PSE and power gains

Just wondering what peoples thoughts are on any power gains with PSE? I've dyno'd my car several times and each time I've tried it in the default position of PSE 'on' in the noisy mode...and again with PSE switched 'off' in the quiet mode. Porsche claim no gains from the PSE. That's not what I've found... Now me being me, I'm starting to think about this... I wonder what a standard 3.6 C2/4/4S would make with the standard non-PSE exhaust? I wonder if the PSE adds nothing, but does artificially 'restrict' in quiet mode, compared to the standard fit exhaust? I wonder if I can be bothered fitting the pair of brand new 996 rear boxes I have in my garage just to find out? All I can say...is that 3 different dynos, over 3 years, have proved my car to make substantially more power with PSE in the noisy mode.

Well, isn't that quite logical. Surely the principle of any naturally aspirated engine is that power is going to be greater if you can improve the flow of air/fuel in or exhaust out of the combustion chamber ?

There is officially no HP increase with the PSE because PAG would otherwise have to certify another engine that has just a couple of HP more. In reality, there is a power increase.

Go on then, do tell- what are the readings with switch on and off? I've always felt my car was quicker in noisy mode, but a glorious noise is worth at least 50hp! It'd be interesting to see the dyno figs to prove it...

Ok... I've dynod my C4S on 4 different occasions...twice at one place and one each, at two other places (I'll spare you the names and dyno types...but that lot includes 3 different dyno manufacturers) Each time a run has been done in 'noisy' mode... Then a run in 'quiet' mode... Then where possible a third run back in 'noisy' mode to verify that any drop in output was down to the exhaust and not the engine getting hotter and backing the timing out... Basically, the average is between 10 and 15 BHP less - corrected, at the flywheel - than the engine produced in quiet mode. It seems logical to me...but the amount of gains, from an exhaust only, seems slightly too large. Anyone who has used dynos a lot will know how innacurate they can be...and how you don't always get the figures you were hoping for...so take the peak readings with the preverbial pinch of salt. My C4S made 308 BHP this last time (previously it's made 312, 318, 316, 321 etc) with PSE on and 294 BHP with it off. Sadly, I've not had the chance to check a similar 996 non-PSE to see what it was making on the same day, on the same dyno, so the accuracy of my engines output against other 996s will have to remain a guess. So, despite Porsche claiming that the PSE adds nothing...either it does, or in quiet mode the rear boxes of the PSE exhaust actually restrict the flow as well as making things more quiet....which I would suspect is unlikely. To know for sure, I'm going to have to fit a set of standard 996 rear boxes and head off to the Dyno. Not sure I can be bothered... But there you go...interesting stuff. (I thought so anyway!)

It is indeed intesting- thanks for posting. FWIW, I had standard pipes on mine before I had PSE fitted, and I reckon the PSE is noisier than standard, even in quiet mode which would indicate less restriction on the face of it. It would be very interesting to see how your car dyno'd with normal silencers, if you are ever at a loose end...

FWIW after I fitted my sports exhaust (basically a copy of the pre-facelift 996 sports exhaust) my idle revs have dropped (I'll have to check exactly by how much) and so did SNDa's (another PCGB member with a 996 with the same exhaust), so that would indicate lower back pressure (it is constantly 'on', using a bypass pipe). Do you get the same drop in idle when the exhaust is 'on'? (Edited to say) I posted earlier on (I'm not sure where my post went?) that I am surprised by the difference in your cars output compared to Porsche's claims of 320bhp with a stock exhaust (not withstanding rolling road losses). It seems you are losing the equivalent of an X51 pack worth of power (when your exhaust is on 'silent') which Porsche charges around £8k for!

I don't think it's all about reduction of back pressure with a sports exhaust. The sizes and lengths of pipe, silencer volumes, baffle positions and shape play a big part in any tuned exhaust system. When I used to race karts (years ago - and did I mention I raced against Nigel Mansell a few times?) we used to shorten or lengthen the exhaust to suit the track. It could make a small but significant difference to the engine torque curve. Also, I used to design 2-stroke opposed-piston diesel engines in a previous existence, and for fixed speed applications (generator sets etc) we would also tune the exhaust length. The aim was to reflect a negative pressure pulse off the end wall of the silencer to reach the exhaust ports at the correct time in the cycle to give a 'suction' effect and draw the exhaust out. I know I'm talking 2-strokes and 100 years ago here, but I'm sure there are similar principles involved. I have no doubt what you are saying is correct, and it is an interesting observation. Please don't think I'm throwing cold water on the discussion, and it may well be that bypassing one of the silencer compartments with a PSE you are effectively tuning the length in some way. It would be interesting to see power and torque curves of the quiet and loud positions, to see if the gains are throughout the rev range.

