[ShizzySupra]

Originally Posted by Drsagacity

Are you saying that dyno doesn't account for the gearing when it's not 1:1 ratio? On a stock car, rwhp reflects 390rwhp, rated at 455hp at the flywheel. That' is approximately a15% loss. If we apply that same calculation to Laynlo's car, he's running about 827hp at the crank. . .that's pretty sick.

I will have to spend some time looking at the math, but in theory, we should be able to take the RWHP in any gear and apply a factor to account for the gearing for the run and figure out real RWHP.

You can't linearly apply "loss" it's not an arbitrary number across the board. Guessing crank HP is just that, pure guessing. Either an engine dyno or chassis dyno will give you some form of "measurement". A dyno won't take into account the gear either.

[laynlo15]

Yes I pulled in 5th gear and it was 158 mph or so. I have done one 6th gear pull and it was over 180 mph, pretty scary on the dyno. It didn't make anymore power if I remember correctly, I just know I wouldn't recommend it and 6th gear is 1 to 1. I don't know how far I'll go on the stock internals, I'm close to running out of fuel right now and its pretty impressive to pull that much power out of a stock 6.2. I'm going to try one more pulley and it possible with the 70 mm pulley I might run up against the fuel wall that others have. I can spray more Meth/water as I've got it turned back to make more power down low. I'm running about 15 lbs off boost with the 75mm pulley. If I can run the 70 I'm guessing it might be around 18 lbs and I might start to get some slippage from the belt. If I can get the car to hook this weekend with mid 60's temps I might get close to 10.00s@140. I'm about 30 rwhp more from when I went 10.33@135 so I might be a few hp short.

[Drsagacity]

Originally Posted by ShizzySupra

You can't linearly apply "loss" it's not an arbitrary number across the board. Guessing crank HP is just that, pure guessing. Either an engine dyno or chassis dyno will give you some form of "measurement". A dyno won't take into account the gear either.

Yep. I know it's an estimate. But since every dyno shows different numbers, even a dyno is an estimate and it's a tool to compare the impact of changes on that car. You can't really compare dyno numbers across dynos.

I figured that we could know pretty much that the factory rating is very close (455hp). Then assuming you use the same dyno, you will see the % loss caused by the drivetrain. It's an estimate for sure. But, we can use 15% as the basis for doing the math. If a car rated at 455hp puts down approximately 390rwhp. That is pretty accurate (A8).

Similarly, if we take a stock ZL1 with 650HP, it should put down about 550 to the wheels (assuming 15% drivetrain loss). That seems pretty accurate also.

To figure out the power from the engine, it would be reasonable to use 15% drivetrain loss (and any gearing anomalies). It would be really cool if we could have enough data to understand the standard deviation of the mean. But, good enough for government, take the RWHP and divide by .85 (for an A8) and you have your estimated HP at the engine.

[Drsagacity]

Originally Posted by laynlo15

Yes I pulled in 5th gear and it was 158 mph or so. I have done one 6th gear pull and it was over 180 mph, pretty scary on the dyno. It didn't make anymore power if I remember correctly, I just know I wouldn't recommend it and 6th gear is 1 to 1. I don't know how far I'll go on the stock internals, I'm close to running out of fuel right now and its pretty impressive to pull that much power out of a stock 6.2. I'm going to try one more pulley and it possible with the 70 mm pulley I might run up against the fuel wall that others have. I can spray more Meth/water as I've got it turned back to make more power down low. I'm running about 15 lbs off boost with the 75mm pulley. If I can run the 70 I'm guessing it might be around 18 lbs and I might start to get some slippage from the belt. If I can get the car to hook this weekend with mid 60's temps I might get close to 10.00s@140. I'm about 30 rwhp more from when I went 10.33@135 so I might be a few hp short.

Greg,
It would be interesting to see the dyno from 6th gear to see if there was any difference. It definitely doesn't seem like it would be safe to be around that run.

