Weight reduction: Running out of ideas.

I weighed the C5 aluminum front crossmember. It was 35#. Initial problem is that my current steel crossmember is 34#. I cut off all the unnecessary tabs and mounts that are unusable with my C4 suspension, and then cut 7" out of the middle to narrow it to the same width as my narrowed (to C3 width) C4 suspension crossmember. I also took a couple one inch sections out of the longitudinal length to get the LCA pockets of the crossmember closer together so that C4 control arms will fit. It's down to 26# now. I still have to weld new attachment ears/flanges on the part, but I'm keeping my fingers crossed that I can end up at a net 5# reduction off the front axle line.
 
BBShark said:
Is the C4 crossmember a modified part from a C4 or did you make this yourself?
Click to expand...

It's a custom piece I welded up about 15 years ago when I was first putting the C4 suspension on my spare C3 frame. I initially started hacking up a C4 crossmember but I had to cut it in so many places and pieces that I finally decided it's easier to just start from scratch and build my own. (My strategy at the time of the suspension conversion was to make it work and make it not break. Nothing has broken over the years, and I've changed a few minor things regarding the geometry, but the last several years I've been on the third stage, which is weight reduction.) This is the current steel piece next to my first aluminum proto piece. The cutup C5 crossmember is my third proto/attempt at making an aluminum replacement for this steel piece.

I need to get around to taking a picture of the modified C5 part one of these days.

IM002479.JPG
 
This is the present configuration with the top and bottom pieces that were cut out to narrow it to fit a C3 trackwidth with C4 lower control arms, and also the two one-inch slices that were necessary to allow C4 control arms to bolt into the pockets spaced for wider C5 arms.

Knowledgeable readers will notice that the left front (LF) mark appears to be in the wrong spot. It is and it isn't. It's the right rear on a C5, but it only looks to be able to work in my application if I rotate it 180 degrees. I have to notch the rear crossover to clear the oil pan (easier to do in the narrower piece), and my hollow sway bar (off a '93 Firebird) has a rearward offset section in the middle, and it looks like the vee section might just be enough to clear the bar. If it doesn't I'll be scouring the junkyards for a similar tubular bar but without the center offset. (Putting the stock solid C3 bar back on would just nullify the weight loss from the work on this crossmember.)

Doing some quick calculations of material weight for the two mounting arms is causing me some grief. It continues to look like it's going to be a steep uphill battle to get this foundational piece light enough to be noticeably different from my present steel piece.

IMG_0464.jpg
 
Well, recent progress on multiple fronts. I found an '89 Corvette sitting in my local Pik-N-Pul junkyard. First time in decades I've seen a Corvette in a common junkyard. I pulled a few parts off it, including the hollow 26mm front sway bar. It's two pounds lighter than the hollow Firebird sway bar I had on the car, and it's also straight in the torsion section (the Firebird bar had an offset section in the middle, for radiator clearance I assume), so I can now re-rotate the C5 LCA crossmember to its normal orientation, saving me some otherwise needed cutting and welding to clear the oil pan.

I also replaced the rear leaf spring with a softer rate C4 spring (one pound lighter), as the previous spring (Base '84 piece) was just too stiff for the current rear weight of this car.
 
What are the current Stats? Front/rear coming down as you like? Total dropping by pounds - still?
Soon you just might be at the limit. Pulling any creature comforts? Carpet (underlayment/lead sheets-sound) add up too.
Any cross weight challenge? (well, other than driver vs pax)
As my engine is on motor plates, I kinda wish I shifted a bit to the starboard as Pappy did for single seat occupancy.

The softer spring is athwarts - yes? Can't you adjust the rate with bolts? Just trying to recall. The front does that.
I may be dumping my front composite spring as I've finished the pushrod install with coil-overs and replace with an ARB. I'llcheck the pick&pull.

Pics soon and update.

Cheers - Jim
 
phantomjock said:
What are the current Stats? Front/rear coming down as you like? Total dropping by pounds - still?
Soon you just might be at the limit. Pulling any creature comforts? Carpet (underlayment/lead sheets-sound) add up too.
Any cross weight challenge? (well, other than driver vs pax)
As my engine is on motor plates, I kinda wish I shifted a bit to the starboard as Pappy did for single seat occupancy.

The softer spring is athwarts - yes? Can't you adjust the rate with bolts? Just trying to recall. The front does that.
I may be dumping my front composite spring as I've finished the pushrod install with coil-overs and replace with an ARB. I'llcheck the pick&pull.

Pics soon and update.

