Hellcat Dyno

[@srt_n8 16]

http://blogs.motortrend.com/1408_dyno_mighty_challenger_srt_hellcat_camaro_zl1_hit_the_rollers.html?__federated=1

635/591 according to the K&N dyno. They used the 1.29:1 5th gear instead of the 1:1 ratio 6th.

[DevilDogge 23]

11% drive train loss. Is that better than the '14 nag1/6.4?

[Dookie 3]

MT are full of idiots. While the article puts the HC in good light, it's inaccurate. The rated 707 and dynoed 635 is spot on. 72hp loss through the drive train is what i would expect, forget a percentage of deal...It's purely a HP parasite, it takes what it takes, nothing more, nothing less. Nag versus TF...about the same amount of power it takes for the task at hand.

[DevilDogge 23]

forget a percentage of deal...It's purely a HP parasite, it takes what it takes, nothing more, nothing less. Nag versus TF...about the same amount of power it takes for the task at hand.

Not true.

[Pat McCrotch 6]

MT are full of idiots. While the article puts the HC in good light, it's inaccurate. The rated 707 and dynoed 635 is spot on. 72hp loss through the drive train is what i would expect, forget a percentage of deal...It's purely a HP parasite, it takes what it takes, nothing more, nothing less. Nag versus TF...about the same amount of power it takes for the task at hand.

Drive train parasitic may not be an exact fixed percent but unfortunately it's relatively close. As the torque load placed on gears/bearings/pumps goes up so does friction and the power lost converts to heat. ie the train will not consume 72 hp at 10 mph. WOT yeah, power lost to friction will generate some big time heat in short order.

[@srt_n8 16]

I don't buy that it's only a 10.1% loss and they also didn't dyno in the 1:1 ratio gear

[Dookie 3]

Not true.

On a dyno in a selected ratio, yes it is. Prove me wrong...I have dealt with power transmission daily for the last 25 years. Every mechanical engineer I have posed this to has agreed with me, not to mention many high profiled names in the LX/LC industry. You believe whatever you would like, but the laws of physics and engineering have a pretty good argument.

Now, if your gearbox capacity and drivetrain aren't up to the task at hand and more heat is generated that digs into the service factor, then yes, more power will be cannibalized.

[DevilDogge 23]

On a dyno in a selected ratio, yes it is. Prove me wrong...I have dealt with power transmission daily for the last 25 years. Every mechanical engineer I have posed this to has agreed with me, not to mention many high profiled names in the LX/LC industry. You believe whatever you would like, but the laws of physics and engineering have a pretty good argument.

You're saying that it takes 72 hp, no more or no less, to spin that drive line at a certain engine RPM. If that's the case, if the engine was detuned and had considerably less horsepower that it would still take 72 hp to turn it at the same RPM? That is incorrect.

it takes what it takes, nothing more, nothing less.

What Mccrotch is saying above is true. It won't be perfectly linear at 11%, but it'll be closer to that percentage than it will to any constant.

[Dookie 3]

If demand is equal, yes, if demand changes, no. The amount WILL vary with demand, but will not be linear with the amount of hp increased or decreased. So to say it is X percentage is incorrect, and I guess I was wrong to say nothing more nothing less. I stand corrected.

[Drp6982 31]

I think 1.29 gear is close enough...

.

In my dyno experience a true 1:1 read a bit higher then when I dyno'd in 3rd gear on my nag1

[toofart 148]

They probably oversped the dyno on the 1:1 gear. Doesn't the hellcat TF have a 2.65:1 rear ratio?

[Boatman 97]

I don't buy the % argument.

My engine engine dynoed at 1800 or so. So what you're saying is that because I make 1800 or so HP it takes 175-215 HP to turn a trans and rear gear but the 707 HP engine only needs 72-85 HP? That really don't make any logical sense whatsoever.

[toofart 148]

to turn a trans and rear gear

Not to *turn* it, to accelerate it. Dynos measure how fast you can accelerate a mass.

Hop on your bicycle and accelerate as fast as you can to 20 MPH. What does it take to accelerate the same mass to the same speed, in less time? More POWER!

[Boatman 97]

Not to *turn* it, to accelerate it. Dynos measure how fast you can accelerate a mass.

