How much more gain can be had from aftermarket headers compared to the stock headers on a 944 NA. I put in headers on a honda CRX and there was noticable improvments in power and millage, but is a porsches stock header already designed for good flow as is?

 

You can see some nice gains (10-20hp depending on the model)from aftermarket headers on the 944, but they are not cheap, so it is a high cost/hp ratio.