Variable Geometry Exhaust.

[buggaero]

This was just a debut year, and not sure if i am correct, (do it if i am not)....
Not many Variable geometry exhausts in fsae engines?
or that i am unaware.
But i still wanna talk about it. Google isn't helping.
Basically... not being able to complete the picture i'm trying to develope.

[Mbirt]

If you're thinking of incorporating an active or passive exhaust valve for noise reduction, you'll have to pass noise with it in the full-open position per the rules.

If you're speaking of VNT turbos, the GT15 has it and it has been implemented in FSAE IIRC.

[Kirk Feldkamp]

Do you mean something like the exhaust system valves that most every newer sportbike has had at one point or another? I've was part of an exhaust system valve development program at one point, and I can say from experience that you probably shouldn't expect to develop something yourself that aims to do this. Making parts that can rotate/move within the extreme conditions present in an exhaust (and survive) for very long takes some fairly nonstandard materials. Probably the smartest way to incorporate something like this would be to reuse an OEM part.

[vikram.]

what actually do you want it to do? thats the question ,why you proposing this?

[buggaero]

Originally posted by vikram.:
what actually do you want it to do? thats the question ,why you proposing this?

For the benefits of it. Which i think would intrigue anybody for a while.

[Rex Chan]

Sorry to be harsh, but it intrigued me for all of 5 seconds that it took to realise what a unproductive use of effort it would be.

You are correct in that I am not aware of many movable flaps in the exhaust systems of FSAE cars. In fact, not many have them on the intake side either.

I think the answer lies in the results of any FSAE comp: most teams fail to finish enduro or compete in every event. So, to do well at comp, all you need is a working car. A moving flap in your airflow system is not required to create a working engine system. Once you've made a car that can actually compete, then you have to worry about performance. If you're using a 4 cylinder, then you probably have enough forward propulsion. If you're running a single, you're probably trying to shave weight.

In any case, its a moving part that doesn't need to be on your car, so I wouldn't put it there unless it had a significant points or performance difference. There are actually 2 things working against the idea: you don;t need variable geom stuff for the car to work; and it moves, so is inherently less reliable than something that is not supposed to.

The engine subsystem has a lot of bits to it, and thus engine teams usually have lots to do. Make your/their job easy.

Also, the points at comp are now for fuel economy, so try to work at going fast while using less fuel. Ask me about injection timing, injector placement, lambda targets, accel enrichment, overrun fuel cut, ign timing, etc, and I'll have much more to talk about.

[Mbirt]

Originally posted by Rex Chan:
In any case, its a moving part that doesn't need to be on your car, so I wouldn't put it there unless it had a significant points or performance difference. There are actually 2 things working against the idea: you don;t need variable geom stuff for the car to work; and it moves, so is inherently less reliable than something that is not supposed to.
+1. Check out SAE Paper 983046, "Empiricism and Simulation in the Design of the High Performance Four-Stroke-Engine" by the great G.P. Blair. There's plenty to get right with fixed-geometry intake and exhaust first. Two intake tuning peaks and one exhust tuning peak should provide a suitably wide "powerband".

[vikram.]

it intrigued me for more than half an hour in which i was thinking and ya you might be correct with this,but is it worth the time ? and i don't think commercially it has been incorporated so you have to design, fabricate and the important part keep testing it. i don't think you have this much of a time but ya still if you can do that it will be great. i can just visualize because i have been designing exhaust for 4/2 stroke multicylinder engines from a long time.

[Paul Achard]

More weight for a single and marginal performance gain? Not necessarily; I could imagine a variable resonance chamber in your exhaust which far reduces noise for most areas in the powerband, thus allowing for a smaller/lighter exhaust can and no noise- and power-attenuating restrictors in the exhaust system.

[buggaero]

Thanks all for enlightening.
time/output is something i'm well aware of.
Vikram, it has been showing up commercially for a while now.

[vikram.]

enlightening