Possible Group Buy of H&S Exhaust Systems ?

[Jamie Summers]

Guys,
I've long been concerned about track day noise tests in relation to my de-cat / Cup pipe / open airbox set up. Whilst I've not yet been banned from the track for noise I feel it's only a matter of time (reading 105 - 106 db static), especially given the way UK noise legislation seems to be going. I know others, particularly amongst the RS fraternity have also come up against this problem !

I've been looking for a solution (other than going back to stock) to reduce the noise to c. 99db static without reducing power - indeed, hopefully improving on the standard output.

With this in mind I have approached H&S to see if this is possible. Ian at H&S (logs on as 911SSC on this forum) is pretty confident that their very beautiful equal length stainless header system (with heat exchangers), coupled with a suitably tweaked back box can achieve these desired results, and still provide a decent power uplift (though may require a re-map to maximise).

Their 'off the peg' price is £1,600 plus VAT and fitting, but if we get 10 orders they'll do it for £1,400 (and presumably less if we can get more than 10).

Would there be any interest in this ?????

Jamie

 

[SimonExtreme]

Jamie

I have been meaning to reply to this s sorry for the delay. I am a big fan of H&S having had some impressive systems from them in the past. However, I am not yet certain that this is the way forward. In particular, I am not convinced there would be any benefit to a full system and suspect that just doing the cat back would give you the same performance.

The reason for this is that Colin at Ninemeister reports that the limiting factor on our cars is the fueling, rather than the breathing. The limit of about 300bhp on the standard set up seems to be because at that power, the injectors are runnng at 100% duty cycle. Now, it doesn't matter what you do on the breathing side, if you cannot get any more fuel into the engine and you can get the right amount of air for that fuel, any more efficency in the breathing would be wasted. There is the potential for a couple of bhp due to improved back pressure but that wouldn't be worth the cost.

So, to gain more power you need bigger injectors and for that you need to change the ECU. At this point, it seems that the limiting factor is the head and how much it can flow, rather than the exhaust. Now, this is where I need some convincing as I have never seen a car where the standard exhaust manifolds will allow as much flow as the head will allow. But to be fair to Colin, he has flow tested the heads and seems to make a lot of sense so again, there is a suspision that new equal length headers will not see any benefit.

However, I am very interested in a new cat back system that provides suitable silencing so we can get on certain tracks without loosing the flow characteristics of a cup pipe and rear box. This is something I believe that H&S can do for about £600.

 

[Jamie Summers]

Simon,
Seems to make good sense. Whether the equal length headers can really bring anything to the party I don't know, but I'm willing to defer to Colin on that one. Agreed though if H&S could do a suitably silenced back box without adding significant wait or losing out on the benefit of the cup pipe then that would be the thing to go for - though no idea if that is physically possible. ?????????

Jamie

 

[SimonExtreme]

Having spoken to them, I think we both agreed it could be done. The problem we have with the cup pipe and back box set up is that the back box is too small to make a diference noise wise but is very tortuous in terms of the way the fumes have to travel. What was proposed is a box to replace the cup pipe, one exit and no rear box. No G pipe either.

 

[Jamie Summers]

Simon - if they can do that for £600 and bring my noise down to c. 99db then I'd be very keen indeed ! (should also reduce weight a bit if removing the final box silencer)

Jamie

 

[Guest]

Why don't you try talking to some of the gurus in the US - give Steve Weiner at Rennsport in Oregon a call. These guys have done at least as much 964 tuning as Colin. I am not saying Colin is wrong but his theories and experience don't always match with what I would call conventional Porsche tuning wisdom. You can never have too much info on these subjects and I suspect that other tuners have found great benefit in replacing the std 964 exhaust with equal length manifolds like the B&B HEs. If you just want quiet then that's a much easier nut to crack.

Just think for a second. One of the main differences between the 993 engine and the 964 is the exhaust manifold design - 15+hp from this alone, yes?

 

[SimonExtreme]

Richard

Interesting observations and i will look into this. I suspect that I haven't said things clearly enough. I agree that a decent manifold will give you power hikes. However, there is a mximum power you can achieve with standard injectors based on them not being able to operate at more than 100% duty cycle (stating the obvious!!). Once you have reached max duty cycle, coupled with the correct amount of air, it doesn't matter what you do you will not increase max power any more. It is possible to increase torque at certain points of the curve but the gains aren't going to be great.

Now, the question is what is the best way to get to max duty cycle. Over here it appears we achieve this by chipping the OEM ECU and a few other mods. It seems that max power on the OEM ECU and injectors is around 300 bhp with torque in the region of 260 -270 lb/ft, depending on which rolling road you test on.

I am always looking for more info on how to get more power without going the whole hog and fitting new injectors and a different ECU. However, I think that is the route that is required to get above the power I currently have.

 

[SimonExtreme]

I have just checked out the Rennsport website and very impressive it is too. A very useful resxource! It actually seems to support what I originally said. It also gives good reason why in the US changing the whole exhaust system will have a big effect ,while it doesn't over here. The reason is, and I quote from the website

From 1975 until 1994, 911's sold in North America have been forced to comply with ever-increasing emissions standards and noise regulations. This has forced a re-design of the original exhaust system design that has cost a good deal of power

As we already have the original design, I think my comments are likely to be correct and this is suported by the sort of power gains Rennsport are claiming. It seems that once you change the exhaust, 964 dual mass fly wheel for an RS style, chip and drill the air box cup style, the anticipate power is what we are getting over here. However, I will be looking at the matter more closely over the next few days.