DIY 4200 sports cats

[mjheathcote]

I've bought from a forum member a pair of front pipes, with the pre and primary cats, that were replaced due to failure of one of the cats while under warranty.
My idea is to remove my fully functional pair, and fit these, suitably modified.
I intend to DIY a set of sports cats front pipes, having the facility at work of skilled stainless steel TIG welders!
So cut out the front pre-cats, open up the squashed section, cut out the restrictive 600 cell primary cats and fit 200 cell sports cats, then weld a Lamba socket behind the cats.
Looking at the squashed section, either 'larini' style dual pipes, or simply open up the squashed section making it deeper 'fabspeed' style.
Can I be cheeky and ask anyone with the larini ones, the pipe diameter of the dual pipes used under the steering rack?
Regarding the 200 cell sports cats, there are a few that sell them, anyone any experience of good ones to buy, and those to avoid?
For those that have not seen the US Fabspeed front pipes, see below.
Cheers,
Mike

 

[BennyD]

Mine is going up on the ramps over the weekend so, if I'm there when it's airborne, I'll get a pipe diameter for you. Watch this space!

 

[mjheathcote]

Thanks Benny!

 

[BennyD]

No worries mate. Personally I would go for the two pipe system rather than the 'squashed pipe' system.

 

[mjheathcote]

Actually quite looking forward with the standard pipes on the bench, to accurately measure the squashed pipe and calculate what the actual cross sectional area really is compared to the normal diameter.

 

[BennyD]

I don't think it will be a whole lot different but coupled with the choking effects of the standard cats it's enough to strangle the poor thing. It might be worth putting it on a rolling road before you do the mod, and after to show us once and for all the difference it makes.

 

[mjheathcote]

I've had a rolling road session with just the larini rear boxes, 388BHP, would be nice to break 400!
Just found these on the web from the US.
Looks like a single cat, just for the benefit of the O2 sensors!

 

[2b1ask1]

I like that single cat just for the o2 idea but not so keen on that take of dealing with the squash; looks to me like it may cause an awful lot of swirling and not really help much!

 

[BennyD]

I think that is awful; the squash section looks worse than the original and the emissions would likely fail the MoT. Why bother with a cat at all if the car can be made to run without one if you are going to fail the MoT on emissions? Btw, I reckon you will be well over 400 with the 200 cell cats.

 

[mjheathcote]

I think that is awful; the squash section looks worse than the original and the emissions would likely fail the MoT. Why bother with a cat at all if the car can be made to run without one if you are going to fail the MoT on emissions? Btw, I reckon you will be well over 400 with the 200 cell cats.

I agree can't see the point of the single cat as it won't pass the MOT.
Breaking 400 has just to be done!

 

[mjheathcote]

My donor front pipes arrived today, and I have taken a few initial measurements that have surprised me!
The pipe diameter at the connection point to the X pipe is 60mm OD with a wall thickness of 1.5mm. The internal cross sectional area is therefore 2,550 mm2
Measuring the squashed area, maserati have used a larger diameter at this point and then squashed it. Initial measurements of this squashed section indicate that the internal cross sectional area is approximately the same as the 60mm OD pipe, being approx 110mm x 23mm (2,530 mm2).
Therefore it looks rather squashed, but being very wide, it compensates accordingly.
Now I don't know the diameter of the larini replacement pipe, but I am guessing that the pair of pipes replacing the squashed section won't be bigger than 40mm OD. The internal cross sectional area would work out at 1,075 mm2 each, so in total 2,150 mm2, 84% of the main 60mm diameter pipe!
We therefore have a situation where the larini replacement pipe, on paper, is more restrictive on cross sectional area than the original squashed pipe!
If this is the case, unless someone confirms the larini pipe diameters to be larger than 40mm OD, the gain on the larini replacements is all down to the 200 cell cat replacing the 400 and 600 cell cat, not the squashed pipe section at all....
Of course there might be gains from the shape, rather than the cross sectional area...
I'll carry out more detailed measurements but at the moment, it appears simply chopping out the primary 400 cell cat, and replacing the secondary 600 cell cat for a high flow 200 cell sports cat is a simple modification that will yield satisfactory improvements in flow and power!

 

[BennyD]

Like I said before I didn't think there would be a big difference in cross sectional area but it's the shape that concerns me. We need someone in fluid dynamics to show the flow characteristics of the squashed area. The old adage "if it doesn't look right, it probably isn't" might well be true.

 

[CatmanV2]

I have only a very limited experience of fluid flow, but my understanding is that the flow at the wall is significantly slower than the flow in the middle.

