Transmission losses - Mk1 Gearbox?

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Icsunonove
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Transmission losses - Mk1 Gearbox?

Post by Icsunonove »

This rolling road business does my head in. They take a reading on the rollers which reads rwhp (rear wheel horsepower) and then add in a fudge factor for transmission losses to give you the flywheel horsepower. Well the problem is this fudge factor seems to vary depending on who you talk to.

It would be a lot easier if everyone just quoted rwhp. Then you would be quoting like for like (and at the end of the day rwhp is what actually matters).

The only real way to know is to benchtest the engine on a dyno out of the car and then do a rolling road test with it in the car. Anyone done this (expect not)?

What have people heard / been quoted as transmission losses for a MK1?

Thank for any replies, Tom
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Lauren
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Re: Transmission losses - Mk1 Gearbox?

Post by Lauren »

my engine produced 182bhp @flywheel
126bhp @ the engine.

Everbody else there ie Toni, Mark had the same losses.

RWHP is meaningless. Flywheel is the sensible way. Obviously a dyno is the only way to see actual power, but it doesn't reflect the environment in which the engine lives.

A couple of reasons why RWHP is crap is because rollers do not reflect a road surface ie there is lots more resistance due to the two rollers. Tyre pressure and type also makes a significant difference. Worse still if your car is strapped to the rollers then his heightens rolling resistance, so by measuring coast down the drag of the drivetrain can be measured and thus flywheel figure worked out. Tis the only way that makes sense.

So if you think about it the amount of power my car would put down on the road would be more than that measured as RWHP on the rollers.
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Re: Transmission losses - Mk1 Gearbox?

Post by raptor95GTS »

Lauren wrote:my engine produced 182bhp @flywheel
126bhp @ the engine.

Everbody else there ie Toni, Mark had the same losses.

RWHP is meaningless. Flywheel is the sensible way. Obviously a dyno is the only way to see actual power, but it doesn't reflect the environment in which the engine lives.

A couple of reasons why RWHP is crap is because rollers do not reflect a road surface ie there is lots more resistance due to the two rollers. Tyre pressure and type also makes a significant difference. Worse still if your car is strapped to the rollers then his heightens rolling resistance, so by measuring coast down the drag of the drivetrain can be measured and thus flywheel figure worked out. Tis the only way that makes sense.

So if you think about it the amount of power my car would put down on the road would be more than that measured as RWHP on the rollers.


um rolling roads measure roller torque which is then converted to power at the wheels, then the operator makes up a tranny loss and charges you accordingly.

My old mk1 did 80BHP at the wheels with the cam timing out 1 tooth on both cams, then it did 100BHP at the wheels with the cam timing corrected , then it did 110BHP with a mongoose exhaust on it. It had 100K miles on the clock too

Tranny losses are inaccurate since they are measured by using the rollers to turn over the gearbox with the clutch in

Whereas in real life its the engine that accelerates the gearbox and since gearwheels have different profiles on each side of the gearwheel you are going to get different losses depending how you drive the box

USe the same dyno everytime and get roadwheel figures everytime. That way you can compare back to back

Lauren, if that gearbox of yours lost 60BHP I'd of binned it and got a new one
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Re: Transmission losses - Mk1 Gearbox?

Post by feral4mr2 »

i dont know what drive train loses there would be or how exactly you would calculate them ~100% unless you had the engine out and tested at the flywheel and then back in the car and on a roller dyno to give you rear wheel hp. only then i suppose you could calculate what sort of approximate loses you have.
i would have to think the e51 would have more hp loses than a c50 or c52, being a beefer gearbox?

everyone down here just goes on rear wheel hp on the roller dyno's. sure every dyno will read different, useing the same one is a great way to test mods for improvment or loses with each mod you do like allan welsh said.
but then even the good ol g-tech is a handy little instrument for that sort of thing too.

plus but i dont think everyone wants to pull their engine out and get it tested at the flywheel to be 100% on their engines power output... haha


forgive me, i've been down the shed under my 4wd and i'm tierd and grumpy. i could just be dribbling poo. :?
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Re: Transmission losses - Mk1 Gearbox?

Post by Icsunonove »

allan welsh wrote:
Lauren wrote:my engine produced 182bhp @flywheel
126bhp @ the engine.

Everbody else there ie Toni, Mark had the same losses.

RWHP is meaningless. Flywheel is the sensible way. Obviously a dyno is the only way to see actual power, but it doesn't reflect the environment in which the engine lives.

