BHP at the wheels?
Discussion
Hi there, I put my S4s on a rolling road recently and the company gave me the following wheel to flywheel formulas to work to when using an inertia rolling road.
Rear wheel drive = (wheel BHP + 10) x 0.88
Front wheel drive = (wheel BHP + 10) x 0.9
Not sure about 4x4.
Mine ran 333BHP which is pretty good for a 4 pot!
Dave Walters
Rear wheel drive = (wheel BHP + 10) x 0.88
Front wheel drive = (wheel BHP + 10) x 0.9
Not sure about 4x4.
Mine ran 333BHP which is pretty good for a 4 pot!
Dave Walters
Dave,
So, which number is the 333? At the wheels or guestimated at the flywheel? And I wonder what that extra ten is for. Making the customer feel good, in true ACBC marketing fashion?
Also, from the formulae you have there an Esprit would use the FWD formula and not the RWD. The deciding factor is not which wheels get driven, but the configuration: Engine-transmission-driveshaft-differential-wheels v. engine-transmission/differential-wheels.
Dr.Hess
So, which number is the 333? At the wheels or guestimated at the flywheel? And I wonder what that extra ten is for. Making the customer feel good, in true ACBC marketing fashion?
Also, from the formulae you have there an Esprit would use the FWD formula and not the RWD. The deciding factor is not which wheels get driven, but the configuration: Engine-transmission-driveshaft-differential-wheels v. engine-transmission/differential-wheels.
Dr.Hess
superdave said:
Hi there, I put my S4s on a rolling road recently and the company gave me the following wheel to flywheel formulas to work to when using an inertia rolling road.
Rear wheel drive = (wheel BHP + 10) x 0.88
Front wheel drive = (wheel BHP + 10) x 0.9
Not sure about 4x4.
Mine ran 333BHP which is pretty good for a 4 pot!
Dave Walters
Dear Dave,
I am a little lost, are you saying that the bhp and torque figures from a rolling road test will not be the figure "at the wheels"? I was not exactly sure when the calculation is required.
333bhp from the Twink is pretty impressive, what mods?
Cheers
Mark
I asked this question to the company about the gearbox etc. Basically the deciding factor is which way the engine is, inline or transverse. A transverse engine loses more through the transmission than the inline one (so they said). Iam out of my depth about the technical issues but one things for sure, this company is an International size and it's not just a back street garage. I am taking their word for it.
And no, the extra 10 is not to make the customer feel happy, it's just a formula.
Cheers,
Dave walters
And no, the extra 10 is not to make the customer feel happy, it's just a formula.
Cheers,
Dave walters
Dr.Hess said:
Dave,
So, which number is the 333? At the wheels or guestimated at the flywheel? And I wonder what that extra ten is for. Making the customer feel good, in true ACBC marketing fashion?
Also, from the formulae you have there an Esprit would use the FWD formula and not the RWD. The deciding factor is not which wheels get driven, but the configuration: Engine-transmission-driveshaft-differential-wheels v. engine-transmission/differential-wheels.
Dr.Hess
The BHP is at the wheels. I ran 283.1 on my test. Add 10 gives you 293.1 then divide by 0.88 (I told you multiply last time, sorry my mistake!). This give you 333BHP.
Iam running a decat pipe, K&N and the ram air intake. Also I blipped the throttle to over 5K to let the full boost take affect!
Hopes this explains things,
Dave Walters
Iam running a decat pipe, K&N and the ram air intake. Also I blipped the throttle to over 5K to let the full boost take affect!
Hopes this explains things,
Dave Walters
Blipped the throttle at over 5K ?
I thought the operator would have put the car in third and depressed the throttle fully from 1000rpm and put the car under load at certian rev ranges to creat a plot from which they creat a graph?
Not holding the throttle all the way down from the word go would give inaccurate figures. No?
I thought the operator would have put the car in third and depressed the throttle fully from 1000rpm and put the car under load at certian rev ranges to creat a plot from which they creat a graph?
Not holding the throttle all the way down from the word go would give inaccurate figures. No?