[laynlo15]

I don't even know if I have that one. I was on 2 different dynos with in two weeks and I was within 4 rwhp on both and they were both dynojets, I doubt that would be the same if it were a Mustang dyno. Numbers are usually slightly lower on a Mustang.

[PRAY]

Great results Greg.

I have dyno'd at least 20 6th Gens in 5th and 6th. ALL have gained power in 6th. On average it is around 22rw. Some as high as 25rw some as low as 18rw. The mph deal doesn't bother me. The dyno is good to 200 mph and the car is set to 186 for a reason. I do all of my tuning in 5th and then do one 6th gear to get comparable numbers to what a M6 would do in 1:1. The extra load and time under power can expose some things on the dyno that 5th gear won't show you. 5th gear on the dyno equals 3rd gear on the street. How many street blasts end in 3rd gear on the street? On the track a modded car will pull a while into 5th gear. So doing a pull or two in 6th on the dyno has a purpose.

As far as percentages and drive train loss go, the A8 is no more efficient than any Auto before it. It only appears that way due to final drive ration compared to the M6. 5th we get a final drive ratio of 3.51 and 6th is obviously 2.77. The M6 final drive ration is 3.73. The A8 in 5th will usually dyno 25-35rw less than an equally modded M6 even though it has a better final drive ratio. In 6th the A8 closes the gap but will usually be 10rw or so worse for the A8 and that is with a full point higher final drive ratio. So the A8 is no more efficient than any Auto before it. We just get more gears to bang through before 1:1 improving our applied tq to the ground in the lower gears.

[laynlo15]

Yep, I agree. I had never pulled in 6th before, so thought I'd try it.

[DFW1LE]

For A8 cars, you might want to see if any shops in your areas have a hub dyno. There would be no worries being in 6th gear and the results are generally more accurate than roller type dynos.

[laynlo15]

Na, 5th gear is fine. Its just a number and only the track tells the real truth. It might run slower then last year with more hp.

[Drsagacity]

Originally Posted by PRAY

Great results Greg.

I have dyno'd at least 20 6th Gens in 5th and 6th. ALL have gained power in 6th. On average it is around 22rw. Some as high as 25rw some as low as 18rw. The mph deal doesn't bother me. The dyno is good to 200 mph and the car is set to 186 for a reason. I do all of my tuning in 5th and then do one 6th gear to get comparable numbers to what a M6 would do in 1:1. The extra load and time under power can expose some things on the dyno that 5th gear won't show you. 5th gear on the dyno equals 3rd gear on the street. How many street blasts end in 3rd gear on the street? On the track a modded car will pull a while into 5th gear. So doing a pull or two in 6th on the dyno has a purpose.

As far as percentages and drive train loss go, the A8 is no more efficient than any Auto before it. It only appears that way due to final drive ration compared to the M6. 5th we get a final drive ratio of 3.51 and 6th is obviously 2.77. The M6 final drive ration is 3.73. The A8 in 5th will usually dyno 25-35rw less than an equally modded M6 even though it has a better final drive ratio. In 6th the A8 closes the gap but will usually be 10rw or so worse for the A8 and that is with a full point higher final drive ratio. So the A8 is no more efficient than any Auto before it. We just get more gears to bang through before 1:1 improving our applied tq to the ground in the lower gears.

Great info Pray. Great to know. That would mean for an A8, you could probably divide by .83 to get your engine HP. That would make the whp about 20-25 greater to match your experience.

[Drsagacity]

Originally Posted by laynlo15

Na, 5th gear is fine. Its just a number and only the track tells the real truth. It might run slower then last year with more hp.

It will only run slower if you are afraid to launch it, or if you have gained weight from last year. Otherwise, your car is gonna be crazy fast.

[SC88]

So this is what it takes to hear that blower huh? lol! Nice results Don't know if I will ever go up to 15psi but you now have me interested in going down a couple of pulleys.

[laynlo15]

I'm assuming you have a Maggie, what other fuel mods do you have? What pulley are you running now?