Just remember, the combination makes power. A slightly lighter rotating mass not so much.
318 Build Combo Critique
- Thread starter JGC403
- Start date
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T56MaxTorq
Well-Known Member
I agree.
Mag rods are only 5-10 grams lighter. Instead of the engine, think of all the stuff that is attached to the crank, a 904 can save over 15hp in some cases just by reducing weight in internals compared to a 727.
Don't go overboard with the weight reduction. You already have a nice internally balanced engine. You'd see more gains and longer service life by taking a lot of measurements and making every cylinder as consistent as possible to the other. Measuring for pushrods properly, measuring every valve with those pushrods to get consistent lift for all 8, degreeing the cam, a timing chain tensioner is a good idea, lightly cleaning the casting slag out of the heads, super tuning the ignition curve, tuning fuel with an air/fuel gauge. There's lots of cheap stuff that makes power.
nm9stheham
Well-Known Member
If I am thking correctly (while I worry abau this nor'easter taking my partially installed new roof off tonight; what luck!): Those 2 cranks are made to balance out the same bobweight, with the same reciprocating component and the same rotating component. (The 273's piston pins are heavyyyyy to make the reciprocating weight part the same as the 318.) With that being the case, the rotational mass and rotational inertia of the crank itself (which takes energy away from the torque at the wheels under acceleration) will be fairly close to the same, so I would not expect you see any real difference in your application. It might make a difference in a very, very high end drag car.
No, your machinist will be taking weight off of the crank throws with either the forged 273 or the cast 318 with those lighter pistons, and the lighter rods take even more weight off. Taking weight off only makes the process cheaper.
(BTW, if you can balance the rods properly your self, and accurately weigh the parts, and do a bit of math, then you can just figure your own bobweight and give it to the machinist with the crank and save some $$. It takes some good measurement skills and proper technique.)
nm9stheham
Well-Known Member
Just keep in mind that any lighter rotating mass will help the car go faster; if you are road racing or rallying or autocrossing, then it typically gets considered more than for drag racing. Of course, lighter flywheels is the best spot to look for reduced rotating weight.
Agreed but we aren't talking lightweight 2 ring pistons, aluminum rods and billet knife edge cranks or even race cars here. My point is that the op should concentrate more on the combination and less on the factory pieces to make it a few grams lighter.
JGC403
Well-Known Member
Nice 273 build by the way.
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