SCOSaltire

lo

Which is loudest:
MY99 scoob with a Scoobysport centre pipe and Scoobysport back box
OR
same scoob with the PPP centre pipe and Scoobysport back box?


[Edited by SCOSaltire - 6/26/2002 11:06:36 AM]

SCOSaltire

noone knows?

AndrewC

Pure supposition:

Isn't (wasn't) the PPP centre an STi item, which depending on year had either 1 or 2 resonators in it, given this fact I would say that the STi centre equipped car would be a little quieter.

Andrew...

Beastie

iTrader: (2)

No difference with my MY99. However if you have the Prodrive ECU the exhaust is quieter than the standard car. This was very noticeable to me. I am currently running PPP centre and PPP backbox (with PPP ECU) as when I fitted Scoobysport backbox all my low down torque moved up the rev range and the car was not as noisy as before, (pre PPP with only the Scoobysport backbox fitted.)Also my max boost dropped with the Scoobysport backbox with the Prodrive ECU.

One thing I can say, it goes like a bat out of hell. After fitting PPP, I asked garage to check performance cause my boost gauge wasnt reading very accurately. My wife took the car in and they said there was nothing wrong, but they said they tweaked it and i would definitely notice it now. Dont know what they did, but it flies. I recalibrated the boost gauge against a calibrated gauge and I am boosting 1.23Kg/cm2 max.i.e. 1.21 bar or 17.5psi

Beastie

SCOSaltire

less performance

thats quite a high psi for ur prodrive kit.
my car runs about 16.5 psi (JB could confirm this probably)
who set that up for u?

Beastie

iTrader: (2)

SCO It moved the torque higher up the revrange. Putting the PPP backbox on moved it back down. This means that power is available low down about 2500rpm and from there it just ramps up with that typical Prodrive roar from the exhaust.

The drop in boost with the Scoobysport must have been due to lower back pressure. I waited for the ECU to adapt but it didnt. I then reset the ECU with no better result. Put PPP Backbox back on and all back to original after a tank of juice.I then went through posts on exhausts and found out that other people had experienced the same problems before me with different makes of exhaust. Before it was tweaked, you had to use full throttle running up through the gears to get the roaring. Now it roars as soon as you plant your right foot and takes off. The car is definitely running leaner than the original ECU as the black soot that used to be around the exhaust has gone. I also seem to be getting better MPG if I behave.

I think we all realise how much difference induction and exhaust can make.

I shouldnt say this, but i have had to drive slower, I overtook some cars (the usual pack of 3 on my private airstrip) and when I pulled in and glanced at the speedo I was doing 130 somethings and i had been cruising at 60 somethings. Clearly (even to me) this was a bit excessive and I have been very careful since. I also wouldnt like to loose my pilots licence and so always try to keep it just under 30 somethings above the airspeed in force.(Hope you are paying attention!)

I guess its putting out about 270 with the original downpipe.
IMHO

It would be nice to meet up sometime.

Beastie

[Edited by Beastie - 6/26/2002 4:01:43 PM]

john banks

270 with the original downpipe is optimistic when I had 257 with a full decat PPP and a Dawes at 18 PSI - ran 17.5 PSI on the rolling road, with more boost across the range than the PPP ever could. Depends on your choice of rolling road I suppose.

The PPP aims for 15.7 PSI - if it goes a lot higher it will exhibit underdamped boost control especially in high load low temperature conditions. At 17.5 PSI problems are likely - I could get mine to 17 PSI before it fluctuated, but it was happiest at 16.5 PSI.

Beastie

iTrader: (2)

John
The car is under warranty and drives like a dream. I have driven STIs and know what 276BHP feels like with shorter gearing.I didnt say the car had 270bhp, I just said I thought it did IMHO.In fact it cannot be far off. I seem to remember you saying that you thought it was faster than yours when I had the AE800 ECU in it.I didnt agree with you!
Lets be clear I am not saying it is holding 17.5psi I am saying that this is peak. It seems to hold 1.2Kg/cm2. Perhaps when it was tweaked they changed the restrictor.

It is all academic anyway and I will not be drawn into an arguement on what is and what isnt. I am happy with the performance now, and before I was a bit dissapointed after my 97MY which had more lag but also more punch. I would say I have the same punch now but from lower down the rev range and I have the same power higher up.

