MazdaManiac

iTrader: (3)

Chassis dyno = real numbers
Engine dyno = fun numbers

No one drives an engine.

Furthermore, all the other dynos in this comparo are chassis dyno results.
When you have that, please post the results here for actual comparison.

alz0rz

iTrader: (41)

I would ride my engine all day if I could.

MazdaManiac

iTrader: (3)

It would burn your crotch and right ankle pretty badly.
Not to mention, you wouldn't be going anywhere!

laythor

who would want to go anywhere with an engine strapped to their crotch?

MazdaManiac

iTrader: (3)

That's how I roll.

Hymee

iTrader: (1)

Here is a simple question for you then, Jeff.

Are you saying that the figures presented in the graph at the top of the previous page...



... is power at the wheels?

Cheers,
Hymee.

Flashwing

For the sake of argument having dyno numbers which represent power generated at the wheels rather than an engine dyno would provide some consistancy. Otherwise, there's the risk that people will mistake engine dyno numbers for chassis dyno numbers.

I think we can agree that in order to be able to accuratly compare all FI products that we have to use processes which are as similar as possible.

As for which are "fun" or "real" numbers, I would instead make the argument that "useable" power is more important than "actual" power. I'd say the power which actually gets put to the road is the most important because it's what is actually driving the vehicle.

Either way, I agree that having a streamline dyno comparision is important. Otherwise, we'd have to insist everyone post engine dyno results with their FI kits.

MazdaManiac

iTrader: (3)

That is how I measured it when I ran that car.
Because of time constraints, removing the motor from Jorge's car would have been impractical.

Hymee

iTrader: (1)

OK then... Here is the scoop.

I believe a lot of you guys looking at these chassis dyno plots have missed something quite important. I'd almost go to the extreme of saying that what I am about to reveal is uncovering a huge conspiracy that will leave quite a few of you amazed and having to re-evaluate what you have believed to be the truth.

Firstly, yes - I know those other plots are from chassis dyno, whereas my recent plots are from an engine dyno.

Yes - it is correct then that the measurements are being taken at the wheels. What is not correct here is when you look at the figures and say they are "wheel horse power". That is simply not the case, and I can quite easily prove it.

In general, the plots in question are showing Engine RPM. That is the first clue. The second clue is that the plots show torque and HP crossing where they should do at 5252 RPM. The reason that must happen is the inextricable relationship between HP and Torque. For the units we use here (HP and lbs-ft) the “magic” number where HP=Torque is 5252RPM.

So what does that mean? If the HP and the Torque are the same at 5252 rpm, then it must mean that the HP and Torque are “at the flywheel”. There is no way the road wheels were spinning up to 9000 RPM!!!! Yes – a measurement is being taken at the tires, but some processing of those measurements is taking place to give an estimated calculation at the flywheel.

Another clue as to how these figures in these chassis dyno’s are “flywheel” values, is the fact that the torque numbers themselves are plotted. Now, lets say the engine makes 140 lbs-ft as claimed in these plots, and backed up by the manufactures claims of around 156 (to ensure we are in the correct ball park). The final drive ratio (i.e. the diff) is 4.444:1. This has a torque multiplication effect. So if the engine was making 140 lbs-ft and ignoring drivetrain losses, and assuming for simplicities sake the gearbox is in “top” gear (1:1), the 140 lbs-ft from the engine would be 622 lbs-ft at the wheel (140 x 4.444). The plots don’t claim 622 lbs-ft “wheel torque” do they?

But this would be close to the figure actually measured at the wheel. If you took into account the fact they normally we run chassis dyno’s in 3rd gear or 4th gear, then the torque at the tire would be even more.

For the sake of the argument, if one was to assume the 140 lbs-ft was the figure at the wheel, then the engine would be making a ****-ant figure of 31.5 lbs-ft. I know they are not regarded as torque monster engines, but come on…

So the 140 number (or those in that vicinity) must be a number that has been calculated back to flywheel numbers. There are a few ways the dyno can do that. Sometimes they have an engine RPM (tach) sensor, and they know the RPM of the dyno roller. So it is easy for the software behind the scenes to work out the overall ratio between the engine and the wheels. So it can take the “big” torque number measured at the wheel – something in the order of 600 lbs-ft in the case of the subject chassis dyno, and scale it back to a flywheel number using the overall drive ratio.

Torque DOES work this way. Power does not. Ignoring mechanical/frictional losses, power does not change through a gear ratio. Mechanical/Frictional losses mean that in reality you car makes less power at the wheel than it does at the engine/flywheel. But it makes a truck load of more torque at the wheel – that is why the gearbox is there and the final drive ratio is what it is.

