heff0018 wrote:Thanks, the dodge/valiant drives like a boat so you not far wrong there.
Sorry Heff0018,
I thought it was in a boat.... ignore the boat side of things, i must be confusing yours with another project. If you wish to do balancing of the engine then you can, if this is not a race car and thus sqeezing every last hp out of the thing is not your goal then dont work too much. The amount of difference is not that critical. It can be when the cast pistons are heavy as hell but these are not factory pistons from what i have seen so will have been changed at some stage anyway.
To give you the idea I specifically built a 308 holden motor with a 253 crank because they are naturally lighter. This was a race car and I needed it to rev. Reciprocating mass is the killer for the engine to rev but the other side effect is that the lighter the mass for rotational the quicker it will loose revs as well (read going up a hill and not thus is slows down because the stored interia drops quickly. The pistons I used were so light that they were literally half that of the originals. Using a 308 crank I would have taken that much metal out of the crank counter weights that the crank would have potentially be compromised.
I do not see a need to balance in a street car unless constant heavy hard pulls are expected. If this is a cruiser with occasion blast then it should be fine. For piece of mind, weight all of the conrods, gudgeon pins, rings, pistons and bolts and compare them to the new stuff you are using. Let see whether there is a huge difference.
Charlescrown wrote:A good set of forged pistons will be balanced very accurately. I never could work out how they calculate the added weight to the crank when balancing but do know some crank configurations the don't add any weight just spin it and check the dynamic balance as a separate unit to the up and down static weight of the pistons. The rods get a bit more complicated. I have never had a rebalance done for forged pistons and never noticed any extra vibration.
The vibration for most of this happens at a micro level. It is actually engine harmonics and therefore not always felt through the car. Balancing a rotational mass is easy and just a heap of mathematics. If your balancer is worth their weight in gold then they will also take into account the oil weight that would be within the system. The method of balancing is matching the parts of the cylinders so that they are technically identical in weight. This will be swapping pistons and rods until over all it is balanced. Then calculations are made for how much weight to put on each of the journals to simulate what the cylinder component weights are, then the weight plus the crank are spun up with harmonic sensors to measure and allow the crank to be matched to the cylinder vertical or horizontal motions. This in turn then like balancing a car wheel gets weight added or in most cases removed. Have you ever driven with a non balanced wheel? the effects are not that great and the harmonic will happen about the 80 km/h mark. it is not terrible but sometime annoying. My race cars never have there tyres balanced. firstly the tyre surface changes to much as the slick wears that a balance when fitted would be different after the first heat cycle and secondly i am not at 80km/h for very long and thus it generally will not have a fit again until 160km/h which again i am not at for very long. Whereas on a road car you spend alot of time at 80km/h and thsu it is annoying if not balanced. Having stated that if you are doing 160km/h in a road car then you might have other issues.......
If you want to have less of a boat Heff0018 then look at going to the smaller Chrysler cars.... Galant, Lancer, Hillman, Sunbeam, Humber. Heck I would even suggest Sigma. Small fact for you, when Chrysler bought Rootes group they actually put a 318 as an option into the Humber supersnipe. There are mean that took this option. Chrysler owning Rootes also spelt the end of the Tiger seeing it was powered by a Ford v8 (Cheapest Shelby car ever, and one of the rarer). Similarly Chrysler had an option of the 318 into the Galants. This was optioned only in Japan and only in the coupes. There chassis were designed to take this large engine and was continued across tot he sigma. Infact the rails in the sigma are identical to the Galants, they just moved the steering box to the other side of the rail and made the car a little wider to accomodate the exhaust etc that was needed for the 2000 and larger offerings. While Chrysler never optioned the 318 into the Sigma it is essentially a bolt in option. Chrysler cars are awesome, it is just a pitty Chrysler today is a former shadow of what they were originally.
Cheers
oldn64