You're such a dark horse Richard! [ ] Very good info there...how would you explain the loss in power on a PSE'd car? I'd be very annoyed to learn that if I had a PSE in quiet mode I'd be down all those horses on stock, and no extra horses on 'on'? I'm guessing the exhaust was never really designed properly to be 'off' as the placement of the diverter valve makes the system badly tuned (ie worse than stock). But if Robertb is correct and the PSE in quiet mode is louder than stock, that doesn't really make sense either. I'll just get my coat [8D] Very interesting thread though Ess_three, as I've never seen any figures for a dyno'd PSE system before.[ ]

Ok...I couldn't comment, sadly. ...and me being me, I think I'll have to try it one day just 'because'. It'll annoy me if I don't. I have to be careful though...messing about with 3 cars at the same time will land me in hot water with 'her indoors' and the doghouse is getting all to comfortable as it is...

As Glen says, he would have to put the standard exhaust back on to get a comparative reading betweel standard and 'quiet PSE'. I just think it would be interesting to see the curves, and see what affect it has when switched between modes.

I can't say I've noticed Rodney. Sadly, I'm 150 miles offshore on an Oil Platform at the moment...so I can't pop to the garage to check. I will though...when I get home. I'd urge you not to read too much into the figures as this dyno just happened to be the latest one I've used...my Golf GTI which makes 195 BHP on several dynos but only makes 180 on the dyno I had the C4S on this last time...so it appears the dyno does under-read slightly, compared to what I'd expect.. However, accepting that the figures seem a tad low, the drop in power with PSE on/off would seem to be far more than I'd have expected.

I personally think the same way. Looking at the PSE I can't see that it's any less restrictive than a standard 996 rear box...but it does change the tuned length, and resonance properties - presumably the resonance properties are where the 'tuned' sound comes from. All very interesting (to me at least!)

Despite mine coming with PSE fitted, I have a pair of brand new 996 rear boxes in my garage...so maybe one day i'll prove one way or the other. Ideally, I'd need to sweet talk the dyno place into swapping them over whilst I'm there, to keep tyre pressures, ambient air pressure & temperature, fuel type and dyno settings the same, for the most accurate results possible. If I hadn't been so rushed when getting ready for heading back offshore, I could have provided this information. I have the dyno plots, of PSE on and PSE off, overlaid on the same graph, showing power and torque (also I have air/fuel ratio and other such information) Basically, PSE adds power from pretty much idle, but does take a marked climb above where the last stage of VarioCam kicks in... It's a pretty linear gain though. I can't remember if the torque was affected. If people are interested, and you can wait a week, I'll scan the plot when I get home and post it up.

That would be great! Thanks!

Right you are... Further info in a weeks time.

I've been looking at the various options for a PSE for ages but can't bring self to spend the £1200+ Porsche want. I did buy a set of brand new rear boxes cheap on eBay with the idea of modding them but they are still sat in the garage after a year. On to dyno-plots. Here's one I had at done a couple of years ago at Weltmister Silverstone on a club dyno day. Just for comparison for when Ess_Three posts his up. It's with my completely standard exhaust. plot of my 2004 C2 I must get another one to see if things have changed. Subjectively it still feels about the same power, it's just me that wants to go quicker.

Now, I have a plan. Porsche's exhaust upgrade is expensive, sounds good, but possibly does funny things with the power output. Cheap performance exhausts on ebay seems to work, but we don't know how they affect the power. But Richard has a) the know how to tune exhausts and b) a manufacturing business to make them. So how about Richard sets up a new business to buy in the cheap exhausts, optimises them for power and sound and then sells them to all us 996 owners at a price which is attractive to us, but allows Richard to buy a 996 TT and retire in (say) 5 year's time ? Sounds like he could do a version that, rather than just an on/off switch, would have a switch that selects between - going shopping - fast B road hack - Motorway (UK) - Motorway (Germany) and - Track Day settings. What do you think ? P.S. Do we need to ask who won, Richard ? You or 'Red 5' ?

LOL put me down for a Hamilton Zorst (tm) [ ] Hold on im still not done talking up 996 turbo priced yet!! [8D]

Now if I can make £200 on each exhaust, and a cheap TT will cost about £45k, I only need to find 225 cheap exhausts to modify and get 225 of you to sign up, and it's sorted! That's not allowing for development, so maybe 300 would be closer to the mark. [ ] [ ]. I've had better business propositions - I'll stick to working far a living, thanks! [ ] [ ] Me and my mate "Nige" were both big lads for Junior class (I'm talking 1965 here!) so used to struggle against 4ft midgets with a much better power/weight ratio. He had a much bigger share of success though - far more talented than me, quite obviously. I don't actually remember much about the actual racing to be honest, and I'm sure he wouldn't have a clue who I was, but my daughter found some old programmes in the loft. "Is that THE Nigel Mansell in your race?" she asked. "Oh, yeah, Nige and I go way back......"

