Dyno questions
Discussion
Unless they take the engine out there is no accurate way of measuring the crank HP - it is a guesstimate! Although the graph invariably claims to show 'crank' HP it is just a calculation of RWHP plus either 15-10% or 'coast-down losses'.
Most use a 'coast-down' technique where they measure RWHP and then see how much power is lost on the coast down to 0mph - this is then added to the RWHP to give the 'crank' HP.
So if your RWHP is 240bhp then your crank HP is 'calculated' to be 276-288bhp.
The only true measurement you can (and should) compare is RWHP - assuming the rolling road is accurate.
Most use a 'coast-down' technique where they measure RWHP and then see how much power is lost on the coast down to 0mph - this is then added to the RWHP to give the 'crank' HP.
So if your RWHP is 240bhp then your crank HP is 'calculated' to be 276-288bhp.
The only true measurement you can (and should) compare is RWHP - assuming the rolling road is accurate.
Wheel horse power is the ONLY useful one, and that is only really useful if you compare it with a before & after mods tuning etc.
Far too many Tuning shops use the Adjusted (read adjustable) figures to make to make up necessary HP to meet the thousands of pounds spent on tuning.
No two dyno's will give the same readout (rarely anyway) plus the weather & temp can have a significant effect too.
Far too many Tuning shops use the Adjusted (read adjustable) figures to make to make up necessary HP to meet the thousands of pounds spent on tuning.
No two dyno's will give the same readout (rarely anyway) plus the weather & temp can have a significant effect too.
Dyno is just short for dynonometer.
You have bench/engine dyno and rolling road dyno - one requires the engine to be removed - partially if the dyno can be attached to the driveshaft (but then that also incurs losses) or completely - and one requires you to put your wheels on the rollers!
It's just that it's a bit expensive to go down the bench/engine dyno route to just check out a re-chip.
You have bench/engine dyno and rolling road dyno - one requires the engine to be removed - partially if the dyno can be attached to the driveshaft (but then that also incurs losses) or completely - and one requires you to put your wheels on the rollers!
It's just that it's a bit expensive to go down the bench/engine dyno route to just check out a re-chip.
A Dyno is a measuring tool, thats all. It is only acurate when it's calibration is good, and ambient conditions are compensated for. The only acurate figures are the measured values.
In the case of a chassis dyno, or rolling road, this is the HP and Torque applied to the rollers by the wheels. In the case of an engine dyno, it's the HP and torque available at the crank.
If an "at the flywheel" figure is being offered from a chassis dyno be wary, some are fairly acurate, some are pure guess-work. Some dyno's offer a transmission loss calculation based on the "run down" of speed once the load has been removed and the throttle closed. This estimation of transmission loss can be added back onto the "at the wheel" figure.
Some dyno operators simply apply a "rule of thumb" like a 10% loss. This is obviously rubbish, a 50hp car looses 5hp and a 500hp car looses 100hp ?? I don't think so. There are so many variables to consider, even a couple of extra PSI in the tyres can effect the result.......
Some figures quoted seem so far fetched that you have to wonder what's going on........ Now I'm not saying this happens ever
, but here's a little trick !! When the operator applies the load there will be a "flash" figure, the measurements will peak initially then settle back down when everything balances out. If you record or capture that figure it will be the highest measurement of the day, and bigger is always better, right ?? 
We test each and every one of our gas turbines using a 'slightly' bigger version of an engine dyno. All are corrected to standard or 'ISO' day to ensure they make rated power and to assure quality.
In the case of a chassis dyno, or rolling road, this is the HP and Torque applied to the rollers by the wheels. In the case of an engine dyno, it's the HP and torque available at the crank.
If an "at the flywheel" figure is being offered from a chassis dyno be wary, some are fairly acurate, some are pure guess-work. Some dyno's offer a transmission loss calculation based on the "run down" of speed once the load has been removed and the throttle closed. This estimation of transmission loss can be added back onto the "at the wheel" figure.
Some dyno operators simply apply a "rule of thumb" like a 10% loss. This is obviously rubbish, a 50hp car looses 5hp and a 500hp car looses 100hp ?? I don't think so. There are so many variables to consider, even a couple of extra PSI in the tyres can effect the result.......
Some figures quoted seem so far fetched that you have to wonder what's going on........ Now I'm not saying this happens ever
, but here's a little trick !! When the operator applies the load there will be a "flash" figure, the measurements will peak initially then settle back down when everything balances out. If you record or capture that figure it will be the highest measurement of the day, and bigger is always better, right ?? We test each and every one of our gas turbines using a 'slightly' bigger version of an engine dyno. All are corrected to standard or 'ISO' day to ensure they make rated power and to assure quality.
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