Weight reduction: Running out of ideas.

Is it the vibration of the box itself that is producing the sound? Maybe some dead soft aluminum strips on the outside "diaphragm" might help

I was working on a project recently where we had to attenuate sound produced by flow through a jet engine component. I was able to identify a large peak frequency with a cell phone app. It's called FrequnSee.
 
You could search something called boom tubes by Dr Gas.
 
You could search something called boom tubes by Dr Gas.

It used to be called spin tech, but it looks like he calls it spin pro muffler. Might work well in you design. He published his theory on how why it works.
 
Ok, so I just read through the whole thread. Good read! Your level of dedication is impressive.
My only 'helpful' comment is have you thought of going with a tubular frame? I've heard good things about SRIII's and supposedly they're a lot lighter. They can also be set up to take C4 and C5 suspensions. Since you already have the C4 suspension, that gets you a ahead a bit. Something like that might open you up to a lighter C4 diff, as well. Admittedly, you might be too far invested in your current frame to switch, however.
 
69427 said:
rtj said:
Did you install an alum block bb? I thought you posted photos of one.
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Yeah, did that a few years ago. So far it's held together, although I do tend to keep the RPM within reasonable limits to ensure some longevity.
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I've been a long time interested viewer of your weight reduction posts. Wonder why you keep rpms down with the aluminum block. I have a Keith Black BB aluminum block in my project 70. I believe it's designed to tolerate large boost supercharge pressures. I don't think it's an optimally light weight BB.

It's just a matter of dollars..if you have an aluminum BB and aluminum heads, you can buy titanium rods and intake valves. Last time I looked, I think the titanium rods were about $700 to $800 each.

If you (or me) were one of those Silicon Valley stock option holders cashing out in the 100's of millions, we could have the C3 body and chassis duplicated in carbon fiber and magnesium. Dream on.
 
BBShark said:
Is it the vibration of the box itself that is producing the sound? Yep. Maybe some dead soft aluminum strips on the outside "diaphragm" might help.

I was working on a project recently where we had to attenuate sound produced by flow through a jet engine component. I was able to identify a large peak frequency with a cell phone app. It's called FrequnSee.
Click to expand...

Larry, I'm not bright enough to completely follow that. Would I be welding in some annealed strips, or something?

ps: The cell phone app sounds neat. Unfortunately I'm still too cheap to get a smart phone. ;)
 
greg75vette said:
Ok, so I just read through the whole thread. Good read! Your level of dedication is impressive.
My only 'helpful' comment is have you thought of going with a tubular frame? I've heard good things about SRIII's and supposedly they're a lot lighter. They can also be set up to take C4 and C5 suspensions. Since you already have the C4 suspension, that gets you a ahead a bit. Something like that might open you up to a lighter C4 diff, as well. Admittedly, you might be too far invested in your current frame to switch, however.
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I've asked several guys with the SRIII frames and one guy with one of those 4" tubular Grand Sport replica frames about the weight of those things, and nobody has been able to tell me anything. And to be honest, I think I could weld up an aluminum frame cheaper than what the steel aftermarket frame guys are asking for their stuff. I priced out some aluminum tubing a while back, and I think I could get sufficient material for a complete frame for about $2k. Not cheap, but I would love to build one as an interesting engineering project/exercise.
 
Working on a couple items (rear exhaust Y-pipe and batwing replacement) to try to pull a couple more pounds off the car. Here's the current setup (steel tubing Y-pipe and C3 batwing).

IM002296_zps94f63d2b.jpg

I pulled the Y-pipe off to weigh it and make a replacement piece in aluminum tubing. Here's the current piece and the partially tack-welded replacement (I can't weld the two end pieces on until I finish the other welds and grind/smooth the internal weld surfaces first). The welding is going damn slow as it's difficult to weld much of a bead length each time on this thin stuff without burning through the walls.

IM002461_zpsb7bdffa3.jpg

The new piece is slightly different shape as I cut and shortened the inlet tubes at the mufflers so I could replace that length with extra lengths of aluminum tubing. Should be about a five pound reduction in weight.

