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Hotdogs only exhaust
https://ausmini.com/forums/viewtopic.php?f=5&t=10376		 Page 1 of 2
Author:  jill200sx [ Mon Aug 22, 2005 2:28 pm ]
Post subject:  Hotdogs only exhaust
Im a big fan of hotdogs, and previously had an 18" straight through hotdog and nothing else. I know after reading the forums this isnt good for lack of back pressure and burning valves (possibly).
I talked to the local exhaust place and he asked the Perth exhaust guys and they recommend 2 hotdogs.
One spiral louvred hotdog 9" at the front with a Perforated hotdog 9" at the rear. This will give me some noise but enough back pressure. Would you guys agree? Would that combination be ok?
Author:  kazjim [ Mon Aug 22, 2005 3:10 pm ]
Post subject: 
This is one thing that seriously Irks me .....

How can back-pressure be a good thing ?

I've yet to see any quantitive data to prove that some Back-pressure is "needed" .

Most of the rumors started when they would take the exhaust off and run the engine without a pipe.... and without re-tuning for the new dynamics THEN bad things can happen.....

:roll:

Sorry, I dont buy this one.... Why dont motorbikes burn valves ? stationary engines ? Super-tankers ?

Hmmmmmmm
J
Author:  fuzzy-hair-man [ Mon Aug 22, 2005 3:23 pm ]
Post subject: 
I was wondering this myself, just though I'd keep quiet for a bit :D

Vizard's book says the RC40 cause it has very little to no back pressure, the way he explains exhaust sizing is that you want you pipe to be large enough that you have no back pressure but small enough that you have high exhaust gas velocoity (speed) so that you get some exhaust scavenging and so that the exhaust gasses don't stop and turn around and go back into the cylinder head during overlap, making the mixture not so clean.

How an absense of back pressure burns valves I don't know, ow maybe it has something to do with the mixture going lean if exhaust gasses return to the cylinder :idea: :? EDIT: Nope , that's silly :oops:
Author:  jill200sx [ Mon Aug 22, 2005 3:31 pm ]
Post subject: 
so, if I were to use 1.75" pipe from the extractors with just the spiral louvred hotdog, that would be ok? I dont see the point of using 2 hotdogs when surely one would do.
If I were to go one 12" spiral louvred hotdog, that should keep the noise down reasonably well, or would it be too noisy you think?

Anyone else running only a hotdog?
Author:  fuzzy-hair-man [ Mon Aug 22, 2005 3:44 pm ]
Post subject: 
1.75" seems to be the best size for the 1275 the hotdog (I'm not an exhaust person so don't even know what it looks like :oops: ) may have better or worse flow than the RC40 (does it have any flow figures that tell you how much it flows?).

As for noise I guess it is up to your tastes and what you can get passed by your authorites :lol: 8)
Author:  awdmoke [ Mon Aug 22, 2005 3:54 pm ]
Post subject: 
I had an unbaffled 2" system :D
VERY LOUD !
If had been on any other car, I would have been yellow stickered within a week. Worked a treat but :wink:
Author:  minicranks [ Mon Aug 22, 2005 4:18 pm ]
Post subject: 
I have a single promuff exhaust on mine and very very little back pressure is quit loud but have had no hassles with valves and anything else really,
I get a good power curve and dont feel that i would be loosing out if i stuck a hotdog in the circuit.

When i first read the heading i thought you were goint o show us how to cook hotdogs on the exhaust, yummy food on the go.
Author:  gafmo [ Mon Aug 22, 2005 4:40 pm ]
Post subject: 
Have you seen a Muffler on a ...V8 Supercars....1/4milers...NASCAR's...F1

yer they pull the motors down and replace things after each race (Except F! now)..but they have no back pressure
Author:  jill200sx [ Mon Aug 22, 2005 4:55 pm ]
Post subject: 
so if I want my engine to last longer, go for more back pressure Gaf? Avoid the hotdog all together?
And this RC40, its just a muffler? Wont any "sports" muffler do (if I dont go hotdogs)?
Author:  gafmo [ Mon Aug 22, 2005 4:56 pm ]
Post subject: 
No I'm saying stuff the back pressure...all the people who race cars and bikes don't have back pressure
Author:  awdmoke [ Mon Aug 22, 2005 4:58 pm ]
Post subject: 
That's a syllogism. They strip down turbo race motors the same, and they have a relatively high back pressure. Race motors are stripped regularly to ensure reliability at high rpm and full load. Bearings & rod bolts are the components most often replaced, not valves.

Any time you change the way an engine breathes - cam/air intake/exhaust - the carby must be adjusted to correct the mixture or you can damage the valves (& more).

More importantly most stock cam profiles work better with some back pressure & a loss of low/mid range torque can result with a free flowing exhaust. But like jim says, the engine must be set up for it.
min. back pressure = max. peak power
Author:  meeni [ Mon Aug 22, 2005 5:40 pm ]
Post subject: 
i dont see how little to no back pressure would effect the engine, mine runs fin with a single got dog!
Author:  speedy [ Mon Aug 22, 2005 5:46 pm ]
Post subject: 
Found this, very useful article that explains the difference between back pressure and exhaust diameter, and the correlation with exhaust velocity.

http://www.proficientperformance.com/te ... essure.php
Author:  jill200sx [ Mon Aug 22, 2005 5:59 pm ]
Post subject: 
ooo so I can have hotdogs :) and get it tuned :) Yay!

Can any mechanic tune it? Id rather take it to Automotive Tuning Centre in Perth coz they rebuilt my weber and they apparently know webers and Minis well, but I wouldnt want to drive it to Perth (2 hours plus drive) if its running overly lean as that could damage something :?: Any reasonable mechanic can tune it to be running half decent?
Author:  gafmo [ Mon Aug 22, 2005 6:21 pm ]
Post subject: 
Get it to a Dyno..as we are doing in a couple of weeks time..they will give tell you if its running Lean or rich..and if they know webber/Dellies they should have the appropriate jets required..addtional if they know Mini's that would be a bonus..so do a bit of ringing around and ask questions..maybe give ATC a call and see if they know anyone around your area :wink: they will also give you your ultamit BHP which will give you braging rights 8)
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