[Eric_Oz_S2]

As the title suggests, I'm curious as to the real world hp and torque people have been getting with their D1R install. Has anybody put their car on the dyno?

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[flash]

lol - i have about 140 runs



i'd also like to see other readings though too. i know what we got on mine and on brian's, but so far that's it. i think mrmister did a post track super hot pull though and got what i expected given the heat soak.



i wrote a whole section in the pdf file about the kit explaining this, and have done so in threads here as well, but the obvious big problem with dynos is not having a "before" reading to which to compare. because they vary so much, as well as the conditions of the car, it's really hard to see what is there without it.



but i'd like to see it just the same



i'm actually going to try to track down a dynojet (not many people use those around here anymore, as they have moved on to more accurate dynos) - because the guys who want to show off bigger numbers use them, i need to find one.

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[flash]

i'm getting closer to making this happen now.



this is important, as there is WAY too much misinformation out there about dynos. i just saw yet another example of somebody misrepresenting and inflating a dyno chart.



the simple mistake was in determining a 17% drivetrain loss. 17% is typical of a car with a traditional driveline, but is only applicable at factory power levels. drivetrain loss does not increase because you make more power. calculating any "percentage" for drivetrain loss when working on power increase calculation is flawed. instead, you need to use the actual loss number, and continue to use that. it's fun to do, because the numbers are always bigger, but it's not accurate, and can get way off the higher you go.



for example, if a stock 968 makes 203 at the wheels, and 240 at the flywheel, then the drivetrain loss is 15.4%. the loss is 37hp. the amount of resistance is the same regardless of what the engine puts out. if that same 968 engine is then supercharged, and makes 250 at the wheels, the loss is STILL 37hp, and NOT 15.4%, so it makes 287 at the flywheel.



so, another example would be if it made 292 at the wheel. it would then make 329 at the flywheel. not the 343 claimed.



there is still another flaw in the math though. that is assuming the factory number of 240 to be correct. to really get it right, you need to actually measure the loss. this can be done on many dynos. the loss can vary quite a bit, so you really need to do this. i have seen runs on a car with a 12lb flywheel with loss numbers as low as 9.5kw, which is only 12.75hp.



the other thing to remember is that dynos vary brand to brand, so you can only go so far in determining what you get.



that's why i need to find a dynojet, with the eddy current pack, and then get the numbers everybody is looking for.



i plan to get on this in the coming weeks.

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[bombfactory]

Flash I know a guy with a Dynojet in Westminster. Let me know if you'd like his info.

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[flash]

send it over. i'll find out what the story is and if it will work.



i need to call duane too. i know he has one, but not sure if it has the eddy current pack or not, nor do i know how willing he is to do what i need to do.

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[jfrahm]

I'm totally indifferent to dynos for peak numbers and bragging rights but they are pretty interesting for before/after comparisons and to understand the shape of the HP and torque curve.



Yes the driveline loss expressed as a percentage is overly simplistic but I disagree that it's a hockey stick curve where it hits, say, 40HP to turn the driveline and stops increasing. I feel that the more power you put through the driveline the more friction and drag are induced. This is not likely to be linear but as long as it's pretty consistent and you understand that the peak numbers are probably overstated (if corrected) then so what.



We have had local dyno days and IMO the dyno operator or the dyno itself seemed to be designed to make adolescent buys excited about their cars and not to deliver accurate peak HP numbers. I'd still be interested in doing a before and after on my non-D1R SC car but here at altitude my numbers would have a lot of scaling done to them. The shape of the curve and the delta between the two would be interesting though. Since I have a couple pulley options and plan to even limit boost at the top end I'd be better served with something I can use more or less legally on a flat-ish section of nearby highway.



That's assuming I get time to mess with the project some more.

-Joel.

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[flash]

the friction is an extremely small part of the drivetrain loss, and has nothing to do with the amount of power produced. the only way there would be an increase in friction is if the acceleration of the masses increased. i'm sure there is a minute increase, but it would be so small that it would be a rounding error. if we were talking about the difference between 100hp and 1000hp it might factor in. but the difference between 240hp and 340hp would be negligible, and well within the tolerance of the dyno itself. the energy required to maintain rotation of the masses is where most of the loss comes from.



as for limiting boost et all, yeah, that's why i designed the kit as i did. funny how one by one i keep seeing the design features of my kit get incorporated into that company's kit. i can't wait to see how much of what i am working on now gets incorporated into it.

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[jfrahm]

I would suppose that the pressure and friction between gears and the CV bearings and the like goes up a lot quite a bit when more force is applied. It might be a surprising amount, I do not know. It takes very little HP to spin a driveline when there is no load on it so the difference between loaded and unloaded is pretty huge. Throwing 30% more load at it is probably nontrivial.



As for me limiting boost, it is because I am indifferent to the high RPM peak boost but I do like having a few PSI at the midrange so I am probably going to go with a small pulley that I have tested in the past and found to be a blast to drive with. I feel that at peak RPM the boost available with this pulley might not be safe for the rest of the motor. Tuning I think is doable but the 968 piston skirts are short and it'd be easy to scuff the bores and generally make a hash of things. Since I am not tracking the car I spend a very small amount of time over 5K when things are happening pretty fast, and having an extra couple psi up there is probably not worth the risk unless the motor is built for boost (and at that point why bother building a 4 banger?)

