just wanted some clarification one way or the other on my thoughts.

from dyno runs ive seen on gtroc the same spec cars are making consistently around 50 - 70 bhp more on dynapack hub dynos compared to brake roller dyno dynamics. now ive convinced myself the dynapck must be reading high or the dd is reading low.

am i right in thinking a mark shead MAD built car had its engine on an engine dyno and then went on dyno dynamics and was within a few hp ?

 

surely it depends on the dyno operator too. Its not difficult to add a few calibration figures where the customer wont understand to make their 1.1 saxo look like its got 130bhp from an air filter and exhaust........

 

I have only run once on a dyno pack and the Supra made 872hp at the hubs which I thought wa a bit high,
One of my dealers maps on them he recons about a 10% loss to take it to the tyres is about right to get it to a dyno dynamics fig,
I have run a few from a superflow engine dyno to a Dyno dynamics and they have had 22 to 25% losses if you want to make it to a Flywheel fig,
There own losses is a flat 21ish % so quite close on 4wd cars.

Mark

 

It tends to be roughly right that the hub figure on Dynapack is equivalent to the projected engine figure on DD (or indeed any other trusted dyno), so really defeats the object of the so-called accurate hub dyno.

 

thats cool thanks peeps ive got flamed abit but stood for what i believe its nice to hear from trusted tuners that i aint been talking poo lol

 

thanks mate, my car at 1.2 bar made 460 rwhp and 543 fwhp, now 1.5 bar around 500 rwhp id hope, i was also curious how accurate that was as engine never went on engine dyno after the build only dd rollers.

 

sounds like dynapack gives big power figures like dynojets in america.

its a common thing to say that a dynojet wheel figure is the same as our flywheel figure.

 

But why do people here insist in using guesstimated flywheel figures in the first place ?

And really...who caes whether the numbers compare to different dynos ? They never do so why keep trying to make them ?

 

ive already mentioned wheel figures aswell and mark has backed it up with an engine dyno comparison so please dont start on this AGAIN !

i havnt asked opinions on dyno accuracy on the whole so lets just keep this thread on topic as to why consistently dynapack over reads.

 

But who says it does over read ? Who says the rest dont under-read ? Which is right and which is wrong ?

What is more important, is that any readings it gives, are consistent. And you seem to say that they are consistent.


IMO the numbers are totally irrelevant, as there will always be disputes. Gains seen before and after tuning are important, as is performance on the track.
If you want to compare numbers, only compare with other vehicles or engines used on that exact same dyno. Not others.

 

the issue, say for example i got a power figure from one dyno.

in my case it was mikeanics on congleton, i got 283bhp with a cat on, since his rollers only read up to 300bhp when i decatted it i had to take it somewhere else, it then did 334bhp at the same boost........do i know i have actually gained 51bhp just from a decat....sounds extreme but i cant go back and check as ill max his dyno out.

And im not gonna put my cat on and take it back to the new rollers to get another figure.

What the OP is saying is that you really should be able to go to any dyno and them be comparable, im not saying exact numbers but not 10-15% out, 1-3% i think is fair...even at 3% on his engine thats 16bhp out

 

Not sure if you was on here when Spadge was but he took his car to 2 rolling road shoot-outs in one weekend.

On the saturday at EA his car made 485bhp (i think it was)
On the Sunday at another set of rollers it made about 445bhp

Either way he had a 40bhp difference with just a change of rollers so i'd say there is quite a variation with different rollers against each other

 

did it 'make' different power, or did the dynos just read different power?

 

An engine Dyno does, Mark has found DD rollers are very close to the guesstimated flywheel figures while other are not as accurate.

 

Dyno dynamics used a fixed percentage for predicted 4wd gearbox losses, and its the same on every car you run, but clearly the losses are actually the same on every car you run, so it stands to reason that it will be very accurate for some cars and less accurate for others.

Personally I really rate dyno dynamics in general though just for their consistancy and the transparency in showing the config variables on the graph etc so you can see someone hasnt had the temp probe in their cup of tea or claimed the test was done up mount everest on the barometer etc. (ie they can still be fixed but at least you can see they are fixed, lol)

Ive not used a hub dyno, so cant comment on them, but in general I think you should just find a roller you are happy with as a benchmark and always tune your car to that so you know if you are getting better or worse, its pointless comparing between different setups.

 

Chip,

Cup of tea you say. Coffee ftw. Now you know how i made so much power

Taken from my rolling road day

 

EA's rollers were one that notoriously over-read anyway. So, I'd more have believed the 445bhp figures in any case.

Incidentally, at the TOTD Rolling Road day about 3 years ago, I ran my car at APT on our DD at about 8.00am and made 290bhp (at 1.2 bar IIRC), then drove to TOTD in Uxbridge and ran my car about 3 hours later and made 290bhp there too. So, whilst I realise that they are both DD systems, it does prove that it is possible to drive a significant distance from one DD to another, operated by two different people and make comparable power, which is what DD claim is possible and certainly appears to be the case. The so-called 'guessed' flywheel figures aren't really a guess, they are a fact/calculation based estimate and tend to be close to what you'd expect, given the manufacturers figures (allowing for over/under quoting depending on manufacturer) and what mods, if any, have been done.

