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Temperature correction on a dyno

Temperature correction on a dyno

Temperature correction on a dyno

Quick query:
A dyno manufacturer is claiming that their machines correct for temp, i.e. will give the same output figures regardless of temp, a test vehicle will show the same power whether tested at cold or hot days.

Without a MAF is this possible?

For example, pre-det due to high temps, how can a dyno pick that up and correct? Surely engine power response in relation to intake temp is hardly linear (or an easy calc) - especially when you take into account forced induction, compund charging, intercooling, etc.?

Or am I about to be amazed at modern dyno equipment?

RE: Temperature correction on a dyno

Their not talking about the dyno controlling the engine itself, they're saying the data captured is normalized for the current atmospheric conditions.

Dan - Owner

RE: Temperature correction on a dyno

The correction factors are different for FI vs NA (or at least it was in the SAE correction factor used when I did diesel engine testing back in the 70's).  It was not a linear correction factor, I had it programed into my HP11C.

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Temperature correction on a dyno

Thanks Dan / Dgallup

I thought it was an odd claim, given that the difference between testing at a high temp vs a low temp would be pretty big.

e.g. my own car (Mitsubishi VR4)

Last tested at 42oC / 108oF. 280 bhp
I'd expect this to be much higher output at lower temp, for example at 10oC/50oF

Can a dyno software "correct" / normalise for this range?

I know that the limiting factor is the fuel pump (in my case) - it'll only feed so much juice.
I can think of other things that might complicate the correction, like intercoolers. I'd expect better power with a lager intercooler - but the temp probe in the intake isn't going to know how big/the effect of my intercooler, so how can the correction be done?

(thanks for putting up with my musings, btw!)

RE: Temperature correction on a dyno

I very much doubt the fuel pump is in any way the limiting factor.  Engine power is nearly always a function of how much air the engine can pump.

In my old copy of SAE standards, J1349 is the one that corrects measured power to standard conditions.  It may be superseded.  It includes forced induction and those temperature ranges.  Here are some excerpts (I'm sure the formatting won't come through):

Symbols Term Units
CA Air correction factor
CF Fuel correction factor
fa Atmospheric factor
fm Engine factor
fd Fuel density factor
fv Fuel viscosity factor
a Pressure sensitivity exponent
b Temperature sensitivity exponent
S Viscosity sensitivity coefficient
D Engine displacement l
B Inlet air supply total pressure kPa
t Inlet air supply temperature °C
P Inlet manifold total pressure kPa
r Pressure ratio
q Fuel delivery mg/L cycle
bp Brake power kW
fp Friction power kW
ip Indicated power kW
n Engine speed min-1
F Fuel flow g/s
SG Fuel density at 15 °C kg/L
V Fuel viscosity at 40 °C mm2/s

c = Refers to data corrected to reference inlet air and fuel supply conditions
o = Refers to data observed at the actual test conditions
d = Refers to the dry air portion of the total inlet air supply pressure
r = Refers to the reference test conditions per Section 5

Standard Condition - Recommended Test Range Limits
Inlet Air Supply Pressure (absolute) 100 kPa —
Dry Air Pressure (absolute) 99 kPa 90–105 kPa
Inlet Air Supply Temperature 25 °C 15–40 °C

5.5 Power Corrections—The performance of SI and CI engines is affected by the density of the inlet combustion
air as well as by the characteristics of the test fuel. Therefore, in order to provide a common basis of
comparison, it may be necessary to apply correction factors to the observed net power to account for
differences between reference air and fuel conditions and those at which the test data were acquired.
5.5.1 All power correction procedures for atmospheric air are based on the conditions of the engine inlet air supply
immediately prior to the entrance into the engine inlet system. This may be ambient (atmospheric) air or a
laboratory air plenum that maintains air supply conditions within the range limits defined per 5.1.
5.5.2 On any engine where the power output is automatically controlled to compensate for changes in one or more
of the listed inlet air and fuel supply test conditions, no correction for that test parameter shall be made.
5.5.3 The magnitude of the power correction should not exceed 5% for inlet air or 3% for inlet fuel corrections. If
the correction factor exceeds these values, it shall be noted in accordance with 8.1.

