hacker-pschorr

Right behind those is the Shark Tuner L-Jet,,,,,,,,,right?

John Speake

You cannot be serious !

RDS928S

Here is what the blackbird needs:http://www.bmcairfilter.com/infoCDA.asp
Internal venturi with carbon fiber shell. Much nicer than those hookie clear filter covers.
Also available in silver carbon fiber.
I will ask Dave to sell me just the rear section coming off the MAF.
Then adapt the BMC CDA's in place of the cone filters with clear housing.

Rich

hacker-pschorr

Cool - that might work for my supercharger setup.

928SS

not a bad idea - but it's for 1600cc motors.... will they fit under the hood too? look kinda big...

RDS928S

Rob,

the CDA's are for all size motors. They make a special pair for the BMW M5 v8 as well as big Audi motors etc.http://www.bmcairfilter.com/VisDetailDyno.asp?ID=2
http://www.bmcairfilter.com/VisDetailDyno.asp?ID=5
http://www.bmcairfilter.com/VisDetailCDA.asp?ID=142

Rich

928SS

just need to go to home depot and get that Y thingy from the sewer dept and we'd be ready to rock!

Louie928

I was going to say something about this guy's ramblings, but probably not much of point to spend my time on it. Basic thing to remember is that if you are going to measure power and have it mean something you have to correct it to a standard of some sort. That is a standard air pressure, intake air temperature and humidity. There are two "standards" in common use. SAE and "Standard". Correcting to SAE standard which is probably the more correct means correction to a 77F (25C) air intake temperature and 29.6" hg atmospheric pressure. Correcting to "Standard Day" conditions corrects the power back to 59F (20C) and atmosheric pressure of 29.92" hg. Naturally if you correct to "Standard day" conditions, you'll record higher power because the intake temp is lower and the atmospheric pressure is higher. It would be really dumb to do a dyno run and not correct the readings back to some standard. To not do so would make the numbers meaningless. A run an hour later on a different car with the shop temp different would give different numbers even though the output of the two cars may be the same. Same car on different days with different atmospheric pressures would show different outputs even though no change was made to the engine. You've got to have a standard if you are going to compare one run to another run. On most dynos I know of you can elect to not use any correction and use the raw numbers. That's fine and you can do the correction math yourself. Some dynos do have some voodoo numbers you enter which is supposed to compensate for driveline loss, or apply losses found during a coast down run. If the dyno is using those "corrections" to come up with a ficticious set of numbers, sure it's bogus. The normal environmental conditions during the dyno run should be used to correct back to a baseline though.

Regarding differences bewtween inertia dynos and loading dynos, of course there are some. The inertia dyno cannot compensate for the built in inertia of the driveline components of the car itself. The loading dyno doesn't have that problem. Loading dynos are very useful when tuning because the RPM can be held while tuning a set load map site. It's a lot more difficult to do that on an inertia dyno. It can be done. A couple days ago, I was talking with a tuner in Florida. Their shop has two dynos. A loading type and an inertia type. They use either one depending on the application of the car. For a drag car which will always be accelerating for only a few seconds, they use the inertia dyno. For a NASCAR car, it's the loading dyno. However, even though they use the loading dyno for initial tuning, they always do the final on the inertia dyno and run it through all the gears. The mixture will be different from say, 4k to 7k, in 2nd than in 5th and they want to see what it is in each gear as it accelerates. Running up through the lower gears gets the combustion chamber up to temp when they hit top gear which gives a better correlation to actual use than a 4th or 5th gear run only. You may have noticed that cars are almost always accererating when under WOT power. Never held at a steady rpm for long. The exception would be an ORR car. That lends big credence to an inertia dyno to better replicate actual use.

As for one being able to more accurately measure some power level than another. All dynos measure torque. Whether it is acceleration rate of a known mass, or force on a lever arm of an eddy current retarder, it is torque that is measured. Horsepower is always calculated from torque. Some dynos synthesize torque using outputs from pressure and flow transducers on a fluid pump. That seems to work too. Of any of those measurement processes, measuring the acceleration of a known mass is the easiest and most fool proof. No dyno equipment calibration required initially, or changes with age, or changing temperature, or one session to the next. My inertia dyno uses an encoder on the roller shaft. It outputs 1000 pulses per rev and measures the acceleration rate (time) between each of those pulses. No accelerometers involved. It's not uncommon to see consecutive dyno runs show power within less than 2 hp run to run.

worf928

Louie, is that figure of repeatability absolute or based upon a percentage? In other words, repeatability within ~2hp regardless of the motor or ~2hp for your 600hp monster equating to roughly 1/3% and thus we might expect 1hp repeatability on a 300hp lump? From your description I would think that the measurement of torque would be extremely accurate. On the other hand...

