De-Plenum'd my car yesterday - Big Improvement
 

I posted a thread a few weeks ago asking if anyone else had been disappointed with the RSS plenum for the 997S. My own experience of adding the plenum to my car (stock apart from AWE cats and mufflers) was that it lost torque, very noticeably, right across the rev band (with the possible exception of between 5000-6000 rpm). This was contrary to the general concensus - that the plenum had a positive effect on most people's cars.

Greg at RSS pointed out a couple of small possible install errors (centring the plenum properly for example) that I took care of. I ran the car with the plenum for several weeks but it never felt quite right. Anyway, yesterday, I removed the plenum and replaced the stock, plastic tee. What an improvement! All the extra mid-band torque that the installation of the cats gave me is now back (with the plenum, it had disappeared - it was like stock again) and the car fairly flies from 6000rpm to the red line. The overall experience is a huge plus. The only tiny loss is at approx 5500 rpm but the gains everywhere else are ten times what's been lost.

I wonder why my experience is so different to everyone else's? Has anyone else tried reverting to the stock tee to see if there really was any real improvement with the plenum? Installation of the plenum does make the engine subjectively smoother, but I believe that's because it isn't pulling anywhere near as hard.

The one thing that I did notice on removing the plenum is that it's a different size and shape to the tee. The plenum's 'nose' where the throttle body attaches, is about 1" longer than the 997S tee. I didn't have the chance to take any pics, but if you put the tee and the plenum together and line up the outlets (they're exactly the right size and dimensions by the way) you can see the 'nose' is simply the wrong length for the 997S. The plenum is the right part I think- it says 996/997 on the casting - and the tee is the correct 997S part.

So for me at least, it looks like the plenum causes significant losses across much of the rev band in return for a tiny, localised increase at 5500rpm. The plenum is now on my shelf and I have a faster car as a result.

I know there are some 6-speeders looking to have dyno runs done with the plenum. I'd only suggest they check very carefully what happens between 3-5000 rpm (where the biggest losses were on my car) and over 6000rpm (where again my car was slower with the plenum) not just at 5-6000rpm where the major 'gains' are claimed.

I know this view will be controversial, but I can only report what I find. To be totally fair to the plenum (unless Greg tells me I've got the wrong part, given it's a different size to the tee - then we re-assess) I will give it another try once my AWE headers arrive and are fitted. I don't really see why this should make a huge difference however.

Ian W

Ian, the bottom line is, it's your car. If you put a part on that in your opinion didn't live up to the hype, cool, no sweat, put the old one back on and you still own a PORSCHE!:D:D Having fun is what this is all about. Remember? Lifes too short to sweat the BS. Get in that car of yours and drive it like you stole it.

You mean there's any other way? :-D

Ian

Ian,

Very good post. Thanks for that. I too have the plenum, but realized a bit of a gain with it, possibly due to the fact that I have a blower. I could see that helping.

Thanks for the honest analysis. Rock on.

Jared

Interesting comments. I have been considering this mod and I am awaiting the dyno reports. We will see.

I am also waiting to see what happens on the dyno.

Thanks for the post Ian, maybe the right hand drive makes every thing work in the opposite.;)

hmmm. makes me want to hold off...

thanks for the input . someone just talked to me agbbout installing them but will hold off for now...

mk

I knew it would be something simple.... :D

Ian

Try reinstalling it and driving as fast as you can in Reverse. That way you will be on the left side of the car hilarioushilarious but don't hit anything!

This will totally, scientifically, and positively work. Yeah. As long as you only use your mirrors. You turn around to look out the back window and it sounds like a Hoover vacuum with the flu.

Yeah. Of course I'm serious. Geesh.

Actually it would sound like a hoover with a cats tail stuck in it hilarious

interesting experience

[quote=blakt out;1796946]..... it sounds like a Hoover vacuum with the flu......quote]

Only with the factory exhaust... :)

Ian

that's usually what happens when you put an obstruction in the path off air flow. maybe you installed it upside down?