SCCA It classification calculations

[Streetwise guy]

Further to my repeated whining about the new IT classifications, here is the new SCCA guidelines.  Enjoy the read.


1. Introduction

This guide is intended to complement the Improved Touring ruleset, providing the details and
guidance necessary to consistently apply the rules in the areas of assigning weights to cars, and
communicating with the members when it comes to weight changes. The document is written
to be a set of strict guidelines but not rules. Perhaps unlike the rulebook, all effort should be
made when interpreting this document to understand the intent of what is written rather than the
absolute specifics of the chosen wording.



One of the attributes of IT that makes it attractive to members is the large list of cars that are
included. To that end, we strive to be inclusive and class nearly any car that anyone requests.
Care must be taken, however, when a car might prove to be either too fast for our fastest class
without excessive ballast, or might be difficult to pin down its specifications. Older cars, in
particular those built before the start of the SAE Net specification for horsepower, can be
particularly vexing.



Weights of Improved Touring cars have two components. The primary component of the
weight is derived from the physical attributes of the car (and derived ONLY from those
attributes.) In addition, after some racing history has been established in Improved Touring, the
car might have a Performance Compensation Adjustment (PCA) assigned by the ITAC in order
to keep competition equal. There is a limited amount of time after weight has been assigned
where PCAs may be assessed.

2. The Weight Assignment Process

The principle of the process is that three components go into making a race car fast:
acceleration, braking, and cornering. The process attempts to equalize the acceleration ability
of cars by putting them all at the same power-to-weight ratio. Then to equalize braking and
cornering, there are "adders and subtractors," that is, adjustments to the weight, to compensate
for physical attributes that are meaningful and abnormal for the class in question. In addition,
all FWD cars get a weight subtractor. Cars with displacement that is significantly different from


the norm for the class in question can also have weight adjusted. The reason for that is that
peak horsepower does not tell the whole picture about acceleration ability. What we would
really need to know is the shape of the horsepower curve, or more accurately, the area under it
for the appropriate part of the rev range. Since this is not realistic with more than 300 cars
listed, we need to approximate it. It is generally understood that larger displacement cars are
likely to make more power in the lower part of the rev range than cars with smaller
displacements. Due to this, it is likely that the part of the horsepower will stay close to the peak
for a wider range. We use displacement instead of the peak torque metric because the number is
easier to confirm, and is published in the ITCS for all cars.



The list of adders and subtractors is below. Note that while there might be other factors that
could be used, the ITAC has chosen this list to be those factors that are most significant and
most measureable. Changing the list of adders and subtractors is effectively a change to the
process and this needs to be undertaken with care, as it could cause the need to reassign weights
to all cars in a class. See the last paragraph of this section for more detail.



The power-to-weight ratio targets for each class are as follows:

ITR: 11.25 lbs/hp

ITS: 12.9 lbs/hp

ITA: 14.5 lbs/hp

ITB: 17 lbs/hp

ITC: 18.84 lbs/hp

The horsepower used for the calculation is the most complicated part of the process. It can be
determined by one of two methods: "published horsepower" or "known horsepower."



Published Horsepower

In this method, the peak horsepower numbers as published by the vehicle manufacturer
is the primary component. Most cars can be expected to gain about 25%-30% above
their stock peak horsepower when all of the modifications allowed by the IT rules are
made. This assumes that the stock horsepower is specified to the "SAE Net" standard.
It can be safely assumed that all cars after 1974 are specified this way. If the car is older
than that, good care should be taken to ensure that the published number is really SAE
Net. If the number is not available in SAE Net, it will be difficult to use this method.



Specifically, all cars should be assumed to gain 25% above stock horsepower in IT trim,
except that multivalve engines in ITB and ITC should be assumed to gain 30%.



If nothing is actually known about this engine when built to the limit of the IT rules, but
yet, the ITAC believes that the 25% or 30% number is in error, then one ITAC member
should present a case as to what the correct "power multiplier" should be, and then the
remaining ITAC members should each register a "confidence vote" in that number. If
collectively the ITAC believes with 75% confidence that the alternate number is likely to
be more accurate, then that number can be used. Note that if dyno results are being
considered, then the "known horsepower" method should be used, and not the
"published horsepower" method.



Some examples of non-standard multipliers that have been used in the past are that
inline-6 engines have generally been seen to make 30% gains, and the '80s-'90s
multivalve Honda motors have been seen to make 35% or more.