Once this chassis dyno equipment has a torque number “at the flywheel”, and it knows the flywheel RPM, then it can easily calculate the HP. It is simple math. Like I said, torque and power are inextricable related to each other. The HP plot comes out, and it crosses the torque plot at the magical 5252 number, and everyone is happy as that is where it should be.

The result… Estimated flywheel horse power, via a measurement at the wheels.

So when you guys say “we made 300 whp (and implying you can add another xx% for drivetrain losses, so I must be making 350-400 at the crank)”, you have been conned. Sorry to put it bluntly, but that is the case, and the proof is presented above.

Therefore, my results I have posted are very comparable, but a lot more accurate.

I hope this clears things up, and sorry if I have spoilt your beliefs or interpretation of these chassis dynos results. I do not have a problem with chassis dyno’s in general. But any chassis dyno I have posted on here shows the wheel speed, and never the torque. It is showing the ACTUAL power measured at the wheel. Not the Estimated Power at the flywheel as derived from a wheel measurement.

I have attached a revised plot where I have overlayed the output of a STAR Mazda engine for comparison. It makes our 225 HP N/A engine look a bit weak. The data is from an actual superflow engine dyno result sheet I saw on one of visits right after SSX.

Cheers,
Hymee.

Hymee

iTrader: (1)

Furthermore - a chassis dyno is no more an indication of how the car drives than the engine dyno.

There is nothing in the engine or chassis dyno that shows driveability or throttle response. The reasons why can be left for another instalment.

Cheers,
Hymee.

MazdaManiac

iTrader: (3)

Very nice.

Were it only true.

Having the benefit of seeing the same motor on an engine dyno and then on a chassis dyno, I must, unfortunately, disagree with this assessment.

The key word in the above dissertation is "calculated".
On a chassis dyno, the calculated value is RPM. This is not a minor fact.

I don't deal with Star Mazda motors, but having put the same Rolex motors on both an engine dyno and a chassis dyno, I can tell you that not only is the output considerably different, the shape of the curves is completely different.

There is a lot more going on than a simple set of "calculations" done by either dyno.

I guess the pivot in this discussion will occur when the above mentioned supercharged motor is measured in a chassis on a chassis dyno.

Brettus

iTrader: (2)

this is gunna be good

Hymee

iTrader: (1)

It is absolutely true. The proof / key to my claims is the torque numbers.

And you can't compare one chassis dyno with another. There are a tuning tool, not an absolute tool. Especially when one gives a result that is a derived flywheel value.

Brettus, I think about those Apache helicopters in the Gulf War that picked off that convoy of enemy vehicles...

Cheers,
Hymee.

Brettus

iTrader: (2)

I read your post and it just confused me . You have done engine dynos that show 215-220 hp at the flywheel . On a chassis dyno the numbers are in the 165 -175 hp range for a "stock" motor .
Explain the difference and how this relates to your SCd engine dyno numbers and maybe i'll understand better .
My understanding is that your 330hp SC engine will be just shy of 300hp on a chassis dyno - does that sound about right ?

bose

iTrader: (5)

I'm just gonna say one thing about dyno's and then go back to reading. From what I can tell there is not a 'standard' for calibrating them. There is not a possible way to say the numbers given are absolutely correct or not. Besides numbers don't mean crap when talking about how fun a car is and how well it handles. Yes more power if fun, I want FI badly. But I'm not concerned how high the numbers are, I just want it faster with a nice 'safe' tune.

paulmasoner

iTrader: (1)

this whole topic is redundant. the fact is, people want a means to judge what they have and compare that to others, and also to claims of manufacturers. It is NOT practical for normal people to use and engine dyno. So that means they use chassis dyno's - regardless of WTF they actually measure, and regardless of how inaccurate they can be.

its the only flippin option for 99.9% of people, so we do what we can to ensure accurate and comparable results, ie STP correction etc....

In reality it doesnt matter what the chassis dyno's everyone else uses measures, as long as we are all being evaluated/measured in the same manner

who gives a **** what the real numbers are? if we cant compare it to anything else it doesnt matter

alz0rz

iTrader: (41)

Thus baseline.

qtwre

iTrader: (1)

Hymee, I see what you're saying but a chassis dyno will still calculate those flywheel numbers after drivetrain loss so it will always read less than a reading from an engine dyno. I think that's the problem when it comes to comparing the graphs on the first page of this thread to your graph. They account for drivetrain losses while yours doesn't.

rotarygod

First off I'd like to say that if anyone here is basing their opinion on which kit to buy based on what a dyno chart shows them in relation to another kit's dyno chart, they're idiots!!! There's FAR more to it than that!

