i bought a '98Z. The owner had installed a Borla cat back with the least restrictive plate in, a whisper lid intake, and 4.10 gears. He said he had it on the dyno and got 306 hp ast the rear wheels

I'm wondering how much power is lost thru the drivetrain (Mine's the 6-speed). I thought I'd heard 30% once, but that seems too high. Also, will going back to the stock 3.42 affect rwhp? And what about putting in a slightly mroe restrictive plate in the borla (these 2 things being done for autocrossing). And, what gains will sythetic tranny and diff fruid yeild?

Thanks.

 

I heard it was 20% for A4 and 15% for M6. I don't know this for a fact but those are the numbers I remember seeing.

So if that's correct then you have a 15% drivetrain loss. I believe the 306 RWHP. Seems about right for a 98 ls1 with lid and catback. I'd say an average 98 M6 stock dynos 295 RWHP and 11 RWHP for lid and catback is right on. In fact I would not be surprised to see you dyno slightly higher. Different dyno machines on differnt days can have different results.

Congrats on your LS1!

 

I believe the avg. for M6 cars is 15%, A4s about 18%
higher (numericaly) gears will lower your MEASURED hp too. So figure your flywheel estimates a little higher.