Sometimes it is best to agree to disagree!! Ooops I havent mentioned the K&N.

Beastie

PS John, I am really surprised that you havent blown yours up yet!!



[Edited by Beastie - 6/27/2002 9:42:15 AM]

john banks

I have no wish for an argument, but open forums are for open debate and I'm disagreeing with you on this one At Star Performance you would not get near 270 BHP with the original downpipe and a TD04L with a PPP controlling boost. At Power Engineering with a downpipe 270 BHP has been seen with a PPP. What you are enjoying is a considerably fatter low down torque curve than an STi which makes it feel quicker. A TD04L cannot compete with a VF28 for top end power given that the VF28 will give less back pressure, lower charge temperatures, the STi has more advance, a bigger intercooler, shorter gears, and holds more boost at the top end than the PPP ever could with a TD04L. Bear in mind the typical 1-1.5 seconds quicker 0-100 time for an STi compared with a PPP car in the tests that have been done.

Cars always feel faster as a passenger.

1.2kg/cm2 is 17.1 PSI. In making the restrictor smaller you get a higher peak, but the PPP ECU still has a 15.7 PSI target and a 4x4 correction table to bring it back to 15.7 PSI which it manages with varying success. However, it doesn't manage well a 1.4 PSI peak above target and at some point it is likely to overshoot and then undershoot and in worse cases oscillate (you are unlikely to get this until it hits 19 PSI). It is probably underdamped already if you viewed it on a Select Monitor rather than a gauge, and will only do it more so in cold weather. When it does it it feels very disappointing indeed.

In terms of blowing mine up when I am logging EGT, intake temp, ignition timing, knock correction, lambda, boost and injector duty cycles I think I've taken every precaution and if it blows up it will not likely be anything I have done. I am only running 2 PSI more than you with a bigger turbo and bigger intercooler with waterspray, lots of octane and better breathing, so not that risky

I hope you don't get bored of the PPP like I did as it is a slippery slope thereafter. They all gave me about 6 months and I am afraid they were right. Bigger turbos put your car into a much more satisfying performance bracket - the TD04 is dying from about 4500 RPM even with no actuator pressure.

[Edited by john banks - 6/27/2002 10:01:27 AM]

Beastie

iTrader: (2)

I am glad we are not having an arguement. You had me worried there for a second. I really think we are contaminating the original thread though. My apologies SCO.

I agree with everything you say. However, I still think my car is putting out about 270 but can we consider 259 then for cash?

You will need to let me try an Ecutek 2 some time.

Take Care

Beastie

SCOSaltire

dont be sorry.. tis good reading.

the car with std ppp bb does *seem* faster...
or rather
the car with scoobysport bb seems slightly slower...
revs dont *seem* to rise as quickly..

but then maybe that the nice 15/50 oil doing that.

Beastie

iTrader: (2)

SCO. I ran about with the Scoobysport for a while, but really missed the raw power lowdown I had with the PPP backbox. I really liked the sound of the SS, though not as loud as before PPP, but in the end decided performance came first.

My wife knew immediately I had changed the backbox and complained that the car was now uncontrollable! (as wives do, not that I have had more than one!) Therefore, it is not my imagination cause I didnt tell her (and she didnt see me change them) as she said how much better the car was (easier to drive)with the SS on.

Latest complaint is everytime she looks at the speedo it reads 100. She got flashed by a speed camera and is now paranoid about everything.

Isnt life fun!!

Beastie

[Edited by Beastie - 6/27/2002 12:52:38 PM]

john banks

You won't get much extra out of a Tek 2 compared to a PPP. However it is not difficult to beat the +10% peak power which the PPP gives (237 on engine dyno vs 215 standard) with custom mapping, but at Star you still need a big turbo and more boost to get anywhere remotely near 270 BHP.

I have sold the PPP centre and backbox to switch to something less restrictive. The chassis dyno figures are not well controlled since they are on different days, but getting rid of the PPP centre seems to be worth 10lbft, and the better backboxes seem to gain across the range not just at the top.

The airflow across the range was higher with a Blitz NurSpec than the PPP backbox even at the same boost and RPM increments across the range (using accurate datalogging not subjective measurements) were the same or better, and the ignition could advanced about 1-2 degrees extra. That's why I keep harrassing T-uk for it for every track day.



