Brass throttle blades?

[Boosted LS1]

I was wondering if there's a preference to use brass instead of mild steel for throttle blades. It seems very common but isn't exclusively used. I'm making some throttle bodies and wondering which material to use. Has anybody got any comments which may help, thanks?

[stevieturbo]

There's always the risk of corrosion with steel.

[Pumaracing]

Unless you can point to an actual example brass is indeed exclusively used for throttle butterflies. I've never seen anything else used in either carbs or TBs and we've made throttle bodies for 15 years. Like these.

http://www.pumaracing.co.uk/TBs.jpg

Mild steel would be stupid. It rusts like buggery.

Edited by Pumaracing on Monday 25th July 10:26

[Boosted LS1]

Thanks Puma, you to Stevie. Ls engines don't use brass in the throttle body. I favoured brass, I guess it won't suffer corrosion when 'icing up'. I'll go for brass then. Have you any advice you could share regarding the machining of the blades and tolerances in the choke area?

[davepoth]

It's brass on an SU carburettor, as it is on a Weber.

[Mr2Mike]

The clearances are pretty tight; I suspect the butterfly material would have to have similar expansion characteristics to the throttle housing to prevent either sticking or lots of leakage when closed under extremes of temperature.

FWIW the throttle bodies on some bikes have two sets of throttles, one in the normal location controlled by the throttle cables and one the upstream of the injector controlled by a servo motor. The upstream butterflies appear to be made from an aluminium alloy, and the downstream ones are brass.

Edited by Mr2Mike on Monday 25th July 21:38

[MattYorke]

The ones on my hilborn intake definately aren't brass.

[Pumaracing]

Boosted LS1 said:

Have you any advice you could share regarding the machining of the blades and tolerances in the choke area?

There's really no point making them from scratch when you can buy Weber ones for a few quid each unless they absolutely have to be a non standard size. Then you just have to drill and tap your spindle for securing screws at the appropriate places to match the butterfly. The choke would just be bored to the nominal size of the butterfly i.e. 45mm or whatever to within a couple of thou.

[Boosted LS1]

^Thank you Puma.

[rev-erend]

No need to re-invent the wheel after all..

[Boosted LS1]

It's an Ls7 casting a bit like a Kinsler so the intake ports are bridged together. So, not quite individual TB's hence my not reinventing the wheel

[eliot]

I use 2.5mm ally on my 72mm rover plenums.

[Pupp]

Maybe worth bearing in mind that brass can have compatability issues if/when in contact with methanol, given increasing mixes of that in modern fuel. Think some grades are less susceptible and probably not a huge issue upstream of the injectors...

[Boosted LS1]

I'll fetch my castings this week, I'm chuffed. As for the brass blades it was also pointed out to me that they can make a good earth should there be a spark in the neighbourhood. I suppose that would have been essential in the carb days?

[virgil]

What about stainless? Stiffer that brass so can be made thinner, won't rust.....

[Boosted LS1]

^That's an interesting idea.

[Pumaracing]

Stainless steel is expensive and can be very hard to machine, especially trying to take the final small cuts to get something to an exact size. If it starts to work harden during machining then you're pretty much buggered unless you can finish it by grinding. No one in their right mind would use it for throttle butterflies.

Brass is easy to machine, it cuts very cleanly and precisely to an exact size with a sharp tool, it's more than strong enough for the job, it doesn't corrode much and it's proved to be the ideal material for a century or more. Why reinvent the wheel?

Aluminium would be ok and is similarly easy to machine but in an aluminium bore it would have a greater tendency to wear or gall against the bore surface. Tribology mandates than you ideally use different materials in contact with each other to minimise wear. Usually one hard material against another softer one such as a hardened steel gudgeon pin in an aluminium piston, a soft white metal bearing against a steel or iron crank journal or a rubber oil seal against a metal shaft. What you then find to your surprise is the harder material usually wears faster than the softer one but that's another story.

[spend]

Thinner doesn't really help you either, its the spindle & screws with greater x-section at WOT.