Light makes might - but I want more light

[L48]

When I bought the 75 I kinda thought it would be light and good for racing. That has proven not to be the case, and I more or less gave up on drag racing the Vette.

Then recently I was reading some comments from Evolution1980 regarding C3 weight. So I looked up the numbers and found my 1975 has a curb weight of 3690. In 1975 A/C was not standard equipment so I presume this weight does not include A/C.
In 1980 A/C was standard and the curb weight is 3282. Yikes 408 pounds lighter with A/C added in!

So now I am thinking maybe I want another Vette, one I can put my racing drivetrain in, and the 1980 (maybe 81?) seems to fit the bill nicely.

Questions:
1) Can I use the non-A/C unit from an older C3 in a 1980 car to further reduce weight? (I really want the heater for defrost and cold days) Removing A/C should be worth 60-80 lbs easy.
2) Does anyone know what really was changed to make it lighter? I saw the 80 has lighter top panels and thinner fiberglass, but there has to be more.
3) Is the rear center section different between the 75 and the 80 - the latter presumably being lighter?
4) Has anyone else taken on a similar lightening project - can I get one of these around 2800 lbs?

And I don't plan on remodeling any survivor cars to do this. I'll be looking for a relatively inexpensive low rust car that has already lost its original engine should I choose to go this route.

 

[JohnZ]

The diff and support was aluminum in 1980 - about 50# lighter than your cast iron diff and steel crossmember.

The rear spring was composite in 1980 - about 45# lighter than your steel spring.

 

[6880 Mike]

...Questions:
1) Can I use the non-A/C unit from an older C3 in a 1980 car to further reduce weight? (I really want the heater for defrost and cold days) Removing A/C should be worth 60-80 lbs easy....

Depends. AC was stock in the 80-82s so the firewall is cut for the AC heater/defroster core and box which has a larger opening than non-AC cars.

2) Does anyone know what really was changed to make it lighter? I saw the 80 has lighter top panels and thinner fiberglass, but there has to be more....

Greater use of aluminum (differential and rear carrier), thinner windshield and door glasses; thinner panels in the doors skins and hood; plastic seats; plastic interior trim, R4 compressor instead of the old A6, etc.

3) Is the rear center section different between the 75 and the 80 - the latter presumably being lighter?...

Yes, different. Frames are different too, because of the new-for-80 carrier.

 

[Steve Ference]

You can make a 75 L48 light enough for racing but its costly and drastic for a daily driver.My car weighs 2880 lbs. recipe as follows,remove carpets,internal door panels,all plastic trim,passenger seat,replace driver seat with lightweight aftermarket unit,heater matrix and pipework in passenger footwell,radio,smog pump and pipes,replace water pump, intake manifold,carb,air cleaner,heads with aluminum,remove cast iron exhaust manifolds and replace with headers.If you want the car to be quick, install a big cube small block, mines a 434 13.5 : 1 AFR headed 700 HP + 300 HP NOS baby!
Not as GM intended but it does the job!

 

[Evolution1980]

Are you looking to make a drag car that can be used as a daily driver? Or are you looking for a daily driver that can be taken to the drag strip?

And why did you choose the C3 platform over any other, beit a different Corvette generation or completely different car line?

You can pretty much take any vehicle regardless of it's curb weight and make it fast. Example: jet powered semi's
That's why I'm asking because I'm curious as to what your motivation is or what is the overall end result you are going for.

 

[KANE]

... Then recently I was reading some comments from Evolution1980 regarding C3 weight. So I looked up the numbers and found my 1975 has a curb weight of 3690. In 1975 A/C was not standard equipment so I presume this weight does not include A/C.
In 1980 A/C was standard and the curb weight is 3282. Yikes 408 pounds lighter with A/C added in!

I always considered the 74-79 Vettes the Daisy Fuentes of sharks!


I got my old 1978 to weigh in at 3300lbs with a half tank of gas. Here is what I did to get her there:
- Light weight hood
- Fiberglass rear bumper cover (using only an impact bar behind it!)
- 80-82 seats
- Carbon fiber rear mono spring
- Astro tops
- Absolutely NO sound deadening (or mass backing for that matter!)
- Light weight aftermarket aluminum wheels
- Aluminized sidepipes
- Fiberglass sidepipe covers
- No smog / emissions gear (no cats, no EFE)

FYI- I also had a 700R4, TPI, AC, and a stereo!

 

[L48]

Thanks for all the replies so far. And keep ‘em coming.

And why did you choose the C3 platform over any other, beit a different Corvette generation or completely different car line?

The decision is not made yet. I am considering it seriously and trying to determine how "practical" it would be.

what is the overall end result you are going for.

This is a good question. For short answer skip to bottom
I bought the 75 at an estate sale with the impression that the fiberglass Corvette would be a lighter chassis to put my racecar drivetrain into, and it was not.
The "racecar" is a street legal 76 Trans Am with 350 Chevy, 700R4 and 4:56 posi rear end. In the cold air it runs 12.60’s. (runs on 87 octane btw)
Since I bought the Vette the T/A has been largely sitting collecting dust. So the thought occurred to me that I should try to combine these cars into one. A car I can drive to work on nice days (2000 miles per year) and also go drag racing with (maybe 10-15 times a year). I’d really like to run 12 flat and I think I can get there without any major engine work if I can shed 500 lbs and make a few minor performance improvements. I’ll need an automatic for bracket racing consistency.
Having one vehicle would also cut down on maintenance (batteries, brakes, hoses, insurance, etc).
For years I have been thinking about replacing the T/A with something lighter. I have looked at some Vega-style cars, even some "pro street" types with plenty of mods for racing, but I just can’t warm up to driving a Vega or similar type car. I’m biased toward GM so that limits my choices, and it would have to be 25 years old so I don’t have to worry about e-check (emissions testing).
A solid axle car would probably be easier but I’m sure not the first one to try to do this with a Vette.
Other pluses I can see with the Vette is better weight distribution and better weight transfer (due to stiff frame) should help also. The wheel well should be big enough to put a tire in there that can make traction for a small block powered Vette.
Bottom line: daily driver capable, runs 12 flat on low octane gas, use for occasional drag racing, not too expensive, has some style. Handling and braking a plus.