 

Its the worlds simplest calculation as far as im aware.
For 4wd its :
flywheel = wheels/0.79
and IIRC for 2wd its:
flywheel = wheels/0.85

Sounds crude, but it makes SO much more sense than all these "calculated from rundown losses" figures, which are demonstrably a complete and total nonsense of course.

An ATW figure is far more indicative of the cars performance anyway and is what we should all be using really, but we are all too used to hearing flywheel quoted so it seems alien to most of us.

 

That is spot on for mine

Steve

 

Chips calculation is also spot on for mine. well within 1.x bhp anyway

 

So a dd roller bases it's engine figure on a 15% transmission loss on a 2wd and 21% on 4wd

wouldn't a fwd car have less tranny losses than a rwd? Due to no prop and a built in diff?

And wouldn't a Subaru style 4x4 have less loss than a Cossie style? Again due to the built in front diff? No seperate front diff n prop.

 

3.3bhp out to mine so i'd say about right as well

 

When comparing a Dyna pack vrs Dyno dynamics are the fly wheel results different due to the fact theres no weight of the wheel and drag of the tyre when its bolted to the hub, so should use the same calculation for transmission losses compared to the Roller set up?

What you you then use for a transmission loss foumla on a Hub dyno? 10% of the wbhp on a RWD car? Sorry if this is when Mark was getting at.

 

Mine works out at 0.37bhp lol

Steve

 

I think it might be something like 15% for FWD and 18% for RWD actually mate, apologies for the misleading way I wrote "2wd" instead of "fwd".

And yes the losses on different cars of the same type are of course different, but wont be handled differently by the DD rollers, as they cant possibly be.
So if you fitted a straight cut gearbox to your car and DD'd it before and after, the wheels figure would go up a touch, and the losses would stay the same percentage so its guess at flywheel would go up a touch as well.

 

I was always told
11% fwd
18% rwd
24% 4wd

but as said who gives a shit atw is where it's at lol

 

I really cant imagine that the 11 an 24 in that should be so far apart.


I know this is an over simplification, but working on the basis that the 4wd has 3 diffs and a box, and the fwd has 1 diff and a box.

11 = d + g
24 = 3d + g

24 - 11 = (3d + g) - (d + g)
13 = 2d
6.5 = d

Which would kind of imply that it thinks that you would lose more power through a diff than through a gearbox?


If you run similar numbers with the 15 and 21 which IIRC the DD uses, its a lot more sensible at the end of it!

 

Yes lol

 

Not for me i prefer fly calculated on an Engine Dyno. Mine will go on the RR to give Mark more info on their accuracy at high Power.
Whats wrong with mega high readings anyway 700 sounds better than 600 when you showing the graph to your mates . Remember 99% wont time their cars to prove the actual Power so whats the harm if it makes them happy.

 

No they didn't, I really believe my FRST made 207bhp

 

my standard 150k XR4x4 made 170+bhp at EA :Cry:

 

Bet it wasnt running right if it only made that much at EA

 

Im sure i have a graph from EA showing 390bhp on greens and 1.7bar peak boost

Steve

 

well mad have said dd is pretty accurate to engine dyno so yes that means dyna pack over reads.

anyways il say it again thats not for this thread so take a hint ! lol

 

thats within 2 bhp of my fly figure aswell.

 

exactly mate and dyna pack seem to pretty consistently make around 10% extra power and ive seen quoted alot (its all in the tune) bla bla bla whatever ! one has 50 whp more on 95 ron and a less spec head "but its a hub dyno so it must be accurate" and i think its a load of tish basically. 10% makes sense as 10% of 500 hp is 50 whp !!!

 

Bunch of dyno queens

 

Due to discovering a cracked block earlier in the year i rebuilt my YB with Nicasil liners, new pistons machined to give the same compression ratio as before, new arrow crank etc, run in and done a couple of power runs on a bench dyno but did not finish the mapping due to an electrical gremlin.
I then went to Track n Road to finish mapping with the engine in the car on their rolling road, unfortunately they couldnt stop the car doing burn outs on the rollers and they reccomended that i bring the car back with the rear suspension locked so that they could pull it down harder on the rollers, i returned and we still had a lot of wheel spin issues but ended up with a 2 bar run giving just over 501 bhp at the wheels and 581 at the crank.
I have now been to TDI at Thurrock and had it checked on the hub dyno and it made 544 bhp at the wheels (+43 bhp) We were then able to alter the ignition map to gain approx 15 bhp and the car was then mapped at 2.2 bar giving 570 bhp at the wheels. ( slightly less than before)
We did try turning the boost up a bit more with no significant gain as the turbo was running out of puff (GT3582R)
Conclusion - TDI's hub dyno read 8% higher than Track n Road rollers.

I hope those that are interested find this information usefull.

 

I would trust T&R's setup over the other, I have never known of a car to come out of there with what anyone would call unrealistic figures.

There is a chance that any wheelspin could of had a effect on the lower figures but I really do believe they have a very accurate setup.

 

If he's referring to TDI as Torque Developments.

I think it's safe to say TDI's results will be more accurate than any inferior dyno. TDI use Rototest, there is no better dyno.

But either way, it's the before and after that matters.