Driveline losses

[StanTheMan]

It's fair to say a stock standard NA6 gets around 60-65 RwKw on the Dyno.

That'say around 25-27% loss through the driveline.

Obviously that loss becomes less if we were to turbo or modify the engine ? Or does the loss stay pretty consistent provided nothing gets changed along the driveline.

Just trying to work out rating at crank for my son.

[Magpie]

Can of worms... Only way to 'calculate' is to use an engine dyno then dyno the car.

Try rwhp/.85=BHP

The arguments against the above formula include, but are not limited to the following:

1. As power increase so does heat therefore more drivetrain loss
2. The amount of static friction in the components, this includes tyres
3. FWD/RWD/AWD
4. Manual/auto

[StanTheMan]

its going for a power run on Monday.

no idea on estimate. somewhere close to 110 whp maybe? theoretically it should be around 120-125? with the mods done to it on the Standard ECU.

previously with similar cams it had 140 whp but standard compression with an adaptronic.

so lets for the moment say it does go all the way to 120 that would make it 141 hp on the crank.
that would make it 105 kw at the crank
which is 110 kw per tonne which is P driving legal.
however it is 29% increase in power which is then considered a performance vehicle and therefore not legal.

[Magpie]

If you are trying to keep the car P legal, not sure what that is for where you are then you are best to search the internet for the argument that best suits the result you want. If you need 29% then search for 'legitimate'/empirical evidence to support your argument, look hard enough and you will find it!

[StanTheMan]

My son is super conservative.

he's worried more than I'm. He's a very good driver too.I'll have no issues throwing the keys in his direction.

he quizzed me the other day. Am I allowed to drive this?

I chucked a Trump. Alternative reality and some half truths.

[StuwieP]

Check whether modified cars are ok at all.

The rules changed recently but when I was on Ps about 4 years ago the rules were no V8s no turbos etc (which I know they got rid of) but you couldn't have a car with a modified engine either (at all AFAIK, even if under the general power/weight exception clauses)


edit: I wrote my response before thinking to look which state you were from. May need to figure out what "significant engine modification" means. Could be a PITA if NSW's RTA is as bad as Vicroads at providing info or advice.

stolen from your local RTA website:

From 1 August 2014, a high performance vehicle is defined as a vehicle which:

Has a power to tare mass ratio (PMR) of greater than 130 kilowatts per tonne or
Has had a significant engine modification, or
Is listed in the Roads and Maritime Services document Novice Driver- High Performance Vehicle Restrictions as a high-performance vehicle.

[bruce]

Any rules would be kW at the engine.
They'd use the factory figure for P rules.

[StanTheMan]

Correct. AU is metric and the do specify at crank power.

[StillIC]

It's fair to say a stock standard NA6 gets around 60-65 RwKw on the Dyno.

That'say around 25-27% loss through the driveline.

Obviously that loss becomes less if we were to turbo or modify the engine ? Or does the loss stay pretty consistent provided nothing gets changed along the driveline......

I used to read 'Cars and Car Conversions' magazine all through the 90s. Their technical editor used to publish rolling road dyno figures in every edition, including driveline losses. These were measured by having the roller push the engine, effectively, so the measurement was not necessarily the same as on power losses, as the losses were measured on the less worn, non driving side of each gear tooth. But the losses at the tyres would be consistent, but greater than road losses due to the shape of the roller.

Anyway, driveline efficiency ranged from about 70% at worst to about 85% at best, where 4wd cars had the most losses, front drive cars the least and rear drive cars inbetween. (This small range of efficiency seemed independent of modifications, changes to engines, gearboxes and so on. Indeed, when I studied such losses when I started Engineering we used to use a fixed fraction, not a number that changes; just as static coefficient of friction between smooth surfaces is independent of normal load and is also simply a fixed fraction.)

I hypothesise that the bevel gear mesh in the final drive of the rear drive and 4wd cars is a bit power hungry, and that the closer the diameters of these two gears the more efficient the mesh is, hence the ND having a 2.9 final drive ratio and being an efficient little jigger.

So for an NA, I would estimate no better than 80% driveline efficiency, probably more like 75% and maybe even 73% as you suggest. In short, I agree with you.

[StanTheMan]

Does that mean An NA6 fitted with a 4.1 diff would have less driveline loss than one fitted with a 4.3?

[CoffeeBoss]

he quizzed me the other day. Am I allowed to drive this?

Well isn't he coming along nicely


Sent from my iPhone using Tapatalk

[StanTheMan]

he quizzed me the other day. Am I allowed to drive this?

Well isn't he coming along nicely


Sent from my iPhone using Tapatalk

He is . Days of the baby'seat in the mx5 eat are gone. He's driving this thing now.

[StillIC]

Does that mean An NA6 fitted with a 4.1 diff would have less driveline loss than one fitted with a 4.3?

That's what I believe, all else being equal.

I should have also stated that different gear ratios in the gearbox will have different efficiencies, where a direct drive 1:1 ratio will be most efficient.

[MattR]

Well if you carry the results around with a weigh bridge ticket and a power to weight ratio calculated for constable plod to show the car is legal, a good dyno operator should be asking:
"And what power figures would sir like to have today?"
Other than that if it has a snail your son is probably sh*t out of luck if he pulled up by plod