probably a silly question but, why do most drag cars run stinger (straight out) exhausts??? do they run better without the back pressure a muffler provides????

matt

define exhaust back pressure please , its always confused me

i dont know much about it i just assume a motor will run better with a bit of back pressure. back pressure is the resistance of the gasses to flow through the exhuast, some one else may explain it better

matt

if all other things are equal (ie air /fuel ratio etc) the muffler will slow it down

oh ok, you learn something new every day!!!

thanks
matt

Plus there's nothing like waking up in the morning at a drag strip listening to a flat four barking through a stinger

Why not just have no stinger or muffler at all?

You need backpressure of some kind. But in a drag racers case, the extractor tubing alone towards the flange for the stinger is sufficient.

But i dont know if backpressure is the right term. See... from what i'm aware of, its to do with air velocity. Smaller diameter tubing with same rate of air flow has greater velocity of air going through than a larger diameter tube.

A wider diameter exhaust tube with same rate of air flow as the smaller diameter tube has larger volume, slower air flow.

By finding a 'balance' to create maximum air velocity, by manipulating tube diameter without large restriction (and too much back pressure) it results in a 'relative' vacuum at the exhaust port as the momentum of the air exiting the exhaust (due to its velocity) continues to 'suck out' exhaust gas inside the tubing as it goes the exhaust pipe.

Extractors take advantage of this, by lengthening the pipes correctly to collaborate with the timing difference of the exhaust ports. They work with the 'pulses' of the exhaust gas to maintain a continuous flow and continuous forward momentum of the exhaust gas exiting, to keep 'sucking' out the gas from the port.


Eva seen how shizzy any motor runs without any exhaust manifold at all?
Its a mess. efi or carby...

Load like a tractor on the dub though haha.

its similar, but opposite to velocity stacks on a heads intake, choosing the right size for best possible air velocity. or even TVIS, taking advantage of the 'natural supercharging' effect.

they make the car pretty useless for driving between o and 2k-ish but rock after that...

and they sound awesome I got one fro my thunderbird from action day, spent 2 hours cleaning it up.. and it looks sweet... under my bed with the rest of the exhaust. all ready for the set up!

I ran several runs with the stinger and several with just the open header on my drag bug. It definately ran stronger with the stinger.I think it has some sort of scavenging effect too especcially at speed.

Best person to chime in would be Brad "westi" from Westside, but the way I see it is:

Stingers work because we need some sort of exhaust tail section after the collector to help with wave scavenging, there is less loss of velocity and would probably work even better if they were the same dimension from flange to exit as there are no expanding gasses past the collector therefore continuing velocity.

They sound great because they simply exaggerate the sound of the exhaust pulse.

Mufflers are just that, used to soften the sound and pulse of the exhaust gasses.

Think of it like running your tap to fill a cask, the water traveling through the small pipe is traveling at a fast rate and losses velocity as it fills the cask, although exiting at the same volume but a slower rate through a larger hole.

Your engine has 15 psi (1 Bar) of atmospheric pressure sitting at the inlet and another 15 psi lurking at the end of the tailpipe. The inlet stroke creates a pressure differential and the atmosphere goes rushing inward. The exhaust valve opens and there is a pressure rise in the tube followed by a strong "vacuum signal" as the gases head down the pipe. The vacuum signal or low pressure that follows an exhaust event can be used to help scavenge the cylinder during overlap when both exhaust and inlet valves are open. Conversely, during this overlap period, the increase in "backpressure" can cause these burnt gases to re-enter the combustion chamber and contaminate the inlet charge. Result...loss of power. The way to look at exhausts is to view them as a way to maintain the highest velocity that will not impede flow. As velocity increases the pressure drops and the engine can become more efficient. As bajachris88 pointed out, there's all the variables of length, diameter, rpm, collector size, etc. There is no "one answer".

At the end of the day they look good ,sound good, make people ask "whats that for" and people trip over them.
All good for me.

hahah people trip ova them... lol

I definitely gotta make it to the drags then!

I nearly tripped over Craigs on the dray rat at action day....... don't tell him.

Awwwwwwwwwwwwww YEAH!




Pardon the messy room... lots of assignments going on. hahaha

Quote:

Originally posted by Duanepipe At the end of the day they look good ,sound good, make people ask "whats that for" and people trip over them. All good for me.

I have one to put on Buz at Warwick but you wont trip over it as Buz isn't lowered

Exhaust systems are a 'Black Art' - just look at 2 strokes and their expansion chambers. In 1969 I drove a Vee, which came with 4 separate pipes, 1.25" dia. After talking with Bruce Peters of Sonic Speed Equipment (they made a VW exhaust system), I made a 4 into 1 using smaller (1.125"dia.) primary pipes, and a single 1.25" dia. tail-pipe. This gave a 4HP increase on the Dyno! That's an extra 10%!!!!!!! Bruce told me that they (Sonic) virtually threw away their books on exhaust theory, and used the Dyno to experiment with different ideas.

Cheers, Greg

greg, doesn't surprise me, but exhaust design has come a long way since 69'. I'm sure there are a few good books you could get to help these days .

speaking of stingers on Fvees. I saw a whole bunch of Vees running stingers last weekend at Wakefield. A few were running hotdogs, but the one that got my attention was this setup...

its like the dual cannon motorbike stylin kinda thing.

me likes

Best guys to learn from are engineers in F1, lots of R + D on N/A.