Gross Horsepower LT-5

[efnfast]

It just seems there are so many interpritations of hp.
With and without headers or exhaust.
Same for intake.
Air quality.
What day of the week it was, ect,ect.

[Hib Halverson]

Originally Posted by tpepmeie

Ok I found the article. March/April 1998 Legend magazine. Page 14 is an article by Graham describing the 93MY changes.

"405 bhp was realized in GM Test 1 spec, which means with full vehicle inlet and exhaust system,

in GM Test 20 form, ie., dyno headers and no inlet restriction the 1993MY engine produced 445 bhp with optimized spark and fuel (LBT/MBT)."

So we have two different GM test specifications, with a 40bhp difference with headers and optimized tuning. What I don't know is what atmospheric correction factor GM uses for each of these tests. I believe it is probably 77F / 990mbar (SAE J1349) conditions, but I can't certain.

Doesn't really answer the original poster's question, but offers some insight into the difference with open headers/intake.

Glad you found the article, "tpepmeie".

Seems I was wrong about the early engines...375 SAE net and 415-hp (rather than 425) gross seems to be the case.

The SAE net is SAE J1349. I've heard of the other test, but never knew what the GM designation was nor do I know the correction, but I'd say you're right on 77°F. It wouldn't make sense that GM would use two different atmospheric corrections.

[scottfab]

Originally Posted by efnfast

I must agree with Paul, all this manipulation of numbers is meaningless. As Paul said, "where the rubber meets the road". SAE corrected or not, me and the guy next to me are breathing the same air when the right foot hits the floor.

I'd have to agree also but I suppose there'd be a few it means something to just like regular C4s with a ZR-1 badge on them
HP #s are great talking points but ETs are better

[Dynomite]

Originally Posted by tpepmeie

You clearly mean that it is all *meaningless* to you, right? If it were meaningless to everyone, we wouldnt have a lengthy thread here, right?

The numbers are meaningless to those that do not understand the numbers or the "manipulations" of the numbers (the math)

Most designs that I know start with manipulations of numbers (math) of some sort. And we (some of us) can get pretty close to the end result where the rubber meets the pavement with the math

The GM Engineers did not design the engine and drive train by running ETs (trial and error) I would guess. They did the math

[Hib Halverson]

Originally Posted by Paul Workman

(snip)
But, back on topic, there's gross and SAE net and RWHP and RWHP "under the curve". JMO, but HP at the wheels, where the rubber meets the road is the only meaningful measurement. Everything else is just so much hot water generated that means nothing, far as performance goes, methinks.

Originally Posted by efnfast

I must agree with Paul, all this manipulation of numbers is meaningless. As Paul said, "where the rubber meets the road". SAE corrected or not, me and the guy next to me are breathing the same air when the right foot hits the floor.

I'm not so sure we should rush to accept the idea that chassis dyno numbers are a true "benchmark" of engine performance.

There are many factors which skew chassis dyno numbers but have nothing to do with engine performance. In no particular order, some of them are:

1) tires...casing design, tread configuration and tread compounding. (I once did a back-to-back test of two tires just comparing tread confiuration and compounding-the tires were both on the same casing design-and the differece was 5-hp at the wheels. Same dyno, same pressure, same vehicle, some IAT and ECT, and tests 10-min. apart.)
2) tire pressure
3) dyno type, inertia or brake
4) single roller, two rollers or no rollers (direct connection to axles)
5) roller surface
6) wheel spin or lack thereof
7) trans type
8) trans lubricant and lubricant temperature.
9) rear axle ratio, lubricant and lubricant temperature
10) powertrain mountings
11) coolant temperature and temperature rise during test
12) different in IAT of more than 7°F regardless of correction
13) technique of dyno operator
14) condition of dyno

So, you see...chassis dyno numbers should be taken with a "grain of salt". They are embraced by the aftermarket performance industry and the enthusiast community because chassis dynos have been well-marketed by their manufacturers, they're loved by the automotive press and widely used by tuners. Chassis dynos are cheap and easy and perfect for bragging rights but fraught with potential inaccuracies.

I'm first to admit to using chassis dyno data all the time. Sometimes I strive to eliminate as many of the potential inaccuracies as possible. Sometimes I don't, but I know in the back of my mind that engine dynamometers are far more accurate devices for comparisons.

As for corrections...the belief that atmospheric corrections don't make a difference is just ridiculous. In fact, when I look at chassis dyno data, I'm more concerned with whether or not a correction has been applied and if so, what correction than I am with the inaccuracies of chassis dynos.

Recently, I was discussing a particular engine modification package with an aftermarket vendor. I asked for some of his confidential test data and he provided it. Same engine, same dyno, same test run...the engine made 646.0-hp "standard" corrected and 613.9-hp SAE-corrected.

See why the aftermarket and braggers like "standard" corrected data rather than SAE-corrected?

But, SAE-corrected is much more characteristic of the real world because of its use of 77°F for intake air temperature.