Sometimes horsepower specs vary among multiple model years of a car listed on the
same spec line. In this circumstance, the ITAC must do research to understand what has
changed on the vehicle to change the horsepower. If the only changes that account for
the horsepower differences are changes that are authorized by the IT rules (e.g., software
tuning), then the smaller horsepower can be used. However, if there have been any
changes that would not be authorized by the IT rules (for example, the camshafts are
different), then the higher horsepower should be used. If it cannot be determined, then
the highest horsepower available should be used.



Known Horsepower

In this method, the horsepower number published by the manufacturer is ignored, and
instead, the expected horsepower comes from another source. These days it is pretty
common to have dynamometer results, usually from a chassis dyno. For chassis dynos,
the ITAC standard is that RWD cars have an 18% drivetrain loss (from crank to wheels)
and FWD cars have a 15% loss. Thus, for example, if a RWD car is "known" to make
150 horsepower on a chassis dyno, then the "expected horsepower" for power-to-weight
calculation should be 150/.82, which is 183. Care should be taken that the highest dyno
numbers seen are used, and that cars classed by this method should be at the limit of the
IT rules.



In order to use this method, an ITAC member should put together a set of documentation
that proves what the maximum known horsepower is. Then each member should say
how confident he/she is in the documentation, considering the source, how well-
prepared the measured cars are, etc. If the average confidence is 75% or greater, then
the "known horsepower" method may be used to derive the expected horsepower.



A 75% confidence level is a pretty high level. It is expected that the committee would
bring with them a healthy amount of skepticism when it comes to reviewing dyno sheets.
One should take into account the source of the info, the shop that ran the dyno,
information about how well-prepared the car and the engine car, who did the build, and
any hidden motives of anyone involved in providing the data. In the best of
circumstances, dyno results are hard to trust as they can be extremely variable even
when all conditions are the same. It is reasonable to look at on-track results of the cars
in question to see if the perceived acceleration matches what the dyno sheets appear to
say.



All dyno sheets should be posted to the thread on the letter-tracking site that is
associated with the letter under discussion. That way all information associated with the
decision is saved and findable. The letter number is known by the author and also
published in Fastrack. Any CRB or ITAC member can then find that letter number in
the system and find all dyno sheets associated with its weight decision.



Using one of the above two methods, a vehicle makes an "expected horsepower" (max crank
horsepower in IT trim). That number is multiplied by the power-to-weight ratio for the class in
question to get the "base weight."



Then, adders and subtractors are applied. They are as follows:

. FWD cars get a percentage-based subtractor: 6% for ITR, 5.5% for ITS, 2% for ITA and



ITB, and 0% for ITC. Note that AWD cars should not get this adjustment.
. Cars with double-wishbone suspension get a 50 lb. adder.
. ITR cars with both FWD and front struts get -50 lb.
. Live axle RWD cars in ITR get -50 lb.
. Mid-engined (engine between driver and rear axle) cars get +50 lb.
. Cars with abnormally small or large brakes for their class get -50 lb. or +50 lb.
. Cars with excessively low or high engine displacements, or excessively high or low peak
torque, can be adjusted up to the following limits. (For example, a very-high-
displacement, very-high-torque car would get a max of +50 in ITB). These are
maximums, and this adder is not absolute. The ITAC should use its judgment about
whether or not these cars are likely to accelerate slower or faster than an "average" car
for the class. Note that rotaries should be considered small displacement engines.


Class

Normal displacement
range (liters)

Large
displacement /
high torque

Small
displacement / low
torque

ITR

2.2 - 3.8

+150 lbs

-100 lbs

ITS

2.1 - 2.9

+100 lbs

-50 lbs

ITA

1.5 - 2.5

+100 lbs

-50 lbs

ITB

1.7 - 2.3

+50 lbs

-0 lbs

ITC

1.5 - 1.7

+50 lbs

-0 lbs



"Normal" is one standard deviation from the average piston-engine size in each class



The weight should be calculated for all classes that might make sense, and the fastest class in
which the car could be expected to make weight should be chosen. For example, if a car is
known to weigh 2800 lbs stock, and it might weigh 2400 in ITA or 2900 in ITB, the question is:
could this car possibly lose 400 lbs legally under the IT rules? If not, it should be classed in
ITB. We do not dual-class cars in Improved Touring, with only one exception. If a new class is
created, then cars already classed but would be a better fit for the new class can be dual-classed,
both in their existing class and the new class. If the new class succeeds, the previous listing
should be removed.



