Diet question?

[IMR-Merlin]

Posted this over in the turbo forum, hoping someone here might have an answer for me.

Thanks in advance
Diet question?

I am looking into ordering my cage material this week or next and I am trying to decided between 1 1/2" .090 wall and 1 1/2" .120 wall. I want to have the car be SCCA compliant and the cut off point between the 2 would be a curb weight of 2500 lbs.

I am gutting the complete car, no AC, minimal heat, Recaro SRD seats in front, no sunroof, but full weld in cage.

I was thinking I would be able to come in under the 2500lb limit with ease.

Anyone see a problem with this?

Thanks

Brendon

[racer]

I'm not sure a stripped 930 (as you define) will get there. Also, you need to consider YOUR weight once in the car.. so 2500 may really mean 2300 (wet - ie, fuel, oil etc) before you get in. What if you carry a passenger? another 200lb? So that means 2100lb wet... not likely

You would need to due the full weight loss.. ie body panels (bumper shocks, bumpers too), lighter wheels jut off the top of my head.

Someone has to have a list out here somewhere about weight loss and how much can be "comfortably" pulled out.. and at what cost.

[IMR-Merlin]

If I am going to do any club events or SCCA events I won't be running with a passenger, but you bring up an interesting point. Does SCCA scale the car with driver? From my reading of the rules regarding cage diameter and wall thickness I just saw vehicle weight vs wall thickness.


As for stripped, I am going with a minimalist build. Stripping everything not needed for street application. Only keeping a small blower for defrost, no sunroof, FG bumpers with light weight mounts etc, etc....

[IMR-Merlin]

In further research, looks like the cut off point is 2700 lbs per page 108
http://cms.scca.com/documents/2011%20Tech/2011%20GCR-printed%20version.pdf

Just don't want a built car with a full weld in cage that is 2750.

[racer]

I've not read too many a thread about 930s being stripped out, but the ones I have seen (non turbo "impact bumper" cars) seem to get (reasonably) around 2400-2500lb, so knowing if the guidelines include person(s) might be important.


Not sure if you use harnesses, if SRD seats would be preferred. Plus, I think they are heavier than true shell type seats (you want to save weight right?). GCR-99 mentions "fixed back seats"

What do you, or a cage builder, deem the weight difference of the CAGE between the two specs? ie, would running the thicker cage add a minimal amount of weight, in addition to improved strength?

I know you specifically mention SCCA, but what about NASA or PCA, should you find in the future you want to run events with them? What SCCA Class would your car run in?

[IMR-Merlin]

I am planning on having this as a all around weekend car. 2 seater with minimal comforts. I do have a lightweight shell seat that I can put in if I want to do a race weekend, but the SRD's are already prep'd for the 5th belt if I want to use them as well. I will be fabricating my cage and doing all my build. I have a 10 year racing background stemming from 7 years in NASCAR as a builder, 2 years in IMSA as a crew chief and one year as Skip Barber that I took for a summer job. So the fabrication will all be done in house. Besides the added weight of the turbo, inter cooler and plumbing, what else would add to the weight between the NA and turbo cars?

Thanks again for your time

[racer]

Fender flares, Larger wheels, brakes and those "comfort" items like Sunroof, Power windows, Power Mirrors, depending on year, Power Seats too all come to mind. Not sure if there are other "little" things like larger torsion bars (ie, heavier bars); not sure if the trailing arms are heavier (certainly stronger and longer though). Rear wiper? heavier rear spoiler.

[IMR-Merlin]

No sun roof, 935 style mirrors, seats have been addressed, no rear wiper, single front wiper, no torsion bars (full coil over), no AC, no heat except for defrost, no fresh air blower, etc.

[RaceProEngineer]

Originally Posted by IMR-Merlin

. . . . . but you bring up an interesting point. Does SCCA scale the car with driver? From my reading of the rules regarding cage diameter and wall thickness I just saw vehicle weight vs wall thickness.

Most sanctioning bodies ( including SCCA ) quote minimum weights "as raced", meaning all fluids, minimum of fuel, plus driver AND his equipment.

If you are looking at the weight savings between .090" and .120" DOM mild steel for the cage, you might consider using chrome-moly -- lighter weight, stronger, AND allowing a smaller diameter tubing. Of course, if you are looking at the cost savings between the two thicknesses of DOM, then chrome-moly will not apply.

