^^^ on Dynapack tires are not relevant... dyno in first post was on a dynapack... I'm not sure is you are referencing a particular dyno result that is posted - or just making a general statement as it pertains to roller type dynos... if its the later, I concur - its one of the reason Dynapacks are a better source for testing.

 

This only matters on roller style dynos like Mustang or Dynojets, doesnt play a part at all on Dynapacks as it reads it from the hubs.

 

I thanked Shawn for the suggestion about the SAE paper.

All I know is what I've experienced firsthand, which is to say that the Dynapacks I've used for testing all read lower than the Dynojets I've used and roughly on par with the Mustang dynos I've used. This is obviously contrary to what you and Shawn have experienced, and I respect your experiences. My apologies if it came off otherwise. I certainly do not have all the answers on this (or any other!) topic.

FYI, I spoke to the people from Dynapack at SEMA a few days ago and they were not surprised to hear that I was seeing lower #'s on the Dynapacks I've been using for testing. They felt that was normal and related to the way their system is calibrated to convert to a WHP rating by using vehicle specified weight, gearing, etc.

Anyway, for me the only real take-away from this discussion is that we should all be sure to test our cars on a single dyno so that results are comparable from test to test. Trying to compare results from one dyno to another is futile. Clearly there are Dynapacks that read higher/lower than other Dynapacks and higher/lower than other types of dynos.

For the guy requesting a vid, here you go It's part of a larger vid I've been putting together about the G's build-up:

 

I just attempted to browse the thread from the beginning and after 1.5 pages realized this has gone full circle back to the same stuff that was being discussed 4 months ago...

no point in perpetuating this...

 

Hah...totally agree with you there, OCG35. I will shut up now

But before I do ... I read that SAE paper recommended by Shawn and it is a very interesting discussion of inertia dynos and their limitations. The importance of mass equivalence between the dyno roller and the vehicle itself really lit a bulb for me, as did the discussion of strap tension and rolling resistance. Definitely brings home the point that inertia dynos aren't going to produce as accurate or repeatable a WHP and WTQ estimate as a hub (load cell) dyno does, and it also helps explain why we see so much variation in dyno results from machine to machine. What it doesn't discussion is dyno calibration and software differences, which I'm sure also play an important role when it comes to differences seen between dynos of the same brand and of different brands/types.

Now more than ever I realize we cannot make generalizations about dyno brand X reading higher/lower than dyno brand Y. It's a totally futile observation to try to make. My bad and thanks for the great discussion.