Date: 16 Feb 2005 15:09:46 GMT From: Dave Hinz <DaveHinznospamcop.net> Subject: Re: new saab motor for 9-3 series
On Tue, 15 Feb 2005 23:25:20 +0000, Colin Stamp <col.dustbinnospamp.plus.com> wrote: > On 15 Feb 2005 21:08:59 GMT, Dave Hinz <DaveHinznospamcop.net> wrote: > >>Please define "harsher" in engineering (or just real) terms. > > By harsher, I mean more vibration transferred to the engine mounts. Can you cite evidence for this, specifically in regards to Saab's dual balance shaft I4 design that's been in use for a decade or more? > Every time a cylinder fires, the engine gets pushed upwards with the > same force that the piston gets pushed downwards. Also, the engine > gets twisted backwards with the same torque that twists the crank > forwards. Yes. > It's not possible to balance either of those forces out. Counter-rotating balance shafts. > Balance shafts etc. can only compensate for the moving masses of the > pistons, rods and whatever. The forces from combustion change > dramatically from overrun to maximum torque. How much of the vibration is induced by the combustion vs. the reciprocating mass? > The flywheel won't help > either. Well, it has some effect, but there's no differentiation there because (as far as I know) all cars have a flywheel of some sort. > One very effective way of reducing this vibration is to > increase the number of cylinders. The pulses are moved closer together > so they overlap more and their peak value is reduced for a given > average power. Have you driven one of these cars and found vibration to actually be a problem? Theoretical "6 is a bigger number than 4" stuff aside, what are you feeling that apparently others are not? Have you measured the vibration transmitted to the driver in one design vs. another? Have you considered engine mount geometry and dampening characteristics? There's a lot more to this than "6 is bigger than 4". >>> Robustness doesn't come into it. There's some >>> very flimsy engines with thriving aftermarket tuning businesses >>> attached to them. >> >>Yes, and Saab engines aren't among them. One would think that those >>who buy the V6 because it has more pistons, would be _more_ likely >>to demand performance upgrades - and yet, they're still not out there. > > I don't do marketing, but I bet it's lack of demand more than anything > else. V6s are seen as a "luxury" engine as opposed to a "sporty" one. If you say so. For whatever reason, nobody offers performance upgrades for the V6, so if you want power, the V6 is the wrong engine to buy. >>Well, different technologies for different needs. In my part of the >>USA, the side roads where I live won't be bare for about 2 months - >>hard packed snow/ice is the road surface. 2" snowfalls barely make >>mention in the news, let alone a disasterous traffic situation. >> > Yep. We're not set up for snow at-all. It's cheaper to just let it > completely pole-axe us for a couple of days a year. So, kindly don't destroy the design made for bad weather just because you don't get it. I mean, I haven't gone and said "take off the windscreen wipers because it doesn't rain much here", have I? >>If you say so. Me, I see it as a sign of what's do-able or not. >>Saab tuning is enough of a niche market in the first place, after >>all. > > Yep. And the Saab V6 is a niche within that niche. It's niched out of > existence. I thought you said you preferred it? >>Can you quantify "smoothness" as used in this context, please? > > I'm still defining it as the quantity of vibration that gets > transferred into the engine mounts. But, who cares how much gets _into_ the engine mounts? It's what gets _out_ of them that matters. >>Have >>you actually _driven_ a dual balance-shaft Saab I4? Or, even a single >>balance-shaft Saab V4? > > I've got a 9-3 Aero. It's plenty smooth enough for me, but I'm easily > pleased as far as smoothness is concerned. Well then. > My gut feeling is that the > V6 156 did have less vibration on full throttle than the Saab, but on > either car at full throttle, you have plenty to take your mind off any > vibration :o) So, it's a guess based on a preconceived notion, with no actual measurement to back it up. I understand. I think you're worrying about a non-problem.
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