Cheers - Jim
Click to expand...
Stats, currently the car is about 2690# with 4-6 gallons of fuel (and no driver). The last time I weighed the car it was 2720#, and I've pulled about 30# off the car with lighter or modified parts. I pull weight off any place I can safely do so, and as a result I'm at roughly a 1400/1300 F/R and 1380/1320 L/R weight distributions (I haven't had the opportunity to measure or calculate the corner weights). Certainly not ideal, but amusingly my front axle weight seems to be lower than a C8's. I've moved the alternator and battery to the right side to distribute the weight better, but there doesn't seem to be much other stuff that can be moved.

Haven't really pulled out any of the creature comforts. It's first and foremost a licensed street vehicle, and most of the cars I share the track with are street cars, so stripping the car out just doesn't seem cricket.

I've entertained moving the engine over to the right, but the packaging just won't allow it. There's only about a finger's thickness room between the block and the UCA.

I've got coilovers up front, and the C4 spring in back, so I can adjust ride height and corner weights, but not rates.

I'm entertaining changing the rear rotors for a bit less weight. I have lightweight two-piece rotors up front, but stock C4 rotors in the rear. I've upped the rear brake bias compared to the stock C3 ratio, but the rear rotors are still not having to work that hard with the light rear axle weight. I'm curious if some skinny non-vented rotors would be a touch lighter, and still do the job. I currently have undercar air directed at the rear rotors, so that should continue to help with any rotor change. It may or may not work, but I'm going to do some research to see if I can find any rotors that would fit and what the weight would be. Five bolt pattern and non-vented may be like hen's teeth though. I suppose I could redrill them if necessary.
 
69427 said:
Stats, currently the car is about 2690# with 4-6 gallons of fuel (and no driver). The last time I weighed the car it was 2720#, and I've pulled about 30# off the car with lighter or modified parts. I pull weight off any place I can safely do so, and as a result I'm at roughly a 1400/1300 F/R and 1380/1320 L/R weight distributions (I haven't had the opportunity to measure or calculate the corner weights). Certainly not ideal, but amusingly my front axle weight seems to be lower than a C8's. I've moved the alternator and battery to the right side to distribute the weight better, but there doesn't seem to be much other stuff that can be moved.

Haven't really pulled out any of the creature comforts. It's first and foremost a licensed street vehicle, and most of the cars I share the track with are street cars, so stripping the car out just doesn't seem cricket.

I've entertained moving the engine over to the right, but the packaging just won't allow it. There's only about a finger's thickness room between the block and the UCA.

I've got coilovers up front, and the C4 spring in back, so I can adjust ride height and corner weights, but not rates.

I'm entertaining changing the rear rotors for a bit less weight. I have lightweight two-piece rotors up front, but stock C4 rotors in the rear. I've upped the rear brake bias compared to the stock C3 ratio, but the rear rotors are still not having to work that hard with the light rear axle weight. I'm curious if some skinny non-vented rotors would be a touch lighter, and still do the job. I currently have undercar air directed at the rear rotors, so that should continue to help with any rotor change. It may or may not work, but I'm going to do some research to see if I can find any rotors that would fit and what the weight would be. Five bolt pattern and non-vented may be like hen's teeth though. I suppose I could redrill them if necessary.
Click to expand...

Wow, 2690# is a LOT! Do you know what the car was from the factory?
 
I had a look see in my files of "Things I made Need Someday."
Attached is a method I snatched from another web page that explains how to measure the weight on all four corners without scales.
Might be interesting to trial until you get scales. The maths are straight forward. It uses tire pressure and contact patch.
Equal and opposite action/forces -- just like we learned in school.

Maybe you'll find it useful.

Cheers - Jim

ps - I'll drop in the tech folders too.
 

Attachments

BBShark said:
Wow, 2690# is a LOT! Do you know what the car was from the factory?
Click to expand...

I honestly don't know. My guess would be somewhere in the 3400# ballpark. In addition to all the usual steel and cast iron original parts in these antiques, my car had the factory steel wheels, of course, but it also had those outrageously heavy optional wheel covers. I was working at a gas station at the time I bought the car, and I was used to popping hub caps and wheel covers off cars to fix or rotate tires, but that had not prepared me for how unbelievably heavy those covers were.

I have to confess I came to the "lighter is better" philosophy later than I should have. I used to just focus on more horsepower for better performance, but my eyes were opened big time during a track day a bunch of years ago. I was all prepped up for a fun time, just looking around at all the other cars there, and which ones appeared to be quick and which were probably moving chicanes. One guy there had a little station wagon looking Japanese shitbox thing, and I figured (wrongly!) that he was in the moving chicane category. He didn't have any impressive horsepower, and so he wasn't that quick down the straights, but damn, he wasn't slowing down much for the corners. He was making such good time through all the wiggly parts of the course that I couldn't overcome that advantage down the straights. I was so damn impressed with his showing there that I had to walk over to where he was pitted later and compliment him. After that I've tried when I can to reduce the vehicle mass that my tires have to contend with around the track.
 