A couple of reasons why RWHP is crap is because rollers do not reflect a road surface ie there is lots more resistance due to the two rollers. Tyre pressure and type also makes a significant difference. Worse still if your car is strapped to the rollers then his heightens rolling resistance, so by measuring coast down the drag of the drivetrain can be measured and thus flywheel figure worked out. Tis the only way that makes sense.

So if you think about it the amount of power my car would put down on the road would be more than that measured as RWHP on the rollers.


um rolling roads measure roller torque which is then converted to power at the wheels, then the operator makes up a tranny loss and charges you accordingly.

My old mk1 did 80BHP at the wheels with the cam timing out 1 tooth on both cams, then it did 100BHP at the wheels with the cam timing corrected , then it did 110BHP with a mongoose exhaust on it. It had 100K miles on the clock too

Tranny losses are inaccurate since they are measured by using the rollers to turn over the gearbox with the clutch in

Whereas in real life its the engine that accelerates the gearbox and since gearwheels have different profiles on each side of the gearwheel you are going to get different losses depending how you drive the box

USe the same dyno everytime and get roadwheel figures everytime. That way you can compare back to back

Lauren, if that gearbox of yours lost 60BHP I'd of binned it and got a new one


Allan, that's exactly my point :D . If you were trying to reject 60hp of energy you'd need an gi-normous gearbox oil cooler radiator just to maintain the gearbox oil at a steady temperature! The numbers just do not stack up at all! :?
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Re: Transmission losses - Mk1 Gearbox?

Post by raptor95GTS »

yup 60BHP is around 44KW = 44 single bar electric 1KW fires. Something dont add up
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Re: Transmission losses - Mk1 Gearbox?

Post by Lauren »

allan welsh wrote:
Lauren wrote:my engine produced 182bhp @flywheel
126bhp @ the engine.

Everbody else there ie Toni, Mark had the same losses.

RWHP is meaningless. Flywheel is the sensible way. Obviously a dyno is the only way to see actual power, but it doesn't reflect the environment in which the engine lives.

A couple of reasons why RWHP is crap is because rollers do not reflect a road surface ie there is lots more resistance due to the two rollers. Tyre pressure and type also makes a significant difference. Worse still if your car is strapped to the rollers then his heightens rolling resistance, so by measuring coast down the drag of the drivetrain can be measured and thus flywheel figure worked out. Tis the only way that makes sense.

So if you think about it the amount of power my car would put down on the road would be more than that measured as RWHP on the rollers.


um rolling roads measure roller torque which is then converted to power at the wheels, then the operator makes up a tranny loss and charges you accordingly.

My old mk1 did 80BHP at the wheels with the cam timing out 1 tooth on both cams, then it did 100BHP at the wheels with the cam timing corrected , then it did 110BHP with a mongoose exhaust on it. It had 100K miles on the clock too

Tranny losses are inaccurate since they are measured by using the rollers to turn over the gearbox with the clutch in

Whereas in real life its the engine that accelerates the gearbox and since gearwheels have different profiles on each side of the gearwheel you are going to get different losses depending how you drive the box

USe the same dyno everytime and get roadwheel figures everytime. That way you can compare back to back

Lauren, if that gearbox of yours lost 60BHP I'd of binned it and got a new one


Everybody elses gearbox showed the same losses as mine. I have found through using quite a few different rolling roads that quoted flywheel figues and wheel figures (always showing 60bhp loss) to be plus/minus 1bhp. I only use rolling roads to compare mods i've done and have one that i use for repeat comparisons of course.

the 60bhp loss is easily explainable, think about friction of the two rollers etc..

Anyways Allan, i'm not going to debate this as i had a similar argument on the US SC forum, they did not understand that rolling roads are different in the way they measure here than in the US...
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Re: Transmission losses - Mk1 Gearbox?

Post by raptor95GTS »

no worries lauren
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Re: Transmission losses - Mk1 Gearbox?

Post by Icsunonove »

Allan,

My final year project at uni was to do with energy balance calculations on a Ford Valencia engine. Basically I started off with the calorific value of the fuel and tried to work out where all the energy goes to before it hits the road. Basically I got some good results with the engine on the dyno, but before I could bolt a gearbox on, the engine gave up as I had run it for too long at maximum horsepower.

To be honest I find the difference between rear wheel horsepower and estimated flywheel figures absolutely laughable. The heat rejection required to make these figures feasible beggars belief. The only meaningful figures are rear wheel horsepower, the flywheel figures are absolutely meaningless.

Best regards,

Tom
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Re: Transmission losses - Mk1 Gearbox?

Post by feral4mr2 »

Lauren wrote:Everybody elses gearbox showed the same losses as mine.

how did everyone get a difference between flywheel output and rear/rolling output? all pull your engines or am i missing something here??
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Re: Transmission losses - Mk1 Gearbox?

