How dyno numbers are utilized by ITAC

G

gran racing

Super Moderator
When dyno results are supplied to the ITAC for review, how is that information interpreted? What I mean by this is the process generates the crank HP rating versus what most of us would provide, the wheel HP rating.

Does the ITAC have assigned drive train losses for various cars for this purpose? If so, what are they?

Does the different type of dyno being utilized impact the calculation to what the crank HP rating equals (using the supplied wheel rating)?

What, if any, other factors are used in making the wheel to crank HP calculation?
 
During my tenure, we used 15% loss for mid-engine and FWD and 18% for RWD.

For me, DynoJet info needs a ton of 'backup', meaning lots of data from lots of sources. The nature of the system doesn't lend itself well to tight repeatability. The next most common is the DynaPack and is very close unit to unit but still can be manipulated with manual inputs. Common misconception, or old school thought, is that they read low compared to Jets. Back to back testing has debunked that for us.
 
Having seen for myself how easy it is to manipulate the numbers.................... I'm not so sure how much stock we should put in these numbers.

(when I say "manipulate", i don't mean it like someone is purposely trying to pull a fast one. It's just that there are many variables that can be easily changed.............)




.
 
THis is the area where the Process is not so subjective, which concerned all of us (I think that is fair to say). Kirk came up with a solution, which is called the "confidence factor" vote where we all act as checks and balances on the others in assessing dyno and other power information.

But in short, while the procedure is faily loose, we:

1. Look at and assess the dyno sheet, who it came from, type of dyno used (ALL are manipuable and Jeff is 100% right you have to be wary of all of them), etc. to determine how much trust/faith we put in the number. Obviously, the more sheets we have the better.

2. Then we use the 15/18% drivetrain loss numbers Andy mentions (debate over those as well) to figure out how much gain over stock we are seeing.

And then we have a big pow-wow where we bang on drums, commune with the Great Spirit and pull a number our of our ass! Seriously, we do have a pow-wow where we each state our confidence level in the numbers and then vote on what we think is the right gain modifier.

The worst thing about the system (but necessary) is using dyno numbers that can be gamed. The best thing is that we as a group all work as checks and balances on the others to avoid a bad result.

So far it has worked.
 
Hey Jeff.

You posted the specific document in a previous post. It might be helpful to post it on this subject in the title.
AJ
 
JoshS said:
Probably better to post a link to the SCCA site instead of an attachment, so that if it changes, the latest one will be there.
Click to expand...

Probably better to DO BOTH, so that WHEN changes, there will be a some documentation of the history of how we got where we are.

K
 
Andy Bettencourt said:
During my tenure, we used 15% loss for mid-engine and FWD and 18% for RWD.

For me, DynoJet info needs a ton of 'backup', meaning lots of data from lots of sources. The nature of the system doesn't lend itself well to tight repeatability. The next most common is the DynaPack and is very close unit to unit but still can be manipulated with manual inputs. Common misconception, or old school thought, is that they read low compared to Jets. Back to back testing has debunked that for us.
Click to expand...

I have had two cars that were first dynoed on a DynoPac and then on the DynoJet at work. Both cars made the exact same whp on both dyno's.
 
bamfp said:
I have had two cars that were first dynoed on a DynoPac and then on the DynoJet at work. Both cars made the exact same whp on both dyno's.
Click to expand...


yea, well, YOU know what you're doing, lol.

Blake I bet Andy was thinking about hoe Jets are found on every street corner in all sorts of condition....they can be very accurate, but as you know, half the battle is the operator.

When I was on the ITAC my degree of confidence was increased if the data being considered came from Blake....
 
Last edited:
I did send you guys my 914's engine dyno charts and chassis dyno charts. I only wish something had come from that info.:(
 
bamfp said:
I have had two cars that were first dynoed on a DynoPac and then on the DynoJet at work. Both cars made the exact same whp on both dyno's.
Click to expand...

And this backs up what I said. When you go Jet to Jet the customer needs to notice things like tire positioning on the rollers, strap tension, etc in order to get the kind of consistancy I think people expect.
 
I've read two articles -- one sent by Bob Dowie and the other by JimmyC on the Brown Board -- that show how easy it is to manipulate dyno data with correction factors, etc. I too at one point believed Dynapacs always read less than Jets, and Mustangs too. I now know that is completely false and totally up to the operator.

I think, honestly, this is one of the reasons I (and perhaps others) have in my mind "strengthened" the 25% default. Unless you, like with Blake, you know the dyno, the operator and the conditions, you are setting yourself up to be gamed.

All of this just reinforces what I remember being told from the start: dynos are great tools for comparative TUNING on the same dyno. Beyond that, comparing dyno to dyno is fraught with danger.

This remains the "dangerous" part of the process. If we move from 25% to 30% on a 100 hp ITC car that's almost 100 lbs. And it would be based on dyno data showing differences of 5 hp, which is getting past the resolution capability of even reliable dynos.
 
Last edited:
I dynoed my car with street tires and the Hoosiers back to back on the DynoJet. It made a 5 whp difference between the two. The race tires making less. The amount of toe you run can also effect the dyno results.
 
Very close. The street tires were taller and were on heavy steel wheels and they still made more HP.
 
I believe that is a reflection of the drag of a sticky tire v.s. a street tire. I have seen the same things on drag cars and the "1000hp supras".
 
You must log in or register to reply here.
Back
Top