Flat plane C6 Z06. Dreams do come true

[MX793]

How does this differ from what I said? (they were of course testing and building 1972 models in 1971)

The SAE standard has also changed in that time (inertial dynos didn't even exist)

You said SAE net has changed from testing undressed engines to dressed engines, which is not correct.  Up through MY 1971, manufacturers rated car engines using SAE gross.  Starting for the '72 MY, they were required to use SAE net.  The end result was a substantial (20-30%) "on paper" drop in horsepower ratings across the board despite engines that were in many cases unchanged between model years.

Yes, SAE net testing and rating procedures have changed slightly since 1972.  There were adjustments within the past decade or so that result in slight "on paper" power rating decreases for a number of engines and manufacturers (seemed that the Japanese carmakers were most affected).  But nothing like the switch from gross to net.

I'm not aware that manufacturers use inertial dynos when certifying engines.

[Soup DeVille]

You said SAE net has changed from testing undressed engines to dressed engines, which is not correct.  Up through MY 1971, manufacturers rated car engines using SAE gross.  Starting for the '72 MY, they were required to use SAE net.  The end result was a substantial (20-30%) "on paper" drop in horsepower ratings across the board despite engines that were in many cases unchanged between model years.

Yes, SAE net testing and rating procedures have changed slightly since 1972.  There were adjustments within the past decade or so that result in slight "on paper" power rating decreases for a number of engines and manufacturers (seemed that the Japanese carmakers were most affected).  But nothing like the switch from gross to net.

I'm not aware that manufacturers use inertial dynos when certifying engines.

No, not what I said.

[MX793]

No, not what I said.

The SAE net in '71 was a different test, procedurally than it is now; and a lot of driveline changes since then as well. It also wasnt flywheel hp as we understand it, but gross horsepower, where not even parasitic losses like the alternator and power steering pump weren't counted.

Emphasis mine.  It wasn't SAE net at all in '71, it was SAE gross.  SAE gross that was used then is a different test from SAE net used from '72 to present.  They are two different things and two different tests.

[Soup DeVille]

Emphasis mine.  It wasn't SAE net at all in '71, it was SAE gross.  SAE gross that was used then is a different test from SAE net used from '72 to present.  They are two different things and two different tests.

The second sentence referred to gross versus fwhp. My wording may have been unclear,  but anybody not being a pedantic pain would have realized that.

[GoCougs]

The SAE net in '71 was a different test, procedurally than it is now; and a lot of driveline changes since then as well. It also wasnt flywheel hp as we understand it, but gross horsepower, where not even parasitic losses like the alternator and power steering pump weren't counted.

Prior to 1972, many gross ratings were exaggerated courtesy of testing a blue printed and curated motor running on super hi-test, which no volume-produced motor of the time could live up to (although some motors, usually the hyper performance mills like the 426 Hemi, Boss 429, ZL1 427, etc., were purposefully underrated).

Plus, designs for accessories - radiator fans (now electric), steering pumps (mostly now electric), water pumps, exhaust, accessories (clutches), etc. - were not optimized.

In short, artificially strong spec + inefficiency accessories is not the case today.

But logic solves this for us as well. A 505 LS7 hits an engine dyno with 675 hp? In the age electric fans, alternator clutches and electric steering, where does 170 hp go??? Any legit engine dyno test of a stock LS7 shows 550-575 hp.

TL;DR - SAE drop to NET is 10-15%. Plenty of modern/current stock engine dyno tests out there tells us this. No legit motor or test shows a 25% drop from gross to net.

[Soup DeVille]

I do believe some AWD/CVT setups approach that- but not what we're dealing with here.

[MX793]

I do believe some AWD/CVT setups approach that- but not what we're dealing with here.

You appear to be talking WHP.  Manufacturers don't rate at the wheels via chassis dyno, they rate at the crank.  Driveline loss is not included in either SAE gross or SAE net testing.

[Soup DeVille]

You appear to be talking WHP.  Manufacturers don't rate at the wheels via chassis dyno, they rate at the crank.  Driveline loss is not included in either SAE gross or SAE net testing.

