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Discussion Starter · #1 ·
Dear All.

Had some experiences last week on a couple of Dynos that I'd like to share.

Before the Ten of the Best I ran my car on a Dyno. After TOTB I had a certain part changed and decided to Dyno the car again. It made 40 bhp more than the previous run (and I was told this part would give me 30-40bhp more by the way) at the same Dyno. To boot the car felt much more responsive/quicker on the run down to the Dyno so I wasn't suprised when it made more :) . This was last Tuesday by the way.

Last Thursday I decided to go to another Dyno 'just out of interest' and also to be nosey :D . Ran my car and was suprised that the figure was lower. Now you think why suprised :eek: . Well I'll explain.

Another car had been Dyno'd on the same Dyno, as I had been on Tuesday, and this car made 50 bhp MORE at the Dyno on Thursday :confused: .

Now I can live with certain discrepancies, and understand that one Dyno may read higher or lower than the other, but this is just downright confusing.

Any ideas anyone ?

And NO I'm not saying who the Dynos were before anyone asks as I don't want it to get personal ;) . I just feel that I'm ragging me car and ain't too sure where I really am. Except that on the road it feels good now after all the work I've had done.

Bye for now.

glen
 

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When we looked at static tuning/development methods for our race program, we heard numerous stories about how you'd never get the same power outputs twice on a rolling road without the entire national grid powering your cooling fans.

Particularly for turbo applications trying to simulate the air flow conditions you'll get on the road is very hard to acheive and as a result depending on how good or bad the cooling is, you'll see quite wide differences in power figures from day to day. Not slamming the methodology of the rolling road, but certainly for Turbocharged cars we had it on authority that it wasnt the way to go.

Obviously this is just our experiences, we settled for an engine dynomometer from Superflow in the end, although removing the engine from a road car every time you want a power run isnt practical...

Good luck with it though, I'm looking forward to seeing this beastie at a meet!

Cheers,

Dan
 

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Discussion Starter · #3 ·
Cheers Dan

The only prob was that one was up and one was down with regards to the previous figures.

The Dyno on Tuesday has been used many times before and has replicated power figures from different cars in the same state of tune.

Is it also better then to keep to one Dyno that gives the same flow of air all the time therefore giving consistent readings. Well as consistent as is poss I mean :) .

glen
 

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You are right, it is confusing!

Ahhh, I've re-read it now :rolleyes: and see what you mean, 50 Bhp is quite a fat discrepancy I must admit...
 

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Glen,

I suppose there is a certain amount of tolerence built into the figures you get +/- 5% for instance.

if your car was making 500 bhp and you dyno'd 50 less somewhere and 50 more somewhere else this is only a 10% discrepency.

I would have thought your car is making over 600 nowdays so this swing isnt as great as a 50 bhp swing would be in my car.

I know 50 ponies is 50 ponies but when you already have shitloads of them you wouldn't miss the 50 in normal road conditions.

another thing, when you are highly tuned then a number of factors could conspire to give you lower figures, time of day, air pressure, tyre pressure, induction charge temperature, oil condition, a +/- 5% tolerance on the rollers all of these could easily add up to a 50 bhp loss when you are at the type of power you have got.

sorry to waffle on. As long as you are consistent on the one set of rollers you usually use, then you can compare what you get to the mods you have made.

Are you gonna spill the beans and tell us how much power you got then ??? go on go on.

/Steve
 

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Happy and Sad

Horrible running your car on the dyno init, you think youre doing good, happy with the figures etc and then a new run shows something different, it pi55es your off cos the car feels better I bet but shows lower figs.

Out of interest, actual total figures are not important if you dont want to tell but, where did you lose the BHP? was it on the fly figures or the wheels and was the drag the same or different and did the difference between the fly and wheel BHP differ the same amount as lost on the total fly figure? Interested to know as the dyno sheets I had previously run showed all different figures but I was in the middle of changing lots of things at the time so not a real comparision tbh.

Was your Torque different as well?
:)
 

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Glen,

Did the other car have the same dia. wheels as you ?
If not did the Dyno Operator compensate for wheel dia. in the figures ?

Was the other car a Skyline ?

Like Dirk suggested, the % transmission loss can account for huge discrepancies, especially with the likes of the Attessa system is transferring a certain amount of toruqe / power to the front wheels.

If your car was struggling to get traction on the rollers then it would send a different level of power to the fronts. If this was the case, then changing the tyres could show a change in output at the wheels.

Then again I may be barking :eek:
 

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GTRs vs Rollers

Since I was there for one of the sets of runs and without giving anything away (I hope you don't mind me answering Glen).

Both cars were GTRs.
Both were measured in 4wd, on both dynos.
The power figures compared are power at wheels for both cars.

One car gained circa 50bhp, one car lost circa 50bhp, hence the confusion.

I don't think there are answers to this debate, but I agree with what Glen is saying which was also what several tuners have said:

Dynos are great tools for tuning (same car, same day), but don't read too much into the numbers.........

Guy
 

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Guy has hit the nail on the head - thats what I/we heard too ...

Rolling roads work fine for on the spot up and down measurements (bit more boost, new exhaust etc), but for engine development or accurate monitoring of power outputs - its out of the car and onto a proper water-brake engine dynomometer.

Speaking of which we have a fully equipped engine test cell with a two year old Superflow SF-1 dynomometer in which you can hire for a few days (www.abbottracing.com) if you guys wanna REALLY see what power you have! Obviously though, this doesnt take account of transmission losses or any weird quirks that the ATESSA-ETS system would factor in - ie. the engine comes out of the car!

And for any tuners that would like access to this facility - lemmi know...

