Ruuning Without a Balance Belt...
- Thread starter 944 man
- Start date
I remember when my car (2.5 Lux) ran with the balancer shafts a tad out of kilter and it was horrible - lots of vibration and it felt like (I know it wasn't ... ) one of my old minis running with the dizzy swung too far retarded. Unless, of course, I've misunderstood the question ... but, I thought all/most modern 4-cylinder engines in excess of 2.2 litres were intrinsically/dynamically unbalanced ... hence Mr Mitsibushi et al's clever inventions?
Rob
Rob
I researched it heavily. A summary is as you say circa 5bhp to be freed up, but the downside is that the worst of the vibration supposedly occurs aroun 3,500 rpm and it is masked by the engine mounts so you don't realise how badly the engine is shaking itself. Clearly for a car spending much time on the road that sounds like a bad thing for the engine itself and the mounts. For a track car where the revs will always be significantly higher I believe it's a good mod.
Caveat above as it's all received wisdom; I ran my balance shaft after the research so can't speak from experience.
edited for typos because I'm sloppy
Caveat above as it's all received wisdom; I ran my balance shaft after the research so can't speak from experience.
edited for typos because I'm sloppy
944 man
Active member
I will add, that Ive driven a car where the balance belt had snapped and the owner had been lucky in that the cambelt hadnt snapped too. It was rougher at tick over to low revs and progressively less noticable as the revs rose. That limited experience is very different to living with it day to day of course. Its not nearly as bad as a misadjusted balance shaft, but it may seem it after a whole days driving on the road.....
There are other downsides; the vastly accelerated wear of the engine mounts which are taking up all the vibration so you don't feel it, plus the likelihood of cracking something in the exhaust, be that downpipe or manifold.
Of course on a track car that is all less relevant as well as less likely due to the normal operating range of the engine speed.
Of course on a track car that is all less relevant as well as less likely due to the normal operating range of the engine speed.
944 man
Active member
It is a track car, but I need to retain day to day reliability. Engine mounts are an Achilles heel on all cars (although later type mounts are more hardy), so Im always expecting the offside one to fail. The oil pickup pipe failure would be a much larger worry though and it wasnt something that I was aware of.
I shied away basically on the strength of driving the car to/from the track, though in the end it was much more road usable than I had expected and got a lot more road miles than planned. I lived quite a long way from every track as well so it may have been a bigger issue for me than you.
The oil pickup develops a crack where the pipe meets the base, sometimes starting as hairline and growing, sometimes just a big catastrophic failure.
The oil pickup develops a crack where the pipe meets the base, sometimes starting as hairline and growing, sometimes just a big catastrophic failure.
jr2015
New member
I agree with all the above, and would say it would not be worth the supposed gains at the expense of reliability/ expensive damage. Incidentaly , it was Dr Fred Lanchester who devised the contra- rotating balance shaft in the 1920`s later taken up by Mitsubishi. Another example of British technology exploited outside Britain.
If you want to go faster with reliability, why not remove weight? It should be possible to get the same ammount of increase in performance without sacrificing reliability.
jr
If you want to go faster with reliability, why not remove weight? It should be possible to get the same ammount of increase in performance without sacrificing reliability.
jr
pauljmcnulty
Active member
And Porsche had to pay a royalty for every engine using it apparently. [8|]
944 man
Active member
He also invented the disc brake!
Without acid dipping it, the car is already about as light as it can go. Its a non-sunroof car: polycarbonate windows and hatch; rear wiper removed (obviously); window regulators & motors removed and metal removed from the doors; all carpets and sound deadening removed; 5.5kg composite seats replacing the originals (one only fitted atm); rear seats removed; electric hatch release removed; all of the tyres have been treated and the spare wheel and tools have been removed (but Im running with the spare again as the back was sat up like a dragster!). Further to this the car has lightweight GRP front panels, a lighter exhaust and Im just about to drill out the rear compressed fibre bumper..... I intend to replace the rising lights with fixed GTS-type parts in the near future, as soon as I can successfully form a pair of covers (this is one of the few instances where Perspex is better than polycarbonate, which is hygroscopic. No matter how carefully I think Ive dried the bast*rd stuff, it keeps coming out of the oven full of bubbles!). The only other things I can think of are a lighter 35ah battery (planned); 8" & 9" Fuchs (far too expensive now) and removing the rear speakers. Im reluctant to do this because my iPod wont turn up loud enough to drown out the ringing in my ears, that Im suffering from driving such a noisy car.....
It has been suggested that I could lose 20 kilogrammes myself too, but thats not quite as easy.
Without acid dipping it, the car is already about as light as it can go. Its a non-sunroof car: polycarbonate windows and hatch; rear wiper removed (obviously); window regulators & motors removed and metal removed from the doors; all carpets and sound deadening removed; 5.5kg composite seats replacing the originals (one only fitted atm); rear seats removed; electric hatch release removed; all of the tyres have been treated and the spare wheel and tools have been removed (but Im running with the spare again as the back was sat up like a dragster!). Further to this the car has lightweight GRP front panels, a lighter exhaust and Im just about to drill out the rear compressed fibre bumper..... I intend to replace the rising lights with fixed GTS-type parts in the near future, as soon as I can successfully form a pair of covers (this is one of the few instances where Perspex is better than polycarbonate, which is hygroscopic. No matter how carefully I think Ive dried the bast*rd stuff, it keeps coming out of the oven full of bubbles!). The only other things I can think of are a lighter 35ah battery (planned); 8" & 9" Fuchs (far too expensive now) and removing the rear speakers. Im reluctant to do this because my iPod wont turn up loud enough to drown out the ringing in my ears, that Im suffering from driving such a noisy car.....
It has been suggested that I could lose 20 kilogrammes myself too, but thats not quite as easy.
944 man
Active member
Porsche more than broke even with the Tiptronic royalties, I believe.
Lanchester invented the balance shaft, but Mitsubishi patented a unique and original variation. I believe that Porsche developed their own version (which would have been royalty free, if not patentable itself), but the two bearing Mitsubishi version perfromed better...
pauljmcnulty
Active member
I'd enter it for the National concourse.....[8|]
sawood12
New member
Not in time to prevent the untimely death of James Dean apparently, who cancelled his order for a Lotus that was the first car to have disc brakes because it was taking too long and got the drum braked Porsche in which he ultimately crashed. I don't think balance shafts would have helped him though.
The balance shafts are not there just to reduce vibration for comfort reasons, but also to reduce the stresses and loads on the rotating masses of the bottom end. Running any machine in an out-of-balance state is not a good idea and certainly not worth a measly 5hp and a few KG. You will not notice 5hp and a handful of KG in the dynamics of the car. What do you think the increased vibration is doing to the loads of the piston rings against the sides of the cylinder walls? or the increased load on the engine bearings.
Don't they replace the other half of the engine that didn't make it from the 928? In other words were deemed necessary for the 4-banger from day 1, but as it's the bastard child of another engine rather than a proper design in its own right I'm not sure what that makes the true answer!
sawood12
New member
They are there as an essential part of the engines primary balance. I've read a good detailed explanation of how it works somewhere in my distant past, something to do with the fact the engine is quite large for an in line 4-pot therefore as the crank counter-balances rotate from BDC towards TDC the magnitude of the sideways component forces become much more significant than that you get with smaller in-line 4-pot engines, and it is these sideways forces the balance shafts are counter-acting. You get away with it with a 5 or more cylinder engine as the crank arms are not all on the same plane.
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