The low down gains of the std PPP on this graph against a standard STi5 on an optimistic dyno show that the STi will murder the PPP if you are in the right gear. Bigger turbos really do rule, and the TD04L should be put to death because quite simply it is crap.

SCOSaltire

JB
does it tie-up with our subjective thoughts?:
that the SS bb gives less low down torque compared to the prodrive one?

the reason for this thread was to find out if the SS centre gives loads more noise compared the the PPP one.
but...i am also interested in matching the right exhaust to the prodrive chip to give most torque midrange...

john banks

I reckon that most backboxes except the standard one would outperform the PPP one across the range - it is too restrictive, but nice and quiet - depends on how much of a performance nut you are. If you don't have really high power or airflows, or have the standard downpipe or a small turbo it might not be worth bothering changing it, but it was really holding my car back - you could tell every time the Blitz went on - quite dramatic difference - not just noise you could see it on datalogs. If the original downpipe is in the way, then that should go before worrying about backboxes - the biggest gains seem to arise from sorting the downpipe and working backwards.

My choice for a centre would be a RESONATED magnex - it supposedly flows better than the PPP/STi decat centre and is allegedly quieter.

The Blitz NurSpec is just plain antisocial, esp with a straight through centre. The HKS Hiper on a car with an HKS tubular manifold was actually quite civilised, and the airflow was spectacular - mostly down to the manifold, which had almost as much effect as my hybrid turbo although it does cost double the turbo price.

The other thing to note is that a car can feel quicker if it is more jerky. Hence a Dawes car with a loud backbox and a sudden rush of boost can feel quicker than a smoothly building progressive torque curve. Turbos feel far more exciting than they go because of that change from low to high acceleration. Acceleration building smoothly on a fast NA car can feel a bit dull even though it is quicker overall than the whizz bang nothing one minute, all hell breaks loose the next delivery.

You can map a car to make it feel quicker by knackering the low down torque and bringing the boost in with a bang, but it is slower overall, less smooth and gives more wear and more difficult to control when there are grip/traction issues

[Edited by john banks - 6/27/2002 2:26:09 PM]

Beastie

iTrader: (2)

SCO try it yourself. I wouldnt be running the PPP backbox if it wasnt faster with it.It definitely gives more lowdown torque. This is actually borne out by Johns Graph although I cant understand why peak torque is so low.

I agree with John that the PPP backbox is more restrictive and the SS more freeflowing. However, this isnt always a good thing as the way the engine breathes changes the torque line quite dramatically.

I suggest that with the SS backbox having less back pressure the boost was more easily controlled by the ECU. This is what led to a lower peak and held boost. In fact when I first put the SS on the car overboosted once and dropped right back. I reset the ECU but still did not achieve the low down power I was seeking although top end power was unchanged with boost held about 1.15kg/cm2.

Prodrive talk about the cone effect with the PPP. This refers to shoving more air into the cylinder and the PPP backbox is an important part of this.

Quite frankly, I wouldnt be saying there was a difference if it wasnt quite marked, and it certainly was. I am not getting a sudden power surge though as John suggests, but just loads of power throughout the rev range starting from as low as 2400rpm.
My MY97 had the sudden thrust thing about it, where it was lag city then BANG. When I traded it in, the salesman took it out to check it and I had to argue with him that it wasnt modified. The power delivery was the same as the STI I later drove but a little less pronounced. I also noticed with the STI that I always thought I was going faster than I was, probably due to the skittery suspension, but with both MY97 and MY99 cars I am always going faster than I think.

One thing I have noticed is that my exhaust smells funny, at first I thought it was just the wool packing (all new exhausts smell for a while) but the smell persists and the exhaust is slightly black, rather than the incredible sooty deposits I had before with the Standard ECU. This points to me that the car is running leaner and is substantiated by the improved fuel consumption when driving like a nun. (not often) Acceleration is increased throughout the range.

Of course John has more accurate detail on this, all I have is a seat of the pants feeling, which is all a bit vague.

I asked about a Scoobysport downpipe, and the local dealer gave me some blurb about cars being stopped and tested on the A9 for emissions especially Scoobies. Basically they talked me out of it.
Ill just need to tell them more forcefully next time I get a chance!!

Currently my Warranty is intact, although the K&N could get me into trouble. This again I reckon is worth a few bhp. Why? because I noticed a difference in the engine/exhaust note at full chat.

