Hi am thinking of getting some GT SPEC headers as I have just over the 350bhp mark. or am I better of getting my old ones ported. Also will I need it mapping or not, can you tell a difference in power as I have heard that some people loose bhp when changing there headers

 

bttt

 

At that level I'd put the GT Spec headers on (IMHO) as you'll probably be looking to upgrade further so I dont see much point in getting the std ones ported out - a messy job (unless you pay someone else) and given the GT Spec headers are quite cheap its a bit of a bargain to go that route
Headers cost me £425 brand new and they are fine on a 500bhp engine

Do remember to get the after market headers wrapped, this should last at least 2-3 years before it needs replacing

You will definately need a remap, as you would too if you ported the std ones

Loss of BHP - never heard of that - wouldnt be loads of people putting after market ones on if that was the case ;-)

 

Putting on tubular headers will probably loose you spool of 150-500 rpm depending on design.
At 350 bhp you would be better with properly ported O/E headers and a matched up-pipe which will result in improved spool and power gains across the rev range.
Some cheap header sets will loose you both power and spool.
Many cheap header sets crack after a short period in service, usually on the welds at the collector on the driver's side because the material and quality of welding cannot withstand frequent heat cycling.
Your ECU has a degree of self learning and will tolerate a change of headers without a remap, especially on later cars but for optimum results you are best with a remap, certainly at the point where exhaust, headers and pannel filter have been changed a remap is necessary.
GT Spec headers are not cheap headers and they are well made but you will still notice a signifigant loss of spool over O/E and especially over O/E ported and matched up-pipe. I know this because I run a set of these well over 500bhp.