Dyno

[SuperRedMR2]

I am getting my car Dyno'd this morning at Atspeed in Rayleigh.

Hoping to get at least the standard of 122bhp.

I will post the results up later

[cartledge_uk]

Dont forget to upload the details to the garage

[SuperRedMR2]

I was hoping for at least 120bhp and its come out at an estimated 130.6 so not so bad.

[aw11rally]

Do you know what the wheel bhp figure was?

Impressive flywheel estimate though, sounds like you've got a good'n.

[SuperRedMR2]

Yeah I do know what the wheel figure was. I thought it was appalling so I dont really wanna say lol

[Lauren]

Yeah I do know what the wheel figure was. I thought it was appalling so I dont really wanna say lol

Should have pumped your tyres up to give a higher whp figure.

Seriously don't worry about it WHP can vary enormously and they always come out very low on MK1's. I had something like 182bhp at flywheel and 126bhp at the wheels. This came out the same on numerous rolling roads (rolling roads are not dynos BTW).

[cartledge_uk]

can you post the graph please

[Jim-SR]

Yeah I do know what the wheel figure was. I thought it was appalling so I dont really wanna say lol

Should have pumped your tyres up to give a higher whp figure.

Seriously don't worry about it WHP can vary enormously and they always come out very low on MK1's. I had something like 182bhp at flywheel and 126bhp at the wheels. This came out the same on numerous rolling roads (rolling roads are not dynos BTW).

wheel horsepower is the only one that is of any accuracy. the fly power readings are estimated and usually over-estimated by huge amounts in my experience.

a stock AW11 should be making somewhere around 100bhp at the wheels to give 122bhp at the fly. for 130bhp it needs to be making about 107bhp at the wheels. 126bhp at the wheels is about 150bhp at the fly. 31% transmission loss is absolutely ridiculous, you dont even get that much on a 4WD car.

and a rolling road is a dyno (which is short for dynamometer). its a chassis dynamometer, as opposed to an engine dynamometer. there are all sorts of dynos, i own a damper dynamometer which tests shock absorbers.

[SuperRedMR2]

Spot on Jim, it was 107 at the wheels!

I'll post a picture of the graph probably tomorrow as I can't scan or take a picture of it at the moment.

[Lauren]

I'll bet though a stock mk1 will not get close to 100bhp at the wheels. As I said before I experienced around a 50bhp difference between fhp and whp and this was true of all the other sc's that went on the same rollers.

This was true of pretty much all the rolling roads we tried so they were consistent.

Sorry but I don't believe whp is any more accurate as things like tyre pressures affect it.

[JMR_AW11]

Bit out of my depth here because I have little practical experience...

But power is the rate of doing work.

I think different rolling roads will give different power readings at the wheels because they will not all prsent the same 'task' to the car. i.e. the rolling resistance will vary. In an ideal world this shouldn't matter as the rate of work can still be worked back from this but I'm not so sure this is true in reality.

i.e. will a car be capable of the same rate of work up a steep hill compared to a shallow hill?

You would like to think the answer is yes (in theory) but I'm not so sure this is true in a practical test.

I would have thought there would be higher losses in the car's drivetrain on a steep hill due to the high friction and relatively poor efficiency. This would muddy the results.

I reckon the only way to measure an engine is to do it directly on a dyno.

But some people will prefer wheel HP. However this is probably only relevant to a specific rolling road. This is fine for making comparisons during tuning

[Lauren]

Actually what's interesting Jeremy, is that we tried 3 cars on the same 4 or 5 rolling roads and got the same results on all, well within 1bhp or so both for whp & fwhp.

[JMR_AW11]

Actually what's interesting Jeremy, is that we tried 3 cars on the same 4 or 5 rolling roads and got the same results on all, well within 1bhp or so both for whp & fwhp.

That is interesting but then again other people get different results on different rolling roads.

I know they can compensate for different weather conditions but there are a lot of variables.

I do remember having my red mk1 on a RR in Cheltenham and seeing a paltry 111bhp fly and about 88bhp at the wheels. The RR technician said that he usually saw about 110bhp on his RR for mk1 MR2s but I was a bit disappointed...

However, I did get the blue mk1 mapped about 5 years ago at Powerstation in Tewkesbury and it gave about 120bhp predicted at the fly but only 75bhp at the wheels. I have the readout here and that's what it says.

I don't think there was anything wrong with the blue mk1 in terms of performance so I'm at a loss as to why the readout says 75bhp at the wheels but 120bhp at the fly.

So that always puzzled me.

[Lauren]

That is interesting but then again other people get different results on different rolling roads.

I know they can compensate for different weather conditions but there are a lot of variables.

I do remember having my red mk1 on a RR in Cheltenham and seeing a paltry 111bhp fly and about 88bhp at the wheels. The RR technician said that he usually saw about 110bhp on his RR for mk1 MR2s but I was a bit disappointed...

However, I did get the blue mk1 mapped about 5 years ago at Powerstation in Tewkesbury and it gave about 120bhp predicted at the fly but only 75bhp at the wheels. I have the readout here and that's what it says.

I don't think there was anything wrong with the blue mk1 in terms of performance so I'm at a loss as to why the readout says 75bhp at the wheels but 120bhp at the fly.

