Halfing throttle shafts, worthless or not?

[IsaacHayes]

I'm sure you've all seen ported or performance TB's that have the front half of the shaft cut off so all you see is the 2 screws. This supposedly would let more air by. Looking at it you think it might be a good increase in area.

But what do you all think? Does it do anything to increase flow? Or is it a waste of time?

Is it a possible reliability issue?

[SappySE107]

I don't what that does to the path of flow. Its like an airplane wing if you cut half of it off.

[scrappy]

I think it would weaken theshaft too much for me to want to do it.

[IsaacHayes]

I read on gm high tech performance they put on a TB that was halved and knife edged and plugged up some holes for the IAC that might cause turbulence and they got 11 peak hp, but that's on a big high hp V8. And the peak was up very high in RPMs.

Maybe on a 3100 you'll get .25hp ? 1? It does look like it would let more air by.

I don't know about turbulence affecting it.

I do see a lot of the performance TB's being offered as doing this but I wonder if it makes a difference or is just to make it look better like you're getting something really cool....

[geoffinbc]

Some sanctioning bodies limit throttle bodies to a certain size. In this case where you must extract every last ounce of airflow out of the limited throttle body size you might cut the shaft down to get what you can. Otherwise it is mostly a waste of time. Unless you have allot of extra time and you are looking for a make work project.

[IsaacHayes]

Hmm well what if you're on a budget and need greater than 56mm of TB, but can't afford anything else.....

Cutting the shaft would be quick with a Dremel.

I wonder if halving the shaft would gain you the equivalent of 1mm more diameter or something?

[SappySE107]

I think I posted flow differences at the intake valve with a 56 and 65mm TB using a ported manifold set and mild porting on the 3500. I don't have any way of flowing just the TB, since that is more CFM than my setup is for.

[ForcedFirebird]

I wonder if halving the shaft would gain you the equivalent of 1mm more diameter or something?

You would have to formulate...

Let's say we have a 54mm TB.

circumferance=diameter*3.14
area=3.14*radius*radius

54mm*1mm=54mm new clearance by removing 1/2 the throttle shaft...

area=27mm*27mm*3.14=2289.06mm of area + the 54mm from the shaft removal...2343.06mm^2
You would recieve a 2% increase in area (little over 1mm in total area, not circumference).


The ammount of work it would take would be justifiable as replacing the throttle plate with a larger one, or getting a bigger TB.

AND as Ben said, what would it do with the turbulance that could potentially cause vacuum pockets where you didn't want them?

[StudlyCamaro]

I think it would weaken theshaft too much for me to want to do it.

i did mine probably 4 years and 60,000 miles ago with no problems

Unless you have allot of extra time and you are looking for a make work project.

thats why i did mine

[IsaacHayes]

Hmm I need to measure the thickness of the protruding of the shaft and then calculate it.

Getting a 2nd TB for the shaft to play with and then comparing them (butt dyno only though) might be something I will do in the future... I don't think any 3400 TBs had the "C" type linkage on them. If I had a spare one I'd mess with it for fun.

I could measure before and after and calculate area... Take the front off, get some flat screws, thin the back side shaft down, cut the protruding screw threads off...

Replacing the throttle plate or getting a different TB would equal lots of money. :P A dremel and 45mins of time would probably be all it would take me.

The way I calculated I subtracted from the overall area the shaft area before and after modded then compared. Would it be accurate to convert that area back to diameter? Then you could compare that to a larger diameter TB....

[torq455]

ehhh, waste of time. do some gasket matching.

[XLR8ING]

All the TBs I used to sell had half the shaft removed where the plate bolts on.
Theoretically, you're gaining 3-4mm at WOT. I've seen absolutely no reliability issues that come from removing half the shaft.

I've also done this on stock TBs. Again, no disadvantage to it that I've seen.
You could likely even remove the shaft from the TB while still in the car, but the angle of the TB on some cars would make it a pain.
Time to do this would only be 30 min to an hour.

[IsaacHayes]

I've already got gasket matched stuff. Just need the most cfm from my 56mm TB as possible as I'm too poor to get the billet 65mm unit.

I may go ahead and do it some day. Hopefully there won't be turbulence issues, and the neck extends so far down the 3500 plenum hopefully that wouldn't matter by the time it opens up.

Taking off the TB without that coolant pipe mount will be a quick task. If/when I do it I will measure the half shaft and post numbers and such.

[torq455]

I've already got gasket matched stuff. Just need the most cfm from my 56mm TB as possible as I'm too poor to get the billet 65mm unit.

I hear ya there man! Some say it works, others don't notice anything. I say what the hell. Can't hurt.-shrug- Maybe it's more for a stock TB instead of the bigger ones.

Hey Franz! It's nice that every once in a while you let us know you are still breathing out there! :P