Hop on your bicycle and accelerate as fast as you can to 20 MPH. What does it take to accelerate the same mass to the same speed, in less time? More POWER!

That's not what I'm saying. Just a % of loss from a Engine dyno to a chassis dyno.

[DevilDogge 23]

I don't buy the % argument.

My engine engine dynoed at 1800 or so. So what you're saying is that because I make 1800 or so HP it takes 175-215 HP to turn a trans and rear gear but the 707 HP engine only needs 72-85 HP? That really don't make any logical sense whatsoever.

Kind of. Remember, it won't be perfectly linear, and the more you get to the extreme, like your engine's numbers, the less linear it'll be.

This is from a mechanical engineer with his PE license who's specialty is internal combustion engines;

Good question. I'd say you'd probably get a different result and not get either one of those scenarios exactly. However I'd err to the side of a general 11% loss.

Friction through the drive train is a function of loads on bearings and mostly gear meshing/face speeds and I'd suspect it's quite non-linear in nature. Also there are losses in the slip mechanism, either the torque converter or the clutch. Aka, 707 HP with the accompanying twist of say around 700 ft lbs is putting loads on gear surfaces that the smaller engine couldn't produce. A lot of the friction in a drive train comes from the faces of all the helical gears meshing together. The more torque they transmit, the higher the face loading and thus friction and losses. I think that's why heavier duty trannies and gear set ups take a thicker grease. The torque being transmitted and thus the normal forces on opposing gear faces are a lot higher and thinner greases just get squeezed out, where as a thicker grease can take the "squeezing" and still stick ot the surfaces to provide lubrication. Also with helical gears it's a function of speed too, not just torque since they slide into mesh and don't just bang together like straight spur gears. That banging is what causes the whine in reverse, it's a lot of times a straight spur gear because it doesn't get the use a forward gear does and they're cheaper to cut.

I would say you would lose around 11%, not the original 72HP. the loadings on gears and bearing would be less severe and thus less loss. It takes 72HP to twist the train at that loading and speed, but would take less power to twist at a lower loading or slower speeds. It's not possible that the train loss is a static figure. Also you can spin just about any drivetrain with your bare hands or a small lawn mower engine slowly, so as loading goes down the friction does also. So at small loads, the friction is also small.

If I had to guess I'd say you might get less than the 11% loss with the smaller engine but hard to say, other than it it's not going to rob your smaller engine of 72HP right out the gate.

[BayouTigress 73]

So here is what little I know. I have seen tables in articles on line that drivetrain losses range from 12%-20% from the crank shaft to the wheels. Some drivetrain loss components are constant and some components are variable in a single drivetrain. So I am not surprised it dynoed less than 707. In fact I was guessing closer to 625 rwhp. So this is better than than I hoped.

[Dookie 3]

Kind of. Remember, it won't be perfectly linear, and the more you get to the extreme, like your engine's numbers, the less linear it'll be.

This is from a mechanical engineer with his PE license who's specialty is internal combustion engines;

Good question. I'd say you'd probably get a different result and not get either one of those scenarios exactly. However I'd err to the side of a general 11% loss.

Friction through the drive train is a function of loads on bearings and mostly gear meshing/face speeds and I'd suspect it's quite non-linear in nature. Also there are losses in the slip mechanism, either the torque converter or the clutch. Aka, 707 HP with the accompanying twist of say around 700 ft lbs is putting loads on gear surfaces that the smaller engine couldn't produce. A lot of the friction in a drive train comes from the faces of all the helical gears meshing together. The more torque they transmit, the higher the face loading and thus friction and losses. I think that's why heavier duty trannies and gear set ups take a thicker grease. The torque being transmitted and thus the normal forces on opposing gear faces are a lot higher and thinner greases just get squeezed out, where as a thicker grease can take the "squeezing" and still stick ot the surfaces to provide lubrication. Also with helical gears it's a function of speed too, not just torque since they slide into mesh and don't just bang together like straight spur gears. That banging is what causes the whine in reverse, it's a lot of times a straight spur gear because it doesn't get the use a forward gear does and they're cheaper to cut.

