Gross horsepower vs. Net horsepower

[HustleRussell]

I was curious which engine has more horsepower L78 with gross 375 or late model 5.3 with 300 net?

[X33RS]

Depends on who's tuning it and who's running the dyno 

I've never dyno'd the 5.3's but have done a bone stock 2004 model LQ4 364 ci (6.0) complete with it's truck intake and after tuning I got 367 gross HP out of it on a DTS.  I kind of doubt a stock 5.3 would do better than that.   

Factory rated the LQ4 anywhere from 300 to 325 net depending on which truck it came out of.  The factory tunes in these things are pretty lame.  They wake up with a few strokes on the keyboard.

[Mike S]

 I read somewhere that net was approximately 80% of gross for a rear wheel drive car.

Mike

[X33RS]

I've seen some drastic changes like that with my own cars, first dynoing the engine in a dyno room, then installing it in the car full of all accessories, air intake, exhaust etc...then hitting the chassis dyno pushing through 400 turbos with and without loose converters, and 12 bolt or 9 inch rears.  The difference is pretty dramatic in some cases depending on the car.

[ban617]

Would it be fair to say you lose 20% hp on average going from an engine dyno to a rear wheel dyno ?

[69Z28-RS]

Generally, losses are figured as between 15-20%, depending on the losses in the specific automobile eng-drivetrain.   

[X33RS]

Yeah that's what they say but I've found the differences can be much higher than that myself.    In the dyno cell I'm running the engine with no accessories, no air cleaner, electric water pump (usually), electric fuel pump, and in some cases dyno headers.  All this is done to facilitate hookup and time involved.  It's also in a controlled environment.

Once installed in the car and on a chassis dyno, I'm running the air cleaner, PS, mechanical fuel pump (in some cases) and a mechanical water pump, mechanical fan,  full exhaust system in some cases with original exhaust manifolds, then through the trans and rearend, even the type of rear gear, tire and wheel combo has some affect.

It's vastly different from car to car.  Take a 69 Z for instance, no PS, running through a 4 speed, you won't see as much of a drop.  My chevelle however with PS and AC, running through a 400 turbo with a 3800 converter, the difference is pretty drastic.

Toss in the differences between dynos and then things are jumbled even more.  It's too difficult to just put a number on it.

[Mike S]

 This is one article about measured loss I was able to find that I remembered had good comparisons:
http://www.hotrod.com/how-to/transmission-drivetrain/ccrp-0311-drivetrain-power-loss/
 
   When you look at today's engine net HP output and factor in the approximate losses to get gross output used in yesteryear's specs, today's motors are so superior. Couple that with today's tire and chassis design I can see why some of the new cars today can blast a 60's vintage off the road, and with a quiet exhaust to boot 

Mike

[BillOhio]

We have a semi with a 500 horse Cummins in it. It was having a problem and they put it on their Dyno to warm it up to start checking it out. The guy called and told me they got it looked over and I said well how much did it have on the dyno. He said 500 and I thought of that seemed strange he said that those engines typically run 600 horse and they call them 500 because that's what they were putting out the wheels. So that truck was losing 100 horse

[Mike S]

 I'm searching for the article that was a comparison with the same motor used on different transmissions with one being a FWD. I was surprised at the HP loss with a RWD due to the hypoid design. The FWD put out more HP to the wheels compared to the RWD. This was for comparisons only and not indicative if it would put it to the pavement under a hard launch.

Mike