Cheers,

Dan
 

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Discussion Starter · #12 ·
The thing is

nothing had been changed between the 2 cars from one Dyno to the other so irrespective of rim sizes etc., it shouldn't matter. I like to work on the power at the wheels figures and the %'s lossed/gained are based here.

The other Skyline was standard so the increase of 50bhp is quite phenomenal. Mine isn't 600 engine bhp yet (and God knows how I'm suppposed to work that out,) and is not too highly modded and runs nice and sound.

The whole confusing point is where exactly am I. I'm not bothered if me car shows 300bhp or 800bhp. Its how it performs on the road that matters I suppose.

I think the only thing I am going to read into this is that I am going to keep with the same dyno whenever I make any mods. This should then mean that whenever I make a mod I can be pretty sure that what I have done has made an improvement, or not.

See ya.

glen
 

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dyno results

well i told you all about dynos weeks ago and how easy
it is to make cars look as if they have more or less power
than what they really have.

but i was told that i was being to critical.



KEV
 

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dynos

HUH,
DYNOS Glen are you really trying it on or what, how can you expect 2 different dynos to read the same value, surley you dont expect the same they are calibrated differently for a start and they only read the figure that represents their calibration,

take air temperature and density into account and wheel spin and dyno operators into account before making conclusions as to how dynos predict power they are only a guide as to how well your mods are doing after all you can feel the difference in your power when you drive the car cant you ! sorry mate but your post is crap you cant get the same reading from 2 different dynos,on the same dyno if you are carefull with the recording of the air inlet temperature and humidity and loading and all the parameters you can re- represent the figures for as long as you want to why should a static dyno be any better than a chassis dyno for this it isent it is just the static dyno can only give the power at the crank and that seems to be all anyone is interested the power at the crank, so great let it be the static dyno gives power at the crank and the chassis dyno gives power at the wheels brilliant both the powers are measured in the same way with same expensive load cells, 2 different static dynos will give different readings so glen what is the point of your post or do you need to be told TRACTIVE EFFORT thats what its about on a chassis dyno but i thought you would know that
REGARDING ACTUAL NUMBERS NO MATTER HOW YOU LOOK AT THEM THEY MUST BE REAL OR THEY WOULD NOT BE THEREcos if not there is no point in trying to get them and all manufacures would not quote them and all dyno manufactures would not make them from 0.5 to 5000 bhp
Gary
GT-ART
 

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Discussion Starter · #15 ·
Dynos

No I'm 'trying it on' and I don't believe my post to be 'crap'.

I have had chats with you and Mark and others re the differences between Dynos. Not being as technologically minded as you tuners I decided that I wanted to go and experience it for myself first hand and, was most suprised that 2 cars gave different readings being up and down from their previous Dyno runs (I'm getting bored repeating myself.) I thought they would have read the same way at least. What I put up in my post was my experiences based on the 2 two Dynos, hoping for it to be followed up with open discussion.

To call someones post crap is rude and disrespectful. If you take any notice you will see their are a lot of other new members on here who are probably going to be interested in this subject and may take something from it.

Ah well never mind :( .

glen
 

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I am not at all suprised that a different Dyno has given you different figures, for many of the reasons already covered.

however I would have expected the two cars tested to be be different in the same way, ie both up or both down. I also would have expected the %age difference to be about the same.

I would suggest that it perhaps had more to do with the operator than anything else.

Simon
 

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Glen,

I am definitely interested in this discussion, as it is such a well-debated (or should that be mass-debated ?? :rolleyes::D ) topic. How many times have we all been asked "How powerful is it ?" by onlookers ? And virtually every Skyline advertised for sale states a BHP figure. Personally, I would have thought that the best way to back up any of these claims is to actually get the power "measured".
Whilst I agree that you will get different readings on different days/conditions/test equipment etc, I thought that it was perfectly reasonable question to ask :
Why, for two vehicles measured at the same two places, under the same conditions, does the power deviate in opposite directions (irrespective of the absolute numbers) ?

I would be interested to hear more (constructive) comments on this subject.


p.s. Gary, I'm sorry to hear that the :mad:anger-management:mad: course is not working out.
 

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Glen,

I was hoping for some sound factual answers as to why the figures head up and down so much, I was under the impression that the point of a dyno (chassis or static) is to give you a way to measure power, if you can rely on them from day to day to be atleast reasonably accurate then there seems little point. I agree, a 50 Bhp discrepancy is unacceptable.

I know that we have to calibrate our static dyno with a balance weight system (torque-arm principles) each time we use it, and we get power figures that when taking atmospherics into account are within 5 Hp of each other run after run, although admittedly thats usually only engines of around 200-210 Bhp.

Guy,

According to the SF-1 setup books, the loadcell is capable of measuring upto 1000 lb/ft of torque between 3000 and 6500, 900 lb/ft at 7000 and 800 lb/ft at 8000. As the revs get higher its ability to hold that level of torque decreases, but if you actually had an engine that delivered 800 lb/ft at 8000 RPM, it would be 1218.5 Hp, so I dont think it'd run out of capacity...

The SF-1 doesnt have a "power" limit as such, only a torque limit - because (without getting techy) power is simply the result of Torque with rotation, as below:

HP = (Torque*RPM)/5252

or

HP = (Torque*2*pi*RPM)/33000

Same result either way, just whichever formula you prefer ;)

Cheers,

Dan
 

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Power

Dan,

Thanks.

I am thinking about getting some of my future GTR engines mapped on engine dynos, to save the stress on the car.

I knew the bhp/torque equation, but was interested to note that there are some dynos out there that read only bhp and don't quote torque.

Unfortunately the 'dyno debate' tends to get messy very quickly as several people have vested interests in either their own quoted figures or disparaging others.

Guy
 
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