Also working on trying to replace the C3 batwing with a C4 D36 piece. The C4 part is 7# lighter than the C3 piece.

IM002463_zps4273e03c.jpg

The 3/4" adapter plate/ring will add back a couple pounds (after significant final shape trimming), but I should be able to nullify that by being able to eliminate/replace the current adapter brackets for the (C6) toe arms and the rear spring, and also possibly being able to use shorter spring hanger bolts due to the higher spring perch on the C4 cover. So far it looks like I can drill the C4 cover to match six of the C3 cover bolt locations (the same number as I'm currently using with the C3 batwing). The other two bolt locations are going to be harder to accomplish at the moment.
The hardest part of this change will be narrowing/welding the batwing width to match the current narrowed batwing, and also probably needing to revise/replace the batwing frame-tabs to accommodate the slightly different location of the outer mount bushings.
I should be able to get about ten more pounds off the car with these mods, although I do wish that ten pound reduction was from a location up front and higher, but I'll have to take it where I can get it.
I'm still trying to work out the design for an aluminum replacement of the front suspension crossmember to take 5-10 pounds off the front sometime.
 
Thats a nice couple'a lbs!
Any worries with cracking from heat cycling?

Has someone mentioned aluminum wiper linkage? not much weight to lose, but could be easy to fab
 
Wiper door?? alumium but could be made from plastic with a bit creative work......that grate/vent in front of the door?? same thing, bolt on plastic....

as for the operational stuff.....not saving any weight either way IF it retains being functional.....all that stuff is aluminum....:crutches:
 
vette427sbc said:
Thats a nice couple'a lbs!
Any worries with cracking from heat cycling? Don't know yet. The pipes are pretty far downstream and subject to a lot of wind cooling so I'm hoping they don't experience a lot of thermal growth during use. I'll find out regardless, I suppose. In the mean time I've learned to keep the old stuff in the trailer and take it along with me to the track days so I can swap out any new parts that fail.

Has someone mentioned aluminum wiper linkage? not much weight to lose, but could be easy to fab
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I've taken a couple quick glances at the linkage but haven't got much further than that. You're right that it's not much weight, but it is above the c/g of the vehicle, which makes that weight removal inviting. So far it seems like 90% of the weight I've been moving off this car has been under the c/g.
 
I was going through a bunch of files from my tear-down and body off. Came across this pic of the sound insulation in the back of my 78. Don't know if you've any joy like this in your 69 - but that's a good chunk of "fat," if you can.

12695485a18704d07.jpg

Cheers - Jim
 
Bad Bird said:
How wide a rear tire can you run with the C4 rear suspension and stock '69 bodywork?

Cheers,
Matt
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Presently I'm running some C5Z wheels (10.5" width) with 285/18 tires on the rear. I could have fit some 295/18 tires there, but the incremental price difference was too damn high for just 10 mm of additional tread.

I have some 315/16 tires on my C4 that I've been meaning to try on the 69 when I get a free moment from other more "important" projects.
 
phantomjock said:
I was going through a bunch of files from my tear-down and body off. Came across this pic of the sound insulation in the back of my 78. Don't know if you've any joy like this in your 69 - but that's a good chunk of "fat," if you can.

12695485a18704d07.jpg

Cheers - Jim
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Damn, it's hard to turn down a weight number like that, but until I can figure out how to get the exhaust termination box vibrations toned down a bit more I can't afford to get rid of any sound insulation quite yet.
I would like to find some high temp insulation sheeting that I could just stick to the top surface of the box.
 
69427 said:
Bad Bird said:
How wide a rear tire can you run with the C4 rear suspension and stock '69 bodywork?

Cheers,
Matt
Click to expand...

Presently I'm running some C5Z wheels (10.5" width) with 285/18 tires on the rear. I could have fit some 295/18 tires there, but the incremental price difference was too damn high for just 10 mm of additional tread.

I have some 315/16 tires on my C4 that I've been meaning to try on the 69 when I get a free moment from other more "important" projects.
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Wow, I'm surprised. That's quite wide considering. Did you notch the frame at all the gain that tire width, or does the C4 knuckle and links give you more room?

Regards,
Matt
 
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