7.1 Instrumentation Accuracy—The following minimum test instrumentation accuracy is required:
a. Torque—±0.5% of measured value
b. Speed—±0.2% of measured value
c. Fuel Flow—±1% of measured value
d. Temperature—±2 °C
e. Air Supply, Inlet and Exhaust Pressures—±0.1 kPa
f. Other Gas Pressures—±0.5 kPa

8.3 Recorded Test Data—Record the following minimum information at each data test point:
a. Brake torque
b. Friction torque (if measured)
c. Engine speed
d. Fuel flow rate
e. Fuel supply pressure and temperature
f. Ignition and/or injection timing
g. Oil pressure and temperature
h. Coolant temperature
i. Inlet manifold air temperature and pressure
j. Total pressure drop across the inlet air system
k. Total pressure drop across the auxiliary cooler (if applicable)
l. Total pressure drop across the exhaust system
m. Smoke (optional—CI engines only)

Did the dyno operator take all that into account?  I doubt it.
I would post the correction factor formulas but I'm sure the formatting won't come through so it would be jibberish.

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Temperature correction on a dyno

Well that's certainly the most comprehensive answer I could have got! Thanks!

What's the addendum in 5.5.3 where the correction factor>5%?

Re: fuel pump being a limiting factor, in the VR4 it is. Mitsubishi went a bit nuts with the engine management but didn't boost the fuel pump to match. It's possible to run out of "overhead" in the fuel pump without even modifying the engine (very cold days, not enough fuel for the air)

RE: Temperature correction on a dyno


For std OEM cars you are correct, however with "tuned" cars or hot rods, especially turbos with bigger inter coolers and turned up boost, OEM injector capacity normally becomes the first restriction. This is normally resolved by replacement with higher capacity or simply increasing fuel pressure. The fuel pump capacity then becomes the limiting factor, especially at increased fuel pressures and excessively rich mixtures to suppress detonation.

See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
for site rules

RE: Temperature correction on a dyno


He's only at 280 BHP, stock fuel pump will certainly handle more.

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Temperature correction on a dyno

I would not be all that certain. The pumps that come as OEM on older Honda 4 cylinder engines are only really good to about 250hp.

Anyway, back to correction factors.

You can accurately correct for air density, except that you might optimise at low density, but might not be able to realise the theoretical increase at high density due to detonation or engine durability thresholds overtaking airflow as the limiting factor.

See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
for site rules

RE: Temperature correction on a dyno

I'm confused... which car are we talking about here?  The stock 3000GT/Stealth VR-4 was sold with 296/320bhp (depending upon model year), and even the latest model Galant VR-4 only had 276bhp.  Where does your 280bhp figure come from... is it the Galant?

Either way, that stock pump should have no difficulties handling that.  My impression is you think you'll get a massive boost in power by testing at lower temps, but it's not going to be so large as to be measurable on any but the best butt-dynos (i.e., don't expect more than, say, 10-15bhp, less at the wheels).  This is, after all, a mere sub-2000cc engine.

If you're seeing a lack of fuel, my guess would be partially clogged injectors or a leaking/bypassed diaphragm in the fuel rail/pump system (it is an old model, after all).

Dan - Owner

RE: Temperature correction on a dyno

'97 2.5L V6 twin turbo. Galant/Legnum - japanese import (I'm in Ireland by the way)

[off topic] These can suffer what is known as "fuel cut" - the EMU intervenes because it thinks it can't supply the fuel required compared to the air it's pumping in. The mapping requires "overhead"  - it overfuels if the EGT gets too high (i.e. run rich to cool EGT) It's unusual in that this engine, if overboosted from the stock 8/9psi to say 11/12psi it hits this "limit" in the mapping. Stock cars have even been known to hit it at cold temps without increased boost

[on topic] You hit the nail on the head Dan. The 280 figure is my own car - stock turbos & intercooler but appears to have been remapped in japan. Dyno'd at 280.1 @ 42oC, on pretty rubbish Irish petrol. Was wondering if a cooler intake temp may have popped it over the 300 mark (wishful thinking I know, looks like I'll need a bigger intercooler)

And don't despair at the "small" engine. My '68 stingray makes up for that clown

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