Quicksilver

[dermotbell]

Everybody seems to go for the Peco exhaust. As this is a 2 1/4 inch system which causes the overboost problems, why not go for a quicksilver exhaust (making for Lotus cars for years) which is a 2 inch bore.

No overboost and a similar price. Is it just the extra bhp and sound people are after, or am I missing something else??

[ailwyn]

My understanding of the overboost problem is that it's not limited to 2.25 and bigger exhausts.

The squish in the stock 2" exhaust, it is commonly believed, was put there as a deliberate restriction to the exhaust flow in order to fix overboost issues and this was deemed cheaper, and quicker than re-engineering the wastegate etc.

If I understand correctly, the 2.25 exhaust will provide around 30-40bhp over the stock (with squish) exhaust. Any idea what the 2" would provide?

At £250 per system, the Peco seems to me to be very good value for money.

If you do have a Peco and suffer from overboost, then I believe there are two methods of curing it, either place a 2" restriction (gasket etc) into the system or port the wastegare from 16mm to 20-22mm.

If you go for the Quicksilver exhaust, post your findings here so that everyone can make a better informed decision when it comes to exhaust options.

Ailwyn

[dermotbell]

I started looking at them because Pat Thomas of Kelvedon mototrs fits them. He says there is no problem with overboost so I am assuming they have a restriction somewhere in the system already.

[Elanlover]

If its a 2" bore then that IS the restriction that helps prevent overboost. Going to 2 1/4" or higher creates the overboost situaiton as the exhasut flows more freely/quickly.

As for the extra horsepower with a larger bore exhaust, is it really that much???? I recall reading a few posts that seem to indicate that its not that much and that with Alan's chip you are getting most of the benefits that a larger bore exhaust would deliver???? Now, I've simply been "mentally" filing these comments away for a time I look at doing the exhaust over so I could be way off on this one. Also, the squish may be there only as a way to ensure the exhaust has the minimum clearance from other parts and the body as opposed to a self-induced restriction.

There's been some additional thoughts on this issue over the last few months (and I'm now wishing I could remember the contributors and where the threads are on the forum). Would be curious to know what the impact of a new 2" exhaust without the squish AND Alan's chip would be.