The thing is I hear things with engines that others dont notice, this may be something to do with the fact I have been taking engines apart for 25 years and know what sounds right. Not much of an argument I know. But as John says this a public area open to give your opinion, because with a subjective opinion from as many sources as possible an educated decision can be made. I am airing my opinion and that should not be undermined.

John keeps on mentioning Star rolling road, as we all understand the figures from this rolling road differ from other rolling roads. This is all down to calibration of the equipment and the equipment in use. That is why it is better to compare cars on the same rolling road so that the figures mean something. But, we all know, that ambient temperature/humidity/underbonnet temperature/fuel and fan facilities, not to mention the weight applied to hold the car on the rolling road all play a part in the figures.

Next week I am dyno testing two 5400BHP engines, and these arent the biggest I have tested.(I know doesnt prove anything, but then I have nothing to prove)

Just my opinion
Dont flame me!!

Beastie

Beastie

iTrader: (2)

http://dyno.scoobynet.co.uk/uk/jason_jarvis.htm

Interesting reading and without a K&N filter too!

Hope you dont mind Jason! Thanks.

[Edited by Beastie - 6/27/2002 4:21:28 PM]

john banks

If it is a panel filter you might get one BHP. If it is an induction kit you will probably lose a fair bit off the bottom end in exchange for a bit up the top as the PPP is not mapped for it. There is a nasty lean spot as standard coming onto boost shared by the PPP and the AE800/1/2 which is exacerbated by most induction kits, and you can see it filled in on the dyno when you add fuel even to the standard car.

When Prodrive quote 237 BHP on an engine dyno for the PPP it puzzles me how adding an induction kit or panel filter makes it 270 BHP. I'd buy you a lot of pints if you can get that on any UK dyno with your downpipe still in place, and I'd buy you a pack of crisps to go with it if you could then outdrag an STi 5 or 6 Subjectivity is nice but where are the 270 BHP dyno results? However, I think we all agree that chassis dynos in common usage are inaccurate enough that only comparisons on the same day and conditions are possible and that there are a lot of variables to account for, but to double the Prodrive quoted improvement attributed to the PPP when it only runs 2 PSI over standard is optimistic.

Regarding exhaust back pressure, Julain Edgar (21st Cent Performance) writes:

"Contrary to popular opinion, any exhaust back-pressure harms performance. There is no properly tuned engine where increasing exhaust back-pressure causes an improvement in power, torque or fuel economy. However, the maximum effect of exhaust pulsing and scavenging may come from an exhaust system small enough for some exhaust back-pressure to be developed. This means that for naturally aspirated cars, as big an exhaust as possible should be used once the tuned length part of the exhaust is passed. Turbocharged engines simply require the biggest exhaust that can be fitted after the turbo."

The author goes on to quote tests on Subaru flat fours that show in none of multiple configurations did increasing exhaust back pressure improve performance.

Not saying this is gospel, but the bigger the exhaust the better on all the Subarus I have played with so far.

The PPP ECU fuel map is virtually identical to the AE800 map for all the light throttle and cruise areas, and on full throttle uses richer fuelling by up to 0.6 AFR points. At peak power point it is mapped for 1 PSI more and a 72.2% v 70.6% wastegate duty cycle, and typically in the midrange and top end it runs about 3 degrees more ignition advance. So presumably the light throttle/cruise gains are a result of the exhaust.

BTW I am not undermining you I am just politely disagreeing. No offence intended or taken. Prefer to keep it as a technical discussion that way we all learn a bit more and our cars perform better.

[Edited by john banks - 6/27/2002 5:05:31 PM]

SCOSaltire

JB
one day u are gonna be able to jump through multidimensions

i am gonna have to read this again this evening to get it to sink in.

does it follow then that the biggest drain pipe possible from the turbo back would be the best option for the prodrive chiped car, assuming the std DP is still there?