... to calculate power from the drum acceleration IIRC you need accurate tachometer data. Yes? Do you have any opinions or data on the fidelity of the tach measurements?

Louie928

It's an absolute type thing not a % of hp. Unless something changes between runs they are usually less than 2hp difference although I haven't measured really low hp engines. That doesn't seem to be much of a function of the engine power. 928s with the wiggly curve won't be that close, but my GT is, and a friends 914/6 was close on different runs too. The '85/'86 seems to not have the wiggles on the top end like the S4s do so they are usually close run to run too. You are very correct that the measurement of drum acceleration has to have very accurate and fast rev data. This dyno uses an angular encoder on the roller shaft which outputs 100 pulses per revolution of the roller. That's a pulse for every 0.75" of the 24" diameter roller circumference. Some other specs are timing accuracy +/- 0.1usec, speed accuracy +/- 0.001 mph, RPM accuracy +/- 0.01 rpm. I'll see if I can dig up some runs we did on an OB with CIS. Those runs were right on top of each other.

worf928

Thanks Louie. It's nice to get a view into the Black Box of the dyno.

I was actually referring to engine rpm data and wondering how that data is gathered or derived. You need that to calculate hp from ft-lbs. (Or if you had dead-nuts accurate data on gearing and loaded tire revs/mile (or if it's the type of dyno that gets bolted to the hubs) I suppose you could it that way too. EDIT: Hmmm.... probably wouldn't work on an auto-tranny though.)

AO

Wow Louie... talk about ramblings...

Your perspective is very insightful. I think the key takeaway (for me at least) was that the loading dynos seem to be closer to each other when comparing dyno runs from different dyno manufacturers.

Comparing a loading dyno and an inertia dyno is a bit like comparing oranges to tangerines. They look similar but are different in the end. However, now that I have found my "dyno guy," all I'm concerned with is my baseline + X.

mark kibort

Louie,

The interial dyno doesnt really need to compensate for the driveline intertia, as it is a true measure of what the car will put down to the wheels for a net HP, or net force. simulates the "real life" operation, as i dont know too many folks that keep their cars at a constant WOT rpm . (except as you say the ORR guys)
Either way, the intertial factor is very small for the rate of acceleration generated at speeds above 40mph. I think the rolling friction of a rolling dyno would be a more substantial factor that wouldnt be present on a brake dyno.

Now, dynos dont actually measure engine torque, it is calculated as well. IN fact, interial dynos by knowing the the mass and size of the drum and the speed changes (acceleration ) can very easily calculate (measure) HP by only knowing the change in kinetic energy. (ie Power). in fact, if you dont have a rpm signal, what is the output of an inertial dyno? Thats right, Power and MPH!
now, it can figure out torque at the driven wheels through the gear box, but those values are never shown. actually, this too is hp, as you still need the speed to calculate acceleration and get the forces required to create that acceleration. So actually, the dyno measures torque and HP, but cant give you engine torque without futher calculations. with the spark input, the dyno then can then generate engine torque values.

I dont understand the level of concern for SAE vs Actual dyno runs. there are a lot of factors with coorection. generally, they are not very consistant from dyno operator to dyno operator. using actual, you have what is ACTUALLY happening. its very repeatable, as long as the engine is producing the same HP . how fast you can accelerate the drum, is how much hp you have.

mk

mark kibort

As i mentioned ,

The dynojet measures rate of speed change of the drum. gearing has nothing to do with the output, but it CAN take a spark signal to calculate engine torque values at any rpm. If the dyno doesnt have engine spark signals, the output of the dyno will just be HP vs MPH. (because thats the only information it knows). HP is the rate of change of kinetic energy, which is easy to calculate with knowing the drum size mass and the speed change. torque at the drum can also be calcuated by the rate of acceleration, but thats a raw aggrigate torque value, that would be meaningless if you saw it. (i.e. 3rd gear 5:1 x engine torque of 300ft-lbs would show a value, if it could be output, of 1,500ft-lbs)

mk

928SS

FWIW, I saw nearly a 40rwhp difference btween greg's dyno and a dynojet w/my slug... and a buddy of mine w/a blown GTS that had a dynojet run at nearly 435rwhp couldn't outrun my 360rwhp slug at the strip side by side... at that point I figured it's all BS in terms of a real #, and just focused on my baseline and mods that affected it.