Weight reduction: Running out of ideas.

Shipping weight for a 1976 Corvette was 3445, curb weight was 3541. Add 200 lbs for a/c, th400, telescoping steering wheel, power windows, power steering, am/fm radio (18lbs for the radio!)
I'm just under 3200 lbs (3160) with a full tank of fuel (I'm supposed to be 3200 for the class I run in) - with 3 gallons it'd be roughly 3060... which makes your weight even more impressive.
That said, my weight bias is almost exactly 50/50 (within 5 lbs)
One of my scales died, so weighing hasn't happened recently - but once resolved I'll see where I'm at now. I suspect I weigh more

*link https://corvettestory.com/specs/1976-Corvette-specs-options.php

Had a spa/mental-health day today, roaming my favorite junkyard. Looked around for parts for a few project cars. Was surprised to find another C4 (an '85) in the yard. Last time I was there I pulled some parts off an '89 C4. I checked dozens of GM intermediate size cars looking for 11.5" solid rear rotors, but kept striking out. Close to closing time I stumbled upon an '11 Buick Regal with 11.5" rotors. The quick measurements I made (and comparing them to the rear rotors on the '85 C4) indicate a good possibility of trying them on my car. The only measurement that looks to be a concern is the center hole. The Buick rotor "looks" like it's maybe .100-.150" smaller. Right now the plan is to stop in there again next week, pull the rear calipers off the Buick and the C4 , and see if the rotors are interchangeable on the spindle/hub or not. I'll also bring my portable scale to measure the weight difference between these two rotors to see if the swap is worth the expense of new rotors and a machining fee.

Well, scratch the rotor swap idea for reduced weight. Went to the junkyard today and pulled rear rotors off an '11 Buick Regal and an '85 Corvette. The Corvette had drilled aftermarket rotors, and some wear, but the Buick rotors had similar wear. I weighed them both with my HF hanging scale, and the Corvette rotors were about two ounces LIGHTER (.12#). Weighed them three times, and the results were repeatable. So, this economical option isn't going to work.

While wandering around looking at radiator sizes and shapes for my street rod truck project, I saw some small radiators that might package in the rear of my '69. In addition to trying to reduce mass in my car, I keep looking for ideas on how to move some of the remaining mass either to the right or to the rear. I keep entertaining ideas on how to reduce the radiator size and weight (and airflow) up front, and move some of the weight and work rearward. Would definitely take some duct work and plumbing to direct the fluids, pretty sure that's doable, but I have no experience on what it takes to pump the coolant in that long of a round trip. I suspect the overall weight of the cooling system would increase slightly, but possibly a better f/r weight balance (currently about 1400/1300 pounds) might net a better handling car. As I heard someone once say, you can only go around a corner as fast as the slowest axle/half of your car.

Just trying to figure out a next move.

Well, my parsimony paid off. Got my "pre-owned and generically priced" 26mm hollow front swaybar (off an '89 C4) finally installed. Went online to buy some poly bushings for it, and for some damn reason 26mm generic poly kits are noticeably more expensive than other kits of similar size range. Surfing the web I found some 26mm poly bushings for a Honda Accord for a pretty cheap price. Bought them, and last week scoured the junkyard for some brackets. No luck finding an Accord of the correct vintage, but did find a late model Jeep IIRC with the correct sized brackets. Got them (and a similar size pair off an Isuzu) for a very acceptable price. I welded short extensions on them to give additional fore and aft adjustment, and I was in business. Total cost for the bushings and brackets was about half compared to buying the generic kit (my labor is free, and the mental health benefit of wandering a junkyard on a nice sunny day is substantial).

Oh, and the weight of this mongrel kit turned out to be four ounces lighter than a generic kit of similar size. Win, Win.

A productive day at the junkyard is a good day. Especially when you are able to piece together exactly what you wanted.

