drivetrain power loss

[wako29]

okay, I got into kind of an argument on another board about this.

Guy said he has 360rwhp on a LT1 Caprice ex-cop car. Then he said that computes to like 450hp to the flywheel. I held up the BS flag on that, as it isn't that much of a loss. Am I right?
Another guy started talking about a 20% loss of power throught the drivetrain and all, and that is way to much IMHO. Not only that, but can't you not measure it with a percentage?

So who is right here? If I'm wrong, thats cool, and I will take it like a man, but that much of a drop seems way to much.

[Joe 1320]

More like 15% loss on a manual, 20% on an automatic. No way an LT1 without heads, cam, headers and cat back (except a power adder) is going to make 450HP at the flywheel. It's just not going to happen as the motor cannot flow enough air to sustain that HP. Even increasing the cubic inches alone won't do that. A seriously thought out collection of parts and dyno tuning would be required.

[wako29]

his sig:

Aluminum LT1 heads ported by Lloyd Elliott, LT4 hotcam, Comp Cams 1.7 rockers, Yank SS 3600, stock shortblock, every bolt-on.

361 RWHP, 363 RWTQ - SAE corrected
13.10@102.81, 1.747 60', 4430 lbs

he is supposed to be very imformative in the area of the Caprices, which is what the forum is about.

[fastTa]

Re: drivetrain power loss

Originally posted by wako29
okay, I got into kind of an argument on another board about this.

Guy said he has 360rwhp on a LT1 Caprice ex-cop car. Then he said that computes to like 450hp to the flywheel. I held up the BS flag on that, as it isn't that much of a loss. Am I right?
Another guy started talking about a 20% loss of power throught the drivetrain and all, and that is way to much IMHO. Not only that, but can't you not measure it with a percentage?

So who is right here? If I'm wrong, thats cool, and I will take it like a man, but that much of a drop seems way to much.

That will depend on what type of tranny, driveshaft, and rear end he is running.

If he is running a 4L60E and the stock rear end, most people use about a 17.5% estimated correction factor for that combo.

However, by the chance that he is using a TH-400 and a 12-bolt or a 9" rear, then a 20% estimated correction factor would be about right.

The only way to accurately measure the power lost through your drivetrain is to establish a HP level with an engine dyno and then to run your car on a chassis dyno and compare the difference.

The chassis dyno numbers will obviously be less than the engine dyno numbers. So by dividing the chassis dyno HP by the engine dyno number, you will obtain a *percentage* of the engine dyno HP.

It is definitely feasible that he is making 361 RWHP given his mods, but to determine if he is using an accurate DT correction factor to *estimate* flywheel HP, we would need to know his DT specifics.

[Joe 1320]

Higher stall converters are known for showing reduced power on the dyno. Most likely his power levels are accurate.

[fastTa]

Originally posted by Joe 1320
Higher stall converters are known for showing reduced power on the dyno. Most likely his power levels are accurate.

Yep, and especially if they run them unlocked on the dyno.

[Injuneer]

I have the actual numbers for my setup, based on the engine dyno pulls and then chassis dyno pulls.

When the car was an M6/Street Twin/12-bolt/3.73's the drivertrain losses ranged from 12.6% at 486flywheelHP to 12.1% at 762flywheelHP.

With the TH400/3,500+ stall/non-locking, everything else the same, the losses ranged from 19.8% at 486flywheelHP to 21.3% at 762flywheelHP.

It would be reasonable to assume the 4L60E would be more in the 16-18% range.

[Joe 1320]

As usual, Fred is right on the money. To add to that, gears, driveshafts along with wheels and tires can contribute to losses as well. The lighter the driveshaft, the lighter the wheels and tires, the smaller the loss from flywheel to rear wheel. Ditto goes for small parasitic losses like disk brake clearance, wheel bearing clearance, transmission clutch conditions, and so on. If enough attention is paid to the little detail items, they can add up to a couple of percentage points. Gears like 4:10s show losses on the dyno compared to 3.42s due to a difference in load on the engine as well. There are so many variables......