PSE and power gains

Ess_Three · Dec 2, 2007

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.

Diesel130 · Dec 3, 2007

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 ?

M030 · Dec 3, 2007

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.

Robertb · Dec 3, 2007

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...

Ess_Three · Dec 4, 2007

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!)

Robertb · Dec 4, 2007

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...

Rodney Naghar · Dec 4, 2007

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!

Richard_Hamilton · Dec 4, 2007

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.

Rodney Naghar · Dec 4, 2007

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.[

]

Ess_Three · Dec 4, 2007

ORIGINAL: Robertb

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.

Ok...I couldn't comment, sadly.

It would be very interesting to see how your car dyno'd with normal silencers, if you are ever at a loose end...

...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...

Richard_Hamilton · Dec 4, 2007

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.

Ess_Three · Dec 4, 2007

ORIGINAL: Rodney Naghar

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'?

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 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'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.

Ess_Three · Dec 4, 2007

ORIGINAL: Richard Hamilton
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.

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!)

Ess_Three · Dec 4, 2007

ORIGINAL: Richard Hamilton

As Glen says, he would have to put the standard exhaust back on to get a comparative reading betweel standard and 'quiet PSE'.

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.

I just think it would be interesting to see the curves, and see what affect it has when switched between modes.

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.

Richard_Hamilton · Dec 4, 2007

That would be great! Thanks!

Ess_Three · Dec 4, 2007

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

watlina · Dec 4, 2007

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.

Diesel130 · Dec 5, 2007

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' ?

Rodney Naghar · Dec 5, 2007

LOL put me down for a Hamilton Zorst (tm) [

]
Hold on im still not done talking up 996 turbo priced yet!! [8D]

Richard_Hamilton · Dec 5, 2007

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......"