Having a road going Fiat with a race engine set up I'm always keen to explore improved gas flow through the exhaust pipe - especially if I can get better hydro carbon and emissions content as a result.
One of the 'Wheeler Dealers' programmes was having major exhaust emissions problems with a replica Cobra and 7litre Chevy V8. Their solution included fitting new twin Cats and a revised design of back box created by Vortex Exhaust Technology.
It looks like a fair idea..... where the back box splits the gas flow into two and is shaped to create a lower pressure zone ahead of the noise absorption package inside the box. In the Cobra programme, these back boxes where fitted last and the exhaust itself then reduced the emissions hydro carbon content by another 40%. That got me interested.
But then internet searches have me genuinely worried. Yes this solution came from the States where it was a lot cheaper. Knowing that the best extraction manifolds in a balanced engine upgrade might give around a 5% additional air flow..... there's no physical way in which a partial vacuum at the back of the exhaust can supply the power boosts claimed (and for small capacity - smaller airflow engines!)
Has anyone come across some more reliable discussions of this Vortex extraction back box?
I saw that episode some time back and came to a couple of conclusions:
1) the system has to be doing something good in order to correct the emissions problems 2) the old exhaust system on that car must have been really terrible 3) they didn't tell the whole story - the exhaust didn't correct the emissions problems by itself but it may have made it possible to adjust the fuelling so that the HC content of the exhaust was within limits.
My last conversation with a engineer from a big car manufacturer was that the cat's in the petrol engined cars are there for legislation only (they *have* to have them) but the engines would meet emissions requirements without the benefit of those catalytic converters. They only become useful when engine tuning is poor and then they are poisoned by the HC content. The solution many of my american friends use is to add rubbing alcohol (ethanol) to the fuel prior to any emissions tests as it disrupts the readings and hides any problems - naturally such things are illegal but it is a very common practice...