"but that's not what we're talking about" must have been another unclear sentence. I'll try to work on that.

[MX793]

Prior to 1972, many gross ratings were exaggerated courtesy of testing a blue printed and curated motor running on super hi-test, which no volume-produced motor of the time could live up to (although some motors, usually the hyper performance mills like the 426 Hemi, Boss 429, ZL1 427, etc., were purposefully underrated).

Plus, designs for accessories - radiator fans (now electric), steering pumps (mostly now electric), water pumps, exhaust, accessories (clutches), etc. - were not optimized.

In short, artificially strong spec + inefficiency accessories is not the case today.

But logic solves this for us as well. A 505 LS7 hits an engine dyno with 675 hp? In the age electric fans, alternator clutches and electric steering, where does 170 hp go??? Any legit engine dyno test of a stock LS7 shows 550-575 hp.

TL;DR - SAE drop to NET is 10-15%. Plenty of modern/current stock engine dyno tests out there tells us this. No legit motor or test shows a 25% drop from gross to net.

Alternator clutches are 1-way clutches that permit rotor over-run, they don't decouple the rotor in the same sense that an AC compressor clutch does.

I'll give you EPAS, but do electric fans not consume power?  Unless your argument is that the dyno run is short enough (or sufficient external airflow is provided by an external fan) that the fans never turn on.  But, fair enough, gross vs net losses of a modern engine shouldn't be as high as a '70s motor.

[GoCougs]

Alternator clutches decouple like any clutch on any accessory - AC compressor, supercharger, whatever - whatever is best for a particular situation, including decoupling when not needed to improve MPG, to improve performance, etc.

99.99% guarantee elecctric fans do not turn on during an SAE net test run. If they do, they are vastly more efficient/effective than a mechanical fan - 1 hp or less parasitic loss - so they'd likely be in the noise of the measurement.

[MX793]

Alternator clutches decouple like any clutch on any accessory - AC compressor, supercharger, whatever - whatever is best for a particular situation, including decoupling when not needed to improve MPG, to improve performance, etc.

99.99% guarantee elecctric fans do not turn on during an SAE net test run. If they do, they are vastly more efficient/effective than a mechanical fan - 1 hp or less parasitic loss - so they'd likely be in the noise of the measurement.

I would be very interested in seeing a link to an actively controlled alternator clutch that cycles on/off based on need (that's actually in widespread use).  The only alternator clutches I'm familiar with are 1-way clutches (OAP) and IDP/OAD types.  Both are passive, mechanical devices that react to changes in belt tension to isolate vibration.  The former simply allows free-wheeling on engine deceleration.  The later allows free-wheeling on deceleration while also containing springs to permit some forward slip to absorb forward belt drive shock.

[giant_mtb]

I did not know alternators had clutches.  I thought they were just sort of "always engaged," but I guess that doesn't make sense since different spinny speeds will produce different electrical output...?

[MX793]

I did not know alternators had clutches.  I thought they were just sort of "always engaged," but I guess that doesn't make sense since different spinny speeds will produce different electrical output...?

Alternator clutches are a relatively recent thing.  To my knowledge, and based on everything I can find on Google, the clutches used today don't so much govern the speeds as they reduce shock/vibration on the drive belt by permitting the alternator rotor to free wheel (spin faster than the input if the input source slows down) or to very slightly lag the input if there is a sudden increase in input speed (essentially a radial spring cushion to smooth out any jolts).  The electrical system has power regulation and conditioning to cope with variable alternator outputs as related to engine speed.  Alternator power is, electrically, very dirty/noisy.  More sensitive modern electronics require power conditioning to accept alternator power (most microcircuits run on something less than 12V, so there's some conversion that has to happen anyway and conditioning can happen in the conversion circuits/devices).

[giant_mtb]

It's good to have engineers here. Thanks!

[Soup DeVille]

over-running clutches on alternators were, until recently, kinda a hot rod thing.

Alternators on many classic V8s ran at about 3 times engines speed, or greater. On a hopped up, lightened flywheel engine, dropping speed fast could throw the alternator belt- and some people claimed even damage the crank nose.

It wasn't until recently that they became standard on some engines.