No car should be forced to carry an excessive amount of ballast for any reason. If the car would
have to carry an excessive amount (say, 300 lbs more than it weighs in street trim) in ITR, then
the car is simply too fast for ITR and should not be classed at all.



Once the class and weight are determined, the weight should be rounded to the nearest multiple
of 5.



Care should be taken when looking at published curb weights. These are all over the map and
don't necessarily reflect real-world weights.



If the process should ever change in any material way in the future, then cars classed after the
change will be inconsistent with those classed before the change. In order to allow for the
correction of such a situation, the 1/1/05 date referenced in 9.1.3.C should be changed to be the
effective date of the new process. For example, if a new process goes into effect on 1/1/13, then
all cars classed before 1/1/13 should be changeable to match the newly-effective new car
process.


3. Errors

There are a few things that can go wrong during the assessment of the process:

1. Input information is wrong


Perhaps the stock horsepower that was used was for European-spec cars instead of US-
spec cars.

2. Actual horsepower doesn't match expected horsepower


As described in section 2, there are two ways for the process to determine the expected
horsepower of a car in IT trim. But perhaps after the cars have been built, it is
discovered that the actual horsepower works out to be different from what was expected.
If this happens, it is appropriate to correct the error (but it would not be appropriate to
assign a PCA – see section 3.) Appropriate caution should be applied when it appears
that the actual horsepower is lower than expected horsepower. How many examples
have been built? How much experimentation has been done in intake systems, exhaust
systems, ECU tuning, carb tuning, compression increases, and the like? If there have
not been several limit-of-the-rules attempts, it should not be assumed that the original
expected horsepower cannot be reached. It often takes years of experimentation to
really maximize the horsepower.

3. A mistake was made while running the process


Perhaps an adder was mistakenly left out.

Note that it is not an error if the process changes and a car classed before that process date is
inconsistent with it. See the end of section 1 above.

4. PCAs

The rules state, basically, that all cars should get a process weight, but within their first four
years after their process-based listing, the club will attempt to maintain class equity, perhaps by
adjusting the process weight through the application of a PCA (Performance Compensation
Adjustment). It is the goal of the rules to allow for this possibility but with the sincere hope that
it will never be necessary.

If a car seems to be more than the sum of its parts, the most likely reason is due to an error in
the process, either in the inputs or in the application of the process. Perhaps the stock
horsepower was incorrect, or the gains in IT trim are much higher than expected, or an error
was made when running the process the first time. Always look hard for such an error before
assessing a PCA. Again, hopefully there will never be an opportunity to use them.

If a car seems to be less than the sum of its parts (i.e., doesn't seem competitive at the assigned
weight), chances are that this is because the car is not really fully prepped, or the driver isn't the
cream of the crop, or because the preparation level and effort put into testing isn't top-notch.
Remember that in almost every case, track records are set by car/driver combinations that are
truly exceptional. Make sure that an apples-to-apples comparison is being done whenever a
request is made to reduce a car's weight. While it is conceivable that a negative PCA could be
applied, this seems even less likely than a positive one.

In any case, a single example of a car is just not enough to warrant a PCA. There should be at
least 5 unique examples of the car in question somewhere in the country, and there must be no


reasonable explanation that would qualify as an error for its aberrant performance.

5. Publishing weights

When a weight is adjusted, the adjustment is published as a TB in Fastrack. The TB should
always include a sentence or two that explains the change. For example, if an error was
discovered (either in the inputs to or the application of the process), a brief description of the
nature of the error should be included. If a PCA has been assessed or adjusted, then that fact
must be published with the TB. If a listing from before 1/1/05 is adjusted via that clause, then
this must be stated, and if a PCA is also included, that should be made clear.

[Al36rx7]

Hmmm...Wasn't our IT based on SCCA IT just a little while ago and there was a call for change?

[Streetwise guy]

There were some concerns about ITGT cars going too fast, so theITGT rules were left alone, and the IT rules were changed to encourage people to turn their legal IT cars into ITGT cars, which would then go too fast.

Does that sound bitchy?  Cause I can make it worse if anybody hasn't caught it yet...

[CRXsi]

I kinda agree with Jim for the most part...I am a little miffed as well that we have gone away from being very close to SCCA rules and amended them to appeal to those who want to tinker. Some of us are planning on attending SCCA and WCMA events. To be competitive in WCMA IT one now needs to "tinker" which also makes the car illegal for SCCA IT. I for one likely won't be competitive for our IT so I can still go play in SCCA and be legal...