LT4 Stock Lt4 H.p. Variations

[Dave C. '04 Z06]

Actually, torque is what counts. Horsepower is just calculated from torque. The higher up in the RPM band your peak torque is, or the more peak torque you make, the higher your horsepower will be.


Also, about Gross HP vs. Net horsepower:
When something is specified as "BHP", or Brake Horse Power, that means the engine was OUT of the car attached to an engine dyno that used a water brake to measure the power output. It has nothing to do with the gross or net results.

Gross horsepower is measured with just the engine and nothing else (not even a water pump) on it, and Net horsepower (like what they switched to in the 70's) is measured with the water pump and all the other accessories attached to it (power steering, Alternator, smog pump, etc...)

Up to this point the manufacturers have not published horsepower numbers that included the chassis and drivetrain.

-Dave

PS: As a note, remember when the LT4 was available as a crate motor from GMPP? It was rated at 330HP, same as when it was in the 'Vette or F-body. If it was a drivetrain measurement, it would have been different (alot lower) for the cars.

 

[XS650]

The terms net, gross and brake horspower are often misused.

SAE J1349 is the official specification for net power rating, J1995 is the spec for gross power rating. You should be able to find the specs in a good public or university library.

The posts here have generally been pretty close on gross power, but the marketing folks also ocassionaly added some power back in the 60s and 70s.

Net power is what is used now and is measured at the flywheel with "all accesories intended top perform it's intended service". It includes the full intake with all ducting and other restrictions, the full exhaust system, emissions controls, cooling system. It does not include the power steering pump or AC compressor.

In common usage there is no difference between horsepower and brake horsepower. Brake horsepower just implies that the power was measured by putting a load on the engine. There are many ways to put a load on an engine.

 

[Edmond]

Net power is what is used now and is measured at the flywheel with "all accesories intended top perform it's intended service". It includes the full intake with all ducting and other restrictions, the full exhaust system, emissions controls, cooling system. It does not include the power steering pump or AC compressor.

How much would the PS pump and AC compressor rob the car of?

 

[XS650]

How much would the PS pump and AC compressor rob the car of?

Aproximately othing when the AC is off. Up to a few horsepower when it is working the hardest in an overheated car that has been parked in the sun. It can't be over 2 or 3 hp driving down the highway or you would notice a significant drop in gas mileage with the AC on.

Info on power steering pumps is hard to come by. My impression from reading various things is 1 to 2 hp when it is doing nothing and about double that when parking.

 

[SurfnSun]

Most of the hp lost is due to the tranny and rear end, accesories play a small role in that.

 

[wx briefer]

60 HP variation does sound excessive. I only have experience with 3 LT4's on the same dyno. All three were within just a few HP of each other. I would expect for such a variance of 60 HP one would have to see a bad sensor, shot Opti-spark, or maybe a little programming on the strong one.

I really am skeptical of the 60 difference in factory, good tuned, similar vehicles.

 

[XS650]

I suspect most of the 60 hp variation is in the calibration of the dynos and dyno operator knowledge and skill. There is a lot of variety in types of dynos and how well qualified the operators are.

You could take the same engine and ship it around the country to different dyno facilitys, and if some of them weren't top notch you would get some widely varied results.