PSE and power gains

[Ess_Three]

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.

 

[Ess_Three]

Power:

 

[Ess_Three]

Torque:

 

[Ess_Three]

Air / Fuel ratio

 

[Rodney Naghar]

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.

 

[Robertb]

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.

 

[Rodney Naghar]

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

 

[Richard_Hamilton]

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?

 

[Ess_Three]

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...

 

[Ess_Three]

ORIGINAL: Rodney Naghar

Very interesting.....did he give you an explanation of the figures and the effects?

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.

The AFR curve is interesting as in the 'On' position the Lambda sensors are making the engine run so rich. Why is that?

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?

These are the first figures I've ever seen for a PSE, excellent post!

I'm glad you find them interesting...I certainly do.

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'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.