ok im having this debate with sombody about a 289 crank and 302 rods and pistons can u run a 289 crank 28oz with normal 302 rods and pistons off a 50oz set up together with out having nething rebalanced?
289/5.0 ?
- Thread starter ls1beater4eva
- Start date
Vipersix
Founding Member
I would say no with 95% assurance. The crank is balanced to the rods and the flywheel is designed for an imbalance built into the rotating assembly. From my understanding, the imbalance is a cheaper route for mass manufactured parts than attempting a zero balance. So your 28oz crank is attempting to balance with a 50oz set of weights.
I have to disagree. The rods on all late model 5.0's, or any 5.0/302 for that matter, are the same C8OE, or D1OE forgings Ford has always used.
The difference is in the crank itself. 28oz cranks need 28oz balancers, and flywheel/flexplates.
50oz cranks need 50oz parts.
While having any combo (even one using factory parts) balanced is is a must for the most performance, later 5.0 rods and pistons on an earlier crank will be "close enough" for FACTORY tolerances.
The difference is in the crank itself. 28oz cranks need 28oz balancers, and flywheel/flexplates.
50oz cranks need 50oz parts.
While having any combo (even one using factory parts) balanced is is a must for the most performance, later 5.0 rods and pistons on an earlier crank will be "close enough" for FACTORY tolerances.
Vipersix
Founding Member
The rods can't possibly be the same. Engine dimensions are determined by the stroke and the bore. Since the 289 and 302 both have 4.00 bore, the only remaining factor to coax out the extra 13 cu. in. is the stroke. Stroke is determined by crank rotation and rod length. In the case of a 289, the rod length is .055" longer. This may not sound like much, and at low RPMs it isn't such a big deal, but centripetal forces increase exponentially with RPM increases. So if smoothness and parts wear isn't a concern, by all means build an engine in that manner.
The entire purpose of the flywheel and balancer are to equalize the imbalance experienced by the crank during rotation due to the rods and pistons. If you utilize a crank designed to offset the weight of a 289 rod/piston with the rod and piston out of a 302, there will be an excess of weight in the counterweight. This will create enormous centripetal forces which could eventually pull a main bearing or induce enough stress to cause the crank to snap.
Food for thought: A crankshaft with only two ounce-inches of imbalance at 2,000 rpm will be subjected to a force of 14.2 lbs. At 4,000 rpm, the force grows to 56.8 lbs. Double the speed again to 8,000 rpm and the force becomes 227.2 lbs. Yet we're looking at a difference somewhere in the neighborhood of 20 ounce-inches.
The entire purpose of the flywheel and balancer are to equalize the imbalance experienced by the crank during rotation due to the rods and pistons. If you utilize a crank designed to offset the weight of a 289 rod/piston with the rod and piston out of a 302, there will be an excess of weight in the counterweight. This will create enormous centripetal forces which could eventually pull a main bearing or induce enough stress to cause the crank to snap.
Food for thought: A crankshaft with only two ounce-inches of imbalance at 2,000 rpm will be subjected to a force of 14.2 lbs. At 4,000 rpm, the force grows to 56.8 lbs. Double the speed again to 8,000 rpm and the force becomes 227.2 lbs. Yet we're looking at a difference somewhere in the neighborhood of 20 ounce-inches.
93 LX
Founding Member
The stoke is also different from 302 to 289. I have seen "5.0" rods used in a 302 that was 28oz so I guess the debate goes on.
Vipersix
Founding Member
Check out this article from Mustang and Fords Magazine. They briefly mention the 28oz vs. 50oz. down at the bottom and discuss the importance of balancing closer to the top.
thank you viper that is what i was trying to say just didnt have all the math doen for him but i was tryingt o explain this to this kid while 88mouse was my wittness but he swears that it will work i am going to show him the artical tomorrow maybe then he will tear this motor down b4 he waste alot more money then needs to be lol thanks guys
93 LX
Founding Member
The article does not say you cant use 302 rods on a 5.0L engine. What it says is when you dynamic balance your crank the rods must be balanced to the crank. The 28 / 50 ounce off set has to be matched to the crank, 28 ounce flywheel/balancer to a 28 ounce crank.
Vipersix
Founding Member
I didn't realize someone was actually attempting to do this; just thought it was a hypothetical discussion. I would highly discourage him from building this setup. Not good in the long run. At the very least, he needs to utilize 28oz flywheel/balancer setup and hope that is enough to adequately offset the different whirling things inside the motor.
93LX is correct by saying the article doesn't prohibit the use of 302 rods on a 5.0 engine (though I think he means 289 since the 302 and 5.0 are the same with the exception of the boss). You're saying the right thing but I don't think you're really grasping it. You correctly opined that the crank needs to be matched to the flywheel/balancer. However, you said the rods must be balanced to the crank. Sorta. Accuracy is in the details: the crank needs to be balanced to the rods and the pistons and the pins and a wee bit of oil.
That makes a big difference. Because now you add the 5 extra grams the longer rod weighs to the weight of the piston and the pin and move it outward .065". This is a difference of 36 g-in per cylinder (or 1.27 oz-in). You're looking at approximately 100 lbs of force trying to rip the lobes off the crank every cycle at around 6000rpm. Keep it at idle and you'll only see about 9 lbs, but 9 lbs of force 50 times a second is pretty rough on the parts. 100 lbs beating on the crank 200 times a second is even worse.
Tell your friend to take the time and money to do it correctly the first time through and he will save money in the long run.
93LX is correct by saying the article doesn't prohibit the use of 302 rods on a 5.0 engine (though I think he means 289 since the 302 and 5.0 are the same with the exception of the boss). You're saying the right thing but I don't think you're really grasping it. You correctly opined that the crank needs to be matched to the flywheel/balancer. However, you said the rods must be balanced to the crank. Sorta. Accuracy is in the details: the crank needs to be balanced to the rods and the pistons and the pins and a wee bit of oil.
That makes a big difference. Because now you add the 5 extra grams the longer rod weighs to the weight of the piston and the pin and move it outward .065". This is a difference of 36 g-in per cylinder (or 1.27 oz-in). You're looking at approximately 100 lbs of force trying to rip the lobes off the crank every cycle at around 6000rpm. Keep it at idle and you'll only see about 9 lbs, but 9 lbs of force 50 times a second is pretty rough on the parts. 100 lbs beating on the crank 200 times a second is even worse.
Tell your friend to take the time and money to do it correctly the first time through and he will save money in the long run.
88mouse
New Member
Yeah the guy already has the motor built. Me and ls1beater tell him its going to beat the bearing out of it.
