Drivetrain and Exhaust losses

[Tallguy]

I think my mind is made up on using a 428FE, non stroked for my Cobra project. I am going through drivetrain design, and want to get an idea of what losses I'll see from BHP to RWHP. I have searched a lot, and based on that and other internet searches I am estimating the following:

Driveline Losses
Manual Trans - 2%
Driveshaft/U-Joints - 1%
Rear End - 10%
Accessory Losses - 2%

Total Driveline and Acc losses = 15%

Sidepipe Losses - 45 HP (guess based on 50HP loss @ 500 HP)

So if I get a 428 motor with 450 BHP I lose:

68 HP in driveline
45 HP in exhaust

Total to wheels = 337 HP which is a 25% loss.

Does this seem right? Are the sidepipes usually that restrictive?? Seems like a lot, but that is what I have seen in the searches I did.

Another thing, on the 15%. It seems like the drivetrain losses should be somewhat constant whether you have 200 or 700 HP and not a %. Same HP to overcome the loss.

Thanks,
Mark