Anchor Motor Mounts $18 each
#226
How much are the shocks?
#227
Nordschleife Master
Originally Posted by SharkSkin
A shock will not manage sustained torque
Shocks are like a low pass filter, slow events go right through, but very fast events hit a brick wall (shock acts "solid"). Except for some kind of rubber "mounting" I would expect a shock to pass the force of engine vibration right through to the chassis.
#228
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According to Porsche the forces involved are about 3 Gs ... page 844 of Porsche Excellence was Expected... " To assure that the least transmission of noise and vibration from this power train to the body, it was essential to position the two pairs of mounts at the nodal points of the complete assembly, those point which remain at rest when the whole system resonates......... small hydraulic shock absorber was added ,in a sea-legged position. These shocks helped the engine transaxle mass serve as a damper for the movements of the body. ..."Freeway" hop subsequent analysis showed that wheelbase length was a crucial factor in the excitation of this unpleasant ride motionand that the hydraulic dampers served to suppress it in the 928" ..... And so it goes the more I think I know the less I know I know ... Porsche designed the engine suspension using the mass of the driveline to damper movements of the BODY ! Improving on Porsche engineering .....Yea right !
#229
928 Collector
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Yes Jim, long before Porsche made the 928 or 924, there were issues with American roads where the freeway sections are of such lengths that a car with 50/50 weight distribution (like the Corvette) was having major freeway hop issues. It was decided (by porsche) that the length of the wheelbase had to be reconsidered because of this. And this was a major deciding factor for them. The 924 was I believe the first recipient of porsche's attention in this regard. From http://www.pavement.com/Concrete_Pav...ign/index.asp:
"....... In the late 1950's, manufacturers of automobiles started receiving complaints of a peculiar phenomenon called "Freeway Hop" that was unique to concrete pavements on the California freeway systems. A study found that, with the suspension systems of certain models of large cars (a 1959 Buick was representative), a harmonic wave of objectionable vertical motion was induced by the interaction of small but repetitive road irregularities and tire-wheel imperfections; the cars were resonant to the repetitive 15-ft. joint spacings. Engineers suggested an irregular join-spacing sequence.
As a result, randomized joints became the standard practice for major roadways in California. Sequences of 13, 19, 18, 12 ft. were used through the 1960's and 1970's. In the same time period, a dozen western states adopted a similar practice for their undoweled pavement designs, and four states extended the use to doweled pavements. Skewed joints accompanied the use of randomized joints. Experience in several states showed that the 18- and 19-ft. panels were too long - they sometimes developed intermediate cracks - so the spacings were changed. For example, California has used 12-, 15-, 13-, 14-ft. sequences in the last ten years or so.
A 1987 FHWA survey reported that about 15 states employ the randomized joint feature. These include seven states that use it in undoweled pavements, three states that use it in plain, doweled pavements, and five states that use it in both undoweled and doweled pavements. Joint spacings and sequences vary from state to state; most have shortened their longest panels......"
"....... In the late 1950's, manufacturers of automobiles started receiving complaints of a peculiar phenomenon called "Freeway Hop" that was unique to concrete pavements on the California freeway systems. A study found that, with the suspension systems of certain models of large cars (a 1959 Buick was representative), a harmonic wave of objectionable vertical motion was induced by the interaction of small but repetitive road irregularities and tire-wheel imperfections; the cars were resonant to the repetitive 15-ft. joint spacings. Engineers suggested an irregular join-spacing sequence.
As a result, randomized joints became the standard practice for major roadways in California. Sequences of 13, 19, 18, 12 ft. were used through the 1960's and 1970's. In the same time period, a dozen western states adopted a similar practice for their undoweled pavement designs, and four states extended the use to doweled pavements. Skewed joints accompanied the use of randomized joints. Experience in several states showed that the 18- and 19-ft. panels were too long - they sometimes developed intermediate cracks - so the spacings were changed. For example, California has used 12-, 15-, 13-, 14-ft. sequences in the last ten years or so.
A 1987 FHWA survey reported that about 15 states employ the randomized joint feature. These include seven states that use it in undoweled pavements, three states that use it in plain, doweled pavements, and five states that use it in both undoweled and doweled pavements. Joint spacings and sequences vary from state to state; most have shortened their longest panels......"
#231
Rennlist Member
Originally Posted by heinrich
Just for my own clarification: There are solid and liquid-filled mounts for ALL years, right?
#233
Rennlist Member
Originally Posted by danglerb
Right, they are for the abrupt torque changes, engaging the clutch, shifting the automatic, the twitch from a throttle blip, that sort of thing.
Shocks are like a low pass filter, slow events go right through, but very fast events hit a brick wall (shock acts "solid"). Except for some kind of rubber "mounting" I would expect a shock to pass the force of engine vibration right through to the chassis.
Shocks are like a low pass filter, slow events go right through, but very fast events hit a brick wall (shock acts "solid"). Except for some kind of rubber "mounting" I would expect a shock to pass the force of engine vibration right through to the chassis.
Brick
Damping
#234
Originally Posted by SharkSkin
Nope -- solid only for the early cars, unless you want to swap crossmembers like Brendan did.
#235
Nordschleife Master
Originally Posted by SharkSkin
Then you don't seem to understand shock absorbers very well. The resistance will increase with speed, but they never "act solid"
Shocks only behave like true dampers at frequencies low enough for some movement to occur. The energy absorbed is the force times the travel.
Sorry if I failed to explain it well enough the first time.
#236
Rennlist Member
Originally Posted by BrendanC
I guess you can drive holes at the right places on the old version K-Member, but it need to be done exactly, and there may be a sledge hammer involved.
#237
Rennlist Member
Originally Posted by danglerb
Engine shocks reduce movement, solid MM have less movement than hydrolic. What gives the glassy feel is allowing some movement, adding shocks would just further reduce the movement of the engine relative to the chassis transmitting more vibration.
The fluid mounts emulate the damping that was originally provided by the shocks. Using suspension as the analogy, these features are the shock absorbers. The rubber in the mounts(early or late) is anaogous to the spring in the suspension. The rubber can wobble and bounce back and forth if there is nothing to damp the motion, just like a car with toasted shocks will bounce and oscillate.
#238
Nordschleife Master
Looking at the cut up MM it isn't clear to me that the hydraulic has any special damping quality at all, just that it might be a bit more wiggly than a solid, more compliant. When force is applied down on the top of a hydraulic MM the sides are going to flex more than a solid, providing more isolation, but I don't see a damping mechanism.
Porsche I am sure designed the motor shocks to match the vibration they wanted to control. My point was that motor shocks might be more suited to a MM that allowed more movement instead of the solid.
Foo, misspelled Hydraulic all day.
Porsche I am sure designed the motor shocks to match the vibration they wanted to control. My point was that motor shocks might be more suited to a MM that allowed more movement instead of the solid.
Foo, misspelled Hydraulic all day.
#239
Originally Posted by SharkSkin
Isn't there a slightly different shape to the crossmember too? I guess that's what you mean by sledgehammer. Oh, and you need the brackets that attach between the block and the mount, if you don't happen to have them already from wherever you found the x-member.