ziperhead

Some interesting reading from Jim Bell on dyno variables

http://www.kennebell.net/techinfo/ge...tVariables.pdf

TurboShelbyGT

I just wasted my time reading that and not unusual, I disagree with someone. Here are some things that made me laugh:

"They don't care about factoring in aerodynamics or road load/vehicle weight." Hmmm, really? His customers don't care about a correct tune then. The numbers on Dynojets are inflated, plain and simple and that is straight from the mouth of the designer of Dynojet. You can not have a 286 whp car make 270 whp on a chassis dyno, there is a LOT more driveline loss than 18 whp on an AWD car. A 550 hp rated Mustang should not make 520 whp to the wheels, there is more loss in the driveline than that.

A few paragraphs down he says he runs his dyno with no smoothing because adding smoothing makes the HP numbers read higher, bull**** again. That's not correct. The smoothing takes the peaks and valleys out of the chart and gives you an average of the highs/lows and you end up with a smaller peak number. It is good to show the overall condition of how the car is running but will also show the highest numbers running it with no smoothing.

Wow, there is a lot in that link you posted.

candymanjl

great honest post. that's my biggest beef with any other dyno besides a dynojet, it's not because it's different, it's because you never know if it's an honest dyno run or not. a lot of brands have some user entered value that you can use to tweak the outcome of the dyno and artificially inflate numbers. it's not that the dyno itself isn't a good tuning tool or not reputable, it's the users that can be dishonest and mess with things.

in my experience dynojets are very consistent from run to run and even between different dynojets. my friends S2000 dyno'd on a 2wd dynojet one day and a 4wd dynojet model on another day and the numbers with within 1-2whp, pretty impressive IMO.

like it's already been said, pick a brand of dyno and stick with it to really see changes before and after mods. on one with a user entered value, like the weight on the mustang dyno, pick a value and stick with it. then you know it's the mod changing the power and not you messing with the dyno.

m260gt

before the blower my car made 232rwhp on the mustang dyno, then i got on a dynojet and it was the exact same....??

candymanjl

I don't, to me those are just more variables to worry about anyway. the more things that dyno is trying to account for the more variables in the calculations. all I want to know is the engine's power, not what the dyno thinks I'd be making on the road. and just because the weight of the car changes that has nothing to do with the power that the motor is making, it's a little silly to me.

I've been able to tune my past cars on a dynojet without any problems. I haven't needed a loading dyno to hit all the tuning points, it'll load up just fine with the resistance of the drum. I know a world class tuner and he tunes on anything, any major brand is as good a tool as the next. there's features and preferences sure, but I don't think you can discount one as right or wrong because you think the drive train loss should be more or less. and really unless you engine dyno a motor then drop it into a car and chassis dyno it you have no idea what the drive train loss really is or if the motor is under or overrated.

as far as the drive train loss, my last car was an S2000 and I dyno'd it bone stock. it put down 210whp on a dynojet and the factory advertised 240hp, that's a 12.5% drive train loss. that seems right but again who really knows unless you engine dyno the motor then test it against a chassis dyno.

TurboShelbyGT

The dyno debate always gets heated, I'll try not to let it go there.

You are NOT able to hit all the cells when tuning on a intertia only dyno, it's impossible. On a 200 whp NA car you may have done just fine tuning on the Dynojet and then hitting the street but I'd venture to guess if you did proper datalogging on the dyno from off idle to red line and then again on the road you'd find that the tune was different, as we've done it on many cars and it's always been the case.

The aerodynamic/road load/vehicle weight are not variables in the power the dyno reads, it is the proper way to tune a vehicle and simulates the road so when you get off the dyno the tuning doesn't change. When we had our Dynojet we ALWAYS had to touch the tune up afterwards when the cars would hit the track/road. The Mustang Dyno adds load to the car dependant on the weight of the vehicle and the horsepower required to move the car at XX mph down the road, just like in the real world.

I can tune any car on our dyno and know when I am done it can go do land speed racing, drag racing, road racing or just be driven around and enjoyed without taking it out for a touch up tune.

Unlike many, I've owned both dyno's. I had a brand new Dynojet in 1998 and had been using them since around 1995 for "tuning", which is a joke in itself.

Believe what you like, dyno where you like. I am telling you all though, there is a difference.

As for the Mustang that made the same power on the MD as it did on a Dynojet, that tells me more than likely the MD was tampered with but then again at 230 whp the difference in percentage is harder to determine, 10% difference between the two is only 23 whp, that could be easily accounted for in fuel and weather changes.

Very good friend of mine has an AWD Dynojet at his shop, dyno'd his car at 910 whp, loaded it in his trailer and drove here from Florida, the car made 803 on our dyno with no other changes. 10% of 910 (just using 10% as a random number) is 91 compared to the 23 on a low HP car.

Have a good day.

Chris07GT

doesn't matter which one you use, I'd just recommend choosing one and stick with it as you make changes to your car so you get an accurate idea of how the changes are affecting the car. I mean don't get a baseline number on a Mustang Dyno, then get an intake and tune and get a dyno done on a dynojet. Most of the shops by me have dynojets, so that's what I use. Again, not so worried about numbers as I am with a/f, curves, etc.

candymanjl

not picking fights but that's not always true, the smoothing doesn't always lower the HP.

on my all motor dyno the smoothing lowered my peak number 1hp. I just went back to the same dyno today with the blower on the car and with the smoothing off I dyno'd 473whp. the same run with the smoothing on max and the power went to up to 479whp.

I could send you the files if you really want. 90% of the time I agree, the power does lower with smoothing, but sometimes the smoothing does weird things and can throw off the peak numbers like with my boosted run today.

mygt500

threads in the right section and interested in watching this thread....