I hope I'm posting it in the right section. Anyway yesterday I dynoed my car on a dynopak dyno and got a baseline run of 278rwhp. After tuning it I got 315rwhp. All of the runs were at 12psi. Now last year I dynoed on a dynojet dyno at 322rwhp @12psi untuned. So now I have a baseline to baseline hp difference of 44rwhp. If I go back on the dynojet will my hp go up to 350-360rwhp or what. Which dyno is more accurate? I really confused now. There is a huge debate going on on my local forum saying that the dynopak is crap. I don't know. Hopefully someone can shed some light on this topic and maybe make it a sticky for future questions.

R.K.

 

I'm not aware of the potential differences between the different types of dynos; however, 322 rwhp @ 12 psi untuned sounds a bit high to me. What was the correction factor on the runs? SAE, STD? You aren't going to make 350-360 rwhp @ 12 psi. AFAIK, stock twins normally max out around 360 whp @ 16ish psi. Someone correct me if I'm wrong on that.

 

That is correct, 360 at 16 PSI. I would say the best you could do at 12 PSI would be 320ish.

 

dynapak is not junk. Actually dynojet is but that's another story. Although dynojet is what everyone else uses and so everyone bases everything on dynojet numbers.

 

They were both sae. I'm not saying that I will make 360hp at 12psi but I'm just saying that there is a big difference on the runs. I believe the correction factor for the dynopak is 1.00 and 1.06 for the dynojet. Here is the link to the dynojet dyno:https://www.rx7club.com/attachment.p...chmentid=66170.
I still have to scan the dynopack graph.

R.K.

 

From what I have been told the Dynopak and dynojet give similar numbers.

Jason

 

The dynapack is closer in design to an engine dyno and it gives more flexability in how you can use it. The dynojet is pretty simple in comparison. If you want to see what the big companies use look up Rototest. BIG $$$$$ They start at about $80k. The dynojet is cheap even compared to the dynapack. $30k versus $50k. Rototest and Dynapack use the same theory. Give me numbers from a dynapack over a dynojet any day, you can tune better on the dynapack too.

 

number 1 difference is the dynopak can do simulated street driving so u can tune low load, partial load cells. so u could actually tuned a vehicle properly to make maximum power and get good gas mileage. on the dyno jet all u get is full throttle runs thats it.

 

Dynapacks will read differently depending on how the operator has it set up. Shawn Church's Dynapack in SoCal, for instance, is known to read higher than most Dynojets. While the Dynapack in Jeff Evans' shop in FL is set up to read lower than most Dynojets.

 

You cannot really compare numbers from one dyno with numbers from another dyno. There are too many variables which affect the hp that is read from the computer screen; too many variables for me to list them all here. Some of the variables are caused by the dyno operator (things like how powerful are is cooling fans; how well do they cool your intercooler,) and also the temp, air pressure, and humidity in the dyno room.
No, correction factors for temp, air pressure and humidity are not accurate most of the time because they usually put the wrong correction factors in. Why do I say this? It's because I have never seen a cheap dyno operator actually use temp, air pressure, and humidity sensors located right at the engine air inlet, which is the only place that really counts.
Most dyno operators run with the hood open. How many real race cars operate on a race track with the hood open, so how true is a HP number generated that way?
Most dyno operators do not have fans that cool as well as real natural ram air pressure working on the front of a well ducted race car.
All this stuff may seem nit-picky to you, but I make my living as a test engineer that tests the thrust (power) of rocket motors for a living. I take great pains to get measurements that have errors of less than 1%. All the things I mentioned above may seem miniscule to you, but if you add up a 1% error here, 3% error there, 3% error from rotating inertia, then pretty soon you add up to a huge error from one dyno to another, or even one day to another.

Don't worry about the number you get from a dyno (unless you are one of those people who don't really race but instead go around and brag about dyno numbers.) The dyno is a tool. Use it to tune your car. Start out with a base line run, make a change, see if things get better or worse, and keep working at it until you have optimized every little bit of your race car. Don't worry about whether the number is 300 or 500; just worry about does this tuning trick make more power or does it hurt things.

 

Here is another anology to dynos - think about weighing yourself on scales. Your scale at home gives you one number, and the scale at the doctor's office will give you another number.
There are differences between the two scales, and there are also other factors that produce different numbers when you weighed. For example, at home you may weigh yourself when you are only wearing shorts, and at the doctor's office you may have on pants, shoes, car keys in your pocket, cell phone, etc, etc.
If you are on a diet and are trying to see how well it works, then the best thing would be to weigh on the same scale every time, and try and weigh at the same time of day, while wearing the same basic clothes. The same principle works with dynos too - stick to one dyno, and try and minimize all the other variables which affect the power numbers.

One more bitch about dyno operators - I have seen some of them put in some really bogus low atmospheric air pressure numbers, which the computer then uses to generate really high SAE correction factor, which then makes for really high final hp numbers. Make sure you pay attention to what kind of correction factors the dyno operator uses. Personally, I like to see the original un-corrected raw data, and then I like to do any corrections afterwards.

 

I just wanted to see and compare the 2 dyno's and see how simular they are. I don't really care about the hp because I know my car is fast but I also wanted to tune it at the same time. Thanks for the explaination and it makes sense.

R.K.

 

would be interesting to know how they calculated the rwhp as the dynapacks measure power at the hubs.

rgds

 

I'm glad to see most people are starting to realize that all dynojet is good for is a number.
you can't tune on one. And isn't this the reason you buy a dyno?

Have a look at dyno dynamics. there one of the best chassis dyno's out there.

 

Er...simple maths. You have torque and angular velocity to play with.

 

I heard that the dynapack is the same one that apex'i and nismo uses. I also heard that the dynapack is better for actual tuning but gives lower numbers than the Dynojet. Can someone verify this for me? However, the dynojet seems to be the standard out there.

 

The dynojet seems to be the standard because they are cheap. The numbers they give only matter bench racing. If you really want to tune your car you need a dynapack(or other similar), if you want to brag about HP figures it doesn't matter which one you use.