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The graphite impregnated ones won't squeak more than likely. I have had the prothane ones on the front end of my truck for 15k and they squeak a little. Really only over speed bumps and when it's cold. The vette has the stock rubber. Either one will be fine.
i'm in the process of rebuilding the front suspension on my 85. about a month ago, I sent an email to suspensions.com and posed the question of prothane vs energy. here's their brief reply --
Good Morning,
Prothane and Energy are close to being just about the same,
both are american made out in California, and both (if purchased through our site) comes with a life time warranty.
the main difference would be that energy has a different formula when it comes to poly, which they call the hyperflex poly, its got a little more give than the Prothane.
to put it in a numbers way, Energy's durometer is closer to 75, Prothane's are closer to 80, meaning Prothane's bushing are harder.
you'll get a little bit more road feel from Prothanes bushings, but thats with any Poly bushing to tell truth.
really its gonna come down to preference, most customer go with energy cause they are a better known name,
but Prothane is a cheaper option some times.
hope this helps, get back to me if you have some more questions ill be happy to help as much as i can.
here's an answered question from energy's site that references graphite --
Question: What is the difference between the Energy Suspension® red and black polyurethane components?
Answer: Both are Energy's HYPER-FLEX™ performance polyurethane formulations. Few of our selected black polyurethane components contain graphite to add a lubrication property. It is not added to the red because black graphite discolors the red polyurethane. Graphite does not compromise our polyurethane formulas.
note that it says "few of our selected...". the way I read it, graphite is not across the board with all black bushings. I have also read on various sites that when properly lubricated at installation, the squeaking issue is pretty much eliminated. one final thing, I did notice that prothane bushing have longitudinal grooves cut into the inner surface of the bushing - most likely to aid in the lubrication. note the inner grooves on the prothane (left bushing)
FWIW, I have used various prothane and energy's, black and red kits in the past, and to be honest, my selections were pretty much based on pricing. as far as the hardness thing, I doubt you'll be able to tell the difference under normal conditions. holding a sample of both, the energy's bushing has a little more give with a fundamental squeeze test. with my installations, l lubed the hell out of my bushing using dow-corning #11 silicone, and to date have not experienced a squeaking issue.
hope this helps....
edit: BTW, if purchasing a C4 suspension rebuild kit, there is about a $70 (US) price difference between prothane and energy, with prothane being the lesser of the two.
Thank You Joe.
I am proceeding with prothane.
Can you confirm the dow corning as '11' or as '111'?
I searched amazon and did find 111 as a silicon oring lubricant.
As always Joe, thanks for your help!
Looking forward to some great music with a couple eggnog and rums tinkering on my car over the festive season.
my jar(s) of D-C #11 are from the late 70's. they've been superseded by something else, but I have no idea what - ??? since this stuff doesn't go bad, I've got enough to last me my lifetime - D-C #111 is probably the current replacement, since my #11 was originally used as an O-ring lubricant. I would use the silicone supplied with the bushings, but I tend to over lube the stuff and wipe off the excess, so IMO, bulk jars is the only way to go. is D-C #11 the same or similar to the supplied silicone, I have no idea, but #11's been working for me for years. besides, it's what I have on hand.
VT3 -- here's a cut and paste from dow-corning's website on #111
Molykote® 111 Compound
Choose the greaselike Molykote® 111 Compound for low-volatility. lubrication of a range of components in your vehicles’ brakes and chassis. This includes components in brake boosters and actuators, including diaphragms, seals, control pistons and reaction discs.
This product can also be used for Powertrain applications.
Qualities
* Service temperature range of -40°C to +200°C * Low volatility
* Compatible with many plastics and elastomers. Water resistance
Hi
I have prothane bushes in my 85, I have regretted it though.
I have found the ride a lot harder than the std rubber bushes, I had used a lot of lube so no squeaks has been a year since the install.
I find the ride around 30% stiffer than before, has got slightly better a year later.
I find the ride very bouncy, mainly due to the resistance of all those bushes from twisting with suspension movement. I lowered the tire pressure to 30 psi to help with the ride.....
I am now going to go to Banski trailing arms with heim joints, that will allow unrestricted suspension movement. Just a bit expensive ... the Banski camber rods have worked well.
Nice easy rear camber adjustment.
Hi
I have prothane bushes in my 85, I have regretted it though.
I have found the ride a lot harder than the std rubber bushes, I had used a lot of lube so no squeaks has been a year since the install.
I find the ride around 30% stiffer than before, has got slightly better a year later.
I find the ride very bouncy, mainly due to the resistance of all those bushes from twisting with suspension movement. I lowered the tire pressure to 30 psi to help with the ride.....
I am now going to go to Banski trailing arms with heim joints, that will allow unrestricted suspension movement. Just a bit expensive ... the Banski camber rods have worked well.
Nice easy rear camber adjustment.
That's my experience...
I understand what you're saying. problem is, OE rubber bushings are not readily available, so poly is pretty much the only solution. I had poly in my old 69 corvette, and really can't recall any difference in ride quality. those old C3's had fairly mushy suspension to begin with anyway. personally, I like a firm ride, so hopefully, it's something I can live with. thanks for the feedback on the tire pressure. i'll have to keep that in mind.
i did find plenty of other discussions about poly bushings but no true reviews after a couple years of service. Its remarkable to me that there isnt a better solution, even if it was a softer (lower shore) polyurethane set. Seems like there should be "stiff and precise handling" and thwn a "softer for touring" package.
From what i gather the oem rubber was the "touring" version and the poly versions are stiff direct and precise.
I am OK going for the harder direct versions. Im expecting it to be super jolty. But also im expecting as new handling when i do the new struts and new alighnment at the same time.
i will likely rip into the steering colum to correct an ever so slight amount of column play.
12-07-2017, 08:27 PM
prothane vs energy suspension bushings hardness
D-C #111 is probably the current replacement, since my #11 was originally used as an O-ring lubricant. I would use the silicone supplied with the bushings, but I tend to over lube the stuff and wipe off the excess, so IMO, bulk jars is the only way to go. is D-C #11 the same or similar to the supplied silicone, I have no idea, but #11's been working for me for years. besides, it's what I have on hand. 
