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200 Cell Cats

Which of the two designs is the quietest? from a db level perspective?

Does anyone know the cell rating of the standard Cats?
 
Martin996RSR said:
I did a lot of research on it before buying the non-X-pipe cats. It was because there was slightly less power to be had from the X-pipe and for me, that performance mattered more than the more refined sound you get.

I did a fair amount of "internet research", which of course should be taken with a pinch of salt. Opinions varied as to what was better, with some dyno's showing non-X, some showing-X. Do you have definitive data on this?

I was thinking this morning of dyno'ing my car as-is, really to provide a baseline against which to judge the new engine when it arrives next year.
 
Taken from 9e's website regarding Kline system which answer a few questions in the thread

"The first point that stood out, was the catalyst design. 600 cell oem cats, and absolutely no balance present in the factory exhaust. replacing this unit for a 200 or 100 cell sports catalyst we were able to achieve some moderate power and torque gains. the second design alteration was to remodel the way in which the exhaust gases interact from opposing banks. Replacing the two piece design for a single piece with our trademark tight radius, laminar flow X pipe, we were able to alter the exhaust pitch, and smooth out the imbalance, this resulted in a far more high revving race car like sound. "
 
Dammit said:
Martin996RSR said:
I did a lot of research on it before buying the non-X-pipe cats. It was because there was slightly less power to be had from the X-pipe and for me, that performance mattered more than the more refined sound you get.

I did a fair amount of "internet research", which of course should be taken with a pinch of salt. Opinions varied as to what was better, with some dyno's showing non-X, some showing-X. Do you have definitive data on this?

I was thinking this morning of dyno'ing my car as-is, really to provide a baseline against which to judge the new engine when it arrives next year.

By all means do your own research. I did mine for the purposes of my own decision. My research was done over a year ago and I'm not going to track down my sources now to satisfy your chest prodding. Part of my research was probably the content linked to on the rennlist site, and another part was a paper on gas flow in tubes and the effect of bends of varying radius. There were probably other sources too. I studied aerospace engineering at uni and I'm used to thinking critically about engineering solutions and informing myself on the science behind the dyno charts. Given you're so critical of internet sources for information, perhaps you could tell me what non-internet sources you would use? I must admit to not having tried my local library for books on 996 empirical exhaust testing, maybe I should have done.
 
I seem to have given offence, which wasn't my intention.

I was asking in the spirit of genuine curiosity whether you had something that was rather more authoritative then what I'd found using Google - there is much written about these cars that simply isn't true when you dig into it.

Anyway, no chest prodding intended I assure you.
 
Sorry Dammit, I probably went a little far.

Basically though, you don't need to read the papers that I did in order to be able to guess that a tight radius 180 bend in an exhaust pipe not far from the collector is going to be more restrictive than an only slightly bent/mostly straight pipe.

Add in the joint between the two pipes at the point of fastest gas velocity (the outside edge of the bend) and you're adding turbulence that probably does more to rob power than any gains achieved by any scavenging effect.

That's why it's obvious that an X-pipe exhaust on a 996 is less efficient than the alternative.

A better solution would be to put a balance pipe between two non-X-pipe cat pipes. You would get the X-pipe sound but none of the losses. There is a Motortrend Youtube show that has done a load of exhaust testing on V8s and they've shown a balance pipe to give negligable gains on the dyno.

If anybody still wants an X-pipe (wel they do look cool I suppose) then get one custom made with the biggest radius bends that you can. My research done whilst trying to figure out the least loss exhuast system for a 996 taught me that bends in the exhaust for 58mm pipe needs to be at least 8 inches to not suffer from serious losses, and there are more gains to be had by making the radius larger.
 
Interesting- what are your thoughts on manifolds?

I need to get those next, and of those available I am likely to pick the Cargraphic 1.75" primary ones- but that's based on diameter rather than radius of bend. Porsche (for the 3.8l X51) pick a three into one 1.85" design, rather than the long separate primary/equal length design of the Cargraphic.
 
The aftermarket manifolds I've seen are all very similar in design and all subject to the same restrictions:
1. The need for ground clearance, so having a tight radius bend very close to the port (a real no no for decent exhaust performance)
2. The need for the collector to be before the point at which the stock exhaust joins the stock cat pipes. - The primary pipes need to be longer and straighter than the packaging challenges allow in order to maximise torque in the rev-range that road cars are driven in.

After market manifolds give a slight increase in HP at the top end beause their greater diameter gives more flow at high RPM, but they almost certainly rob a little torque lower down the rev range where the smaller diameter stock manifold is most efficient. I wouldn't mid betting the same car would feel slightly quicker on the road with the stock manifold and slightly quicker on the track with the after market manifolds.

What this boils down to, is that in my opinion you'll probably get the same benefits with the cheap Chinese stainless ebay manifolds as you'll get with the posh Cargraphic ones, and for a road car that isn't driven by a hooligan you may well be better off with stock manifolds.

Of course, much of this is conjecture and ideally a forum member will get some serious dyno time and do some back to back testing.
 
I did buy a pair of the Chinese manifolds, but they measure 1.65" so I had a crisis of confidence. They are 10% of the cost of the Cargraphic ones however.

My engine will be 3.7l with a rev limit 1,000rpm higher than stock, so (hopefully!) it'll want to move a lot of air at higher revs.

The radius from the exhaust port is a *****- no getting away from the ground clearance issue. That said, I wonder what GT3-RS manifolds look like, design wise?
 
Given the capacity increase and rev limit increase you may well find there are gains to be had from the larger bore Cargraphic exhaust then.

What are you doing on the induction side? From what I've read there are real gains to be had from bigger diameter throttle bodies.
 
:popcorn:

Kudos re. the rather mature and balanced exchange at the top of this page BTW

Backstory: I've ended up with cargraphic 'sport' backboxes, top gear 200 cell x-pipe and OEM 3.6l headers coated by zircotec


Crawling under the car I don't see astounding evidence of the zircotec coating anymore... and as much as I appreciate the top gear part, I'm looking to fit as high grade a CAT as I can afford - hence I was 'future planning' to compliment the backboxes with 1.75 cargraphic headers and CATs (you've no managed to make me question the headers again!... and the x design!)

Q1: do we think there is any magic impregnated benefit to my oem headers having been "plasma ceramic coated"?!!

Q2: why the bloody hell does no one see to do an equivalent design to the OEM headers, just in higher grade material?!!



BTW - have you had a look at the Supersprint 996 headers.....?
 
coullstar said:
I'll be honest I went x-pipe for the sound and no other main reason. Havent really felt any difference in power either way so Im happy.

I totally appreciate the benefits of a balanced system.

Sound is the primary reason I want 200's.

What's the difference in sound between straight and X?
 

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