The difference between 0.88 and 0.9 in the formula is just a guestimation on losses. The more joints / cogs in the way, the more the losses - perhaps the difference of the propshaft!
The "add 10" definitely sounds like a fudge/feelgood factor, how can it be correct?
A car with 0 bhp at the wheels = 11.36 bhp at the flywheel?
A car with 30bhp at the wheels would have (30+10) / 0.88 = 45bhp at the flywheel ... a whopping 33% transmission loss.
The "add 10" definitely sounds like a fudge/feelgood factor, how can it be correct?
A car with 0 bhp at the wheels = 11.36 bhp at the flywheel?
A car with 30bhp at the wheels would have (30+10) / 0.88 = 45bhp at the flywheel ... a whopping 33% transmission loss.
Yes, that's exactly what a rolling road will tell you.
But to get some kind of perspective to stock, people often convert back to crank hp - and it's not that easy ... everything from tyre pressure to oil temp in the gearbox, quality of gearbox, wear in gearbox / diff / propshaft can cause varying losses. The formula is guesstimating that rwhp is 88 to 90% of crank HP if you ignore the fudge factor - but this fgure will vary from car to car. Some rollers can drive the car in neutral at different speeds and measure the effort required to do so. This effort can then be added to the RWHP to get a closer approximation to the crank HP than a simple formula.
But to get some kind of perspective to stock, people often convert back to crank hp - and it's not that easy ... everything from tyre pressure to oil temp in the gearbox, quality of gearbox, wear in gearbox / diff / propshaft can cause varying losses. The formula is guesstimating that rwhp is 88 to 90% of crank HP if you ignore the fudge factor - but this fgure will vary from car to car. Some rollers can drive the car in neutral at different speeds and measure the effort required to do so. This effort can then be added to the RWHP to get a closer approximation to the crank HP than a simple formula.
scoule said:
Yes, that's exactly what a rolling road will tell you.
But to get some kind of perspective to stock, people often convert back to crank hp - and it's not that easy ... everything from tyre pressure to oil temp in the gearbox, quality of gearbox, wear in gearbox / diff / propshaft can cause varying losses. The formula is guesstimating that rwhp is 88 to 90% of crank HP if you ignore the fudge factor - but this fgure will vary from car to car. Some rollers can drive the car in neutral at different speeds and measure the effort required to do so. This effort can then be added to the RWHP to get a closer approximation to the crank HP than a simple formula.
Thanks mate - this answered my question.
So, does anyone with a V8 care to let me know the figures you managed to get from the rolling road?
Gents,
Rolling roads cannot calculate or work out the flywheel fig. It is always an estimate! The only way you can know the flywheel figs to take the engine out and engine dyno it! We always point out to customers that the flywheel figs we provide are an estimate, and we don't use any of this coastdown rubbish either!
Another thing to bear in mind is that turbo'd mid engined cars are a knightmare on the dyno, especially the intercoolers, make sure the dyno you visit can keep lots of air on them or your power reading will be way down. Its not especially good for the car either!
As for blipping the throttle, on our dyno it would cock up the graph right and propper! but ours is not an inertia dyno and hence you get full boost just by putting your foot to the floor and loading the dyno, cos the dyno loads to match the power produced. I've never used an inertia one so can't speak for them.
if anybody has any questions, i'm happy to answer them
Charlie.
Rolling roads cannot calculate or work out the flywheel fig. It is always an estimate! The only way you can know the flywheel figs to take the engine out and engine dyno it! We always point out to customers that the flywheel figs we provide are an estimate, and we don't use any of this coastdown rubbish either!
Another thing to bear in mind is that turbo'd mid engined cars are a knightmare on the dyno, especially the intercoolers, make sure the dyno you visit can keep lots of air on them or your power reading will be way down. Its not especially good for the car either!
