Who has a single crank pulley on their 3.6 and have you had any problems as a result?
03-04-2014, 03:45 PM
#16
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No problems here, but it's early days yet. Don't think it helps idle issues when coupled with a lwf but I still need to run an idle sequence on mine and a live remap. Think the most important thing is to balance everything if you can.
03-06-2014, 04:30 AM
#18
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Not sure how you would have significant vibration in a balanced system. Would the damping not be there to offset the effects of the ancillary items such as Ac and power steering?
03-06-2014, 04:35 AM
#19
Burning Brakes
Torsional vibration from the HVAC compressor. If your car doesn't run with HVAC there is no problem....that's a lot of weight saved if replaced by a single crank pulley.
03-06-2014, 10:46 AM
#20
The damper is a tuned mass elastic system designed to protect the crankshaft from torsional vibrations which are a natural function of cylinder firing. Remove the damper if you want, good luck with that. For me the small increase in throttle response does not offset the loss of protection to the crankshaft the damper provides. Porsche designed in the damper on the 3.6 because of design changes to the crankshaft. Of course all FEAD loads have an effect on torsional vibration at the crank nose but without measuring, evaluating and comparing data from an engine with and without the damper removal is not my idea of a safe engine modification. This based on 15+ years of supplying torsional vibration measurement/analysis equipment plus training and technical support to OEM's and race engine builders.
03-06-2014, 10:56 AM
#21
Burning Brakes
I don't think you read my previous post..
I was looking at a lower pulley / harmonic balance as it is often called. Actually it is only the HVAC pulley that is rubber mounted, the inner two pulleys are solid. I imagine the HVAC is rubber mouted to absorb bumps when the HVAC clutch does its thing. For cars running without HVAC there is no need to have anything but a normal single or double pulley wheel.
It is clear the damping has nothing to do with engine firing order as if often stated.
I was looking at a lower pulley / harmonic balance as it is often called. Actually it is only the HVAC pulley that is rubber mounted, the inner two pulleys are solid. I imagine the HVAC is rubber mouted to absorb bumps when the HVAC clutch does its thing. For cars running without HVAC there is no need to have anything but a normal single or double pulley wheel.
It is clear the damping has nothing to do with engine firing order as if often stated.
03-06-2014, 01:51 PM
#22
I don't think you read my previous post..
I was looking at a lower pulley / harmonic balance as it is often called. Actually it is only the HVAC pulley that is rubber mounted, the inner two pulleys are solid. I imagine the HVAC is rubber mouted to absorb bumps when the HVAC clutch does its thing. For cars running without HVAC there is no need to have anything but a normal single or double pulley wheel.
It is clear the damping has nothing to do with engine firing order as if often stated.
I was looking at a lower pulley / harmonic balance as it is often called. Actually it is only the HVAC pulley that is rubber mounted, the inner two pulleys are solid. I imagine the HVAC is rubber mouted to absorb bumps when the HVAC clutch does its thing. For cars running without HVAC there is no need to have anything but a normal single or double pulley wheel.
It is clear the damping has nothing to do with engine firing order as if often stated.
03-06-2014, 05:55 PM
#23
I don't think you read my previous post..
I was looking at a lower pulley / harmonic balance as it is often called. Actually it is only the HVAC pulley that is rubber mounted, the inner two pulleys are solid. I imagine the HVAC is rubber mouted to absorb bumps when the HVAC clutch does its thing. For cars running without HVAC there is no need to have anything but a normal single or double pulley wheel.
It is clear the damping has nothing to do with engine firing order as if often stated.
I was looking at a lower pulley / harmonic balance as it is often called. Actually it is only the HVAC pulley that is rubber mounted, the inner two pulleys are solid. I imagine the HVAC is rubber mouted to absorb bumps when the HVAC clutch does its thing. For cars running without HVAC there is no need to have anything but a normal single or double pulley wheel.
It is clear the damping has nothing to do with engine firing order as if often stated.
03-06-2014, 06:59 PM
#24
You are right, the outer pulley is rubber mounted but as you can see, it is a very heavy balanced mass that is part of a mass elastic damper system. Yes, the pulley does drive the A/C compressor but it is a mass elastic damper that is designed to protect the crankshaft from torsional vibration. If the only purpose was to "isolate" compressor cycling there would be no reason for the pulley to have this much mass, instead I would expect it to be a very light weight metal pulley with an elastomeric mounting to the hub.
While I have not measured the torsional vibration on the nose of my crankshaft, I would expect the peak amplitude to be quite high if the crankshaft damper was removed. With the damper installed there will be 2 peaks there are much lower in amplitude, these two peaks will be separated at the dampers tuned frequency.
Based on my experience I must say that the damper is engineered to protect the crank and I wouldn't remove it. Of course you can do whatever you want.
While I have not measured the torsional vibration on the nose of my crankshaft, I would expect the peak amplitude to be quite high if the crankshaft damper was removed. With the damper installed there will be 2 peaks there are much lower in amplitude, these two peaks will be separated at the dampers tuned frequency.
Based on my experience I must say that the damper is engineered to protect the crank and I wouldn't remove it. Of course you can do whatever you want.
03-07-2014, 06:00 AM
#29
Burning Brakes
http://forums.pelicanparts.com/911-e...-question.html
The last post in the link above is very informative when talking about the strength of the 964 crank. Dare I say Porsche made a mistake on the 964 crank pulley, introducing a rubber insert only on the HVAC pulley then having to balance that one very same pulley. Imagine the cost of doing this as opposed to what is found on the 993!
As I have said, for cars that run without HVAC changing to a single bottom pulley is no problem at all. I do wonder how many of these 20+ year old balanced pulley's are actually still balanced....
The last post in the link above is very informative when talking about the strength of the 964 crank. Dare I say Porsche made a mistake on the 964 crank pulley, introducing a rubber insert only on the HVAC pulley then having to balance that one very same pulley. Imagine the cost of doing this as opposed to what is found on the 993!
As I have said, for cars that run without HVAC changing to a single bottom pulley is no problem at all. I do wonder how many of these 20+ year old balanced pulley's are actually still balanced....
03-07-2014, 12:11 PM
#30
Technical Guru
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or it was done that way on purpose? If it was only required for cars with AC then Porsche would have only used it on those cars? They went out of there way to produce other (seemingly useless) parts for 964s without AC. And as mentioned above, even the cup cars had them.
It was interesting to seeing all the 997GT3 owners experiencing similar problems (4th order harmonics) when switching to a LWF!
Originally Posted by Vandit
So what's the difference between the 993 crank and the 964 crank that makes the 993 safe to run w/o a harmonic balancer?
The bending and torsional stiffness of the eight-bearing crankshaft was increased by increasing the crank web diameter from 7.9 mm to 9.4 mm. In conjunction with the reduction of the oscillating masses, this allowed the torsional vibration dampers on the crankshaft to be omitted.
The weight of crankshaft as an individual component increased from 14.4 kg to 15.4 kg, yet the total weight of the complete crankshaft assembly was reduced by 0.818kg."
