I was at work today and we were talking about gas prices... My one friends getting a Durrango and he said he's expecting to get around 10 miles a gallon. I said yeah that's about what I get. And the other guy at work said what do you expect you have a 500 horse power truck. That sounds pretty cool, do I have 500 hp at the crank? It's a 2000 and all I really have is a 4# lower, 2.8 upper, chip, open filter and exhaust. I dynoed at 415 at the wheels. What do you think I have at the crank? I think it's under 500.
Thanks, Shane

 

Well, if you go by Gregg Evans calculation of an 11% drivetrain loss, you would have 465 hp at the crank.

I personally think the Lightning's drivetrain loss is greater than 11%.

 

I agree; almost impossible to only lose 11% through the auto trans. I believe the trucks are under-rated from the factory which is why they make 340 rwhp or so stock. I think the 11% comes from 340 rwhp and 380 factory rated which is about 11% loss. That's if you believe the truck makes 380 HP.

Jody

 

Straight from Gregg's mouth:
"The drivetrain efficiency is a combination of transmission, driveshaft lash and final drive gear and lash translated to the hub of the rear wheels. At peak torque (not HP) the generated torque loss at the rear wheel [on the Lightning] is 11.2%, which is way higher than typically seen on an auto. About 20% is the of the top of my head number to use for most autos."

In a later post, Gregg explained that:

"In a Lightning at max torque in 3rd gear (only way to measure it right) it's 11.2%, and I'm not even going to get into how accurate that number is unless you're an automotive or electrical engineer with experience on drivetrain testing. Every time I mention it I get all kinds of "you're phu**ing crazy" comments, but that's the number, if you must know. It also has very little to do with the real world, just know for an automatic it's darned efficient."

Note than the 11% figure is at peak torque and may not be reflective of the powertrain losses at the horsepower peak. However, the math does work. 380 rated crank HP X .89 = 338 rwHP, which is a pretty typical chassis dyno result.

 

I think what he said is that is the loss of torque through the trans only at a certain RPM. doesnt the driveshaft and rear take some power away before the tires though? I kinda think these trucks make more like 400-420 at the crank and theres a 18-20% loss.

 

Still not buying it. Done 100's of chassis dyno pulls and nothing approaches that figure that I've seen, especially in an auto trans. The only way to know for sure is to pull a stock Lightning engine and stick it on an engine dyno. Betting it makes over 400 HP easy.

Jody

 

Yeah, I'm not buying the 11% loss either. The SRT-10 with 500 hp and a manual is dynoing just over 400 rwhp. Don't know how a manual could be losing nearly 25%, and were only losing 11%.

I mean no disrespect to Gregg with my opinion. I'm sure he has forgotten more about our drivetrain, than I'll ever know. I'm just questioning his figures compared to every other vehicle that I've seen dynoed.

 

V's always got his engine in and out
Why not use a built one for comparison.......
Ok I'm sorry V, couldn't resist.......

 

The factor I have always seen used is to divide the RWHP number by 0.8.

415 divided by 0.8 = 518.75 HP at the flywheel.

 

You know it blows my mind how sometimes a genuine expert will give some information. Like Gregg has on that issue and some of you idiots just don't accept it.

Some days this forum is pretty entertaining.

Rich

 

Hey Rich, idiot here! I appreciate Gregg's info and support on these boards. I just think he's way off on his estimate. Maybe he thinks the trans loses 11% by itself and that may be true. But you've also got the rear end, rolling resistance of the tires under the weight of the truck, driveshaft and u-joints, etc. There's no way I'll believe that in total the Lightning only loses 11%.

I've done a handful of back-to-back engine to chassis dyno tests (well, been involved in, weren't my vehicles). The least I've seen was about 18%. I'm sure that there are more efficient combo's than what I've seen done but everyone in the industry seems to agree that the lowest will be with a standard transmission, they just take less HP to turn.

Bottom line, the ONLY way to find out is get someone who still has a stock engine (LOL!) to pull it and get it on an engine dyno with the factory exhaust and intake/air cleaner on it. Then put it on a chassis dyno. I believe that the L engine makes more than 380 HP at the crank. If we go by rated HP figures from the factory, then the LS-1's of the late 90's, early 2000's have incredibly power loss figures of about 1%! After all they're rated at 305 hp in some of the years but will chassis dyno at about 300 rwhp.

Jody

 

Greg is not off on his "estimates" Greg is an engineer who worked on the transmission. That is a measured valued.

11.2% at peak torque in 3rd gear is a fact. Not how much loss there is in first gear at any ramdon RPM not peak torque is up for debate....

but 11.2% is a fact.

Coldie

 

So are you saying it's an 11.2% loss in 3rd gear at the tires? Or is it 11.2% loss through the trans only? I'll buy the trans figure, but not total loss as measured on a chassis dyno which includes the driveshaft, rear end, tires, etc. There is a difference between the two claims I'm asking about.

Jody

 

Thanks for all the replies. I was just simply wondering with the little bolt ons that I have how close I was to 500 at the motor...
If I had to guess I'd say I was a little short. I'd say I'm just over 450 or so. Say I have 365 stock...
4 pounder added what 30-40 at the crank, and 2.8 upper another 15 horse. That's 420 at most. My exhaust say 10hp, chip 15hp, 90mm mass air 5hp, and open filter 5hp. That's 455hp.
That's really all I've got. I think I need a good 25-50 shot to put me at 500 horse. I dont have the port job done to the blower or long tubes... What do you think?
Shane

 

I believe that was total drivetrain loss, but greg has spelled out exactly what that measurement was in different posts. You'll have to do the earch since I'm to lazy. Factory_Tech is his login

Coldie