I'm saying that a bench dyno (water type) is as accurate as the tachometer and the loadcell are.

People who develop race engines for Formula Vee, Formula Ford, etc historically have always used a bench dyno. On a 40HP Vee back in the 70s we could see a few tenths of a HP gain when playing with jetting etc. Every 1/10 of a HP counted when we were chasing Bernie Haehnle,
For this sort of tuning a chassis dyno just doesn't cut it, IMO.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hi Matt
Yes flat slide magie and lucas fuel injected,
the mgb is a torque master from 2500 to 6000 rpm 163 ft lb of torque and 171 hp with an RE83 cam with 5lb boost
Graham Russell

_________________
"It's better to be not informed than ill-informed"

HI Darryl
There is only one correction factor used by engine manufactures and engine builders world wide and thats the one i put up, and with an engine dyno there is only one factor and thats the weather stop listening to people who have had nothing to do with dynos and just chase around on the net an put up silly statments .
Graham Russell

_________________
"It's better to be not informed than ill-informed"

Hi Low n blown
I am possible the only one to do testing between engine dynos and drive on ones and in my opinion MINIS should stay away from drive on dynos in relation to dyno shoot outs,because the more hp you make the greater the los? WITH A 5 PORT MINI what i have found is up to about 90 hp they drop around 30hp
up to 115/120 they drop around 40, 140/145 they drop 60hp and the reason for this is the carbie sitting at the back of the engine, and placing a fan in front of this does not make up for the mph on the road.
The motor i built for john mallam was a cross flow making 163 hp on JOHN COLLINS dyno from newcastle it made 130 hp why because it was pulling air from the front of the car, our group N from canberra racer bought a KAD TWIN CAM motor from KAD dropped 30hp from the engine dyno, put his group N car on the dyno and dropped 60 hp all the testing was done on dyno dynamics dyno and i can give you lots more examples this is why i take no notice of drive on dyno with a 5 port mini.
Oh i nearly for got 100 hp motor in a mini an a 100 hp motor in a sprite or a morrie minor (998) with the same overall gearing the in line cars make make around 25 hp more drive on dyno are very good for falt finding and tuning not for hp readings.
GRaham Russell

_________________
"It's better to be not informed than ill-informed"

Erv was a Kwaka man but I still had heaps of respect for his work...

http://en.wikipedia.org/wiki/Erv_Kanemoto

I was riding Honda....so Pops Yoshimura was my idol

http://en.wikipedia.org/wiki/Pops_Yoshimura

His big bore kits were to do die for...

_________________
"Show me the Mini!"

Just for the Doc..(and me, love the whine of a 6/71 when it gets up and boogies...Army used them in M113 and ASLAV (8 wheelers)

http://www.youtube.com/watch?v=_9J_T9FBZZY

_________________
"Show me the Mini!"

Graham, I'd be very interested to know the technical reasons that make your extractors better then a LCB for the 5 port.
Also if you don't mind ...Why is the centre port significantly larger and the centre branch of a LCB is also larger? As best as I can tell, there's never any doubling up of exhaust charges in the centre port.
Really appreciate your take on this subject.

HI 9yatha
Thanks for that he was a very respected man world wide,but i do have a soft spot for the kwakas.
Graham Russell

_________________
"It's better to be not informed than ill-informed"

Hi MG ROCKET
Why are they better because i played with sizes lengths and collector shapes
To answer your other question the natural freqency of the single pipe will differ from that of the y pipe and are unlikely to be in resonance at the same engine speed,if of the same diameter and length, increasing the diameter of the single pipe a little and thereby making it's volume equal to that of the y pipe should over come this effect, in theory.

Who said my pipes have a larger centre pipe was'nt me.
Graham Russell

_________________
"It's better to be not informed than ill-informed"

Thanks GR.
I did notice your pipes on the MG engine were of the same diameter.
Just that it puzzles why most LCBs have a larger diameter centre pipe.
The larger diameter would slow the speed of the gases in that pipe and it is also longer so.....I thought it must have something to do with timing of the exhaust pulses.
Do you have ideas why BMC made the centre exhaust port larger?
All I can see is the hot gases lingering around there creating heat build up.

Hi MGROCKET
BMC possibly worked on the same theory that i just explained, my be you had better ask maniflow why they made their centre pipe out of 1 3/4 dia pipe after i tried that set up for them back in the early ninties and told them it does not work, they run that size pipe on v8's.
Graham Russell

_________________
"It's better to be not informed than ill-informed"

Would it be because the two smaller bore tubes either side of the centre, create more than enough scavenge at the 3 into one joining piece? So slightly larger ID pipe used to slow things down a tad at the centre port and improve flow? and to get the exhaust charges more in phase?

