2bular Decats Featured

 

2bular De-Cats Vs. others!

My pet hate is the annoying habit of some major exhaust manufacturers to weld mild steel flanges onto stainless steel pipework.

Lotus/Janspeed do this on their V6 de-cat pipes –



Horrible rusting thing – wonder what it will look like after a couple of years of UK winters.

You see the 2bular version (top!)? I hand-fabricate/TIG-weld them now. I used to bend the ‘S’ in one go but the clamping pressure required is too great and it makes a mess of the finish on the pipe – ripples/marks - you can cover them up with a label though!




2zz-ge De-Cat Pipe:

Popular in the USA and a couple of other markets. Fits to the factory manifold/header with bolts/springs to provide the necessary flexibility to deal with the excessive engine/transmission movement on these cars.

Check out the 2bular Vs. Larini designs.




Fitting a De-Cat Pipe is a great way to pick up some more power and get rid of that vulnerable catalyser for track use. Also makes for a much better exhaust sound! Too LOUD for here in the UK though. CEL’s are always a problem too.
On the 2zz-ge I use a 2.5” (63.5mm) diameter pipe. To keep the spring length the same as factory use, I weld the gasket cup to the laser-cut flange. Then I weld a reducer to the gasket cup bringing pipe size down to 2.5”. All TIG-welded.




It’s all about maintaining gas-flow/gas-speed directly after the factory manifold/header. Very important for scavenging at the exhaust port.
The Larini De-Cat design uses a 2.75” (70mm) diameter for the first half of its construction. You can swage/flare that size to form the gasket cup – but it slows the gas-speed down just as it leaves the manifold/header. It’s not possible to swage/flare a 2.5” (63.5mm) pipe out to that diameter. So - no welded gasket cup or welded reducer on the Larini (and others) – saves a lot of time though!

I see other manufacturers using the same 2.75” (70mm) pipe for their 2zz-ge Catalyser AND De-Cat Pipes. One of them even uses a mild steel flange! Depends what you want. I take the time and effort to build what I think is the best solution.
The Larini has brackets to bolt the factory heat-shield to it. But with no catalyser, there’s no real heat issues to worry about, so I don’t use them. I don’t use a one-piece 180deg bend out of the Catalyser/De-Cat Pipe. The pipework comes close to the clam just before it enters the silencer, so I like to swing it away from that area soon as possible. The factory heat-shield wouldn’t fit anyway. Some owners like to wrap the pipe – doesn’t do any harm.


 

Author

Jim@2bular

Master Craftsman in all exhaust systems

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