 

[Evolution1980]

Bottom line: runs 12 flat on low octane gas, not too expensive

Hmmmm...take a vette and put in a big engine with low compression. Then you don't have to worry about gutting it and doing all kinds of mods to shed a couple hundred pounds. I'm know that SuperChevy magazine and similar mags have run articles over the years that have outlined building a huge engine (700+ HP) that runs on low octane. At that kinda power, weight becomes somewhat irrelevant. However, you'll need the rest of the drivetrain beefed up to support all the torque. I'm sure you already figured that.
Anyways, my 2¢ would be to not bother putting any major money into lightening the car and instead put the money into building a low compression, big motor as outlined in any of the hotrod performance mags.

 

[fine69]

Hmmmm...take a vette and put in a big engine with low compression. Then you don't have to worry about gutting it and doing all kinds of mods to shed a couple hundred pounds. I'm know that SuperChevy magazine and similar mags have run articles over the years that have outlined building a huge engine (700+ HP) that runs on low octane. At that kinda power, weight becomes somewhat irrelevant. However, you'll need the rest of the drivetrain beefed up to support all the torque. I'm sure you already figured that.
Anyways, my 2¢ would be to not bother putting any major money into lightening the car and instead put the money into building a low compression, big motor as outlined in any of the hotrod performance mags.

Doh!
:duh

 

[L48]

Hmmmm...take a vette and put in a big engine with low compression. Then you don't have to worry about gutting it and doing all kinds of mods to shed a couple hundred pounds. I'm know that SuperChevy magazine and similar mags have run articles over the years that have outlined building a huge engine (700+ HP) that runs on low octane. At that kinda power, weight becomes somewhat irrelevant. However, you'll need the rest of the drivetrain beefed up to support all the torque. I'm sure you already figured that.
Anyways, my 2¢ would be to not bother putting any major money into lightening the car and instead put the money into building a low compression, big motor as outlined in any of the hotrod performance mags.

I can't disagree with your assessment, and I have been thinking about it the last week or so. However I guess I am still leaning towards lightening the car though. My thoughts are:
* Most of the lightening I plan will not require major money. As far as the A/C, I'll do the fabrication myself if the firewall needs reworked. Acquiring the proper parts (manual steering, brakes) might be a little expensive, but it will be less expensive than the engine buildup.
* Reducing weight and making the car go faster on the same power may allow me to do this without having to beef up the drivetrain to support it.

As soon as the latest round of improvements on my current Vette is done, it will be decision time. If I choose this route I'll definitely get rid of the T/A first to make room for this project.

I think maybe an 81 or 82 might be better since, if I understand correctly, they already have the four speed automatic (700R4).

 

[minifridge1138]

I don't think the 1981 has the 700R4 transmission.
I know for a fact that the 1982 Has the 700R4 transmission.

However, the 1982 also has the Crossfire Injection,
When the crossfire works, it works well. But it is usually easier to get a carburetor working.
If you are going to put the Trans Am's engine into it, then you may not care about the Crossfire.

yes, the 1982 will be 400+ pounds lighter than your 1975, but i'm not sure how much torque the drive train of a 1982 can handle. I have heard that the 700R4 can handle upwards of 600 hp, but i don't know about the rest of the drive train.

Good luck, and I definitely want to know how it turns out.

 

[Evolution1980]

I have heard that the 700R4 can handle upwards of 600 hp

Yeah, if it's beefed up considerably. For some reason, GM went to a rotor front pump with the 700R4's and that's the weakest link. (Ask me how I know!!!) The gerotor setup in the TH350/400's was much more reliable / durable.

 

[L48]

I don't think the 1981 has the 700R4 transmission.
I know for a fact that the 1982 Has the 700R4 transmission.

However, the 1982 also has the Crossfire Injection,
When the crossfire works, it works well. But it is usually easier to get a carburetor working.
If you are going to put the Trans Am's engine into it, then you may not care about the Crossfire.

yes, the 1982 will be 400+ pounds lighter than your 1975, but i'm not sure how much torque the drive train of a 1982 can handle. I have heard that the 700R4 can handle upwards of 600 hp, but i don't know about the rest of the drive train.

Good luck, and I definitely want to know how it turns out.

I think you are right about the 81 - I was confused since the spec section on this sight shows the auto tranny as a four speed - even though it shows the gear ratios for the 3 speed auto. I wonder what is different beside the driveshaft.

I have heard that about the Crossfire. I have no intention of keeping it on there - assuming of course the car even has the engine when I get it.

My 700R4 is from B&M. I recall the documents saying it could handle 450 lbs-ft of torque. I expect to stay under that. Time will tell if the stock rear can handle it.

 

[Evolution1980]

...450 lbs-ft of torque. I expect to stay under that. Time will tell if the stock rear can handle it.

The ZZ4 has been putting 405ft/lbs to my stock rear end for years now without any problems whatsoever. *knock on wood*