ITB size

[sampayne]

I've been messing around with the idea of making some itb's. Yes I know RHD is probably the best option. I want to build my own for the simple fact I like making stuff. I went out on a limb and bought a set of K1200 throttles beause they have good modular design, based off some information I read stating they are 40mm ID. I received them, and it turns out they are 45mm at the butterfly. RHD sells 40mm and 42mm, it's known that you obviously don't want to go too big on throttle size. I assuming these are too big for 2.7 with a 272. Anyone have some thoughts? Is this a lost cause, should I just return them?

[digger]

I'm of the opinion that length is more critical than size but both are important.
Accordingly Mount them along way from head and taper the runner after the throttles to a more correct size and use nice long overall runner length might work ok.

It'll be easier to find a smaller set as space constraints mean doing what I wrote in an e30 chassis is only a theoretical possibility

[zaq123]

http://www.msextra.com/forums/viewtopic.php?f=94&t=6627&hilit=motorcycle+throttle+bodies

[sampayne]

I'm of the opinion that length is more critical than size but both are important.
Accordingly Mount them along way from head and taper the runner after the throttles to a more correct size and use nice long overall runner length might work ok.

It'll be easier to find a smaller set as space constraints mean doing what I wrote in an e30 chassis is only a theoretical possibility

Spacing around the head and accessories will definitely be a concern. I did some more measuring, and the inlet is 47mm, 45mm at the butterfly and down to 42mm on the outlet, so they already have a nice taper, could work out okay.

What is the best way to calculate runner length?

http://www.msextra.com/forums/viewto...hrottle+bodies

Very handy! I was trying to find some master list like this when I was researching earlier. Thanks for the link.

[digger]

Around 12-14" from head face to bell mouth is in the ballpark. On a higher rpm engine slightly shorter might be better or with a lazier lower rpm engine slightly longer.