Just to follow up: Here are a few dyno plots to back up what I was saying... Again, don't read too much into the numbers - I'm not 100% happy with everything...I think the car should have been run in 4th, not 3rd...but hey-ho...the graph show what they show. Blue lines = PSE 'on' (noisy) Red lines = PSE 'off' (quiet) General: Power and torque on the same graph / same axis.

Power:

Torque:

Air / Fuel ratio

Very interesting.....did he give you an explanation of the figures and the effects? The AFR curve is interesting as in the 'On' position the Lambda sensors are making the engine run so rich. Why is that? These are the first figures I've ever seen for a PSE, excellent post! It just seems that not only do you not have any power gains, but you actually see power/torque losses and worse MPG figures. Anecdotal evidence of people saying they feel more power with the PSE 'on' now seems right, but not because of actual power gains, but because of a power loss with it 'off'! Buyer beware.

I drive a good few miles (20k since end Feb), with PSE on and off for long periods (i.e. tanks' worth at a time)depending on my mood! I have not noted any difference in the MPG, nor any meaningful difference in engine delivery. Sometimes I'm sure it just feels livelier in noisy mode, but on occassions I've actually felt it runs better in quiet mode, perhaps because it's less noisy and hence feels like its working less hard. I suspect its broad as its long. It'd be interesting to get mine done on the RR for more evidence, and get someone to put some standard pipes on as a control... I wonder if I could get a mag to sponsor such a venture... I know the guys at Total 911, I may see if they'd be interested.

I have a spare set of facelift stock exhausts lying around if anyone needs them to help with these investigations

Cheers Glen - Really interesting figures. The only thing that I can think of is that there is some difference between the internal construction of the standard and PSE boxes. And, as Rod points out, the quiet setting of the PSE is somehow reducing power compared with the standard exhaust. It needs someone to do a 'before and after' to be sure though. I wonder if anyone has got any noise figures for standard vs quiet PSE? Maybe if someone is doing (/has done) a track day they could compare noise levels on a couple of cars?

As I have said, I too have a set of brand new std 996 rear boxes, sitting in my garage. Ideally though, you'd need to swap boxes on the same day, whilst at the dyno, to try to keep conditions as close to 'the same' as possible to get an accurate comparison. I'd prefer to use a MAHA dyno for this if possible though, as it at least gives standard Porsche power figures when corrected and used in 'coastdown' mode...and I think you should use the gear closest to 1:1 gearing too. But, regardless of which dyno is used and what the headline power and torque figures are, I suppose any on-the-same-day comparisons will be valid. I may well do the testing myself, just to see what happens. Sadly, to get a proper comparison, I think you'd need to use the same car to ensure differences in how the ECU is fuelling and setting the timing, individual engine performance, trye pressures, fuel quality etc can all be discounted as they will be the same on each run....so you really wil have to go swapping the exhaust over to get meaningful data. I'm pleased others find the data as interesting as I do. A magazine test would be very interesting...

No, no explanation... The place we were at is more of an Evo/WRX/STI specialist....and during a VW Rolling Road day.. I only gatecrashed in he C4S as it had just had new brakes fitted all round and I was keen to put a few miles on...and my Golf GTI was nice and clean tucked up in the garage! There are a few things I'm not 100% happy with, run wise...but it was done during a quick Rolling Road shoot out, so I can't complain. The differences are thee to see though...and that's twice I've seen differences on this dyno alone. No idea... And to be honest, I'm not a true believer in the old 'wideband lambda up one exhaust' to get an accurate measurement...it gives an idea, but I'd prefer to see the AF ratio from a properly installed wideband, or tapped off the std sensor, as I'm led to believe they are wideband as standard. None the less...there is a strange difference between the two curves, for an identical car, run 5 minutes apart with only the exhaust resonance changed. Unless, like was suggested previously, the pulse tuning of the rear boxes is indeed affecting the engine to such a degree that it's visible from the AF ratios? I'm glad you find them interesting...I certainly do. I'm not sure about the losses aspect... I'd need to check the car on standard exhausts to know. My GTI reads low on this dyno compared to my 'control' dyno. It reads 182 BHP instead of the more normal 195 BHP...so 13 ish BHP in 200 BH...or a possible 20 BHP in 300? So, the engine is making standard power I believe. Assuming this is the case, and PSE 'off'' makes the Porsche factory dyno'd 316 BHP... then PSE adds to this. Or, as you suggest, PSE robs lots of power. Due to TUV approval, and the way Porsche - like all German manufacturers - tend to play down the power, to some degree, I'd put my money on my C4S making standard power with the PSE 'off' and a bit more with it 'on'...but in order to not have to type-approve PSE, and not have to accept insurance penalties for PSE equipped 996 owners...I'd suggest the power gains are played down. Might be wrong though... Which, sadly, brings me back to another day on the dyno...and a spot of exhaust swapping, to confirm one way or the other.