Enjoyed a track day last week. The rear suspension geometry changes and the front sway bar reduction really helped the car rotate in the corners, and to be noticeably more steady during heavy braking. The car just seemed to go where I aimed the steering wheel. With a big block this car previously always seemed reluctant to flick the front end each way. This was a rare moment of owning this car when changes to it exceeded my hopes. Another item that made all the weight reduction work worth it was the braking into the corners. The car slowed down noticeably quicker than I was used to, and I found myself letting off the brakes into the corners, rather than trail braking. Not a big deal, it was a track day, not a race, so there's more opportunities ahead to adjust my braking points. One thing that did scare me was the brake booster seemed to have only one good application per corner. When I let off the brake, and then reapplied the brake a half or full second later, the pedal felt like I had no boost at all. Firm hard pedal, but seemingly no noticeable deceleration. I'm still trying to figure this out, and I'll be starting a thread in the Brake section shortly to discuss it in more detail.

69427 said:

Enjoyed a track day last week. The rear suspension geometry changes and the front sway bar reduction really helped the car rotate in the corners, and to be noticeably more steady during heavy braking. The car just seemed to go where I aimed the steering wheel. With a big block this car previously always seemed reluctant to flick the front end each way. This was a rare moment of owning this car when changes to it exceeded my hopes. Another item that made all the weight reduction work worth it was the braking into the corners. The car slowed down noticeably quicker than I was used to, and I found myself letting off the brakes into the corners, rather than trail braking. Not a big deal, it was a track day, not a race, so there's more opportunities ahead to adjust my braking points. One thing that did scare me was the brake booster seemed to have only one good application per corner. When I let off the brake, and then reapplied the brake a half or full second later, the pedal felt like I had no boost at all. Firm hard pedal, but seemingly no noticeable deceleration. I'm still trying to figure this out, and I'll be starting a thread in the Brake section shortly to discuss it in more detail.

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big camshafts don`t make vacuum, you might want to try the C-6 (maybe) aluminum master with no booster, you might just kill two birds with one stone, better brakes and a weight reduction, on my racer I ran a stock cast iron manual 1" master cylinder...

69427 said:

Enjoyed a track day last week. The rear suspension geometry changes and the front sway bar reduction really helped the car rotate in the corners, and to be noticeably more steady during heavy braking. The car just seemed to go where I aimed the steering wheel. With a big block this car previously always seemed reluctant to flick the front end each way. This was a rare moment of owning this car when changes to it exceeded my hopes. Another item that made all the weight reduction work worth it was the braking into the corners. The car slowed down noticeably quicker than I was used to, and I found myself letting off the brakes into the corners, rather than trail braking. Not a big deal, it was a track day, not a race, so there's more opportunities ahead to adjust my braking points. One thing that did scare me was the brake booster seemed to have only one good application per corner. When I let off the brake, and then reapplied the brake a half or full second later, the pedal felt like I had no boost at all. Firm hard pedal, but seemingly no noticeable deceleration. I'm still trying to figure this out, and I'll be starting a thread in the Brake section shortly to discuss it in more detail.

Click to expand...

you also might consider a triple disc clutch you can ditch your heavy scattershield, the triple disc has much less rotating mass allowing you to go into corners deeper (braking later) and come out quicker due to less rotating weight...

redvetracr said:

big camshafts don`t make vacuum, you might want to try the C-6 (maybe) aluminum master with no booster, you might just kill two birds with one stone, better brakes and a weight reduction, on my racer I ran a stock cast iron manual 1" master cylinder...

Click to expand...

My current setup is an '84 C4 booster (smallest OD of the C4 boosters, needed to clear my valve cover, and half the weight of a C3 booster), and a C5 aluminum m/c (about 1# with a 1" piston). My current engine combination idles at about 12" of vacuum, as it's also a licensed street car. This setup worked perfectly for the past ten years up 'til the other week.

I'll admit my possible ignorance on the next item. Regarding manual brake C3 Corvettes, I was/am under the impression that the 1" manual master cylinders have a deeper rear conical bore in the rear of the piston to better deal with the brake pedal pushrod, compared to the conical bore depth in the 1.125" PB master cylinders. Is this correct, or have I been fed incorrect information?

redvetracr said:

you also might consider a triple disc clutch you can ditch your heavy scattershield, the triple disc has much less rotating mass allowing you to go into corners deeper (braking later) and come out quicker due to less rotating weight...

Click to expand...

