I have a 1979 L48 which is rated at 195 HP from the factory. Is this measured at the rear wheels or the crank. Yesterday I installed a set of 1.6 roller rockers and noticed a pretty good improvement in performance but also about at 30 degree drop in temperature.

Also does anyone know what heads are on my engine? I'm thinking about swapping them out for a set of modified Vortec's. Any comments or suggestions would be helpful. Thanks

After 1971, horsepower ratings were done at the rear wheels....I have a 1972 coupe, and in 1971 the identical setup was rated at 270 horse....my '72 is rated at 200 horse!

actually, before 1971 horsepower was rated as gross, or horsepower at the flywheel. After 1971, horsepower was rated as net, or horsepower with accessories such as fan, alternator, and power steering. But this is not at the rear wheel, that would be even less yet. A ls4 in 1971 had 330 gross hp, but my 1974 ls4 has 270 net horsepower. Hope this clears things up.

"LESS YET"?!?!AAAAARRRRRRRRRGGGGGGGHHHHHHHH!!!!!!

Your heads should be casting # 462264
Probably a 1.94 /1.50 valve for a L-48 motor.
If you go to a better haed, you need to look at your cam too. The motor has to breathe!
I've had heads re-machined to accept the bigger valves, just a thought, cheaper than new heads!

The way I understood this to be is: gross is measured at the flywheel with no accessories. Net is measured at the flywheel with accessories. Rear wheel is obvious.
My '69 427/390 is listed as gross of 390. The rear wheel was dynoed at 248. In thoery, you loose 15-20% from gross to net and another 15-20% for the drive train.
The exact percents vary with accessories and type and condition of drive train. All new components would be reflected with less of a loss.
I believe it was '72 that companys started rating net (flywheel with accessories) but it might have been in '71.

It was '71, same time they started dropping comp. ratios to allow use of unleaded gas.

Marc