I would say you would lose around 11%, not the original 72HP. the loadings on gears and bearing would be less severe and thus less loss. It takes 72HP to twist the train at that loading and speed, but would take less power to twist at a lower loading or slower speeds. It's not possible that the train loss is a static figure. Also you can spin just about any drivetrain with your bare hands or a small lawn mower engine slowly, so as loading goes down the friction does also. So at small loads, the friction is also small.

If I had to guess I'd say you might get less than the 11% loss with the smaller engine but hard to say, other than it it's not going to rob your smaller engine of 72HP right out the gate.

+1

[Boatman 97]

Here's my take: using a % for a general rule of thumb is fine for the most part but it's really a hard HP number to turn gears.

My point. You engine dyno a engine and it comes in at 800 then put it in a car let's say a six speed so we take out the single biggest factor being the TQ converter and you get 696 on the chassis dyno.

Then you dyno a race engine and get 1750 then put it in the exact same car it's not going to take 227 HP to now turn the drive train when it just turned with 104. That's my point.

[DevilDogge 23]

Here's my take: using a % for a general rule of thumb is fine for the most part but it's really a hard HP number to turn gears.

My point. You engine dyno a engine and it comes in at 800 then put it in a car let's say a six speed so we take out the single biggest factor being the TQ converter and you get 696 on the chassis dyno.

Then you dyno a race engine and get 1750 then put it in the exact same car it's not going to take 227 HP to now turn the drive train when it just turned with 104. That's my point.

I think you'd be surprised at how much closer it would be than a "hard hp" number to turn gears. Have you ever put your bad ass mother fucker on the rollers, knowing that it makes 1800 at the crank?

BTW, this is the question that I asked to get the answer I quoted above;

Let's say you have one engine and one drive train. The engine produces 707 hp at the crank and 635 hp at the wheels. That's a loss of 72 hp or 11% through the drive line.

Now take the same engine and drive line, detune the engine, and now it's only making 300hp at the crank. Will it put out 228 hp at the wheels (300-72) or 267 hp at the wheels (11% loss) all at the same RPM level that it made 707?

Please explain your answer.

[Boatman 97]

I think you'd be surprised at how much closer it would be than a "hard hp" number to turn gears. Have you ever put your bad ass mother fucker on the rollers, knowing that it makes 1800 at the crank?

BTW, this is the question that I asked to get the answer I quoted above;

Let's say you have one engine and one drive train. The engine produces 707 hp at the crank and 635 hp at the wheels. That's a loss of 72 hp or 11% through the drive line.

Now take the same engine and drive line, detune the engine, and now it's only making 300hp at the crank. Will it put out 228 hp at the wheels (300-72) or 267 hp at the wheels (11% loss) all at the same RPM level that it made 707?

Please explain your answer.

My answer is take it to the track as numbers don't lie and a Dyno is really nothing more than a tuning tool. People get a little to wrapped up in the numbers game, understandly so as HP is cool.

I did take the car to a chassis dyno to try and sort out a tuning deal. It was new and we didn't have a convertor that worked, we had a little over 30% slip. I think the Chassis said 1350 or 1400 cannot remember now exaclty what it was.

[Tout 60]

My answer is take it to the track as numbers don't lie and a Dyno is really nothing more than a tuning tool. People get a little to wrapped up in the numbers game, understandly so as HP is cool.

I did take the car to a chassis dyno to try and sort out a tuning deal. It was new and we didn't have a convertor that worked, we had a little over 30% slip. I think the Chassis said 1350 or 1400 cannot remember now exaclty what it was.

Your right about the dyno being a tuning tool Rob

[Adanac Charger 30]

Your right about the dyno being a tuning tool Rob, where I think you may be missing some thing is that loss numbers change with the PA that is being used to generate the higher HP, meaning a nitrous car would loose the least, turbo next and Sc being the highest loss, converter slipage and a few other factors can also be thrown into the equasion.So no you can't use a % in racing applications unless your talking about setups that are simular.

Huh??

HP measured at the flywheel (or at the wheels) doesn't care what kind of motor it is or what kind of PA it has.

[Tout 60]

Huh??

HP measured at the flywheel (or at the wheels) doesn't care what kind of motor it is or what kind of PA it has.

Yea, I just reread it, delete what I said,

[Adanac Charger 30]

Good to hear... I was worried about you.

[lakersfan7272 59]

We've been worried about him for a long time.