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[flash]

boost - that's EXACTLY why i limited boost the way i did. i wanted it to come on early, but cap off early. lol - designing the mechanism for this to happen properly and smoothly was a revisit to my fluid dynamics resources



drivetrain loss - not really - while there is a change in thrust force and angular acceleration, and it does make for more friction, it isn't linear. the change in the neighborhood we are talking about is so small that it really is not worth calculating in. there is a bigger difference between a cold diff and a hot one, which is why i had to take diff temp measurements and control the time between runs when i did the chip and airbox testing, and will do the same thing when we test the kit again.

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[MB968]

[quote name='flash' timestamp='1333462107' post='124401']

the energy required to maintain rotation of the masses is where most of the loss comes from.



[/quote]



I have a clarification question. Assuming the above statement is true, what do you see are the important factors in the equation if not friction?

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[flash]

i'm not saying there isn't friction. of course there is. but what about gravity and inertia? the mass of the wheel alone takes considerable energy to get spinning and maintain it spinning



all i am saying is that it isn't a straight percentage, and as power goes up, while the friction also goes up thereby increasing loss, it does not go up at the same rate. as an example, and these numbers are ONLY for illustration and have no basis in testing, if you had a loss that represented 15% of the stock power rating, and you increase power 30%, you might only see 5% increase in loss, not 30%

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[tamathumper]

That's one of those things I'll have to take your word on. I'd have thought, just as air friction requires a huge increase in power to overcome as speed increases, that the drag of the gears in the oil bath would have done the same thing. But I ain't no engineer. <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />

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[flash]

if we were trying to accelerate through a barrier, like a well of fluid, it would be analogous. however, there is only a film on the gears, and the resistance there is affected by things like viscosity, composition, and temperature. a lighter weight gear oil will produce less drag than a heavy one. a cold one will be different than a warm one.



it's a very complicated formula to calculate it, and too far back in my memory for me to do it. what i do know is that the performance numbers don't bear out the claims of power when you use the inflated numbers due to a straight percentage.



here's one to tangle your brain. if it takes "x" amount of power to accelerate the drivetrain to "y", and if you increase the power at the engine, thereby increasing the frictions and losses for that acceleration, but then you just hold the speed, is that different loss than if you held the same speed with a less powerful engine? in other words, is the loss different between 2 otherwise identical cars, both travelling at the same speed, but one with 240hp and one with 340hp?



aha!



i sure wish we could do that though. it would make my stuff look a lot better too.

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[MB968]

[quote name='flash' timestamp='1333544861' post='124488']

the mass of the wheel alone takes considerable energy to get spinning and maintain it spinning



[/quote]

Yes isn't it only friction (including that from fluid (oil and air) molecules rubbing against one another) that requires that we continue to add energy to keep it spinning?

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[jfrahm]

Holding a speed with a more powerful engine is interesting but IMO irrelevant.

There are more frictional losses (generally) in a larger engine and in the case of a supercharged engine it takes energy to spin the blower, even if it is bypassing. However it's not real significant and I would not concern myself with it.



A 6 and 8 cylinder Mustang going down the highway at 65 mph will use a similar amount of energy but the 8cyl has a lot more swept area in the cylinders (more friction) more cam lobes, more main bearings, etc. There could also be issues with sweet spots for gear ratios which inform engine efficiency but let's assume both cars have been optimized for this for maximum MPG. Maybe the 8 banger gets 1mpg fewer than the 6. However getting up to speed if the driver of the 8 cylinder car chooses to use more HP to get a faster delta V then he'll use a lot more gas, maybe 30% more, during the runup.



The supercharged 968 might use 20-30HP to run the blower at full honk but at cruise it might only be a couple HP and less than 1 mpg. With my kit Carl even suggested that the VE improvement from having the blower would overcome this, I did not observe this myself but have not done a mileage run under decent conditions in my blower car.



-Joel.

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[MB968]

[quote name='flash' timestamp='1333544861' post='124488']

but what about gravity and inertia? [/quote]



I don't understand what gravity has to do with it, could you explain?

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[flash]

lol - i could explain it, but i'd need an easel with charts and graphs.



frankly, i've had way too many "discussions" about dynos already. it is what it is. with a few hundred pulls under my belt, i know what they do and don't do.



as for the bigger engine stuff, that's apples and oranges. the higher power vs lower power of the SAME ENGINE in the SAME CAR and steady state loss is the relevant point. for the purpose of determining power output calculated forward, drivetrain loss figures are only really relevant in steady state.



but that's exactly why the regular dynojet is junk for really figuring out what an engine does. if it can't provide a constant load, you can't tell what the engine is really doing. it's fine for tuning and seeing if something made a gain, but you have to pretty much ignore the numbers.



but, since that's what the majority uses, i'll have to go and get it done on one. this now brings us back to the original topic.

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