So that always puzzled me.

This is why I was saying that of the three of us (Mark, Toni and I) all going on the same rolling roads on the same day got the same proportional result with low whp figures in comparison with fwhp figures which would seem reasonable, ie 182bhp from an AE101 with big pulley, ABV blanked off rising rate fuel press regulator etc (on my car) Toni had a big pulley SC with 180bhp and Mark a slightly oversized Blitz pulley giving 165bhp all of which would be about the expected flywheel figure.

I think the trouble is in this situation that I described and your own experience the flywheel figure would seem to be more representative really.

[aw11rally]

A rolling road doesn't measure flywheel BHP it measures wheel BHP (actually it measures wheel torque then calculates BHP) therefore surely this is the most accurate figure. Anything else is just an educated guess.

Its not worth arguing about, a roalling road should be used to help get an engine setup/mapped rather than a tool for measuring how big ones tackle is (I've always found a tape measure fine for that).

[SuperRedMR2]

not very good quality i'm afraid.

i only got mine done to see what the rebuilt lump was putting out.

[Clarky_X]

Yeah I do know what the wheel figure was. I thought it was appalling so I dont really wanna say lol

Should have pumped your tyres up to give a higher whp figure.

Seriously don't worry about it WHP can vary enormously and they always come out very low on MK1's. I had something like 182bhp at flywheel and 126bhp at the wheels. This came out the same on numerous rolling roads (rolling roads are not dynos BTW).

wheel horsepower is the only one that is of any accuracy. the fly power readings are estimated and usually over-estimated by huge amounts in my experience.

a stock AW11 should be making somewhere around 100bhp at the wheels to give 122bhp at the fly. for 130bhp it needs to be making about 107bhp at the wheels. 126bhp at the wheels is about 150bhp at the fly. 31% transmission loss is absolutely ridiculous, you dont even get that much on a 4WD car.

and a rolling road is a dyno (which is short for dynamometer). its a chassis dynamometer, as opposed to an engine dynamometer. there are all sorts of dynos, i own a damper dynamometer which tests shock absorbers.

SC get more trans loss due to pulley don't they?

[Jim-SR]

you cant count SC power loss as transmission loss, since it loses that power at the flywheel as well. the nature of a supercharger is that it has high parasitic losses, its one of the major negatives when compared to a turbocharger.

transmission losses are losses that occur from the flywheel to the wheels. e.g. gearbox, differential, hubs, etc. the SC has an E-series box which may well have higher losses than a C-series box, but ive never seen anything to verify that. the transmission loss numbers used by any rolling road operator worth their salt will be somewhere around 18% for transverse 2WD applications. there are cars with more, there are cars with less. but ultimately there is no way of knowing specific flywheel horsepower without measuring it at the flywheel. so you use wheel horsepower as the definition of how powerful a car is, and if you MUST estimate flywheel horsepower, then divide it by 0.82.

some rolling roads calculate "coast down losses" and use these as the transmission loss to calculate back to flywheel horsepower (which is generally where the hugely over-estimated transmission losses come from). this is massively inaccurate, completely incorrect, and should not be used as any kind of indicator of power.

126bhp at the wheels of an SC means that the car had exactly that, 126bhp at the wheels! if this was verified by 3 seperate RR's then its probably fairly accurate. theyll have the same 18% transmission loss assumption as every other MR2, so call it an estimated 154bhp at the flywheel. probably about right for old engines with a bigger pulley bolted on. id expect a stock mk1 with an original engine to make about 90-95bhp at the wheels.

with regards tyre pressures, run them exactly as you would on the road (so probably around 30psi). anyone that alters tyre pressure on the dyno to influence power figures is just fooling themselves. you also have to be careful about how correction factors are administered to the rolling road measurements. its VERY easy to manipulate dyno figures, and unfortunately a lot of people do for no apparent reason.

[SuperRedMR2]

I only posted this as I wanted to display what power output my car is currently running.

Why would I want to fool myself into thinking its more than it is by pumping my tyres up - thats just stupid. This is my daily car which does between 300-450 miles a week. I did not post this to cause arguments about what exactly a dyno is or transmission loss - just simply what it is performing at.

If you want to kid yourself by pumping your tyres up, that's your choice, but i'm quite happy with the right amount of pressure in mine performing at 107.6 at the wheels.

aw11rally has given the only worthy reply to this saying i've got a good one, so thank you.

[JMR_AW11]

I only posted this as I wanted to display what power output my car is currently running.

Why would I want to fool myself into thinking its more than it is by pumping my tyres up - thats just stupid. This is my daily car which does between 300-450 miles a week. I did not post this to cause arguments about what exactly a dyno is or transmission loss - just simply what it is performing at.

If you want to kid yourself by pumping your tyres up, that's your choice, but i'm quite happy with the right amount of pressure in mine performing at 107.6 at the wheels.

aw11rally has given the only worthy reply to this saying i've got a good one, so thank you.

Actually you started off hoping for at least the 122bhp standard figure.

This is measured at the engine. You can't measure this figure on a rolling road. Hence the discussion that followed.

I think you spoiled your own thread with your post above....