Well, I still don't think the loss is in the 20% category. I'll give you an example.
My TR ran 126 mph in the 1/4 a few years back. It was a 40* day with pretty good air. Although the air was good my car was not really tuned in. Here's the build-up:
86 TR weighing 3600 lbs w/driver
bone stock suspension (sway bars and all)
stock front rims and 27x10 slicks and 8" Welds on the back
stock gears, slipping tranny (flared good on both shifts) 2600-2800 stall stock size converter ( unlocked )
9" K&N cone filter, stock maf (1 screen removed), 3" MAF pipe
T-63E turbo, Kenne Bell big boy intercooler, stock t-body, hemco 62 mm bonnet
rebuilt stock block, .020 over JE pistons, ESP stage 4 cam (on it's way to flatsville), fully ported stock heads and intake
ported exh. manifolds, 3" ATR downpipe run open
55 lb injectors, Red's 107 chip, (get this) 307 pump, adj reg
C-16 in the tank
27 psi boost in 1st and 2nd gears, 30 psi in 3rd gear
42 psi static fuel pressure spiking to 70 psi in 3rd gear
car was a pig in 1st and 2nd gears and then leaned out big time in 3rd (it popped 4 times in 3rd gear due to lean condition)
ran 97 mph in the 1/8 and 126 in the 1/4. 97 in the 1/8 should be a 121 in the quarter, like I said a pig in the first 2 gears.
If we were to allow for a 20% drivetrain loss I would have needed to make 640 hp to achieve 126 mph with the air conditions that day. Who here thinks my combo was making that much power?
Not me.