vetteonbeach

OK, just a newbie trying to learn all this stuff and looking to make more hp engine out of my L48.... lots of good info found on this topic in the searches on this site and on the internet.

But something isn't making much sense to me... the 290hp GM crate engine looks to have basically equivalent components to the L48 with the exception of the cam: dish pistons, 8.5:1 compression, same valve sizes, etc. The cam in it appears to be the same specs as the L82 cam, but the L82 is 9:1 compression and only 215 at the wheels. I understand the 290 is rated at the flywheel and the L48/L82 is rated at the rear wheels, but something here doesn't seem to add up to me....

what I am missing or misunderstanding here????

thanks,

Michael

MN-Brent

There is the parasitic loss of the accessories for the SAE net rating. -fixed!

IMHO, go LS1. WAYY more power out of the box, less weight, and no BS about flat tappet cam oil ZDDP crap!

Gordonm

GM never rated any of its engines at the rear wheels. It is with all the accessories attached. The is the net HP. Gross HP is just the motor by itself with no accessories. Rear wheel HP is totally different.

MotorHead

They rate crate engines in Gross HP ( as in engine dyno ) because how do they know what is going to be hooked up to them The L82 measured the same way would be about the same or slightly less if you put it on an engine dyno. So yes they are both pretty close when it comes to parts and horse power

I must the run-on sentence king

Vette5.5

Not sure where you ever heard of a RWHP rated factory car, but a new one for me. Since 72' all engine's were rated actual SAE flywheel HP as installed in the car driving the water pump, alternator, ext through the sometime's very restrictive smog exhaust system. Crate motor's are also flywheel HP on a stand, usually water pump, alt, but probably free flowing longtube's and minimal exhaust. The modern head's probably flow much better, and the cam while seemingly similar, is surely computer optimized.

MN80Vette

I have the GM crate a step up from the 290 hp one: 350 HO. I've never had it on an engine dyno, but it's been on a chassis dyno a few times. The last run in May got 293 rwhp and 327 torque. GM advertises the engine at 330 hp and 380 torque.

Estimated crank-rw loss ranges from 15-20% for manual transmission on the CF. With 293 rwhp after a 15% drive train loss, then my GM 350 HO is an over-achiever. Granted, I've tweaked and fiddled with the ignition and 600 cfm carb on my HO, but the GM ratings are realistic and achievable.

If you can scratch up the difference between the 290 hp and 330 hp engines, I highly recommend the HO. Vortec heads flow pretty well, and GM sells a cam kit that will get you just over 400 hp.