Jim CalziaMembers Page The Early 911S Registry

Early 911S Member

Jim Calzia

1973 911S

WHAT'S IT WEIGH?
by Jim Calzia
C&C Racing, Sunnyvale, CA

(reprinted from Autumn 2000 Esses)
1/18/01

Featured in the May, 2001 issue of Excellence Magazine, except this has the weight comparison charts not included in the article

Charts updated, 4/20/01

Home

Welcome

Membership

Publication

Early S Boutique

Member's Pics

Photos

Classifieds

Events

Links

Contact Us

Message Board

Technical Info

In May 1997, I crashed my 1973 Porsche 911S in Turn 1 at Thunderhill Raceway, California during the first ever PUG (Porsche Unlimited Group) event. After 10 months of probation, mourning, and planning (pretty much in that order), I began to rebuild the car to PCA's GT4R rules. Since it was going to be a racecar, the primary design parameter for any part going on the car was "If it doesn't make it go faster, it doesn't go." With that in mind, I kept complete records of what I took off and put on the car, including the weight of each part. Now, three years later, the car is ready to go back on the track. I promised various people who helped me rebuild the car (especially Paul McCain of ORB, Cameron Woods of Cam Engineering, and Danny Irbe of Irbe Design) that I would show the car before I raced it - for obvious reasons! Several people saw my notes and asked for the weight data during a couple of these shows. This paper lists that data and how it was used in the design of my racecar.

Table 1 is a side-by-side weight comparison of original equipment versus replacement parts that went into the racecar. All of the parts were weighed on my Longacre scales. The OE parts are from a '73 911S coupe with sunroof; source(s) of the replacement parts are listed. By keeping track of the weight of these parts, I reduced the curb weight (car plus all fluids and 10 gal of gas) from 2140 lbs at my last event to 1830 lbs! Actually, the 1830 lbs is an estimate; the car weighs 1730 lbs with transmission oil but without engine oil and gasoline ... it's tough getting that tranny oil in with the engine and transmission in the car! I calculate 16 qts of oil and 10 gal of gas will add about 100 lbs for a total weight of 1830 lbs. No matter how you fiddle with this estimate, the car is going to be a lightweight and should therefore be quick. Hopefully, I can use that weight advantage on the track!

The weight of Porsche assemblies that are useful to car builders is listed in Table 2. For example, a sport seat and mount from my '73S weighs 53-54 lbs. Replace two of these assemblies with a 22 lb Kirkey race seat with custom mount and you've saved 78-80 lbs!

Jim Calzia's '73 911S. 5/00

Also, a sunroof is a frivolous accessory on a racecar. By replacing my sunroof and associated gears, motors, hardware, etc. with a fiberglass sunroof, I not only saved 27 lbs, but I lowered the center of gravity of the car. Any car builder can use the data from Table 1 and calculate how much weight can be saved by using aftermarket components (check the weight of suspension assemblies, glass vs plastic windows, or removing the underseal) but remember two important design criteria. You must decide how the car is going to be used (because some changes are not reversible), and do not change the front-to-rear weight distribution too much. The penalty for overlooking either of these criteria is financially and often physically painful!

I have also included calculations for the unsprung weight of my racecar. These calculations are necessary to determine spring and wheel rates and if that expensive brake conversion is really cost effective. Note that even after purchasing some of the best aftermarket suspension and brake assemblies on the market, I saved all of 2 lbs per corner in front and gained 1.5 lbs per corner in the rear! No doubt I improved the handling of the car, but after all of these changes and all of this work, it is clear to me that Porsche did its homework regarding suspensions and brakes. It is difficult and expensive to improve a good thing!

© 2000 Jim Calzia All Rights Reserved

Go to Table 1>>

Go to Table 2>>

All pages copyright © 2000 Early 911S Registry
Information and images contained in this website may not be published, broadcast or otherwise distributed without the prior written authority of the Early 911S Registry.
The Porsche crest is a registered trademark of Dr.Ing.h.c.F.Porsche AG.

