| Author | Message | ||
     Oconnor |
CB James suggested this to me. I hold a lot of stock in what he says after reading his past posts. Has anyone tried? I heard there is a lot to be gained in the header. So I would like to do a header and a drummer. Anybody have any experience with this swap? | ||
| Apex1 |
Aaron had this to say about it: "They went back to 1-3/4 primary tubes for the 12's, right? So velocity will go down. Velocity is: (piston speed in fps) * (bore^2 / diameter^2) Say at 6000 rpm ... the 9's piston speed is 3125fpm which is 52fps. With the stock 1-5/8 primary tubes (1-1/2 i.d. roughly), you get: 52 * (3.5^2 / 1.5^2) = 283fps 280 to 300 is considered the ideal range, below that loses inertia scavenging and above that causes pumping losses from the friction. Now, with a 1-3/4" head pipe (1-5/8 i.d.) ... 52 * (3.5^2 / 1.625^2) = 241fps So it's a little low. To get back to 280fps you'd need to get the piston speed up to 60fps, which is 3600fpm, which is 6900rpm. This difference in exhaust velocity is going to affect the wave timing, because waves are generated whenever the exhaust is allowed to expand (i.e. steps, collector, muffler, outlet). So if it's going a different speed, waves are generated at different times. And therefore lengths have to be different to get the waves timed to arrive at the chamber correctly." I would still like to see a dyno chart with the 12 header on a 9, just to see where it moves the power. | ||
| Usapitbullz |
I have heard a few people thinking of going this route. I'd also like to see the dyno numbers. L8R, JM |