(thinks about keeping away from possible overboost and then changing restrictors, and then having probs when its frosty - after being decatted.)

not that I am gonna get a drainpipe exhaust.. u understand.
i am not worried about scoobysport loudness
but the blitz loudness could cause some probs

john banks

Change the downpipe first - that is far and away the performance killer, then go for the least restrictive drainpipe you can tolerate the noise of. For me that is the Magnex downpipe, magnex resonated centre and a magnex 6x4 - should be quite quiet with the SS headers on too. (There is no particular magnex brand loyalty BTW just what happened to be available as a happy medium). I'll give you a hand with the restrictor if you need it if you buy me a bag of crisps Your car doesn't boost monster high so it would probably be fine just fitted and enjoyed. My car after being PPP'd peaked to 18-19 PSI on a hot day - each car seems different. I have some hose and some drill bits if you need me

Whenever a car has good breathing on it it retards less and shifts much better. Have never been in a really quick car still with the original downpipe in place (of course it could be done). At present I am running with a decat DP, T-uk's straight through centre and the original pea shooter backbox. It is about the same in performance to the PPP centre/backbox combo with the downpipe and has that standard look and (mostly) sound.

Beastie

iTrader: (2)

John
First of all I appear to be running 4.0 psi more than standard (held) and not 2psi as you mention.
Jason made 252bhp with a PPP should he write and complain to Prodrive?
I believe the authors comments about exhausts is fair, however, he is talking about a perfect system, he is not talking about a system with a restrictive catalyst in the downpipe, a non restrictive centre and an STI backbox.(i.e. a dogs breakfast) I know that Prodrive undertook extensive testing and logging to make the performance upgrade as effective as it is. As performance car put it, the PPP is a perfect blend of specially chosen parts, but without one the others dont function correctly.

Interestingly you have not mentioned manifold design, which is THE most important factor in an exhaust system.

It is well documented on this bbs that exhaust systems play a big part in the torque/power curves and in fact all manufacturers can show you the benefit of their system over others. Gas flow is governed by pipe bends/transitions/diameters (increasing and decreasing where gas flow can be accelerated then used to draw the gases behind out of the exhaust and create a supercharging effect) and different designs will always show different results. Turbo charged cars are more complex to calculate because there is always a restriction/back pressure in the system caused by the turbine rotor and compressor power taken.

Induction is interesting also, with a longer inlet tract producing more torque low down and a shorter one producing more power higher up. That is why many cars have inlet manifolds that automatically switch from long to short. Whats the point? well the point is that changing your inlet system will have a direct effect on torque.

Perhaps the most subjective things I can say about my car is that it is faster than it was before, with the PPP backbox low down torque is increased which helps carry the car faster up into the power band. Boost pressure is more than I expected. The car picks up from as low as 2400rpm. I have sufficient power for my current needs I agree that your car with the downpipe fitted was faster and noisier. Therefore, as a conclusion my BHP cannot be as high as I think but remains to be seen.

Beastie

SCOSaltire

beastie
whats this Cone Effect?

john banks

The dyno which Jason was on also rates some standard cars at only 10% less. I got over 290 lbft and 290 BHP on the same dyno in a lower state of tune than I presently run on a smaller intercooler on a hot day, but it doesn't mean I remotely believe the figures and think I have any more than 270 BHP now despite the larger turbo running at 20 PSI and a larger intercooler. It is nice pub talk, but I would be kidding myself, hence all the threads "everyone has 320 BHP". The phrase I think is "bull$**t power figures."

Having tried the PPP ECU with other exhaust bits it actually works better and the idea of it being mapped to an exhaust is a bit fanciful when the fuel map has a few columns added for high load and the ignition map has been systematically shifted by changing whole column headings at a time - it has not been "mapped". Since the PPP map has 15.7 PSI as the midrange target and the standard ECU has 13.7 PSI as the target then if you are running 4 PSI more than you were before then it wasn't running properly before or you are running the PPP at too high boost levels and will eventually suffer fluctuating boost, or your gauge is reading very different to your MAP sensor. It sounds like the dealer has misjudged the size of the restrictor if in the summer you are getting over 17 PSI, because in the winter you will probably see over 18 PSI peaks. Certainly the spikes you get will vary according to the conditions and you are stretching the range where closed loop boost control will operate correctly. To avoid cold weather/high load/high octane spikes you have to have the target boost around or higher than what is achieved in hot weather to allow for the inevitable peak you will get in cold weather. So your restrictor orifice is too small for your ECU. With the way the JECS does boost control if you are getting target boost in lower gears in hot weather you are in for trouble when it gets cold.

The exhaust restriction test used an adjustable restriction in the exhaust system and a very large exhaust with very little restriction after the turbo. The restriction was then increased, and in all but one car there were no gains anywhere from increased restriction over the minimum possible, and in most cases the gains were most obvious at the bottom end. On the one car that did lose the ignition timing was suboptimal when the restriction was removed.

