[PorscheDude]

Any thoughts on these modified balance shafts?





http://cgi.ebay.com/ebaymotors/PORSCHE-par...sspagenameZWDVW

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[Torbjorn968]

Endurance racers in Sweden tend to get rid of the balance shafts, some strenghten the oil pickup doing this.



T

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[SpeedRacer64]

I don’t understand how they could take them completely out without the motor shaking apart?



The ones halved I can get my head around knowing they could use mallory to increase weight replacing reciprocating mass. By why...

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[Torbjorn968]

[quote name='SpeedRacer64' post='48546' date='Mar 2 2008, 03:55 AM']I don’t understand how they could take them completely out without the motor shaking apart?



The ones halved I can get my head around knowing they could use mallory to increase weight replacing reciprocating mass. By why...[/quote]



There's quite a few fours out there with no balance shafts. I believe they where installed in the 944/968 engines to give a bit of the smoothness of larger engines.



I have discussed a bit doing this myself with the team using it. Since it is an endurance team there is some credibility to it and the engine responsible worked for one of the biggest Rally stars in Sweden so should be a good chap. As I understand it it is mostly noticable at low rews but once on the track not a big loss. Quite a lot of weight goes out and in dynamic terms the same operation on a Honda Civic Type "R" equates to 6 hp. I believe it is the japanese version of the "R" having no balance shafts.



//T

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[flash]

having driven a car for 3000 miles straight with a balance shaft belt crumbled up in bit in the bottom of the cover, i can attest to the fact that the vibration is not all that bad



lol - it's a LOT worse when it's a tooth off



i have no idea what other complications there are though - playing with harmonics is tricky stuff - high frequency vibrations can tear apart internals - i'd be wary of such shafts as much as i would lightening a crank - yes, both be safely done, but you have to work out the 4th order math

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[Cloud9...68]

Interesting... So I wonder what's the nature of the harmonics that are responsible for the need for a DMF to completely eliminate the driveline vibration. I'm sure the engineers at Porshe spent plenty of time burning the midnight oil on this one, and, despite having to pay royalties to Mitsubishi for the use of counter-rotating balance shafts (the first time Porshce ever paid patent royalties to anybody), couldn't come up with a way to completely eliminate all sources of vibration from the engine. So yes, I could see how altering the nature of the rotating mass could get very tricky.

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[SpeedRacer64]

Interesting...If you move forward with this please post some of your findings....A few years back I owned a Merkur XR4TI. No shafts, it had an interesting shake to it off idle to 2k and I’ve seen a few of these motors with weak motor mounts shaking around a bit...All at idle...with that said...my understand of the dynamics of physics with respect “how” is very limited in the application.



I still have the lingering question as to why...what’s to gain...”less is more” in the parts breaking mentality.



According to this...I still ask how and why..it's Physics http://www.autozine.org/technical_school...mooth2.htm



L

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[Cloud9...68]

Interesting article... Thanks.



However, it only goes as far as to state that the use of twin balance shafts perfectly cancels the 2nd order forces, which may well be true. But, as Flash says, there are higher order order harmonics at play, and it sounds like these are indeed what's resposible for the presence of enough residual vibration to necessitate a DMF to completely smoothe things out.

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[SpeedRacer64]

Back 2o yrs or so you stuck a big cam in an American V-8 and the more it shook around the better...lol



I see you have a Racer X chip installed...did you notice a change...I have one and have yet to install it.

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[Cloud9...68]

[quote name='SpeedRacer64' post='48601' date='Mar 2 2008, 08:16 PM']Back 2o yrs or so you stuck a big cam in an American V-8 and the more it shook around the better...lol



I see you have a Racer X chip installed...did you notice a change...I have one and have yet to install it.[/quote]



My car came with the RacerX chip (it was owned by a guy who sells them), so it's hard for me to tell. However, I had a problem with hesitation at WOT a few years ago, and one of the things I tried was removing the RacerX and installing the stock chip. This had no impact on the hesitation (turned out to be bad plug wires), but I did notice a bit stonger midrange, and maybe slightly better throttle response, with the RacerX.



Good point about the lumpy cams people used to (and probably still do) put in American V8s. I guess we've come to expect a bit more refinement with our performance over the years. Maybe just more evidence of how spoiled we've become, like complaining about $3.20 gas when the rest of the industrialized world is paying 8 bucks...

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[SpeedRacer64]

With respect to the gas...I know right...but damn...it still sucks!

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