[PS the above could be complete and utter BS ]

_________________
"Show me the Mini!"

Correction factors and dynos:

There is a direct correlation between how much oxygen your engine can take in and the power it can make. For a naturally aspirated engine the only thing forcing the oxygen in is the difference in atmospheric pressure and the lower pressure in the cylinder. Changes in atmospheric conditions change how much oxygen can go in.
- Higher pressure from lower altitude or weather (high pressure system) increases the amount of oxygen that can get in.
- Lower temperature increases air density and increase the oxygen intake.
- Low humidity reduces the proportion of the apparent pressure that is from the vapour pressure of water, again more oxygen in.

Since altitude, temp and humidity change performance, it is necessary to select the "standard conditions" for comparison. Unless you are actually measuring an engine in conditions equal to the standard, you need a correction factor.

Using pure scientific theory, it is possible to correct for the changes in altitude and weather conditions on a naturally aspirated engine. The equations are complex so a simplified version is typically used for automobile engines that experience limited changes in altitude. You couldn't use these simplified correction equations on an aircraft engine.

Since you rarely see an engine dyno tested at the top of a mountain, during a tropical cyclone in a heatwave, while it is raining, you don't see the extremes of correction factors.

The Standard conditions are for low level, mild temps and low humidity. It is therefore hard to get correction factors much below 1 as the dyno would have to be below sea level, on a very cold and dry day.

So we can compensate for atmospheric conditions with certainty. We will still be a bit out because we aren't compensating for crank case pumping losses, the change in intake system resonance with density, the affect of intake temp on the knock point or the ram affect of air velocity into the intake system. You could also argue that temp affects fuel density and vapourisation which affect tuning potential.

Forced induction engines are harder to accurately compensate for as they can draw in more air. Depending on the selection of the compressor housing a turbo engine can still make the same power at high altitude because it can fill the chambers to the target boost level. Caution must be used for large correction factors in these engines.

Different factors:
Historically cars from the USA had higher rated power than those from Europe. This is because the Standard Conditions were different but also because the yanks wanted their engines rated without the losses of the alternator and other 'accessories' whereas the Europeans wanted the nett output shaft power, that you actually use to drive with.

SAE corrections for the losses in accessories are just a guess based on the average of a bunch of US auto engines over the years. It may not represent the actual engine. They have changed the correction over time as the drag of accessories has reduced. SAE and ISO correction factors are therefore different.

Other Corrections:
Engine builders like SAE Brake Horse Power because they put the engine on a 'brake' (dyno) and want to know how much power it makes.
Race car drivers probably DGAF about the brake horse power because it is the power at the tyre/road interface that combines with mass, inertia, frontal area and coefficient of drag to determine how fast they can go.

It is possible to measure the losses in a drivetrain to apply a correction factor to power measured at the wheel drive flange to crank shaft power. The measurement would only be valid for the same type of car with same fluids at the same temps. So if you had a hub dyno and knew the losses for a particular model of car, you could get engine power levels quite accurately. Several tuners are using hub dynos these days.

Tyres are made of a very complex blend of rubber compounds, carcass materials and structures. There are friction, hysteresis and adhesion losses in a tyre rolling on a road. These are affected by pressure, temperature, tyre wear, compound temperature hustory, camber and toe. Placing the tyre on steel rollers and increasing the vertical load totally changes the flexure of the tyre as it rotates. The losses are therefore totally different from on a road.

There are no reliable equations or tables that a dyno operator can use to look up a particular tyre brand/model, temperature, pressure and vertical load and get the power loss when that tyre is on a rolling road dyno. This information simply does not exist. A correct 'correction factor' is therefore not able to be generated. Only a standard set of 'dyno wheels' used for all cars on the dyno would allow you to come close.

Summary:
You CAN compensate for location & weather affects as long as the factor is used in the range it is intended for or you use the real equations.
You need to understand the corrections for accessories.
You can measure drive train losses and use these but they are only valid under limited conditions.
You can't get accurate correction factors for the tyre to rolling road interface.

The way you test and engine also affects the reported power. Engine builders hold the engine at a load point and/or accelerate through the load point relatively slowly getting accurate 'steady state' power at each load point. In 'shootout' mode a rolling road dyno spends very little time at each load point, being more in the acceleration enrichment part of the map. How this affects readings is something the experienced people could tell, not me.

So, I reckon that if you are seeing factors that are higher than 30%, you are well into the guesstimate range of factors and can't trust them.

M

Hi Mokesta

i won't go into drive on dyno because what was writen on that other forum was just rubbish.
You mention about dynoing on the top of mountains etc, well F1 teams come close to this they can alter the humidity to any thing they want up to 100% tempatures above 50 deg c for the conditions in asia.

You mention compensation for pumping loss's, air velocity into air intake systems, but when the engine is on the dyno you have to tune what youv'e built you can't compensate for bad design, but some of the other things you mention are taken care of on motors with computers.
I have done a fair amount of work with people on motors trying to get hp with vacume in the crankcase but we have never found any advantage.
I have found more advantage with the pumping losses on the exhaust stroke with running to high a compression.
When David Visard was out here i was testing one of his new cams 300 deg duration he wanted to run 14.5 to 1 could'nt make the hp lowered the comp up come the hp.

you mentioned about making hp at high altitudes you will never make the hp up high as you will at sea level if there's no air you con not make the power, take a look at thecar PEUGEOT have built for Sebastion Loeb for pikes peak over 800hp and the same sort of torque but at the top of the mountain the expect to loose 30% of there power.
Graham Russell

_________________
"It's better to be not informed than ill-informed"

[quote="Mokesta"]Correction factors and dynos:

There is a direct correlation between how much oxygen your engine can take in and the power it can make. For a naturally aspirated engine the only thing forcing the oxygen in is the difference in atmospheric pressure and the lower pressure in the cylinder. Changes in atmospheric conditions change how much oxygen can go in.

