Evening all.

I'm just throwing some ideas around in my head at the moment, regarding the engine that I am putting in my Sylva Mojo (OKay, not strictly a locost, but I'm trying to keep things that way!). It's a toyota 4a-ge engine, and my original intention was to fit a set of the GSXR throttle bodies, on a custom made (or adapted!) manifold.

Now I am beginning to wonder exactly what is behind this throttle body lark anyway. From my basic understanding of automotive engineering, a throttle body is basically an adjustable restrictor in the air intake for the engine (in this case engine cylinder) right? Usually it is just a simple butterfly valve in a tube, the angle of the butterfly being used to "throttle" the engine?

Is my basic understanding on the right track here? Or is it somewhat off the mark? I know it is way way more complex than that to do properly, and this is where somebody here might be able to help (Cue question 1). So does anyone have, or know of any resources that are available that go into the detail of throttle body design? Web links, books, magazine articles that can be scanned/emailed, that sort of thing would be much appreciated if you know of any!

The reason I am looking into this now, is not because I want to do things cheaply, not because I want an easy way to get throttle bodies, but purely as a learning exercise to help me understand what is going on on a technical level. My intention is to have a go at designing a set of basic throttle bodies, and see how they turn out on the CAD screen. I might get around to making them, then again I might not. For my car, I'll more than likely go with the GSXR TB's.

Anyway, If anyone has any good techincal links/ book recommendations, mag articles that might be an interesting and relevant read, or maybe even manufacturers links that they would care to share, I would be much obliged!

Apologies for the rambling post!
Andy

Hi Andy,

There was a little bit about this in the good old 4-stroke performance tuning - A. Graham Bell book. I dont think it was much though more to do with inlet tract length and plenum volume, but it might be a place to start.

Keep me posted though, would be hugely satisfying to make something from scratch like that.

Geoff

OK...

When people refer to throttlebodies on cars, they tend to refer to ITBs, or Individual Throttle Bodies. These are the Fuel Injection equivalent of fitting nxDCOEs.

In a similar fashion to carbs, fuel injection relies on 2 delivery mechanisms - 1 for fuel, one for air.

On carbs, the air is metered by the butterfly, and fuel delivered by the jets.

Fuel Injection is similar - air is metered by the butterfly, but fuel is delivered by the injectors - essentially electro-mechanical valves. These injectors are normally mounted one on each "throttlebody"

They're so similar, DCOEs can be converted to throttlebodies by sealing the jet holes, and drilling new holes for injectors.

This is hopefully a simple description of Throttle Bodies in the "motorsport" sense, and hopefully makes sense. The next bit is a bit more complex.

In production cars, savings are had by fitting less of items. As such, a single throttlebody is fitted - this is the equivalent of fitting a single butterfly carb, e.g. a std 1300 Mk 2 escort carb.

On production cars, however, the throttlebodies do not necessarily house the fuel delivery mechanism - as it's electronic and not as dependent on fluid dynamics, the fuel can be "injected" anywhere. For efficiency, fuel is injected close to the cylinder head inlet port - often directly onto the back of the inlet valve itself. As such, there is a single throttlebody metering the air for all cylinders, but each cylinder has it's own fuel delivery mechanism.

Well that's what I thought to be honest. The amount of satisfaction I am getting from building a car (albeit a kit car) is good, so actually designing/building parts for the inner workings should be really rewarding.

I'm going to be forced to spend hours dredging the web at work tomorrow to try and discover a bit more about these throttle body things!

Steve, thanks for that explanation. The 4a-ge engine I have seems to have one large throttle body at the end of the plenum chamber that feeds the inlet tracts, and TVIS system.

I'm just wondering now why a butterfly is chosen then? Is it anything to do with gas flow/ dynamics of getting the air into the engine, or more to do with mechanical simplicity?

Cheers
andy

If you're designing your own throttlebodies, each one is essentially just a cylinder with a butterfly assembly in it and a hole for the injector (think the 4age has injector mounts on the head, so you can omit this last requirement in your application)

The trick will be getting the butterfly assembly balanced, and lengths tuned for max BHP from your engine.

Post this same question on the se7ens.net or megasquirt mailing list and I'm sure you'll get a wealth of help from some real experts.

Single butterfly is used basically due to cost and mechanical simplicity - multiple butterflies need to be balanced properly and hence cost more to make and maintain.

One of the Sylva guys used the original 4age system when he originally fitted the engine - would get you running for SVA and give you the time to design an alternative system later.

Thomas' Site




[Edited on 21/12/05 by stevebubs]

Part ot the advantage of seperate bodies for each cylinder is the way they can be all tuned to give the best intake length. The distance from the intake valve to the bell mouth needs to be just right to make full advantage of the pulse action of the engine breathing, something tricky to do with a single 'body set up.

Hi Andy,

Bit quiet on the run up to Christmas is it?

The Jenvey website has some useful info on butterfly sizes, inlet lengths etc etc.

Some TB designs don't use butterflys, but a roller barrel, as used by caterham on the csr260. A quick google came up with this as an example. These have the advantage of nothing sitting in the air flow at full throttle.

I've just updated my website again, so you might find some useful info here

Drop me an email if you have any questions...

Cheers,

Neil

[Edited on 21/12/05 by nre]

I seem to remember an article about porting. It stated that fuel/air in the intake acts differently than dry air. It might have been a density issue. It made reference to port finish and bend radius. I cant remember where I saw this info.... sorry

[Edited on 12/22/2005 by wment]

If its of any advantage to yourself in designing a multi throttled system for an engine i used to own a 1994 toyota celica GT, engine code, 3S-GE, (NOTE NOT THE 3S-GTE) the intake manifold had a chamber which was opened and closed by 4 butterflys activated by a vacuum controled actuator much like a turbos wastegate,

this system was to do with economy and performance at different RPM. What may intrest you however is the 4 butterflys which are joined and i would imagine balanced so could be used for a multi throttle system.