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Performance gains from removing the CATs
Matt Jones posted a query on the V8BB and some useful responses followed as guidance for fellow members. (Nov 08)

Matt Jones' query was straightforward: "does anyone know if there are any performance gains to be had from removing the CATs and replacing with a straight through system?" He was uncertain whether the car would fail the annual MOT without them but was "interested to see if anyone has found any noticeable difference in performance" without them and if there would be an increased in exhaust noise. He added "a friend of mine recently put them back on his TVR because it was just too noisy on long trips."

Bryan Shacklady responded saying "I'll wait for Geoff King to chip in and tell me I'm wrong, but I believe the car will definitely fail the emissions test without them. There is also the question of whether you are driving a car that is roadworthy if you only put them on for the MOT test. I thought we had this discussion before, but unless I am being daft with my search criteria, I can't find the reference." He added he had found a webpage which "suggests that on an removing the CAT on an MGF would cause an emissions test fail, and, interestingly, for very little horsepower gain, which I had not realized. I had thought CATs sapped quite a lot of power, but apparently not. No doubt someone will be along shortly to confirm what the case is for an RV8."

Peter Garton from Germany added that "removing your CATs is probably illegal anyway and your car will definitely fail the MOT. Why not create an illusion in that you get the single silencer unit from Clive Wheatley and really enjoy the superb sound it creates with an increase in power of about 0.1%! This is a one-time job and is permanent, saving all


that shillyshallying about underneath the car" each year replacing the CATs for the MOT.

Geoff King then provided a useful view with "I can't comment based on experience because my V8 Roadster conversion has an open loop fuel injection with no Lambda sensors or CATs and it's old enough (registered anyway) not to require any emissions test for the MOT, but the RV8 has a closed loop injection system with Lambda sensors. That system tries to maintain the optimum fuel/air ratio but it needs the CATs to reduce the emissions to legal levels. It would almost certainly fail the MOT without them. I would also expect power gains without CATs to be negligible - the fuel/air ratio would still be the same - and would you really notice the difference in everyday driving even if the power gain were say 5bhp?"
Searching the V8BB archives reveals the topic was raised by Richard Withington in June 2008 when Geoff King responded "IMHO the removal of the cats will have a negligible affect on performance or fuel consumption, however, there will be a significant increase in emissions and the vehicle will not pass the MOT test."
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