As for blipping the throttle, on our dyno it would cock up the graph right and propper! but ours is not an inertia dyno and hence you get full boost just by putting your foot to the floor and loading the dyno, cos the dyno loads to match the power produced. I've never used an inertia one so can't speak for them.
if anybody has any questions, i'm happy to answer them
Charlie.
vixpy1 said:
Gents,
Rolling roads cannot calculate or work out the flywheel fig. It is always an estimate! The only way you can know the flywheel figs to take the engine out and engine dyno it! We always point out to customers that the flywheel figs we provide are an estimate, and we don't use any of this coastdown rubbish either!
Another thing to bear in mind is that turbo'd mid engined cars are a knightmare on the dyno, especially the intercoolers, make sure the dyno you visit can keep lots of air on them or your power reading will be way down. Its not especially good for the car either!
As for blipping the throttle, on our dyno it would cock up the graph right and propper! but ours is not an inertia dyno and hence you get full boost just by putting your foot to the floor and loading the dyno, cos the dyno loads to match the power produced. I've never used an inertia one so can't speak for them.
if anybody has any questions, i'm happy to answer them
Charlie.
Cheers for the reply mate - I did not think that the V8 had an intercooler?
markuskj said:
Cheers for the reply mate - I did not think that the V8 had an intercooler?
Your right, due to lack of space according to the web.
, well, you learn somthing everday! Rarely come across Turbo cars without them to be honest!
Will make it much easier to run in that case, just make sure there is air to the inlet and plently of air on the radiators.
vixpy1 said:
Gents,
As for blipping the throttle, on our dyno it would cock up the graph right and propper! but ours is not an inertia dyno and hence you get full boost just by putting your foot to the floor and loading the dyno, cos the dyno loads to match the power produced. I've never used an inertia one so can't speak for them.
This isn't what was meant by blipping the throttle to 5k. The 4 cylinder Esprits, there is a special overboost mode. It is enabled by revving to 5k plus whilst the car is not moving. For 30 secs after that, the engine management will allow more boost so you can get some unusually savage acceleration! After that, just hold the foot to the floor and you'll get a higher sustained boost for those 30 secs, subject to reasonable inlet temps etc.
The V8's do not have the same feature. The V8's also do not have chargecoolers (water intercoolers) because at 350bhp without them, there was no need. Renault would not warrant the gearbox for greater than 350bhp. With chargecoolers and the more boost that those would allow, power would rise to 420bhp according to the Lotus V8 engine brochure - too much for the gearbox.
www.lotusespritworld.co.uk/ETechnical/V8_Engine_Spec.html
vixpy1 said:
Cheers for the reply mate - I did not think that the V8 had an intercooler?
Your right, due to lack of space according to the web.
Rarely come across Turbo cars without them to be honest!
Will make it much easier to run in that case, just make sure there is air to the inlet and plently of air on the radiators.
No worries, just being a pedant
I was told that this was also because they wanted to make the boost more manageable i.e. no lag then whoomp.
Again, cheers for the insight
Mark
superdave said:
The BHP is at the wheels. I ran 283.1 on my test. Add 10 gives you 293.1 then divide by 0.88 (I told you multiply last time, sorry my mistake!). This give you 333BHP.
Iam running a decat pipe, K&N and the ram air intake. Also I blipped the throttle to over 5K to let the full boost take affect!
Hopes this explains things,
Dave Walters
Dave,
What gear were you in to make that 283.1 HP?
From my experience using chassis dynometers you are supposed to do the runs in a gear closest to a 1:1 ratio i.e. 4 gear.
If the 5k blip trick only works when the car is at a stand still, how would you have time to get the car up to speed in 4 gear 1-2k rpm to make your recorded run within the 30 second overboost window?
Just wondering
Good #'s by the way!
Hi Mike, it was done in four gear. The mention of the 5K blip of throttle for overboost, is only what I told the operator to do. Whether it made any difference is anyone's guess. All I've done is explained what happened on the day.
Next people will be asking where were the big fans situated, at the front or at the sides where the air intake is?
Cheers,
Dave Walters
Next people will be asking where were the big fans situated, at the front or at the sides where the air intake is?
Cheers,
Dave Walters
Gassing Station | Esprit | Top of Page | What's New | My Stuff