Side running exhausts

[DannytheRadomski]

Why do teams have exhausts that run along the sides of their car? It seems like it would just add weight, a little bit of complexity, and heat the cockpit. The only advantage I can see (and it seems like a stretch to me) is that it could heat the tires and give better grip. This has confused me for a while.

[Racer-X]

If you mean like Illinois does I'd assume its for packaging.

[Mbirt]

Because megaphone http://fsae.com/groupee_common/emoticons/icon_cool.gif

With a single cylinder engine, it allows us to package a reasonable exhaust tuned length without crazy muffler packaging or excessive headpipe bends in the back of the car. There are rules regarding the maximum height and rearward placement of the tailpipe orifice if it exits the rear of the car. Running the muffler forward allows for more muffler length.

The only added weight and complexity would be the requisite heat shielding, but check out Formula North 2013 for some examples with negligible weight. If you're already running a sidepod for aesthetics, I see no added weight or complexity. Cockpit heating from a muffler in close proximity is negligible in comparison to the bundle of glowing snakes an inch from your back on a 4-cylinder car. The acoustic batting in most mufflers insulates to the point that aluminum and carbon fiber muffler shells last thousands of miles on production bikes. Mounted an inch from a closeout panel and with airflow around it, the muffler does little to heat the cockpit.

[Owen Thomas]

I would also like to add that running the exhaust/muffler on the side of the car as opposed to out the rear lowers and centralizes the mass (in most cases). Not really sure where you see the added weight and complexity.

[P. Jayaraman]

Originally posted by Racer-X:
If you mean like Illinois does I'd assume its for packaging.

I was one of the engine guys on the Illinois team the first year we did this (2011).

That year, we started with a more traditional exhaust layout. We ended up having a nightmare passing sound at Michigan. Furthermore, we had some concerns about cooling as our exhaust wrapped around the engine. So between Michigan and California, we made a quick modification to bring the exhaust to the side runner you see now (funny enough, I completely forgot to ask the guys why they retained it).

Ends up sound was still a bit of an issue, but it was attenuated enough to get by a little easier.

Ask me now though and I'll say that our sound problems went a bit beyond the placement of the exhaust.

[DannytheRadomski]

Packaging issues make sense. In terms of weight and complexity I was thinking about the engine being in backwards. For some reason I was thinking of the headers as facing back, making it harder to get the pipes to the sides without going through/melting everything in the way.

[BluSTi]

We're running ours to the side because the muffler would stick out too far from the rear if we went the other direction. Also, you can balance the weight by sticking an oil cooler in the other sidepod.

There are other good reasons to do it, too.

[P. Jayaraman]

There is one pretty major risk though: if your brackets or supports for your muffler fail, things like this happen:

Illinois car on fire (http://www.youtube.com/watch?v=KEdhVpj2AYQ)

[Paul Gerisch]

Like Owen Thomas sais: It's to get the weight to the middle of the car. This reduces your moment of inertia.

And I'd say you don't want to heat up your tires with your exhaust. Then your left tire and your right tire would have different temperatures and therefore different grip.
There are other ways to get your tires up to temperature if you have problems. But I have never experienced problems with low temperature at the rear tires. You will have an influence on your tire temperature but I would say you shouldn't let your tail pipe point on the tire.

Addition: In my eyes your tail pipe should always point a bit into the sky. Think about the measuring method at the noise test...
In Italy 2011 an Indian Team came to us to ask for mineral wool because they were not able to pass the noise test. Our exhaust guys went to them and saw, that their tail pipe pointed in the direction of the microphone. They suggested to change this by turning the end cap at the damper. Afterwards it pointed 45° into the sky in a vertical plane (not horizontal as before). They easily passed the test with this configuration (without more mineral wool).

[icireland]

I've noticed a few teams running side exhausts with the muffler exit pointed directly into the oncoming air flow (i.e. in the direction the car is travelling).

It is my understanding that you want as little resistance as possible for your exhaust flow, so wouldn't this hinder it? Or is there some kind of underlying witchcraft going on that makes this preferable?

[PatClarke]

Originally posted by icireland:
I've noticed a few teams running side exhausts with the muffler exit pointed directly into the oncoming air flow (i.e. in the direction the car is travelling).

It is my understanding that you want as little resistance as possible for your exhaust flow, so wouldn't this hinder it? Or is there some kind of underlying witchcraft going on that makes this preferable?

As a new Forum member, you should introduce yourself and identify your team.

As for your query, think for a moment about the pressure in the exhaust gas flow Vs the air pressure when the car is moving forward, even at top speed.
Realistically, there is no real restriction to gas flow, even if a forward facing exhaust doesn't look too intuitive.

PC

[JWard]

A colleague did a hand calc at the time and it came out in the tens of mBar. Anyone care to stump up some numbers?

[Simon Dingle]

Four-Stoke Performance Tuning (3rd Ed.) by A. Graham Bell has a table on page 24 with pressure rise against vehicle speed. This table lists 100kph as having a 5mbar pressure rise.

He was looking at pressure rises in an inlet manifold due to ram air, but I don't see why the numbers wouldn't be roughly applicable to a forward facing exhaust.

[Z]

Dynamic pressure (= stagnation pressure) = half-rho-V-squared.

So if,
Rho (air density) = ~1.2 kg/m^3,
Velocity (say ~max for FSAE) = 30 m/s = 108 kph,
then
Pressure = 0.5 x 1.2 x 30 x 30 = 540 Pa.

And since
1 Bar = ~100,000 Pa,
the stagnation pressure is about 5 mBar (or 1/200th of atmospheric pressure),
as before.

Z

[JWard]

Wait, I remember, he made the joke to a doubting Thomas that if it were a ram air exhaust (sidepod shroud for the fwd facing exhaust) it was in the tens of mBar.