Exhaust System

[MicrapowerIRL]

Ok heres my query, on a budget, i want a back box that sounds nice n raspy sporty baaaappppp, but when u let off te accelerator shel burble n pop while deaccelerating if you get me?
Any suggestions lads? Greatly appreciated

 

[The Jamm]

cheap universal exhausts sound pretty good, you just have to be handy with a welder or have a mate who can weld to get them on and looking good

 

[jamieccc]

Cherry bomb


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[The Jamm]

this is how mine looks with a £30 exhaust off the bay

 

[TheKingGrim]

Go for open headers each cylinders got its own pipe itl pop like a bag of corn in the microwave and youl have 4 exit pipes on the back

 

[infinity]

Go for open headers each cylinders got its own pipe itl pop like a bag of corn in the microwave and youl have 4 exit pipes on the back

That actually looses power, you completely eliminate any scavenging effect

 

[Antony]

That actually looses power, you completely eliminate any scavenging effect

Scavenging is negliagable on a modern fuel injected engine.

It refers more to 2 stroke and carboureted engines that rely on vavum and exhaust velocity to purge the cylinders of exhaust and suck in more fuel and air respectively.

Does nothing to a car with electronic fuel injection.

And certainly nothing noticeable on a car with compression below 10:1.

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[frank]

infinity probably means port scavenging eh, 4-2-1 tuned primaries

 

[Antony]

Still not noticeable at these power levels.

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[frank]

so a janspeed mani gives no gains then ant ?

 

[infinity]

Does that mean ill have the same gains by putting 4 tubes that don't connect instead of the manifold?

 

[frank]

the exh pipe diameter will have a gasflow effect on a single cylinder engine, and a 4-2-1 has an additional effect on the pulse scavenging eh, but its nothing to do with fuel injection or c/r tho (valve timing and manifold design basically)

 

[Low Rider]

Scavenging is negligible?

That can go in the same drawer as engines needing back pressure to make power.

I feel a Gordon Ramsay moment coming on so I'm just going to go and lie down for 10mins to recover from that one LOL.

 

[TheKingGrim]

meh ive always been taught the better a car breaths either end the better it runs but dont quote me on that as im an agric mech not car so id have though zero restriction on the cylinders via exhaust would be better than the back pressure given by a 4 into 1 manifold

 

[frank]

meh ive always been taught the better a car breaths either end the better it runs but dont quote me on that as im an agric mech not car so id have though zero restriction on the cylinders via exhaust would be better than the back pressure given by a 4 into 1 manifold

zero restriction for a turbo diesel tractor yes

 

[TheKingGrim]

zero restriction for a turbo diesel tractor yes

actually open headers would be terrible on a turbo diesel tractor as youd be missing out the turbo xD its more something youd fit to an bike or an unturbo'd petrol or a gocart looks mean as hell though with 4 pipes popping and spitting

 

[fuzzy-hair-man]

The best way of explaining I've seen talked about the airflow as 'slugs' of air each having mass and interia.

The exhaust port on a 4 stroke is going to see 1 high pressure 'blow' phase to 3 phases doing nothing 'wait', so with straight exit for each pipe there will be blow, wait, wait, wait, blow, wait, wait, wait,....
All that slowing down and speeding up takes energy.

But it would get worse because the 'tap' if you like gets turned off immediately and quickly after the exhaust stroke so the fast moving slug all of a sudden has a vacumn behind it trying to slow it down / reverse flow..

So what if the pipes join up after enough length in the primaries to fit a slug?

Well after the join there will now be another slug arrive at the join in time to avoid the vacumn forming so the slug will keep traveling down the exhaust nice and quick.

The join with a 4 cylinder will see: blow, blow, blow, blow,....

Sure that is an ideal situation and there are certainly simplifications, but it is better than 'put a big whacking pipe on each cylinder.'

Franks has done some pretty cool practical experimentation with burble manifolds etc so I trust he knows what he's talking about.

Another way of looking at it is that sound is energy so all that noise, popping and farting is energy that could be used to make the car go forward. So the ideal then would be a silent exhaust with no mufflers etc required, cause mufflers are absorbing energy from the exhaust.

This is the model I have in my head so it's only an approximation of what's going on, it will be changed next time I read something interesting on the subject.

 

[MicrapowerIRL]

Thanks lawds


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