who much hp will a header add to a 13b na with cone air filter

 

10 - 20 depending on what's behind it.
Check the pics linked in my sig.

 

Enough to notice. The numbers depends on the header.

 

Hmm if i have an all stock rx7 with an auto (s5) will a header make a difference someone told me there was a guy with a 2nd gen and an auto in it that ran 15's for like 3,000 in mods can anyone commfirm this?

 

Yea - mine is crudely home made, but I only had $300. for the whole system.

The real RB header is absolutely worth the money if you can swing it.

 

yeah, I got the RB header/presilencer and it made a huge difference. I definitely recommend it.
The only downside is that it is very loud.

 

so will say 10 to 20 hp

 

No numbers yet...Although I did notice a significant Increase In power at top end with the sacrifice of bottom end torque.

 

has anyone got any opinions on a header and then reletively stock exhaust after?

Or how about mine...I haven't driven it yet so don't know what to expect...header to 2.5" tubing to the "Y", then 2" tubing to stock mufflers.

Also, can anyone give me the tubing diameter of typical headers? I am making one and I'm assuming 2.25" tubing will be great from each port, then into a 2.5" mid-pipe.