just the subj

To: Moders
i wasn't sure where to post the question

 

I believe they are filled with water or sand?

 

Approx. 3,000lbs.

 

there around 3,000 a drum.....the shipping weight of our dynojet 248 was 8,000. a moster forklift was used to get it out the back of a trailer.

 

If you are talking about rolling resistance, I think I recall it simulates a car weight of 2400 lbs. Don't know if that's why you asked. Just thought I'd throw that out there.

 

John/Colonel, you are right in the eye!!! LOL
So, i was wondering how much RWHPs should i subtract from dyno numbers to get a real ones ?

 

For the Colonel's car.. not much

 

LOL ))))
That's right!!!

But i think my question is valid and if someone's EGO is not too big about his/her dyno numbers they would love to know the asnwer as well

There is big difference between PCM dyno and Dyno Machine... i would like to know how many free HPs dyno gives me...

 

I'm not sure I understand what you're asking. What free HP are you talking about?

<--Featherlight Racing Co.-->

 

well, you see, when you dyno car on a Dyno-Machine it's much easier for the car to pull bigger numbers, because dyno drums weigh less, but in real world, when you drive the car under 100% load the PCM dyno shows lower numbers then DynoMachine numbers, since in real world car is heavier and so the real world numbers are the "right" ones, right?

If you take the car in 4th gear to the redline and then see your PCM dyno #s, they are lower than Dyno-Machine numbers, but i don't want to take my car to red line in 4th gear to see my numbers

Am i making sense now :p?

 

PCM dyno numbers? Well I don't know a thing about that (something you're reading on a diagnostic scanner?) but a chassis dyno tells your RWHP based on how fast you can accelerate a known (the rollers.) It doesn't matter what your car weighs...it's still accurate. 400 RWHP to the ground is 400 RWHP regardless of if the car weighs 5000 or 500 lbs.

 

you can always do it in say 1st or 2nd gear...and do some simple math.....if hp at 1:1 = 400
then hp at 2:1 should = 800 you can do any gear as long as you know the gear ratio and do the math. I think thats what I remember bein told....

hp is just a ratio of speed and how fast you get to that speed over a given distance at a given weight.....
Simple Rough Estimate Calculator this is not exact...they are rough #'s...but it gets you real dam close.

or...just go to a dyno shop and do it in 4th gear at a 1:1 ratio....

 

Gears multiply torque to the wheels. Not horsepower.

 

If you're turning a 2500lb drum and you tune your car while driving on the road, won't the PCM being seeing nonaccurate loads. For example, if I do my tuning by looking at how my 3600lb car is running at the top of 4th gear while driving 120 down the road and program it for max power. Then if I get my car on a 2500lb drum dyno, the dyno won't be putting enough of a load on the car to get the same results as I would if I was making a 1/4 mi pass. Am I making any sense? Or is 10am in the morning still to early for me to be thinking?

 

Horse Power is figured out from torque....
HP= (Torque x RPM) / 5250

ever notice all charts torque and HP cross at 5250...no matter what you got for #'s

thats why you can divide by gear ratio...

 

Felton, you are correct in that load does effect tuning somewhat. That's not to say that you can't tune a car on a non-loaded dyno though. You just have to understand how much it effects it (not that much really) and compensate. It'll run a little richer when pulling it's own weight so if you want a 13:1 ratio, set it for about 13.3:1 on the dyno.

 

This got me thinking though. When you strap the car to the dyno and put up xxxhp and xxx tq. Is that the same when your on the cemement. I was thinking like this: Picture yoursef on a bicycle on top of a set of rollers. It would be easier to get started on the rollers and you would be ablle to accelerate faster than you were on the ground. Thats why im thinkg that even thoug you may be puttin down XXX on the dyno. are you putting down xxx at the red light.

 

Don't outthink yourself. Yes, the power to the rollers is the same power that is to the ground on the street. It's measured on the rollers at the ground (the rollers ARE the ground), remember that. You're not going to suddenly have less power just because you're not on the dyno anymore. You're car is still running the same.

 

And BTW, if your bike was strapped to a dynojet, it would be ALOT harder to accelerate since you would be turning 2400 lbs worth of rollers! But, your HP to the ground would be the same at max output regardless.

 

dynos are calibrated to their drums so that your HP and TORQUE are accurate...the only thing that changes is that you get the tire spin factor on the street.....