I personally don't care either way how it's measured. As far as I'm concerned dyno's are nothing more than tuning aids. The difference is do you only want to know what the engine is doing or do you want to know what your drivetrain is doing? All I really care about is the percent gained over an established baseline and what that gain looks like in the rpm range. I don't care about exact numbers at the wheels or the engine compared to someone else's car or test methods. We can argue all day as to which has more relevance. If I had to pick one I'd just leave it at the simple fact that race teams, and engine/car manufacturers all use engine dynos as they want to know what the engine does and not what the rest of the car does. There is a place for that though.

I do see value in a chassis dyno though. However I must point out that if they were exact, why do the 3 main chassis dynos out there all give different readings when they are supposedly all calibrated to a particular standard? Shouldn't they all be the same? Aren't they measuring the same thing? If they are then they should give the same readings as each other. They don't! It's because of this that makes it hard to tell which to trust. I see people say that Mustang dynos read low and then try to extrapolate what a Dynojet would make only to use that number as their reference. Why? What makes the Dynojet the defacto standard? Is it the fact that it reads the highest and makes everyone feel all warm and fuzzy inside whereas the other doesn't and the highest must be the correct number? I have yet to see a chassis dyno that can hold an engine at one particular rpm regardless of load or have one that can increase the engine rpm at any particular load a set amount over a set amount of time. I see chassis dynos as nothing more than tuning aids for the street and their numbers shouldn't be viewed from the point of view that they are correct but rather estimations. The important thing is looking at the curve. You can also see if power gains or loses when changes are made. Tuning aid. The actual number presented is really unimportant in the long run. It's for this reason that even a G-tech pro is a useful tuning aid.

Hymee in my opinion still has the be all end all nicest forced induction system for the RX-8 so what his numbers say on paper compared to someone else's don't really matter to me. I see everything I need to know. The whole package is absolutely world class top notch and there is nothing else anywhere for the RX-8 that can say it's had the level of detail, attention, and workmanship performed on it that his has. Of course a dyno doesn't show that either! Am I biased towards Hymee? I don't own one and probably won't. I don't have an RX-8. He doesn't pay me to say good things about his product. I am however biased towards things that are well thought out, designed, and engineered and that just so happens to be his system. What others try to compare to it or how is irrelevant. I don't care. It's comparing the acceleration of a Z-28 to a Ferrari at that point and we know what can happen there and who goes home with which at the end of the day.

Nemesis8

iTrader: (3)

Should we not just be interested in the overall gains of the same car, on the same dyno, from when it was stock to when it was force fed?

Kane

iTrader: (1)

These are relative measurements of relative values.... that is why they are so hard to directly compare.

They just don't stack up the way we all want them to... I kinda wish they would just drop the scales all together and just worry about the changes measured from one set-up to the other relative to the same motor stock. But it isn't ever going to happen cause everyone wants to dumb it all down to a single number.

paulmasoner

iTrader: (1)

i agree with RG on almost all points here. the only thing is that most owners dont so their own tuning, and most owners are most concerned with dyno plots for means of comparison, thus these two threads exist....

yes the chassis dyno's are all different, and likely inaccurate. But how many people here are going to run to an engine dyno everytime they spend a few hundred bucks on parts? engine dyno's are simply impractical for owners, and even for many "producers"

So we do the best we can with what IS practical. This means SAE corrections, smoothing factors, understanding trends between different dyno manufacturers(like mustangs read lower than dynojets)....

Not knocking Hymee's product(or the man) a single bit, but i think he does need a chassis dyno. no one viewing this thread is tuning that motor, so all we are doing is comparing - thats what this thread and posted dyno plots are for. you cant compare engine/chassis dyno numbers, and even those smart enough to be looking at overall shape etc need to realize that the curve may be very different on a chassis dyno.

Kane

iTrader: (1)

Except Paul; they can't be compared.... I mean you can line 'em all up so people can see cool stuff - but to get wrapped up on one vs the other is stupid.

The only thing that can be compared is gain over the "pre-mod" set-up on the same engine....everything else is just for bragging rights.

paulmasoner

iTrader: (1)

your right, but you also KNOW thats not what happens in reality. in reality people see 2 plots, and they make a determination that one is better than the other - usually with little to no clue as to how the plots were derived.

i mean really - how many threads have been started here in the last 5 years talking about one intake over the other because the dyno's showed 17 and 21HP increases respectively?? thats how it is man, whether its legit, or consistant or not.

thus all the correction factors exist - to try to make them as realistically comparable as possible.

rotarygod

Since each kit out there probably has more potential in it than is represented in the posted charts (except for those Greddy POS's), I still don't see what the point in comparing them is? It's very easy to go change those results and if that's possible, the only thing a dyno chart tells you (aside from the fact that Greddy sucks) is really the least important. It tells you nothing about workmanship, design, or quality of components used.