What are the characteristics of short vs long tube headers and what applications are each best suited for? I've heard not much performance gains from shorties and as much as 50 rwhp with LT's?
Its all about exhaust pulsation. The long tubes are tuned to provide the easiest exit of exhaust without taking to much back pressure away. Shorties do the same thing but on a smaller scale and not nearly as effieciently. Although, without any other mods, even long tubes won't do much for performance but will make it sound much better. On the other hand if you plan on forced induction or some aftermarket cams, long tubes are a must if you want to get all the potential out of your motor.
So basically, long tubes promote scavengeing, which is when exhaust air is pulled out even before the piston starts to come up on the exhaust stroke and before the intake valve closes completely. This helps combustion which in turn increases horsepower. (IIRC)
Thanks guys. My car is SC'd and I'm looking for both better sound quality and increased HP.
My next mod is CAI, smaller sc pulley, new idler with a custom tune from JDM. Truthfully, I am a little concerned about voiding remaining 6 mos. of Roush warranty, but am thirsty for more HP but not at the sake of blowing it up. Do you guys have an opinion on this mod?
After this I'm doing the LT's. I'm sure I'll have to update my tune when I put on the LT's, but just wanted to confirm I'm on the right track with LT's vs Shorties.
When you put on the smaller pulley I am assuming that you will be hoping for 12psi.
The stock AFR from roush can be leaned out to about 11.95, and then the timing can be bumped up to almost match the MBT table. You may also want to raise the maximum Throttle % at all RPMs up to 80%. When putting in longtubes disable the rear O2s, and up the base fuel a little bit (~2%). You can set the max wheel torque error to 50,000, reduce the value required to enter WOT to remove the minor delay that you'll experience in fuel compensation for WOT.
ChangeMax MAF count to 1023, and MAF min to 50. This will allow your MAf sensor to read more accurately at the high volume your supercharger will make with that pulley. Also set Min and Max Barometric to 27 to disable it so that it doesn't screw with your WOT fueling.
Change the Open Loop delay ramp to 0, and set the Open Loop delay blend to 0.5 > This will make the car respond to WOT better by delivering the AFR change faster.
Also set the CYL AIR WOT MULT to 1.9 so that your car never goes superlean.
There can be more to it, so feel free to PM me if you have ?'s.