RE: Tubi Sport Manifolds...
The manifolds have two purposes:
-increasing performance,
-increasing reliability (if you know anything about the 355 manifold failure problem, you'll know this is a VERY common issue). If you track the car a lot and really thrash it - like Luigi does, then they are a very good idea.
- On their own they will add a very small amount of horsepower:
They work best and will deliver maximal power increase when the car is "prepared" - before you consider them you should already have AT LEAST a Tubi Silencer, Test Pipes/Hi-Flow cats, Sport Air Filters - with all these options you may gain ~40 hp in total... (from mid-range up only, with marginal torque loss at the bottom)......
But that is just the beginning: The more the car is prepared, the more you will get from them and when I say prepare - I mean in the "competition" sense of the word - i.e tweaking the engine/ECU etc and you will get a proportionally larger increase in power from them.
The funtion of the sport manifolds is to be part of a total performance "package" where the car is aggressively set up and you want the ultimate in exhaust flow collection with as low amount of backpressure as is necessary for the engine to operate 100% reliably and that's what they do...
They are Thermally Insulated for 100% reliability during EXTREME use and actually accelerate exhaust flow through the piping. On the F50, the Tubi Manifolds are actually double-walled for maximum reliability.
Here's a picture of them on F355: