302 Build Ideas

[kilgorq]

You can keep on believing that, but it doesn't make it a fact

Have you ever seen how engines are balanced?

When counterweights are cut down in size, something has to make up for the loss in weight. Racing machine shops regularly do this for a variety of reasons including providing more clearance to pistons in a stroker to reducing windage--BUT--when they do that, usually they "internally balance" the engine (no imbalance weight on the flywheel or the damper) by the use of heavier metal.

To do this, they drill holes in the remaining counterweights and add metal sufficiently heavy to replace the mass of the counterweight material that was removed.

In situations where the counterweight diameter was reduced, they have to use quite a bit of this heavier metal in order to get it close to the same "weight" (if you will) of that particular counterweight before it was reduced in size.

If the shop is only switching the rotating assembly from externally balanced to internally balanced, they don't need to use nearly as much--BUT--Because the location of the heavy metal is closer to the centerline of the crankshaft, it weighs more than it did placed further out on the flywheel.

When Ford removed the weight from the crank, they increased the imbalance to make up for it.

Now, you contend that this will make your engine "rev faster", but as I've already mentioned in a previous post--the resistance to the combustion pressure at the top of the piston due to the weight of the rotating assembly is the same (intertia) because the effective rotating assembly weight was not reduced overall--the connecting rods and pistons weigh the same, or are within a few grams of the assemblies prior to the reduction in crankshaft weight.

This is mostly due to centrifugal force, and the fact that while the actual weight of the crank was reduced, the placement of the heavier imbalance creates a situation where the same force is available to counteract the weight of the connecting rod/piston assemblies.

If you like, you can verify what I've described here with any physics professor . . .

What you say about the Centerline and Centrifugal force puts this in perspective. I follow the logic here.

I have seen an engine getting balanced but not to the point that they are cutting down the weight of the rotating assembly. They were weight matching the pistons and rod assemblies.

 

[6Stang7]

If you want the engine to "rev faster", trimming the weights on the crank is a poor way to do it. The relatively small diameter of the crankshaft assures a small "moment" of inertia, resisting changes in rotational speed.

Bingo; you hit the nail on the head. Inertia is a moment; quantity and position. Position has a much greater effect (distance is squared) on the total inertia of an object then mass does.

 

[Sicarius428]

If you already have damage to the block, I would scrap it. A decent 5.0 block can be had for cheap and would be a better start than a damaged block which will cost you money. Roller cams are also a huge perk too. For a street motor that won't see more than 450hp the 5.0 block will be fine if that is a consern. As for the heads, it depends on what application you want to do with the car.
Kevin

 

[D.Hearne]

-BUT--Because the location of the heavy metal is closer to the centerline of the crankshaft, it weighs more than it did placed further out on the flywheel.

When Ford removed the weight from the crank, they increased the imbalance to make up for it.



This is mostly due to centrifugal force, and the fact that while the actual weight of the crank was reduced, the placement of the heavier imbalance creates a situation where the same force is available to counteract the weight of the connecting rod/piston assemblies.
.

Only thing is you seem to be also skirting the fact that the weight added to correct the amount removed is less, so there was a weight savings there that improves the inertial resistence in that area. So in theory, the engine should rev a bit more freely, even though the gain will be something that could only be proved electronically. And your top statement here is bass-ackwards. The centrifugal force exerted is more as the weight is moved outward from the centerline of the crank. Just looking at the difference in the size of the counterweights on either flywheels or flexplates (28 vs 50 ) proves this. Ditto on the balancers, although not as much. The 50 oz balancers have much larger counterweights than the 28's. And also a balance shop will only add the amount of counterweight needed to target a specific rpm range. No engine is perfectly balanced at all rpms.

 

[rebel65]

:OT:

So I bought a couple 67 coupes yesterday and they came with a few different goodies in terms of spare engine parts. I want to build a nice engine for one of the cars. I try not to do anything with engines and leave it to the pro's, but I want to atleast have some background before I start looking for a shop to do the work. The parts I got were;

-stock 302 block that has some damage to one of the cylinders. I think it will be reusable if I want.
-brand new set of Edelbrock victor Jr heads. I can pull the PN if there is a big difference.
-A Weiand tunnel ram intake with dual 4barrel edelbrock carbs. Not sure how great the carbs are, they are basically new, but I will not use this intake.

So should I just buy a shortblock from CHP or Ford and throw these heads on with a decent intake? I want to keep the car very streetable, but would like to get around the 400hp mark.

Should I sell everything and start fresh? If I were, what is a good 302 block to start with, the newer 5.0's?

Thanks for any advice.

-Ryan

DO you want a Torque Monster or a HP Down the Stripper.

those heads are great, but lack somewhat in the torque department. but what they lack there they MORE than make up in Peak and Average HP. so do you want a car that gets down a strip fast or that moves you off a stop light. that's all you need to figure out to keep those heads or ditch em. otherwise a stroker or even just a turbo/supercharger should probably keep you happy. you can either get that one cyl sleeved or get later model roller block. you can make your block a roller motor, but the cost involved fixing what is wrong with that one and upgrading to the type of parts needed for a roller you might as well just get a new block as a couple said. this is if you want a little monster under the hood that is.. if you want a real mild motor keep the 302, keep the Vic. Jr. and rev that bad boy up. ( just do as wicked said get that compression up )

 

[stonecoldtx]

Only thing is you seem to be also skirting the fact that the weight added to correct the amount removed is less, so there was a weight savings there that improves the inertial resistence in that area. So in theory, the engine should rev a bit more freely, even though the gain will be something that could only be proved electronically. And your top statement here is bass-ackwards. The centrifugal force exerted is more as the weight is moved outward from the centerline of the crank. Just looking at the difference in the size of the counterweights on either flywheels or flexplates (28 vs 50 ) proves this. Ditto on the balancers, although not as much. The 50 oz balancers have much larger counterweights than the 28's. And also a balance shop will only add the amount of counterweight needed to target a specific rpm range. No engine is perfectly balanced at all rpms.

I tried to edit and state the point I was trying to make, and I can see from your quote that I missed editing some of the text

What I intended to say was that when racing machine shops either reduce the size of the the counterweights or internally balance the engine using their original size, they use heavy metal which is considerably heavier than the metal that was removed, and the reason it's required and it's so heavy is because it is closer to the centerline of the crank as compared to the imbalance weight on the flywheel/flexplate and damper.

This makes the weight of the counterweight equal to what it was before it was reduced in size, or more than what it was if the engine is being internally balanced.

Make sense?

 

[D.Hearne]

I tried to edit and state the point I was trying to make, and I can see from your quote that I missed editing some of the text

What I intended to say was that when racing machine shops either reduce the size of the the counterweights or internally balance the engine using their original size, they use heavy metal which is considerably heavier than the metal that was removed, and the reason it's required and it's so heavy is because it is closer to the centerline of the crank as compared to the imbalance weight on the flywheel/flexplate and damper.

This makes the weight of the counterweight equal to what it was before it was reduced in size, or more than what it was if the engine is being internally balanced.

Make sense?

Gotcha. But another reason for using mallory metal is to balance the engine for higher rpms than the factory ever intended. Higher rpms need more counterweight.. Same was true back in the days of steam locomotives.