Early 911S Member	Jim Calzia	1973 911S
	WHAT'S IT WEIGH? by Jim Calzia C&C Racing, Sunnyvale, CA (reprinted from Autumn 2000 Esses) 1/18/01	Featured in the May, 2001 issue of Excellence Magazine, except this has the weight comparison charts not included in the article Charts updated, 4/20/01
Home Welcome Membership Publication Early S Boutique Member's Pics Photos Classifieds Events Links Contact Us Message Board Technical Info
	In May 1997, I crashed my 1973 Porsche 911S in Turn 1 at Thunderhill Raceway, California during the first ever PUG (Porsche Unlimited Group) event. After 10 months of probation, mourning, and planning (pretty much in that order), I began to rebuild the car to PCA's GT4R rules. Since it was going to be a racecar, the primary design parameter for any part going on the car was "If it doesn't make it go faster, it doesn't go." With that in mind, I kept complete records of what I took off and put on the car, including the weight of each part. Now, three years later, the car is ready to go back on the track. I promised various people who helped me rebuild the car (especially Paul McCain of ORB, Cameron Woods of Cam Engineering, and Danny Irbe of Irbe Design) that I would show the car before I raced it - for obvious reasons! Several people saw my notes and asked for the weight data during a couple of these shows. This paper lists that data and how it was used in the design of my racecar. Table 1 is a side-by-side weight comparison of original equipment versus replacement parts that went into the racecar. All of the parts were weighed on my Longacre scales. The OE parts are from a '73 911S coupe with sunroof; source(s) of the replacement parts are listed. By keeping track of the weight of these parts, I reduced the curb weight (car plus all fluids and 10 gal of gas) from 2140 lbs at my last event to 1830 lbs! Actually, the 1830 lbs is an estimate; the car weighs 1730 lbs with transmission oil but without engine oil and gasoline ... it's tough getting that tranny oil in with the engine and transmission in the car! I calculate 16 qts of oil and 10 gal of gas will add about 100 lbs for a total weight of 1830 lbs. No matter how you fiddle with this estimate, the car is going to be a lightweight and should therefore be quick. Hopefully, I can use that weight advantage on the track! The weight of Porsche assemblies that are useful to car builders is listed in Table 2. For example, a sport seat and mount from my '73S weighs 53-54 lbs. Replace two of these assemblies with a 22 lb Kirkey race seat with custom mount and you've saved 78-80 lbs!	Jim Calzia's '73 911S. 5/00 Also, a sunroof is a frivolous accessory on a racecar. By replacing my sunroof and associated gears, motors, hardware, etc. with a fiberglass sunroof, I not only saved 27 lbs, but I lowered the center of gravity of the car. Any car builder can use the data from Table 1 and calculate how much weight can be saved by using aftermarket components (check the weight of suspension assemblies, glass vs plastic windows, or removing the underseal) but remember two important design criteria. You must decide how the car is going to be used (because some changes are not reversible), and do not change the front-to-rear weight distribution too much. The penalty for overlooking either of these criteria is financially and often physically painful! I have also included calculations for the unsprung weight of my racecar. These calculations are necessary to determine spring and wheel rates and if that expensive brake conversion is really cost effective. Note that even after purchasing some of the best aftermarket suspension and brake assemblies on the market, I saved all of 2 lbs per corner in front and gained 1.5 lbs per corner in the rear! No doubt I improved the handling of the car, but after all of these changes and all of this work, it is clear to me that Porsche did its homework regarding suspensions and brakes. It is difficult and expensive to improve a good thing! © 2000 Jim Calzia All Rights Reserved Go to Table 1>> Go to Table 2>>




	All pages copyright © 2000 Early 911S Registry Information and images contained in this website may not be published, broadcast or otherwise distributed without the prior written authority of the Early 911S Registry. The Porsche crest is a registered trademark of Dr.Ing.h.c.F.Porsche AG.