Lastly...

Originally Posted by scottfab

(snip)
HP #s are great talking points but ETs are better

ETs are either the most inaccurate way to bench mark engines or the most accurate way to benchmark the whole "package"...driver and car.

Do drivers are bragging about their engines. The first driver who majorly sucks on the starting line and has crappy tires but has a really good 350 in a ZR1 might go 13.2 The other driver who gets really good 60-foots, has his/her tire configuration just perfect but has a so-so 350, can run a 12.8.

So...who's got the best motor?
But...who's got the best ET?

[scottfab]

Originally Posted by Hib Halverson

ETs are either the most inaccurate way to bench mark engines or the most accurate way to benchmark the whole "package"...driver and car.

Do drivers are bragging about their engines. The first driver who majorly sucks on the starting line and has crappy tires but has a really good 350 in a ZR1 might go 13.2 The other driver who gets really good 60-foots, has his/her tire configuration just perfect but has a so-so 350, can run a 12.8.

Sounds like a line of hair splitting to me.
ETs can be the best way to measure overall performance there is.
Sure some exceptions can be brought to bear but there's many more exceptions that can be added.
Why even the effect of the moons gravity has an effect and the
imperfections on the asphalt under the right rear wheel. There
could even be a mosquito hit the windshield and slow it down.
Same driver running two different cars on the same night could even have
different wind conditions, a huge fly hit the windshield plus the major effect of 0.01oz of more fuel in one car vs the other. gezzzzzz
Seems like an exercise in futility to me.
A huge amount of meaningless exceptions can be added to dyno derived HP numbers too but I won't go there right now.

HP numbers are a fine metric but so is how many dimes you have in
the change holder. Being able to wave bye bye puts the "P" in performance. It's all together a better metric whether it's SAE or standard or pure air guitar corrected numbers.

Originally Posted by Hib Halverson

So...who's got the best motor?
But...who's got the best ET?

Whose got the shiniest dimes in the change holder?
Depends on the quality of the eye looking at it and the ambient air quality that the light goes through. But it should be SAE corrected air quality else
it's all for naught. And one should use proper wide spectrum light to test with and of course the angle of reflection should be at 90deg +/- 0.0000001 deg or the error will be so great that all bets are off.
Which is the better car?
1. 10,000 rpm V8
2. 502ci V8
3. 1800lb with driver
4. first over the 1/4 line

Answer: depends on which one I'm sitting in and Voltage measured at the spark plug of course.
Any hair that is split can always be split again until it looses meaning.

[XfireZ51]

Pretty much why you judge power on basis of trap speed not ET. Trap speeds can vary based on track setup.

[Paul Workman]

The trouble with standards, are there's so many to chose from:

J1349 circa 1972, June 1990, 2004 (crank hp)
J1995 (gross hp)
J607
J2723 certification spec
VCA (UK certification spec)

And, NONE of these address AVERAGE torque or hp at the wheel!

Bottom line: You can measure at the crank, or you can measure at the wheels, or somewhere in between. But, trying to predict one from the perspective of the other is full of variables as to make an absolute prediction either way almost folly.

I believe the trick is to pick the one that best fits the application, make the measurements as a base case for comparison to future improvements or modifications.

Examples: Engine builders with clients paying for results aren't interested in driveline losses. Drag racers aren't interested in peak hp at the crank, they're interested in trap speed (and ET to a lesser degree).

To get J1995 (crank net hp) I have to pull the motor. But, considering inertia of drive line hardware (including rotating mass), the hp number derived is significantly removed from how the car is going to actually perform, at least where differences are subtle.

For seat of the pants fun and a more accurate indicator of drag race result prediction, the inertia dyno measuring output at the wheels is a much better fit. However, quarter mile trap speed is a very good indicator for performance comparision! It isn't perfect either, but it does take into consideration "power under the curve" which is largely overlooked when in a pissin match over gross vs. net vs. shaft vs. wheel horsepower ratings.

Where the rubber meets the road is where real performance is demonstrated...I think is the main point ... at least it is for me. I'm not saying either isn't important in their own right - engine builders have their point of view and race drivers have a different perspective on output. But, trying to predict either from opposite ends of the drive line (read: is it SAE 15% standard loss or some other 18% standard) is where things get fuzzy really fast.

Hib...You said Barney measured 413 at the wheels. You used 18% drive line loss to predict you have about 504 net hp at the crank. My 90 Z measured 432 hp at the wheels, using SAE/Marc's 15% drive line loss, my net crank calcs to be 508 hp. Now, going on net crank hp and nothing else, I imagine it would be a near toss-up in the quarter mile, all things being equal. Care to race and compare??

P.

[Fully Vetted]

[Dynomite]

Originally Posted by Paul Workman

Care to race and compare??

P.

I doubt you would want to race with me

I did the MATH

Cliff

The 500 hp LT5 Rebuild
1991 ZR-1 (LT5) Performance