Ergo squished pipe with same x-section will present more resistance as there is more wall per unit area. The more it's squished, the worse it gets.

I could be talking utter ****, though.

C

 

[VEDE]

The Trofeo cars had the same front cats and squashed bit, but no secondary cats... They still made 420bhp so maybe it can't be all that bad? My understanding is the cats will provide far more resistance to flow than the squashed part will...

Has anyone actually had any scraping issues on their exhaust? I hear the argument for Larini because of ground clearance, but to me a single larger pipe provides the least resistance of all.


Sent from my iPhone using Tapatalk

 

[mjheathcote]

I have only a very limited experience of fluid flow, but my understanding is that the flow at the wall is significantly slower than the flow in the middle.

Ergo squished pipe with same x-section will present more resistance as there is more wall per unit area. The more it's squished, the worse it gets.

I could be talking utter ****, though.

C

If you calculate the wall area of two twin pipes relative to the cross section, and the same for the squashed pipe, the answer is the same, in fact slightly to the advantage for the squashed pipe.

The Trofeo cars had the same front cats and squashed bit, but no secondary cats... They still made 420bhp so maybe it can't be all that bad? My understanding is the cats will provide far more resistance to flow than the squashed part will...

Has anyone actually had any scraping issues on their exhaust? I hear the argument for Larini because of ground clearance, but to me a single larger pipe provides the least resistance of all.


Sent from my iPhone using Tapatalk

If there was an advantage to replacing the squashed pipe on the Trofeo cars, I am sure they would? its not as though there is a ground clearance issue on track. The secondary cats are the most restrictive being 600 cell I believe, so getting rid of them is going to help a lot.
If you have a US type exhaust, which appears to be quite common on later euro cars/GS's as well, its difficult to remove the primary 400 cell cats. So having an earlier/Euro spec car and the ability to remove the all the cats and replace with just 200 cell sports cats has got to be good for power!

 

[MAF260]

I'm going to be doing some investigation later this year for my GS. I'm thinking about changing the manifolds for the non-cat version, changing the squish pipe for 2 round pipes like the Larini version (although not Larini due to their ridiculous prices!) and also swapping the secondary cats to 200 cell sports cats. My main concerns are emissions not passing the MOT and too big an increase in noise, more specifically the droning I get already from the Larini rear boxes at 2.5-3k revs.

 

[BennyD]

I can put your mind at rest re emissions; a pair of 200 cell cats will be emissions compliant, mine are. As for drone, I've no idea, as it doesn't work the same for drop heads with the roof down.

 

[CatmanV2]

If you calculate the wall area of two twin pipes relative to the cross section, and the same for the squashed pipe, the answer is the same, in fact slightly to the advantage for the squashed pipe.

Maybe I'm not explaining myself well (what's new) You're going to get an area (well volume) of turbulent flow near the wall of the pipe. There is going to be a volume affected like that in the squashed pipes.

Quick thought experiment:
Hose pipe or same x-sectional area made up of capillary glass tubes. Which one will provide greater resistance to flow, do you think?

C

 

[MAF260]

I can put your mind at rest re emissions; a pair of 200 cell cats will be emissions compliant, mine are. As for drone, I've no idea, as it doesn't work the same for drop heads with the roof down.

Thats useful to know, thanks. My emissions concern comes from my recent MOT - it took a minute or so at certain revs to get the machine to give the 3 green lights. Given my car is constipated with large cats in the manifold and then a further pair after the squish pipe, I thought perhaps they might all be necessary. Having said all of this, I have no idea how effective they are given they're 8 years old. I'd hate to spend that time and money and find myself stranded at the MOT centre with a car that can't pass the emissions requirements!

 

[SimonCC]

The secondary cats are the most restrictive being 600 cell I believe, so getting rid of them is going to help a lot.


I had the secondary cats removed last month but left the squashed pipes for now as the exhaust engineers said they think it isn't that restrictive being of the same diameter as the round pipe but just flat, and they don't think there would be a big benefit to having 2 smaller diameter pipes a la Larini....also they were actually impressed with the quality of engineering to make the 'squashes'.

I have to admit that I haven't noticed any improvement in performance since the 600 cell cats have gone - the sound is very slightly improved by it still sounds pretty stock if I'm honest.

I've heard a couple of cars with Larini rear boxes and they do sound nice - still not decided if they are slightly on the too noisy side for me though, but I would like to release a little more growl than the stock system thats on the car at mom.