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69427 said:
I honestly don't know. My guess would be somewhere in the 3400# ballpark. In addition to all the usual steel and cast iron original parts in these antiques, my car had the factory steel wheels, of course, but it also had those outrageously heavy optional wheel covers. I was working at a gas station at the time I bought the car, and I was used to popping hub caps and wheel covers off cars to fix or rotate tires, but that had not prepared me for how unbelievably heavy those covers were.

I have to confess I came to the "lighter is better" philosophy later than I should have. I used to just focus on more horsepower for better performance, but my eyes were opened big time during a track day a bunch of years ago. I was all prepped up for a fun time, just looking around at all the other cars there, and which ones appeared to be quick and which were probably moving chicanes. One guy there had a little station wagon looking Japanese shitbox thing, and I figured (wrongly!) that he was in the moving chicane category. He didn't have any impressive horsepower, and so he wasn't that quick down the straights, but damn, he wasn't slowing down much for the corners. He was making such good time through all the wiggly parts of the course that I couldn't overcome that advantage down the straights. I was so damn impressed with his showing there that I had to walk over to where he was pitted later and compliment him. After that I've tried when I can to reduce the vehicle mass that my tires have to contend with around the track.
Click to expand...
Here is something I posted on the C8Z forum. 64# of unsprung, rotating mass is significant!
"Got my track tires mounted. Rear = 330/710X19 Yokohama A005 slick on Forgeline GS1R 13"X19. Combined weight = 51.2#
Front = 310/690X19 Yokohama A005 slick on Forgeline GS1R 11.5'X19 Combined weight = 45.6#
Mounted with TPMS installed. The tires were a little lighter than I anticipated. That is a total savings of 62.4# over my OEM aluminum wheels and Cup 2Rs. Also 20# lighter than CF wheels with Cup 2Rs, using pfg1's CF weights posted above. I will install the wheels/tires this weekend and will check clearances and post photos."
C8Z Track Tires 1.jpg
 
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mfain said:
Here is something I posted on the C8Z forum. 64# of unsprung, rotating mass is significant!
"Got my track tires mounted. Rear = 330/710X19 Yokohama A005 slick on Forgeline GS1R 13"X19. Combined weight = 51.2#
Front = 310/690X19 Yokohama A005 slick on Forgeline GS1R 11.5'X19 Combined weight = 45.6#
Mounted with TPMS installed. The tires were a little lighter than I anticipated. That is a total savings of 62.4# over my OEM aluminum wheels and Cup 2Rs. Also 20# lighter than CF wheels with Cup 2Rs, using pfg1's CF weights posted above. I will install the wheels/tires this weekend and will check clearances and post photos."
View attachment 56401
Click to expand...

We're definitely on the same page regarding unsprung weight and rotating mass/MoI. Reducing mass is almost always desirable.
Due to my self imposed restriction on bodywork modifications and consumables spending, I'm limited on tire/wheel sizes I can fit on my car, hence part of the reason for my focus on weight reductions anywhere I can find it. (Years ago I heard the chief engineer of IIRC Aston Martin say "Weight begets weight." Very true. I've found the reverse is also true. Less weight in one area often allows less structural weight in other areas, which then also allows further weight reduction in brakes/springs/etc.) My current track day setup is 15" wheels with 9" slicks (37# combination), with Wilwood rotors and calipers (14# combination). Not a fancy setup by any measure, but noticeably lighter than the stock C3 parts.
 
With over 700lbs of weight reduction, your wonderful big-block C3 weighs as much as a big-block C3 without any engine. It's got to be exhilarating around the track! :-) I enjoy seeing the creative ways you have taken to get there.
 
Been looking at a bunch of brake websites to see if I can find a lighter rear rotor package, but so far nothing is jumping out as noticeably lighter. The 11.5" (stock early C4 size/diameter) non-vented rotors I've looked at either don't weigh much different than the stock C4 vented rotors, or the weights aren't mentioned in the description/specs. I think I'll wait for a "nice" day this winter and wander the local pick-n-pull junkyard with my portable scale to see what I can find for possible candidates.

Aftermarket two-piece rotors aren't an easy option, as I haven't seen any in 11.5" diameter; running an 11.75" rotor would require fabricating a slightly different caliper bracket, and the expenditure of fabrication time and serious dollars for just a handful of pounds just seems an inefficient move.
 
