pa_sjo

I think some people are forgetting that boost does not equal airflow..... It's possible to get two identical boost graphs but not two identical airflow (and thus power) graphs..

alistairolsen

while Id agree that having the same peak boost will not give the same headline figures, if you can replicate runs so that the curve of boost against rpm is identical and the load is identical, then surely the power at all points WILL be identical!

Chip

iTrader: (3)

On the SAME engine? Not a similar one, the actual one?
At the same point in the rev range, and both at full throttle?

I would argue that in that specific set of circumstances there is an extremely strong correlation between boost and power!

foreigneRS

... as long as the temperature is the same (or potentially compensated for correctly in the dyno calculation, although if ignition is different with a massively increased ACT then power produced will obviously be different)

pa_sjo

My point was aimed around different loading on the engine can show identical boost figures but not necessarily be flowing the same amount of air..

GaryEvo

ignor last nights stuff as car wasnt mapped so redone this morning

have done this test a few times with same results so happy all is as it should be

4th gear is very close to 125mph speed limit on dyno so we would never run this in fourth normally

heres graphs

Chip

iTrader: (3)

Apologies then, I misunderstood you, yes thats possible as the pumping losses will be higher while its trying to spool the turbo against less load I would imagine.

Chip

iTrader: (3)

Wow,

Thats a very unexpected result for me Gary, Im amazed that it would show over 10bhp difference but for LESS boost.

Thats very interesting indeed.

Christian and Beccy

iTrader: (14)

We're now going to try another experiment for you, watch this space.......LOL.

It's Czech Mate

I make it less than 9 bhp ( 8.9 ) difference not over 10?

AlexF

Am I reading this right - the boost difference is about 0.05 bar (0.4psi) ??

Chip

iTrader: (3)

Apologies, I read it as 305 and 316 for some reason.

Was working till 1am and I think my brain is suffering today as a result, lol

Chip

iTrader: (3)

Yes, appears to be, but weird that the lower value is the more boost, even if not much more.

Christian and Beccy

iTrader: (14)

I would suggest 1.18 vs 1.20 between the 2 runs.

We wanted to demonstrate some detailed timing/VVT analysis, but we're going to wait for a better car. This one is not the best basis for this kind of testing.

Chip

iTrader: (3)

Am I right in thinking that rather than attempt to measure transmission losses the rollers have simply added an arbitrary value, which appears to have been losses of 15% assumed on both runs?

GARETH T

i must be honest,, im slightly confused of the results *red faced*

Christian and Beccy

iTrader: (14)

Aside from everything else, we have documented that the car shows more power on the third gear run, despite making slightly more boost in fourth. We have carried out testing on standard cars and although some cars don't make their claimed figures, the most likely result is in third gear, which is why we try to use this gear at all times, as per Dyno Dynamics guidelines.

GARETH T

i just dont understand why

Garage19

I don't understand either Gareth. I don't understand how that fact DD say it must be third gear has any effect on reliable results. All transmissions are different.

I can understand limiting roller speed but which gear you use should have no effect on results. After all, cars have different gearbox ratios, different final drive ratios and different wheels sizes.

Chip

iTrader: (3)

But not all cars have a 3rd gear which is the same ratio?

Ive changed my diff on my mini engine and 4th is now geared how 3rd was previously. So which would make more sense on that instance?

Do they tell you to use 3rd specifically, or is there a rule such as "use the gear which is nearest to 110mph at the redline of the engine, which is typically 3rd" ?

scoooby slayer

iTrader: (4)

when my car was done in 4th it was doing 144 mph ?

GaryEvo

chip yes it was just that 3rd is right for most cars but i think was under 100mph at redline

Chip

iTrader: (3)

Right.

Interesting stuff, as it means (as clearly demonstrated by your runs above) that unless you happen to have EXACTLY the gearing that the dyno is calibrated for, it will be slightly out.

Not a problem I would imagine as it should never be out by as much as the 3% you got there, but still interesting that it will be out by a % or two just as a result of gearing on many cars.



Did you spot the question about about transmission losses, does it just assume 15% for all 2wd cars and some other number for all 4wd cars?

Garage19

I always thought they measured the resistance to the rollers coasting down to calculate transmission loss?

Christian and Beccy

iTrader: (14)

Some Dyno's do that, but not DD.

GaryEvo

my readings from last run i did on evo were 507.4 at wheels and 644.4 at fly

remember though i think if most dyno companys had there way they would never use fly figures

Garage19

So DD just apply an assumed correction?

pa_sjo

GaryEvo- how long does the profile you are using hold the engine at brake loading for each speed break-point?

Garage19

So does the dyno assume just over 21% losses for four wheel drive?

Christian and Beccy

iTrader: (14)

We're not AVA.

GaryEvo

it measures wheel bhp and adds a correction

GaryEvo

theres various shootout modes 4,6,8 4f,6f,8f and all 4wd uses shoot 44

we never use the f modes as runs are to fast imo

i think shoot 44 is about 10km/h/s

alistairolsen

yes, we know that! The question being asked is roughly what percentage the correction is!

From what im seeing hre you could stand on thebrakes during run down and nothing would change, the dyno just takes the wheel figures and adds 15% on this case. Doug is just asking if it adds 21% or thereabouts for 4x4 cars?

Chip

iTrader: (3)

By dividing by 0.79 for 4wd and dividing by 0.85 for 2wd?

ECU Monitor Enthusiast

iTrader: (1)

With the popularity of turbochargers on cars these days, perhaps its time that the DIN and SAE standards were updated .. LOL

GaryEvo

well 27% to wheel figure gives fly figure on mine ill go try a lower powered 4wd

alistairolsen

legend! Im sure i speak for everyone reading when I say that its nice to see someone knowledgeable being open with what they have at hand and contributing to a useful discussion without being all cloak and dagger!

Chip

iTrader: (3)

1 / .79 = 1.27 (there is your 27% Gary)

So looks like my guess was about right, lol

pa_sjo

I don't get the joke? I asked a reasonable question and got a bullshit reply.

Christian and Beccy

iTrader: (14)

Take it easy! LOL.

Most Chassis Dyno's don't hold the car at individual load-points. AVA's does, but I don't see the need for it. Pro's and Con's to it if you ask me.

A massive point against is the strain on the car. Also, how are you supposed to assess the situation with detonation if the car is held for so long at each point? You could end up with a very conservative map. Great for durability, but overkill?? I think so.