So back to the topic - have the least restriction from your turbo back as possible. Some of these exhaust will be noisy you need to pick the combination you are happy with. Whatever, the standard downpipe on the Impreza was one of the most restrictive in tests and added far more restriction that a really bad backbox did.

Pavlo

The test you mention isn't wholly representative though. When it comes to exhaust length tuning, you are looking at pressure pulses, not just gas flow in the exhaust.

Pulse hitting an open end is reflected back as a negative pulse. A pulse hitting a closed end, is reflected back as a positive pulse. I think it's feasable for exhaust pulses to traverse the turbo, as it's not that restrictive. So I don't think it's unreasonable to expext that different designs of silencer, could change the exhaust scavenging.

If the PPP backback has a resonator section built in, I would imaging this is seen as a closed end, whereas the Blitz, SS et all just creates an open ended pipe. So don't you think it's possible that while the PPP increases backpressure (bad thing we agree) it may, at low speeds create some pulsing effects that the straight through silencers don't?

This is all very tenious, as I was led to believe that the tuned section of the pipe ends at the start of the first absorbtion silencer, as it kills the pulses after it.

I wouldn't dismiss one exhaust against another, purely on the basis of back pressure, as there is more going on that pure flow.

Paul

[Edited by Pavlo - 6/28/2002 11:43:12 AM]

john banks

Maybe, but the PPP box kills performance across the range on my car compared to a drainpipe style exhaust. Others say they gained substantially when losing the centre section as well. These are difficult things to test back to back to control all the conditions and resource properly. Does anyone have anything semi-objective that shows an increase in performance anywhere in the range by increasing the exhaust back pressure? The test I mentioned was conducted to try and build a best of both worlds exhaust with some restriction low down to help torque, but the restrictions only lost torque across the range. Maybe the simple restriction was not as effective?

Andy.F

Regarding exhaust backpressure v power, I wonder why the presumably smart engineers at Yamaha have invested in a new twin shaft EXUP (exhaust back pressure control valve) for their latest superbike rocket, the 2002 R1 ?

This bike is running things like titanium exhaust manifolds to save weight yet they bung in a valve to build exhaust backpressure This bike is widely praised for its torque spread.

Pavlo

I think the amount of restriction is not the thing that gives extra torque, rather the manner in which it is applied.

If you think in terms of variable inlet manifolds, (BMW v8 for example), at lower speeds, the 'flaps' are set to give a longer inlet tract. Now this is definitely going to increase pressure drop over the length of the manifold, but the net result is an increase in torque over a specific rev range.

Now if I was to add an equivalent pressure drop, but retain the short inlet tract, I wouldn't get the increase in torque at low revs. In fact the restriction would lose power.

The exhaust back pressure test is akin to the second method of increasing inlet pressure drop, and the results are not surprising,

Paul

SCOSaltire

the new elise 111 has a flap in the right hand tailpipe that is closed for lowdown torque, but open for more performance when up the revs or WOT.
but thats a rover 1.8 na engine
so is the bike

i wonder if Mike Wood would share some technical knowledge here..?

(edited to remove the ? as the bike is na)

[Edited by SCOSaltire - 6/28/2002 12:16:29 PM]

AndrewC

Why do WRC cars run a smaller diameter exhaust on tarmac than on gravel?

Could it be something to do with needing a flatter torque curve rather than maximum power?

WRC engineers have obviously not read the right books

john banks

The author could be wrong, or overgeneralising?

Could the restricted exhaust on the bike and the Elise still be in the tuned area? Certainly Ferrari variably restrict their exhausts but that is for noise reasons I thought?

WRC - could regulations, restrictors, external wastegates or antilag also be factors? Not saying they are, but just because WRC do it doesn't necessarily translate to a road car?

Does anyone have any dyno results that might suggest a more restrictive exhaust helps on a Scooby anywhere in the rev range?

Prodrive need to retain emissions and noise regs with their pack so you cannot expect it to be the last word in performance especially when the original horrendously restrictive downpipe is retained. And the backbox sound is quite nice if you like the "F15" whooshing sound, which is arguably the sound of restriction. Certainly when you swap it for something else it feels like you pulled a few bananas out the exhaust.

[Edited by john banks - 6/28/2002 1:21:09 PM]