Sid why would you want the exhaust not pointed straight back under the car?
Not only do the pipes hanging down between the floor & the ground create more airflow restriction (drag) but the exhaust flow itself is also adding turbulence to the already disturbed flow being generated by the front suspension & the engine cooling system air being dumped out the bottom of the engine compartment.
If the back of the car is higher than the front it will give more area for this mess to dissipate & reduce drag.
If the air dam is lower than all the components under the car, you have created more unnecessary frontal area to the car. If it's all the way down on the ground, like I see so many times at Bonneville, it is having to peel the boundary layer off the salt & that not only takes HP to do, the volume of air displaced by the car is now having to divert into the remaining 3/4 of it's area (two sides & top) & that again takes hp. A flat floor panel with a diffuser is the answer but that puts it in Altered class so you have to do the best you can without it & the goal is to get the front air behind the car with the least restriction.
The Gear Vendor was originally a Laycock O/D from England before they bought the rights to it & Laycock used to list it as having a 7 to 9% hp loss under accelerating conditions in road cars & you know they weren't going 200mph so I'm more than a bit skeptical about that 1hp/400hp loss number, that's only 0.25%.
Running an O/D on the trans to a lower gear in the diff is going to cost you hp, just like having a Quick change with a set of 4.11's & a big O/D in the spur gears to come up with the final number you need. That's an overdrive to an underdrive. If there is no gear ratio option then that's all you can do, just like I had to do on my liner with 2.136 gear sets & 50% pinion O/D units for a final 1.068 to 1 ratio. It's going to cost HP but I have gobbs of the stuff!
Sid.
