs like raped ape, then a 36 mm ITB is going to be about right for EFI...

Its not about diameter so much but about flow.... To big a diameter and you are all in before butterflies are full open, it make a very short pedal range to go from idle to WOT even if butterflies are not full open... Going to be miserable for driver to maintain speed...

Dale

[volksbugly]

When doing EFI think of ITB as same size an carburetor venturies Example if you had 44 idf's with 36 mm venturies and car runs like raped ape, then a 36 mm ITB is going to be about right for EFI...

Its not about diameter so much but about flow.... To big a diameter and you are all in before butterflies are full open, it make a very short pedal range to go from idle to WOT even if butterflies are not full open... Going to be miserable for driver to maintain speed...

Dale

I whole heartily agree with this.

I had a what I think was a 1600, that I put ITBs on 40mm from CB..

it was very ON OFF with the pedal... I had to do soooo much smoothing on the throttle input that it ended up being very off and on. I ended up doing alot of tuning in ITB mode (MS3) and I was able to get it running pretty dam good and with decent throttle, but about the last50 % of my throttle did nothing.




Now you could fix that in throttle with a custom ground cam gear of something, but that isn't needed if you have the correct size. but if you plan on going turbo, then imho MORE is always better. just deal with it... lol as I pull away from a GT500 pulling 4th gear. (true story)

[woodsbuggy1]

http://www.megamanual.com/v22manual/minj.htm#throttle
Here is a handy calculator
I believe that most people use MUCH larger TB's than needed and this can create tuning and drivability issues. I have a hard time understanding why so many people use dual TB's when a single works so well and is far less complicated. Also the junkyard is a great source for good quality parts.
Good Luck
Kenric

[Piledriver]

Packaging, engine requirements, and appearance.

If you are building a stock motor or have a rail buggy, yes, a single is relatively easy.
If you are good at fabrication and have a mild T1, it can work.
If you have a big motor/cam, or a t4 with upright cooling, ITBs work out better.

I fully agree TB size is not the good place to "go large" if in doubt.

A single 42mm on a decent sized plenum is good to something like 220HP using Jenveys calculator (NA)
Quad ITBs, the calcs are entirely different but you still end up with ~42mm@220HP being mid-ballpark. (again, NA)

On a boosted setup quad 38s might limit you over ~500HP. A little. Maybe.