I've looked at those small diameter setups. They're fantastic in every way, except when taking off from a standstill. As I mentioned earlier, my car is still a licensed street car, and dealing with stop signs and traffic is still a concern. I presently have the 10.5" 14# L88 flywheel, a 13# pressure plate (the lightest I could find), and a pretty light 6.5" front damper. Given the M21 and 3.08 rear gear I have, my setup is already threatening to stall the engine whenever I take off from a stop.

Just an update from a change quite a while back. I experimented/installed a radiator out of a 2001 Cavalier 2.2L into the car, taking about ten pounds of material and coolant off of ahead of the front axle centerline compared to the previous aluminum radiator I had. The reason for this radiator choice was it has almost identical frontal area as the stock radiator, but just one row thick. Yesterday was the first track day in quite a while where the ambient temps were hot enough (90*) that I was concerned about the capability of this radiator to keep the engine "cool" (it usually ran 210* on hot track days with the previous name-brand aluminum radiator). For less aero drag/lift I have had both the headlight grills blocked off and most of the two underchin holes blocked as well. The majority of cooling air comes in the center grille, as I'm not running a front plate. To my great relief the coolant temps were at the same 210* as before.

Just dreaming right now, but I would like to put a smaller yet radiator up front (biased to the right), and then add a second radiator/fan in the back between the two mufflers. This dual system would most probably be a net weight increase for the car, but may pay off in better front cornering grip and more weight on the rear axle during accels and braking. I have most of the details worked out, other than a clean way to plumb the lines above/around the rear batwing and halfshafts.

Glad it worked out. Maybe take a look at motorcycle radiators for your remote application. You may be able to find something that fits size and weight constraints if you shop some wrecked sportbikes. One concern will be it may take longer to burp all the air out of the cooling system, but once fully filled and pressurized, you'll be in good shape.

Red77: One concern will be it may take longer to burp all the air out of the cooling system, but once fully filled and pressurized, you'll be in good shape.

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I've been doing a MAJOR cooling System review/rehab on the "Tow-Van." Found a unique tool at HF that helps make the whole "burping" process a piece of cake.


It uses your air compressor to create a vacuum in the system (venturi-effect). Then, you fill and get a nearly full and burp-free fill. I've been using it as a fill and flush (4 times over) and tomorrow will do the final fill. The van hasn't had any service on the coolant system by the PO in the last 16 years - so I don't think I'm going overboard! Tool is right at 80 bucks - but requires a source of shop air.

Cheers - Jim

redvetracr said:

you also might consider a triple disc clutch you can ditch your heavy scattershield, the triple disc has much less rotating mass allowing you to go into corners deeper (braking later) and come out quicker due to less rotating weight...

Click to expand...

Both my son and I run manual brakes in dedicated C3 roadracers with VARA and SVRA without any issues. Much easier to modulate braking and no issues related to vacuum dropping under acceleration. I am running a Tilton 5.5" diameter clutch with an automatic flex plate. You will find this takes weight off the car as well as rotating inertia. A 7.25" setup is also available. Have to spin the tires to launch but that is part of racing or track day. Using a QuickTime scattershield which also reduces weight as it is smaller in diameter than those designed for larger diameter flywheels. Be sure to center any new scattershield. I learned that hard way by welding the input shaft to the throwout bearing at AutoClub Speedway.

1FastRacer said:

Both my son and I run manual brakes in dedicated C3 roadracers with VARA and SVRA without any issues. Much easier to modulate braking and no issues related to vacuum dropping under acceleration. I am running a Tilton 5.5" diameter clutch with an automatic flex plate. You will find this takes weight off the car as well as rotating inertia. A 7.25" setup is also available. Have to spin the tires to launch but that is part of racing or track day. Using a QuickTime scattershield which also reduces weight as it is smaller in diameter than those designed for larger diameter flywheels. Be sure to center any new scattershield. I learned that hard way by welding the input shaft to the throwout bearing at AutoClub Speedway.

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you do NOT need a scatter shield with a triple disc clutch, the QMI and Tilton bell housings are aluminum, I ran the QMI 5.5 with a reverse mount starter reducing my moment of inertia even further...you race SVRA? know this car??