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Old 03-30-2003, 20:51   #1 (permalink)
EL XR6 - w00t
 
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Question Are 6 cyclinders balanced?

Hi,

I was talking to someone the other day and they said most 6 cyclinders (I6 and V6) shimmy when they idle because they are unbalanced (unlike 4's and V8s). What does this mean? Is it true?

Is it also true, the bigger the Cam, the rougher a car idles? E.g Compare XR6 to normal falcons with the larger XR cam.

Cheers!
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Old 03-30-2003, 20:56   #2 (permalink)
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Inline 6 = YES, V6 = No (not without help)

An Inline 6 will have better balance than a 4cyl or V8, so your friend has it wrong.

Read the links on engine smoothness here (towards the bottom of page) http://www.ukcar.com/sframe.htm?/fea...ech/engine.htm

Inline 6, V12 and all boxer engines are inherently balanced. Just about everything else isn't. V8's can achieve good balance with counterweighted cranks due to them being 2x4cyl engines mated at 90degrees, most other engine configurations resort to balance shafts etc or are just plain buzzy!

It also explains why Hi-Po V8's such as Ferrari sound different to mainstream V8's (flat-plane vs cross-plan crank configurations).

Lumpy cams have higher lobe overlap (inlet & exhaust) which causes vacuum to fluctuate at low revs causing the rough idling.
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Old 03-31-2003, 03:25   #3 (permalink)
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I wouldn't worry too much about that. It's more in the engineering in the first place. Like a Nissan or Toyota V6 against a Commadore V6 etc.Ford had V6's back in the late 60's they where CRAPP, over heating, gudgeon pin knock, bearing problems, oil shaft drive breaking, pistons shrinking etc...Hmm sounds like a Gen lll??? Funny though a Commadore V6 is over square [big bore/ short[ish] stroke] but still can't stay together with high-ish rpm, they are externally ballanced also...Meaning they have out of ballance flywheel / h.ballancers to counteract inballance inside engine.. Much like the Windors some are 27ounce once some 50ounce..
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Old 04-03-2003, 22:06   #4 (permalink)
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Inline 6's are the most natuarally balenced engines in the world, with the only one that comes near being the inline 12. So actually, it's the opposite of whatever your friend said.
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Old 04-03-2003, 22:29   #5 (permalink)
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V6's are not very well balanced(from memory due to the rythmic pattern of only having 3 cylinders on each side), i4's are pretty bad because they don't have a lot of cylinders and i6's are much more balanced then any of those.

V8's however are extremely well balanced due to the large amount of pistons and the way it's set up. Rotary's are the BEST when it comes to engine balance because they have rotors that turn more then they go up and down like conventional piston motors.

So basically V6's and i4's are on par with smoothness, i6's are smoother, V8's smoother even still and Rotarys the most balanced of the lot.

Cheers
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Old 04-03-2003, 22:34   #6 (permalink)
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So.. I6's are inheritantly balanced. If an engine is more unbalanced, does it cause a greater vibration through the car or are other factors at play here?
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Old 04-04-2003, 01:12   #7 (permalink)
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Quote:
Originally posted by donuts2001
.....V8's however are extremely well balanced due to the large amount of pistons and the way it's set up ....... V8's smoother even still ....
Ahem

Rotaries, I6, V12 & Boxer engines first, then the rest.
Enough of this V8's do everything better crap.

Quote:
Originally posted by dcliff1
...does it cause a greater vibration through the car or are other factors at play here?
Yes it does but other factors are;
  • clutch &/or flywheel
  • engine ancillaries
  • transmission
  • driveshaft
  • universal joints or CV's
  • axles
  • wheel bearings
  • brakes
  • wheels
  • tyres

and whatever else goes round-&-round or up-&-down.
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Old 04-04-2003, 04:25   #8 (permalink)
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Geeez if thats the case why is the Old Ford OHC motor so harsh for. lol
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Old 04-04-2003, 05:50   #9 (permalink)
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Quote:
Originally posted by svoghia
Geeez if thats the case why is the Old Ford OHC motor so harsh for. lol
Because it has a bloody long stroke and piston speed gets high at any reasonable revs. But hey they hang in there.See how much Ford has changed the bottom end of these engines..e/a to a/u.Using different counterweights.Again it's the original engineering in the first place.The lighter and stronger??reciprocating parts are the better.Latter model 6's have smaller lighter valve stems to keep weight down, so more revable..

If any one saw the program on Discovery a couple of weeks ago called "sercrets of formula one". Shows how light the cranks etc are in a B.M.W motor compared to F1.The F1 crank looks like a coat hanger compared, pistons?? Well there hardly is any, realy.

Also the more cylinders the smoother it "should" be for the combustion/ compression happens more often like on six its three times per rev @120* on eight its 4 times @ 90*..Slightly over square gives a smother revable engine though will lack some torque because of it. Think along the lines of single 500cc bike motor [trial bike] bloody hard to kick start but a 500cc 4 with lots of little compressions is easier to kick start ....Thats where the harshness comes in like comparing a BMW mill to Falcon mill.
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Tuned & maintained by "Peppertree Perfmormance". Dart block, Scat 4340 steel crank, Custom C.P pistons.Oliver rods.. Mal Wood twin plate clutch.. Twin SC61/2's,482 rwkw/ 645 rwhp..
Passengers, myocardial infarction material..
R.I.P Possum...
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