Mokesta.
I wont quote your whole post as its very long, but if your statement were true regarding 'the only thing forcing oxygen into a NA motor was the difference in pressures' then an engine could never achieve above 100% VE. Their are other, just as important factors such as 'port inertia' and 'exhaust scavenge' that many consider equal in importance to the induction of an engine. Especially a high speed race engine. These 'forces' are given energy by a rising piston expelling burnt gases and then this inertia then"pulls" intake charge in (overlap). the bulk of this overlap is happening while the piston is parked at or near TDC.
The intake charge inertia is self explanatory. Also the power produced is dependant on the amount of oxygen in the air.

Correction factors can also be very confusing as their are many different ones and this is as much, the source of confusion for people trying to compare TQ and HP 'NUMBERS' between different dynos and or countries. I have given up trying to compare pommy hp to GRHP or road dyno losses etc. As people have said , compare it to the numbers given on the same correctly calibrated dyno, and you will find out if you have gone forward or backward. This is why you need to know what you want from any dyno figures you get.

The subject of correction factors is a minefield as the SAE themselves have issued/updated several different versions. Then there are ISO and so forth but as mentioned the SAE ones are generally more widely accepted. (rightly or wrongly)
The SAE used a widely accepted correction factor called J1349-JUN90. This correction factor effectively asked the tuner to add (with dyno calibration or calculator) a flat rate of 15% (85% mech efficiency) for mechanical losses, over measured. ie the losses of energy incurred simply by the motor operating, such as friction, heat dissipation etc. So in summary this factor was a measurement of what the purist looks at in terms of the 'theortical power' made by the said motor. or what the motor is making if there was no such thing as friction, drag, heat dissipation etc. Of course this is not as relevant as the 'actual power' being applied/output at the crankshaft.
Think of it like this; If you dynoed your engine using this first factor and got 150hp. Then you unbolted the water pump. alternator, opened up the bearing oil clearances, attached dry sump and then dynoed it immediately (without weather change) and it then showed 155 hp, has your engine created more hp or simply allowed more of it to the crank output? J1349 tells you that you have created 5hp but not increased mechanical efficiency beyond 15%. You can see how they grappled with flat rate of 15% for all 4 cycle engines. The 15% is far too general and therefore even less relevant to any purist that might be interested in what that engine made in a world without friction!
While I agree this factor strives for a higher resolution of info and are primarily for car makers, in a performance sense it outsmarts itself by virtue of 'we cant work put every single engine ever dynoed and its 'actual' frictional losses so we will call it avg 15%.'
Reliability aside, I am just as happy with having 5hp more at the crank via mechanical efficiency as if it were via more VE, better burn rates etc. all measured by crank output on an engine dyno.

Another point Mokesta touched on is the available oxygen. It may be more correct to say that there is only a finite amount of energy available from a drop of chosen fuel and it needs to be mixed with the correct ratio of oxygen to burn its optimum. SAE would have been trying to account for this 'available' energy when coming up with this purist correction factor. It is like they are introducing a fuel economy measure against a yielded power.

J1349 was revised in 2004 with the acceptance that the 15% is too general and the frictional losses should be measured rather than 'guessed'. I still struggle with this version, for performance ,other than it acknowledges the shortcomings of 'one size fits all 15%'. It now wants you to measure the frictional losses, measure the observed/meassured power then correct weather then add these frictional losses to the measured power and then you have your weather corrected theoretical power. I would prefer to see load figures at the shaft because they absoltutely account for frictional losses as per example above.
An engine dyno is a device designed to measure applied rotational pressure (lbs) at a given distance (ft) from the axis. The dyno doesn't know how this pressure is applied. It doesn't know whether its via calibration weights, a torque wrench, a tonne of feathers or a rotating engine being slowed by water, so it doesn't care how much energy is taken up by the engine to operate itself and then apply what is left to the crank, it only knows what is left to the crank (less minor dyno bearing drag).

I think the 'actual' power output is what most performance tuners are seeking and for comparison to others need to be weather corrected within the narrow limits allowed by these factors. Correct calibration is as important if not more important than correction factors for repeatable/comparable figures.
It could be successfully argued that a racer wants to know the output at his wheels but most people would agree that a road dynos relative sensitivity and or accuracy is reduced as the power is towards its lower end capacity and a small and vital gain may be missed by this heavier measuring device.

_________________
The formula for the length of a piece of string is simple: Twice as long as from one end to the centre!