Horse power

[Jack J.]

Just for clarification for myself and others, in today's realistic world, what would be the REAL horsepower rating of a 1964 327CI/365HP Corvette? Thank you. Jack J.

[Joe L.]

Re: Horse power

Just for clarification for myself and others, in today's realistic world, what would be the REAL horsepower rating of a 1964 327CI/365HP Corvette? Thank you. Jack J.

Jack-------


There are numerous ways of rating horsepower and all of them are real. All I can tell you is that in 1964 engines were rated at SAE Gross Horsepower. In 1972 the horsepower rating changed to SAE Net for virtually all cars and light trucks. That same horsepower rating system is used to this day. The 1972 change made it difficult to compare pre-1971 ratings to 1972 or later. However, as a rough "guesstimate" I would say that 365 SAE gross horsepower is equivalent to about 290 SAE net horsepower.

By the way, SAE net horsepower is NOT the same as "rear wheel horsepower" as many folks seem to think. Rear wheel horsepower would be considerably lower yet.

[Mike F.]

Re: Horse power

My 70 L-46 (350/350) made,
341hp/387tq Gross on an engine dyno. (velocity stack, headers, no accessories)
245hp/305tq RWHP on a chassis dyno. (air filter, exhaust manifolds/under car exhaust, alternator, power steering pump)
SAE Net would be somewhere in between. (290hp-300hp?)

Remember, Gross to SAE Net to RWHP will vary based on the accessories and exhaust used on the car.
Water pump, Alternator
Water pump, Alternator, Power Steering Pump
Water pump, Alternator, Power Steering Pump, A/C
Water pump, Alternator, Power Steering Pump, A/C, A.I.R. Pump
Original exhaust manifolds vs. headers, etc,. etc.....(If I had installed headers, my RWHP would have been more. Making the percentage loss from Gross to RWHP look to be less.)

[William F.]

Re: Horse power

Duke has given a formula to convert gross to net to rear wheel hp in previous posts. Maybe he would refresh our memory.

[Joe C.]

Re: Horse power

Just for clarification for myself and others, in today's realistic world, what would be the REAL horsepower rating of a 1964 327CI/365HP Corvette? Thank you. Jack J.

Engines tested were "select" specially prepared engines. Pre 1971 ratings were gross horsepower on an engine dyno with no accessories and were generous by about 7%.

[Joe C.]

Re: Horse power

RWHP x .8 = SAE NET..........for automatic transmission
RWHP x .85 = SAE NET........for manual transmission

These are approximate.

[Duke W.]

Re: Horse power

Duke has given a formula to convert gross to net to rear wheel hp in previous posts. Maybe he would refresh our memory.

SAE gross ratings are corrected to standard sea level conditons, somethings called standard temperature, pressure (STP), which is 29.92" Hg, 59F, dry air. SAE net in addition to having all engine accessories and the OE exhaust system corrects the readings to 990 millibars, 25C, dry air, which converts to 29.235", 77F. This air density correction reduces output about 4.5 percent relative to STP conditons.

In addition to using SAE gross data, GM "rounded" the numbers up to whatever they thought sounded good from a marketing standpoint. The OE ratings, wery typically 10-15 percent higher than what was measured, so SHP/FI small blocks were honestly in the range of 290-310 gross. With head massaging and an honest 10.5:1 CR they will make near the advertised numbers.

Rear wheel observed data should be corrected to SAE net air density conditions. Then it's a matter of dividing this data by drivetrain (which includes tires) efficiencies to estimate SAE net at the crankshaft, which are generally considered to be 0.85 for direct drive manual transmissions (tested in the 1:1 gear) or about 0.83 if tested in an intermediate gear, and 0.80 for automatics without lock up torque converters.

Net to gross conversion at the crankshaft varies widely from configuration to configuration due to differences in exhaust system efficiency and front end accessory load. For small block Corvettes with 2.5" exhaust systems, which are very efficient, the conversion factor is 0.89 based on data I have for identical configurations that were tested on both lab and rear wheel dynos, and the lower SAE net air density accounts for nearly half. This factor will be less for big blocks since the exhaust systems gets a little restrictive at the top end, especially SHP big blocks with massaged heads, and sidepipes are a big time loser because they are very restrictive.

A Flint-built "350 HP" L-79 in good condition with the standard exhaust system will make about 220 SAE corrected RWHP, so the flywheel estimate is 220/0.85 = 260, and the SAE gross estimate is 260/0.89 = 292.

I know of a couple of "327 LT-1" configurations (.030" overbore, high strength conn. rods, massaged heads, LT-1 cam, 10.5 CR) that make 280-290 SAE corrected RWHP in the 6000-6500 range, which using the above empirical conversion factors computes to about 330-340 net and 370-380 gross. With careful setup of OE valvesprings they make useable power to 7200, which is the point of incipient valve float.

Duke