Throttle body shaft grinding down

[Lukitas]

So today i was bored at work and came across this post https://mbworld.org/forums/w211-amg/366071-all-throttle-body-shaft-grind-talk.html basically they sand down the throttle body butterfly shaft. Would this work in our cars? will it be make any difference? I know they sell bored out throttle bodies but i thought this would be a good mod.

[jclausen]

It sounds a bit far fetched, you can only prove modifications on a dyno or a flow bench and I don't see how that mod would help at all. What kind of gains would one expect from this, just clean your throttle body.

[tjm3]

Butt dyno testing. Always works.

Maybe a good mod, maybe not, but where's the proof that the smooth flow around the stock shafts isn't interrupted in a bad way by the grinding?
Flow bench, anybody?

If we added up all the horsepower claims from each 'performance' part replacement we should all be driving cars with 450 or so HP.

[Lukitas]

I am here asking to see if anyone has tested this.

In my mind it works just like getting the throttle body bored out but maybe i am dumb. Since grinding down lets say 2 mm will give me 2 mm of more air not getting compressed or interrupted.

[TostitoBandito]

Never heard of it being done. The benefits will be tiny and probably unmeasurable, much less than say going to a BBTB.

You have to think of the total surface area of the opening relative to how much more area you're freeing up. Say your TB diameter is 70mm and maybe you take off an average of 1.5mm of shaft across that 70mm making 105mm² of gain. Contrast that with the overall area of the opening which is already ~3850mm² . You're talking about like a 3% increase in area. You can get more gain by boring the whole thing out only 1mm more around the entire diameter. Since even the gains from going from a stock TB to a BBTB are generally fairly small like maybe 5hp (with a much more drastic increase in area than 3%), I doubt shaving the shaft is going to get you more than a small fraction of that. Not worth the effort IMO for something on the order of 1hp. That said, if you want to do it nobody is stopping you. As long as you don't break anything it should work and will probably provide some miniscule benefit. I think some of the aftermarket BBTB's may already do this to some extent.

[blckstrm]

So today i was bored at work and came across this post https://mbworld.org/forums/w211-amg/366071-all-throttle-body-shaft-grind-talk.html basically they sand down the throttle body butterfly shaft. Would this work in our cars? will it be make any difference? I know they sell bored out throttle bodies but i thought this would be a good mod.

The Riot Racing BBTB does mention the arm is machined down to allow more air on top of the throttle body machining. It seems like they used to talk about it more, but I can't find the old description. If I recall they only have half a shaft (a half moon) rather than a full circular shaft with a slot in the center for the throttle plate. They've updated their website a bit, but they do still mention it.

https://westcoastriots.com/shop/auto...n-13541433385/

So yeah, I'm sure every little bit helps and when you're making it from scratch or completely rebuilding it this makes sense.

But if you're just doing this in isolation, it seems like a lot of work for very, very little gain.

[NeilM]

Reprofiling the throttle shaft is a normal thing to do when modifying the TB, and yes, the Riot Racing BBTB has this. But of course a BBTB has to have a new throttle plate anyway, so the shaft reprofiling is a natural enough thing to do at the same time.

You’d be hard pressed to find a measurable benefit from just the shaft though.

Neil

[digger]

its common on ITB where the size matters moreso (there is even "shaftless" for ITB's).

with a common TB id forget about it unless you already have the biggest BBTB available already and youre moving a ton of air. the bigger throttle blade the weaker the shaft gets as they are usually a fixed diameter regardless of throttle size e.g. 8mm it is so might not want to go nuts

[pbonsalb]

I am with Tostito on this - very minor gains. But when you are going all out, the little bits can add up. I bought a used Dinan TB years ago. It is bored out a mm or two over stock, a little less than the RR version. There is not enough material for a more significant overbore. Few have done aftermarket TB conversions or adapted them from other cars. The intake manifold hole can be opened a little for a bigger TB.

There are a lot of other mods I would do first. I have been modding my E36M3 for about 14 years and probably won’t stop as long as I have it. Have a few mods planned for this year. Modding is a great hobby. Or maybe an addiction.

[TostitoBandito]

Right, I agree that it may make sense when you're doing something like fully boring out and rebuilding your TB or for the manufacturers of BBTB's, but I think it makes zero sense on its own. It's a "while your in there" thing if you really want to maximize every mm of intake flow and you're the kind of person who's already deleted ASC, 3.5" MAF with silicone boot, M50 manifold or ITB's, BBTB, etc...