Governing Question - TTU P/W Ratios

[STI500]

I have some questions in regards to running a vehicle in TTU class and some things I have been thinking about after this past weekends event at California Speedway.

 

Constants:

Subaru STI = AWD 4 Door

TTU Rules State P/W Ratio >= 5.50

1 Gallon of Gas = 6.1 lbs

 

Details of Vehicle:

Dry weight of vehicle = 2689 lbs

Driver weight = 250 lbs

Half tank fuel (7.5 gallons) = 45.75 lbs

WHP on Mustang Dyno = 500

* Mustang Dyno's are considered "heart breaker" low reading dyno's

** On a DynaPack or DynoJet this would correlate to about 550 whp

 

Math:

2689 + 250 + 45.75 = 2984.75 lbs

2984.75 / 500 = 5.9695

 

Corrections for vehicle per NASA TT Rules

AWD -0.5

4 Door +0.4

Competition Weight -0.35

 

P/W Ratio of this vehicle = 5.5195

If the horsepower is off by 2 = 5.4957

If the weight is off by 10 pounds = 5.4995

 

Some questions:

1. How closesly regulated are the power to weight ratios in the classes? Especially when a vehicle picks up a lot of time from one session to the next (especially as the track gets hotter) or even sets a track record? This could be very frustrating to competitors that believe the car did not meet the rules (how would they prove as such) but if it is legitimate how does the owner/driver truely prove himself?

2. Should Dyno Dynamics and Mustang dyno's be used for qualifying AWD vehicles for Time Trial classes? These dyno's are considered to read low because they have different calibration files loaded into the software for various reasons. These can be loaded at anytime and can severly change the wheel horsepower numbers. Dynojet and DynaPack Dyno's (offered in AWD for both) do not have this option and are calibrated from the manufacturer, so it is much more difficult to manipulate these numbers.

 

Just some information to throw out there for people to chew on.

[kbrew8991]

If you're over/under on something, even if its by a little, doesn't matter - its whats measured post-session in tech that matters. How close you wish to cut that is on you

 

I'll leave the rest of the questions to bigger fish than me

[phoenixR34]

I'm curious what this has to do with Cal. Speedway specifically.

[MSP608]

I'd love to see pics of this STI that weighs 2689.

[STI500]

I'm curious what this has to do with Cal. Speedway specifically.

 

 

There was a scenario like this at California Speedway this past weekend, where things are very close in regards to weights and horsepower numbers for the TTU class. There are a few competitors that believe the vehicle is not with-in spec and others believe it is. To be honest I do not care about the outcome but I do care about how this can be handled quickly and effectively in the future.

 

This event is more of a gentleman’s club and when someone pushes that edge who is to say what? I am not sure what should happen but I am bringing up some important points about the rules (well at least I believe they are important). We want the whole organization to get along with one another as best as possible and when there is some vagueness in the rules it can lead to a lot of confrontations.

 

To go a little deeper the rules themselves are not what is vague, it is the equipment that is used, it will offer different horsepower numbers, specifically Mustang and Dyno Dynamic Dyno's for a multitude of reasons. The other question regards whether or not this vehicle was within spec or not the session it set a track record? There are a few people that say it is not and others say it is… Now what?

 

The previous poster stated that it is very cut and dry when you are over or under. Well who is to say the horsepower was higher or lower by 2 horsepower on a boosted vehicle. How can this be inspected, I find this to be a very tough question.

 

In all if the vehicle was legitimate, than hats off to him, he deserves a lot of respect for being able to dial a vehicle in that close to spec and taking a track record. Lastly maybe I am bringing something up that really has no bearing, we should just let it go and move on with our lives.

 

Now it is time for my coffee…

[yakisoba]

I think it matters a lot. Winners sweat the details. If I knew there was going to be a Mustang dyno at the track, I'd try to get my car done on one before I got there, in case someone protested. Time Trial A is another class where you need to run close to the line.

 

You ask good questions, and thank you for doing so. I've been protested before in TTA and it's uncomfortable, but nothing to worry about IF you are confident in your setup at the start.

 

This year, at 5000 feet, I bet I won't be close to the ratio. I would imagine that the FI cars would have more to worry about in terms of running close to the line.

[Bruce L.]

We want the whole organization to get along with one another as best as possible and when there is some vagueness in the rules it can lead to a lot of confrontations.

 

4 decimal places, seriously?

[Tom A]

Math:

2689 + 250 + 45.75 = 2984.75 lbs

 

I see this and my immediate thought is that you are doing it wrong.

 

The only thing that matters is what the scales say at the track. Guess what, the scales on that day may or may not match any other scale any other day. In fact, I have seen different numbers from simply rolling on and off the same scales.

 

Is this your car we are talking about? You seem kind of vague about it.

 

By the way, you are reading the table wrong. Your claimed competition weight of 2984 falls in the 3000 lb category (equal to or less than) so your modifier is -0.25, not .35, and if you add 20 lbs to safely get the weight above 3001, that goes to -0.2.

 

Trying to cut the weight on to "2984.75" so you can tweak your P:W ratio that close to the limit is foolish. There are too big things you have no control over that can make you illegal, variations in dyno results, and variation in scales. Run it at 3005 and your weight modifier changes to -0.2. A 15lb increase (about half of one percent heavier) will have no meaningful effect on lap times. This isn't Formula 1.

 

So using a safe race weight of 3005 and your stated horsepower, the adjusted P/W is 5.71, well within the safe range. With that, the dyno can show up to ~513 and it will still be legal.

 

If someone really thinks that cutting their power to weight that close is a good idea, I say "go nuts". They are making a significant gamble on legality based on variables they have no control over, for a competitive advantage that is at best trivial. If they are under the limit, yes, even if it is 1HP or 10 lbs that put them under, not only are they illegal, they are morons for putting themselves in that position in the first place.