And from your past experiences you probably already know this, but some sanctioning bodies are becoming more strict on the "letter of the law". For example, there MUST be triangulation in the main hoop, AND it must be in the same plane as the verticle arms of that main hoop. This triangulation must start within 10" of the bend in the main hoop over the driver's head, and extend to the bottom of the main hoop on the opposite side. Stuff like that . . . . .

Ed LoPresti

[RichardNew]

The trick is to build the car as light as possible. Then add lead (weight) back in to the point where you're legal. You can add the weight low on the car. You can also corner balance the car with this weight.

I know teams that remove all of the gauges for qualifying and put the weight on the floor for the banzi runs. They then put the gauges back in for the race. That's also another reason for finding a 120 lb driver. Drivers sit up in the car. If I can find a little bitty driver I can put the needed weight low in the car.

Richard Newton
Vintage Motorsport Magazine

[IMR-Merlin]

Ed, Richard:

Thanks for your input. I think I can whittle to weight down to 2500# less driver for an event I intend to run. This is not going to be a competition car, just something I can do some track days if needed. I want a nice balance between power and weight and the engine for the car is 420HP at the wheels with a conservative tune.

Ed you hit the nail on the head with my approach and I will consider chrome-molly for the cage. Not that there is a huge difference in cage weight, but .030 in steel all the way around a full cage does add up.

Richard we could go on for days talking about qualifying set ups.

Thanks again

Brendon

[Flieger]

I believe you need to heat treat (stress relieve) CrMo steel after welding dor it to have full toughness and not be brittle. Mild steel does not.

[Dave at Pelican Parts]

I think that building the car so that you can use the thinner cage material is a false economy. Just suck it up and use the thicker material. Then put the car on a diet. If you make your target, great! If not, you're still covered.

IMHO going with a stronger-than-needed cage is not something to avoid.

--DD

[aftermath]

Be safe, stronger cage, who cares about a few pounds when it could affect safety. I am adding gussets and extra bracing to my cages just in case a weld breaks, be safe....

[Evan Fullerton]

My cage is getting built out of 1.75"x.095" 4130. With the proper welding rod and large TIG beads 4130 can be used without post weld heat treat. The 1.75"x.095" is slightly lighter than the 1.5"x120" and meets the same weight specs. Went with 4130 mainly due to that being what my builder likes to work with but the added strength in a tin can 911 isn't a bad idea. My feeling is in a weak car like an early 911, you can't go wrong with too much cage. In a later 993 or 996 chassis there might be a valid argument that you can over build the cage and not have enough crumple zone left but in a 911/930, I don't feel that that is really the case. When it is done, hopefully some time this week, I will post up some pics as I spent a fairly significant amount of time designing mine and feel it is about the best you can do short of a full tube frame car.

[Tom W]

Starting with a 964, getting to 2500 lbs (without driver) was non-trivial. You'll need to remove most everything that isn't required. (I removed all heat/AC and venting, everything that could be removed without a complete strip to the tub.

Getting to 2500 with driver will take a lot more effort. I'm at 2380ish and I have absolutely nothing that isn't required (no headlights, no wipers, all lexan and no glass, no factory wiring, etc).

[IMR-Merlin]

Thanks Tom. I have a guy with a 930 around 2300# with lights and some amenities, alum cage. I am going to start the diet next week.

Are you a sun roof on non-SR car?

[IMR-Merlin]

Just wondering what was up with the 11 1/2 lb bars I pulled out of my doors. Looks like they were put in to make the car meet side impact requirements. All the hardware that was holding the bars in was SAE and not metric so I am assuming that this was done to make my grey market car US legal for side impact.

Between both sides I saved 23 lbs!



One bar was completely solid steel.

[RichardNew]

Some really strange stuff went on with gray market cars. I've seen some with wood sticks in the doors. Of course it was painted black so it looked good in the photos.

Richard

[IMR-Merlin]

Originally Posted by RichardNew

Some really strange stuff went on with gray market cars. I've seen some with wood sticks in the doors. Of course it was painted black so it looked good in the photos.

Richard

You can say that again, I have been familiar with this car since 1990 and I bought the car from the 2nd owner (in the states) and it's been in pieces since 94. Since I started digging into it, we've found that the car has had the color changed and I think it was when the "updates" were done because the car was done correctly. All the glass was pulled and the fenders were off. If the car hadn't say outside for so long or I wasn't doing such a detailed build, we would have never known.

I just couldn't believe how heavy those door bars were.