Early vs. Late Chassis structural differences

[Tim Comeau]

Are the early chassis (the unibody itself) really lighter?

 

I'm excluding all the installed gear. Just the sheetmetal unibody.

 

Here's what I know.

* early sunroof has 2 steel rods for cross support- late has 6-piece aluminum I-beams around edge.

* seat floor- this is the biggest difference I've seen. The late cars have an extra subframe for the seats, instead of just one layer of sheetmetal, which tears over the years.

* bolt on tow hooks in front vs. being integral to the unibody?

* antenna hole in LF fender of early cars vs. antenna in windshield of late cars.

 

The aluminum suspension might be lighter, but again, are there any other diferences in the unibody alone? I'll bet Porsche published something that showed all the evolutionary differences that took place in 1985 and a half.

 

So are the early UNIBODIES really any lighter?

[944-Spec#94]

All I have hear are rumors.

 

There could be some differences if they changed the tub for the 951.

 

I just don't know however.

[Tim Comeau]

That makes sense, Joe, but I've been all over these cars up and down now, and I just don't SEE the difference.

Maybe the gauge of sheetmetal used? The only metal weakness I've seen that needed upgrading was the early seat floor. They went to that extra frame and switched from 4, 6mm seat rail fasteners to 6, 8mm fasteners.

 

You know, there are things like the P/S rack that added weight.

- the 90 amp vs LATE 115 amp alter.

Bigger A/C , heater system.

Bigger sunroof motor.

Bigger radiator in late cars

More blades on the cooling fan.

But, smaller LATE starter

But, aluminum suspension in LATE cars.

Early cars have the mechanical auto rising antenna, late cars have the antenna in the windshield.

 

Here's another point. I stripped my 924S (early) chassis the same as I did my 86 944. But the 944 was still heavier. Fenders are a difference there, but still.

How about undercoating, paint, insulation? That stuff too, looks the same to me.

If this is a myth, let's bust it.

[Spec-944#70]

"Myth Busters" Great show, my kids love it.

I think the early cars were lighter as my early car easily made weight and I weigh 220lbs. I still had my complete headlight assembly and didn't have to get creative as to what to remove. I did completely strip and gut my doors as I had NASCAR beams on my cage. BTW my cage was also Chromoly which is alot lighter tham DOM.

[comatb]

BTW my cage was also Chromoly which is alot lighter tham DOM.

I have often wondered about a Chromoly cage. Doesn't it need to be heat treated after it has been welded together?

 

About the chassis weights. I also cannot explain the alleged weight difference, assuming that both are stripped shells.

[Spec-944#70]

Yes the Chromoly needs special attention when being welded which is one of the other reasons besides cost of the tubing it is so expensive. My cage alone cost $3500.

[bnewport]

Tim put a Chromoly cage in my car and it's very nice. I made some tweaks to it like moving the front bar between the a-pillars move forward but it's very tight with the car body.

 

The problem with it is that it's very expensive to tweak. I'm looking at putting nas door bars in over the winter and that will cost a thousand bucks just for that. DOM is a lot cheaper to work on, about 3x cheaper.

 

Chr is about 27% stronger than DOM. Chr doesn't deform in an impact like DOM does. Chr just stays stiff with a little deformation and then it just breaks but the load needed to do this is pretty huge. This means that you will be shaken a lot more in a Chr Mo cage as it translates the G forces rather than absorbs the G force but in a big hit the lack of deformation may prevent injury so long as the extra Gs don't break something inside you.

 

There is no weight break for Chr Mo versus DOM. They both weigh about the same for the same thickness. So, a Chr Mo cage needs to be 120 thickness same as DOM. This means it's not lighter, it's stronger for the same weight.

[Spec-944#70]

You are right about the weights of the tubing but with Chromoly you get to use thinner walled tubes. .120" for DOM as opposed to .095 for 1.750" dia tubing or you can run 1.5"dia at .120" thickness. This is where the weight savings comes in. I was told by my shop who builds race cars and does alot of cages that the Chromoly vs DOM saves about 50lbs. Worth the $? Probably not but my cages sure looked great!

[bnewport]

Are you sure? My car uses 120 thickness so there was no weight saving and some local checking said that 120 was still whats needed for a car of this weight. Are you sure you can use thinner tubes with Chr Mo?

[Snymo]

The 944 rules say follow the CCR for cage design. Based on the information beloe you can use 0.095 ChrMo but you have to go to 1.75" tubing.

 

From the CCR:

15.6.18 Roll Cage Tubing Sizes

For the purposes of determining roll bar tubing sizes, vehicle weight is as raced, but without fuel and driver. Note: There is an allowance of minus 0.010 inches on all tubing thicknesses. Minimum tubing size for the roll cage is:

 

2201 - 3000 lbs.