Post by Icsunonove »

No John, it's just that we in the UK are happy for someone to say it produces 140bhp rwhp but your engine is actually producing 200bhp at the flywheel and we are happy! We are a naive race! (You should be in bed, by the way)
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Re: Transmission losses - Mk1 Gearbox?

Post by Lauren »

feral4mr2 wrote:
Lauren wrote:Everybody elses gearbox showed the same losses as mine.

how did everyone get a difference between flywheel output and rear/rolling output? all pull your engines or am i missing something here??


Well Toni, Mark and I all had our cars on the rollers on the same day and we all got flywheel and at the the wheel figures. they all showed the same difference.

Tom if you put your SC on the rollers you will find you get the same results.
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Re: Transmission losses - Mk1 Gearbox?

Post by feral4mr2 »

hrmm... i wouldnt even want to guesstimate what my engine is making at the flywheel, too hard for my little brain. because everyone goes on rwhp down here i'm happy with what ever someone says i have at the wheels, specialy if it's HEAPS... haha mmm.. i need to build another engine. :twisted:

(You should be in bed, by the way)

hahaha... no actualy it's 7.38am here, and i should be eating my breakfast so i can get to town in time for work.. :lol:
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Re: Transmission losses - Mk1 Gearbox?

Post by feral4mr2 »

Lauren wrote:Well Toni, Mark and I all had our cars on the rollers on the same day and we all got flywheel and at the the wheel figures. they all showed the same difference.

ok, but how did they give you flywheel figures?
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Re: Transmission losses - Mk1 Gearbox?

Post by Lauren »

feral4mr2 wrote:
Lauren wrote:Well Toni, Mark and I all had our cars on the rollers on the same day and we all got flywheel and at the the wheel figures. they all showed the same difference.

ok, but how did they give you flywheel figures?


twas the usual do the power run then clutch in and coast down to work it out.
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Re: Transmission losses - Mk1 Gearbox?

Post by Icsunonove »

John, I have some good news for you :D

According to my basic calculations and our British bull$h1t fudge factor:

I estimate your engine is producing about 270bhp at the flywheel :wink: !

Can you ship it to me from Queensland to Derby when you finally kill it?

I will rebuild it and fit it in my car!

Tom
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Re: Transmission losses - Mk1 Gearbox?

Post by Lauren »

Icsunonove wrote:John, I have some good news for you :D

According to my basic calculations and our British bull$h1t fudge factor:

I estimate your engine is producing about 270bhp at the flywheel :wink: !

Can you ship it to me from Queensland to Derby when you finally kill it?

I will rebuild it and fit it in my car!

Tom


Tom, please remember that the way in which things are measured here are different. I had a horrible argument with teh US guy that runs the US SC list that just went on and on..

Tbh a flywheel figure is perfectly good enough and i have replicated this figure and associated losses on at least 4 different rolling roads all to 1bhp.

Anyways CBA is seriously setting in now when it comes to talking about rolling roads.. so i'm not going to comment further.
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Icsunonove
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Re: Transmission losses - Mk1 Gearbox?

Post by Icsunonove »

Sorry Lauren,

Didn't mean to bore you. It's just that my final year project was looking at energy balance from calorific fuel value to energy dissipated on the road. And to be honest the disparity between rwhp and estimated flywheel bhp is simply a joke. If anyone believes this please understand they are being decieved. The only reliable figure that can be measured is the rear wheel bhp figure, that's all!
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Re: Transmission losses - Mk1 Gearbox?

Post by kaiowas »

Worth a read:

http://www.dynamometer.fsnet.co.uk/powe ... el-BHP.htm

to summarise, transmission losses are complicated, a chassis dyno has no chance in hell of accurately getting a figure for either flywheel power or transmission losses.

If you want to get a meaningful figure to quantify the perfomance of your car stick with rwhp. If you want to show off to your mates in the pub about how powerful your car is feel free to quote the worthless flywheel figures quoted by a a rolling road.

Lauren - just because you can repeated get the same result doesn't mean it's an accurate figure, the coastdown approach to getting transmission losses is not reliable as the gears behave differently when being loaded from the engine end to when their being loaded from the wheel end.
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Re: Transmission losses - Mk1 Gearbox?

Post by Icsunonove »

Good find kaiowas, that explains a lot of what I am on about! :D and I agree with everything else you say.

Still haven't got the answer to my question though.... :(

Surely someone has bench tested the engine out of the car on a dyno and then had it on a rolling road?
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