Thanks Madbill,

The data I have seen from Tony is from one car with several iterations of engine combiations tested on one engine and chassis dyno at the same facility. The next datapoint will be with a big inch motor which should be at least 100HP more than the previous test. This should give us at least 3 to 4 data points with at least a 75-100 HP spread between points to quantify a percentage, fixed loss, or combination of the two. I just don't think you're going to find its a linear progression. There is too much heat energy to account for. Especially when you take into account cars with more horsepower.

Take a car making 1000 crank horsepower. By figuring a 15% driveline loss, you are assuming that you will input 1000 and output 850. So, the loss in the system is 150. You take 150 horsepower and turn it into something else, namely heat...

150 horsepower = 6366.746 BTU/min or 106.1124 BTU/sec thats is a lot of heat energy to have to disapate. And, it may be that we find a certain percentage of fixed loss, and then there may be a portion which is figured on a sliding scale which increases. I don't know yet. I'm still waiting on the last bit of data...


One last thing. Unless you did a engine dyno and then followed it up with a chassi dyno its hard to quantify a dyno result froma year ago, and then following up after a repair. The original data may be skewed unless you can quantify that the motor is still makign the same power it did last fall. Unless you can return to the same dyno and re-run the engine how do you know its still making 830 HP and 560 lb-ft. I've had a motor that just sat for 6 months that was not run that was down 30 HP after just sitting that I had to sort out to get back to "zero".

 

Well in this case the problem was a failed roller in a Jessel rocker, and we felt the power loss was greater than expected from that, so went to the dyno to ensure we hadn't missed another issue. We were at the Mosport road course today, and despite the diff giving us some trouble (wheelspin) exiting onto the straight, and barometric pressure down ~1" from last Fall, we were getting 178 MPH as compared to a best of 180 then, so it would appear our actual power is very close to the same.
The shop we work with at the track had a 350 SBC engine built up and engine dynoed a couple of years ago at 525 HP and then installed it in a vintage 4 speed Corvette and re-dynoed it the same day on a DynoJet, producing 439 HP...

My opinion, unsupported by a theory or details, is that there are half a dozen or more elements contributing to the losses seen on a chassis dyno and that some are fixed, some are speed-dependent, some-power dependent, some increase linearly and some probably at a power greater than one, but that for manual transmissions, conventional drivetrains and engine dyno ratings between 200 and 1,000 HP, 15% is as accurate a number as anyone will get for a DynoJet, absent a major laboratory-grade series of experiments..

 

No, not heat. Kinetic energy. The drivetrain has mass, and it takes energy to accelerate it. Just like it takes more power to accelerate the car more quickly, it also takes more power to accelerate the drivetrain more quickly.

F=ma. Double a, and you have to double F.

Where the confusion comes in, I think, is that when you measure the engine's power at the crank, there is nothing between it an the dyno. If you put a 300 lb cylinder maid out of 45 lb weights between the engine and the dyno, the dyno can't see the weights and would show the engine was down on power, yes? But if you know the moment of inertia of the weghts, you can calculate the actual crank horsepower...

I don't think you're going to see a lot of frictional increases as horsepower goes up. For that to happen, the transmission fluid would have to shear and the bearings would have to touch - which would wreck the tranny in short order. You'll see more losses from the speed increase, since you're pumping fluid around faster, but whether that's a linear thing or not I don't know.

 

My guess is its not a linear loss from increase/decrease in RPM. Working for a large turbomachinery company, our bearing losses (HP) are not linear with speed changes. But the losses we see for large swings in speed are not all that dramatic and the machines generally operate outside the rpm range of most motors in cars, but that depends on machine size obviously. Larger machines dont spin as fast

 

Well, much of the rpm range remains the same no matter what mods you have, so the 15% is probably not due to bearing losses (at least not most of it). I was thinking more along the lines of the dynojet dyno having 84% of the mass after the crank and the drivetrain of the car having 15% (80% and 20% respectively for autos).

 

Are you retarded??

 

Does anyone know if the LS7 cam has a smaller base circle compared to say a stock L92 cam?

Thanks,
Andrew

 

Does anyone have a clear answer to the base circle question? I installed a LS7 cam in my L92 but the valve train seems to be a little noisier than it should be. I am using stock length, hardened push rods and PRC Gold dual springs with titanium retainers.

Thanks,
Andrew

 

If I'm not mistaken, they still run the same base circle as the 02+ LS6 cam. The LS7 cams have a lot more aggressive ramp profile. If you are not running the LS6 yellow springs or better, that may cause the valvetrain to not be able to follow the cam effectively. This might be the culprit with your extra noise. This is all just conjecture as I am not really sure what was installed for springs in the L92. But my LS3 heads cam with the yellow LS6 style springs which is minimal requirement for GMPP's more performance oriented cams. The LS7 has a completely different (from any other LS engine) lightweight titanium valvetrain too.

 

As stated in my previous post, I am using PRC Gold dual springs with titanium retainers. If the LS7 cam has the same base circle as the LS6 cam then that would be smaller than a standard LS1 cam.

Anyone have a definitive answer?

Thanks,
Andrew

 

Anyone?

Andrew

 

That's wierd, I thought I posted the answer 2 weeks ago, guess the post failed from my end.

LS7 base circle is 0.745" radius (give or take a couple of thousandths), this is from a new LS7 cam.

LS7 lifters have a pushrod cup that locates the lifter end of the pushrod approximately 0.040" higher than the regular LS lifters, which no doubt make up all or part of the difference in base circle.

 

The driveline losses on a MN6 C5 have been measured at 17%.

Assuming similar losses for a C6 Z06. with their larger ring gear, a 450 rwhp car would be putting out approximately 542 crankshaft horsepower.

 

The losses in the C5 drivetrain are not a fixed percentage and vary according to the ammount of mass in the driveline. If you go read the posts by Tony Mamo on this he has done extensive testing on his vehicle and seen a fixed ammount of loss based solely on mass. in other words as HP increased, loss remained constant.

I've often wondered if people are so tied to a percentage because it allows them to artificially inflate the crank HP number on their vehicles.

 

J-Rod,

I did a seach of Tony's posts and I cannot find one titled Powertrain Losses, or anything close to that.

Recommendations?

 

Very interested in catching that one too. Certainly drivetrain inertia has a large effect on accelerating numbers, though how it affects steady state power other than tire and related load friction has me curious.

 

Would a LS7S cam work in a 408Lq4 with LS3 heads and flat top pistons?

 

Ok guys A friend of mine is putting togather a LS7 motor. He works at a dealership. The car came in with a spun rod. So he was able to pick up the old motor, at a reasonable price. He is looking to put a cam, headers, maybe a intake and TB on the motor. Can anyone recommend a good proven set up? What cam would you use, what intake, And would you even need a TB? also have you tried the set up you would recommend? If so what kind of pwer did it make?

 

Depends what his objectives are power wise. No need for a TB the stocker is not a restriction. Even with an intake unless you are chasing big numbers......

 

The LS7 needs a couple of reliability improvements:

Good luck with your motor.