Review and adjust weight of ITB CRX Si as appropriate

[tom91ita]

EDIT to restore paragraphs:

CRB Letter Tracking Number #1333

ATTN: SCCA BOD, CRB, ITAC, ImprovedTouring.com May 11, 2010

I would like to make note of an error and/or omission in the assigned weight of the 1985-87 Honda CRX Si (as well as the 1986-87 Honda Civic Si). I am requesting that these weights be properly and actually evaluated. In the specific case of the 1985-87 CRX Si, this car was originally classified as ITA and was given an arbitrary 150 pound addition when it was reclassified as ITB. This weight is inappropriate compared to cars with similarly designed engines in the class as you will soon see.

One basic premise of IT classing takes into consideration certain aspects of power to weight and/or displacement to weight ratios. For example, ITB has used a factor of 17 pounds per horsepower and ITA has used 14.5 pounds per horsepower. This basic formula can be illustrated as follows for ITA:

Stock HP X HP Multiplier X 14.5 #/HP – 50 #’s (if FWD) + 50 #’s (if double wishbone type suspension)

However, there is a rather wide range when it comes to the Horsepower Multiplier. This is in large part due to the wide range of assigned horsepower ratings by the original manufacturers. However, if one looks at the IT expected Horsepower calculated from the assigned weights in the GCR, one can see that similar engine architecture results in similar specific horsepower ratings.

Four Cylinder - 16 Valve Engines

Four popular 16V cars are the 1988-91 Honda CRX Si, Acura Integra, 1.8L Mazda Miata (all ITA cars with the 14.5 #/HP factor) and the 1988-91 Honda Civic DX (ITB & 17 #/HP factor). These cars have the following Horsepower Multipliers (calculated from the GCR and published stock HP ratings).

Horsepower Multiplier = (GCR Weight + FWD adjustment – Suspension adjustment)/(Stock HP)/14.4

Honda CRX Si = (2250 +50-50)/108/14.5 = 1.4368
Acura Integra = (2595 + 50 -50)/140/14.5 = 1.2783
Mazda Miata = (2380+0-50)/133/14.5 = 1.2082
Honda Civic DX = (2240 +50-50)/92/17 = 1.4322

I think the above represents a rather wide range of Power Factors. However, if we consider what the HP per Liter is for the above, we see that the 16V engines all provide close to the same specific HP per Liter.

Honda CRX Si = 1.4368 x 108 / 1.590 Liters = 97.59 HP per Liter Estimated in IT Trim
Acura Integra = 1.2783 x 140 / 1.834 Liters = 97.58 HP per Liter Estimated in IT Trim
Mazda Miata = 1.2082 x 133 / 1.839 Liters = 87.37 HP per Liter Estimated in IT Trim
Honda Civic DX = 1.4322 x 92 / 1.493 Liters = 88.25 HP per Liter Estimated in IT Trim

The IT Trim specific output of the 1.6L CRX and the 1.8L Integra being essentially identical is not that surprising since the 1.8L is effectively a scaled up version of the 1.6L. Also, although the Honda Civic DX is significantly less than the other Honda based 16V engines, it should be noted that this is not surprising considering the car has a dual point injection system instead of the multipoint injection system.

If you prefer to look at the Integra and CRX in terms of #’s per CC, you will again see that they are essentially equal; (Integra = 1.411 #/cc and the ITA CRX is 1.415 #/cc).

Four Cylinder - 12 Valve Engines
There is a limited sampling of 12V cars in Improved Touring. However, there are three distinct engines and they are all Hondas and all in ITB. These are the 1986-89 Honda Accord, the 1986-87 Honda Prelude and the 1985-87 CRX Si. These cars have the following Horsepower Multipliers (calculated from the GCR and published stock HP ratings).

Horsepower Multiplier = (GCR Weight + FWD adjustment – Suspension adjustment)/(Stock HP)/17

Accord = (2550 +50-50)/120/17 = 1.2500
Prelude = (2450 + 50 -50)/110/17 = 1.3101
85-87 CRX Si = (2130+50-0)/91/17 = 1.4092

Again, the above represents a rather wide range of Power Factors. But what is rather unusual about this is that these engines are from a single company and have very similar architecture with the exception of the compression ratio.

So what does the HP Multiplier and IT expected HP work out to for these similar engines that are nearly scale versions of each other work out in terms of IT Trim Estimated HP per Liter?

Accord: 1.25 x 120 / 1.955 Liters = 76.73 HP per Liter Est. in IT Trim Comp Ratio of 9.3
Prelude: 1.3101 x 110 / 1.955 Liters = 73.71 HP per Liter Est. in IT Trim Comp Ratio of 8.8

The Prelude, with its lower Compression Ratio, has a slightly lower specific output. So how does this compare to the 85-87 CRX Si which has a lower CR still?

85-87 CRX Si: 1.4092 x 91 / 1.488 Liters = 86.16 HP per Liter Est. in IT Trim Comp Ratio of 8.7

So the 85-87 CRX Si with a CR of 0.6 less than the Accord is purported to make 12% more power per liter. Also, the 85-87 CRX Si 12 valve engine is purported to make HP/Liter ratios similar to the better breathing 16 valve engines.

If you look at these cars in terms of weight per displacement they are not consistent as well:

Accord: 2550/1955 = 1.30 # per cc
Prelude: 2450/1955 = 1.25 # per cc
85-87 CRX Si: 2130/1488 = 1.43 # per cc

Please note that the12V ITB CRX Si is saddled with more weight per cc than the last three ITA ARRC Champions. And the 12V ITB CRX Si also suspension limitations in that it has front torsion bar springs and a rear beam axle compared to the wishbone style of the other Hondas and Integras.

I believe that the power potential and power to weight factors of the newer and improved 88-91 Honda CRX Si were inadvertently applied to the 85-87 when it was moved from ITA to ITB. Because of this error, the weight should be reviewed as an error/omission.

If the ITB CRX were classed like the Prelude at 1.25 #/cc (after all, the CRX CR is even less than the Prelude), the CRX should weigh 1860 #’s. This means the CRX would be 270 #’s overweight.

It should be noted that I have been told privately that I am tilting at windmills with this request because there are certain ITAC members (and/or former CRB member) who either race the Accord or who race against the CRX that will prevent my car from ever having the weight classified fairly. I, however, think that this should not impact the fair review of the car. But because of this perceived potential, I would very much appreciate a technical reason as to why the CRX 12V motor combination is rated so differently than the other Honda 12V ITB cars.

I do not consider the standard style explanation of “Car is appropriate as Classed” to be an appropriate answer.

Thanks,

Tom