Red77 said:
With over 700lbs of weight reduction, your wonderful big-block C3 weighs as much as a big-block C3 without any engine. It's got to be exhilarating around the track! :) I enjoy seeing the creative ways you have taken to get there.
Click to expand...

Thank you. (y)

The sense of the improvement in acceleration due to the reduced weight seems to vanish rather quickly, as acceleration seems to be the first thing that one gets "used to" in a performance car. I enjoy the improvement in cornering speeds, as I've also been gradually learning more about suspension geometry and have been reducing an initial understeer issue that had accompanied the installation of the C4 suspension. The original C3 suspension had a habit of a snap oversteer in corners on occasion. The C4 rear suspension, on the other hand, is very smooth in a corner, and I've just been trying to "loosen" it up a touch to help the car rotate a touch easier. The one aspect from all this time and effort reducing the car's weight that I continue to be pleased with every track day is the braking ability of the car, compared to how it was years ago.
 
69427 said:
Been looking at a bunch of brake websites to see if I can find a lighter rear rotor package, but so far nothing is jumping out as noticeably lighter. The 11.5" (stock early C4 size/diameter) non-vented rotors I've looked at either don't weigh much different than the stock C4 vented rotors, or the weights aren't mentioned in the description/specs. I think I'll wait for a "nice" day this winter and wander the local pick-n-pull junkyard with my portable scale to see what I can find for possible candidates.

Aftermarket two-piece rotors aren't an easy option, as I haven't seen any in 11.5" diameter; running an 11.75" rotor would require fabricating a slightly different caliper bracket, and the expenditure of fabrication time and serious dollars for just a handful of pounds just seems an inefficient move.
Click to expand...

I have a EBC rotor catalog with rotors listed by size. Searching 292mm rotors with a similar hat offset to C4 Vette (64mm), I get two candidates:

2003 Nissan 350Z- Vented 292mm Dia 62mm Offset 16/14mm max/min thickness

1998 Porsche Boxster- Vented 292mm Dia 67mm offset 20/18mm max/min thickness

Boxster:
1706024730280.png

No weight listed but you might be able to get your hands on them at a local store.
 
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BBShark said:
I have a EBC rotor catalog with rotors listed by size. Searching 292mm rotors with a similar hat offset to C4 Vette (64mm), I get two candidates:

2003 Nissan 350Z- Vented 292mm Dia 62mm Offset 16/14mm max/min thickness

1998 Porsche Boxster- Vented 292mm Dia 67mm offset 20/18mm max/min thickness

Boxster:
View attachment 56461

No weight listed but you might be able to get your hands on them at a local store.
Click to expand...

Thanks, I'll look into these. From the time I've spent looking at different rotor candidates I've pretty much accepted that if I do find a noticeably lighter part I'll end up having to either redrill the bolt circle, hog out the center hole, or cut down the outside diameter.
 
I spent a LOT of time looking at rotors, caliper/pad combos for my IFS and upright design.
You didn't say what weight and szes you were looking at for your IRS.
I did see in my "left overs" (spreadsheet) some Wilwood rotors at just over 7#. Cross drilled and "vaned."
They were 11.75 x 0,81 rotors. The 0.81 were in my cross check for my IFS to get the placement right for the caliper/wheel.
These are 8 x7.0 drill - now you gotta figure out your hat arrangement. (160-5863 part #)

AINT HOT RODDIN' FUN!!??

Cheers - Jim
 
phantomjock said:
I spent a LOT of time looking at rotors, caliper/pad combos for my IFS and upright design.
You didn't say what weight and szes you were looking at for your IRS.
I did see in my "left overs" (spreadsheet) some Wilwood rotors at just over 7#. Cross drilled and "vaned."
They were 11.75 x 0,81 rotors. The 0.81 were in my cross check for my IFS to get the placement right for the caliper/wheel.
These are 8 x7.0 drill - now you gotta figure out your hat arrangement. (160-5863 part #)

AINT HOT RODDIN' FUN!!??

Cheers - Jim
Click to expand...

I currently have stock size early C4 rotors (11.5" by .81"), so I'm focusing on similar diameter rotors for this substitution, and possibly thinner widths or offsets. I don't want to go to 11.75" as these will be heavier, have a higher MoI, require fabrication of new caliper mounts, and slightly alter the f/r brake balance. Plus, the Wilwood rotors require expensive hats, which makes for an unacceptable $/# cost for this minor improvement/change.

Another option I'm researching is possibly taking later C4 rear rotors (12" diameter) and machining the diameter to 11.5", as these smaller offset rotors might be lighter than the early rotors that have the deep parking brake drum type hat. I just need to get some accurate weights of these two rotors shapes.
 
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