1.500â€

[Tim Comeau]

Uh,.......the cage is added in, guys......

We're talking about just the unibody chassis itself.

[bnewport]

My cage is heavy then, it's 1.75" with 120 thickness. Looks like I could probably drop a sherman tank on it at this point according to my local builder...

 

I'm incorrect, the cage is 1.5" with 120 Chromoly.

[944-Spec#94]

Undercoatings?

 

Are the undercoatings the same on early as compared to late chassis? I have heard there is something like 100lbs of undercoating on a 964 chassis.

[Sterling Doc]

Undercoatings?

 

Are the undercoatings the same on early as compared to late chassis? I have heard there is something like 100lbs of undercoating on a 964 chassis.

 

This is what I was thinking - sure looks and feels like a lot of goop under there!

[Tim Comeau]

Yes, I mentioned undercoating, paint, insulation earlier in the thread.......

How heavy could that stuff be from year to year?

 

I'm still not sure.....

[Bradicus]

I feel the 87 and 88 models are heavier. Where some are balasting, I am struggling to make 2600. I have removed most everything and although there is some to go, it will be a bear to get there. I feel, looking at the early cars, that as they 'seem' so identical that the sheet metal is thicker in areas to stiffen. Makes sense as an easy mod by the factory. They obviously looked at improving handling at the 87 change.

 

There IS allot of undercoating and I have not removed it yet. I plan to weight the front fender then strip. I will reweight and post it unless it turns into a super speed secret. Then more is better I say.

[Tim Comeau]

Billy,

Thanks for the self editing. Yes, your cage was built from 1.5 inch x .120 chromally.

Brad,

Please look hard. I'd love to hear that there are some structural differences in the early and late cars. I haven't found it yet. Perhaps we can call someone who worked at the factory at the time our cars were being built and raced? Jurgen Barth?

You know, Porsche PANORAMA magazine is good about pointing out the evolution of the models....anybody have a copy of that mag when the 85.5 model was described? Should have been put out several months after the change- around Oct or Nov of 1985?

 

ps. Idid just remember that there are some small differences in the fender mounting brackets with the late cars having more pieces, thus more weight.

What about the fuel tank? The early steel 17.4 tank has to weigh more than the late 21.1 plastic tank.

The tranny hangers on the early cars are much bigger/heavier than the late model's 2 8mm bolts used to hang the tranny.....

 

WHERE'S THE WEIGHT DIFFERENCE???????????

[Big Dog]

I have an 88 parts car I am starting to dismantle. I propose a definitive program to document the differences between the cars. Someone, please contact a TV company about doing a documentary on this.

 

We get two cars, strip them with the same crew to the same level and weight them up. If there is a difference, start removing all possible components, such as the fenders and reweigh. If that doesn't explain it, start cutting things up and weigh chunks.

 

We will have the answer and a show to boot

[Chuck T.]

i know jim is at least half joking but we might be doing an internet video build / show with DartAuto.com .... more info to come.

[Weston]

i know jim is at least half joking but we might be doing an internet video build / show with DartAuto.com .... more info to come.

 

Would this be comedy or educational? I forsee many silly accidents caught on tape...

 

It's a good idea either way though!

[greg f]

THe front clip from the windshield forward is around 50lb heavier on the 86 up cars. The frame horns, core support, and heater core area are all heavier. The undercoating is way heavier/thicker on the later cars. I am planning to weigh two tubs in the near future. I have two cars to do that I will weigh with just the torque tubes in the cars. Greg F

[944-Spec#94]

THe front clip from the windshield forward is around 50lb heavier on the 86 up cars. The frame horns, core support, and heater core area are all heavier. ... Greg F

 

Would that make it stiffer too? Think they stiffened the chassis for the Turbo and then used the same tubs for all cars?

[Tim Comeau]

Greg,

Thanks. Do you have pics of the areas you're talking about?

I know someone must be around who worked at the factory in the design of the cars........

"Ya, dats simple, vee made deez changes here und here."

[comatb]

THe front clip from the windshield forward is around 50lb heavier on the 86 up cars. The frame horns, core support, and heater core area are all heavier. The undercoating is way heavier/thicker on the later cars. I am planning to weigh two tubs in the near future. I have two cars to do that I will weigh with just the torque tubes in the cars. Greg F

Greg, it would be interesting to know the weight difference of the front clips after all the undercoating has been removed.

[greg f]

Yes, unfortunately we weighed both with the undercoating on before attachment to the wrecked car. ( installed late front clip on early tub.) The undercoating is way more dense and difficult to remove on the later cars. The clip I mentioned was from the firewall forward including the shock towers, wi no headlights or mechanism. Greg F