less rotational mass. less rpm and energy to get to a set speed.
Worth upgrading to 3.73s?
- Thread starter HuskerGT
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less rotational mass. less rpm and energy to get to a set speed.
OnyxCobra
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That makes no sense at all. Yes it has less rotational mass but it's still going to be revving the same amount at any given speed.
Brian95SVT
Legend
Yeah. From what I understand is that the less rotational mass just allowed you to get to said RPM quicker but nothing relating to changing RPM at a certain MPH.
What principle would that be?
You're saying that if you have two identical sets of rotational components in a set ratio, the lighter one spins less? lol.
That's like saying if you have titanium 3.73s they would spin at a lower RPM than steel 3.73s. Changing the weight doesn't change the distance around the gear, and thus doesn't change the RPM.
OnyxCobra
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it's basic physics that the RPMs would be the same regardless of the rotational mass.
the vss/oss is set to a speed the pcm is programmed to. at any given gear numerical you use affects the rpm range. 4.10s would be higher in the RPM range because the trans is constantly using energy to get to said speed and quickly loses momentum off the accelerator. 2.73s or whatever stock gear ford set with had a better fuel consumption range it doesnt spend as much energyto get there and maintains it at that speed.
now here is where the aluminum driveshaft and flywheel comes in. with the less rotation mass the engine has a less struggle(spending of energy) to get to the set speed. mechanically its still attached to the crank and pinion. mix this with the given gear ration it uses less energy. (hence, it revs quicker).. revving is building momentum.
in a gasoline engine the energy is produced by the fuel thats used. less fuel used the more you save.
if you dont see the logic in my explanation. i wont say no more on this subject. you cant win them all.
now here is where the aluminum driveshaft and flywheel comes in. with the less rotation mass the engine has a less struggle(spending of energy) to get to the set speed. mechanically its still attached to the crank and pinion. mix this with the given gear ration it uses less energy. (hence, it revs quicker).. revving is building momentum.
in a gasoline engine the energy is produced by the fuel thats used. less fuel used the more you save.
if you dont see the logic in my explanation. i wont say no more on this subject. you cant win them all.
g36 monkey
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I think you are trying to say it's easier to spin and will save more fuel. Lighter so it's less work for the motor, not that it will make you go from 2500 to 2000 rpm.
Saint
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Yes...spend the extra loot for the master install it and rebuilt the differential too...mine went out a few months after the 3.73 install...not very fun back tracking next week i'm just getting a whole new rear since I bent mine
justinschmidt1
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+1, what your saying verm doesnt logically make sense to me either.
RPM = revolutions of crankshaft per minute
Your speed is based off how many revolutions per minute the crank shaft is spinning and whatever the final gear ratio ends up being through the trans, rear end, and tire height.
Reducing weight on the flywheel and driveshaft will make the car accelerate easier but the crankshaft will still have to spin at the SAME RPM to get the rear end gear to spin at whatever speed it takes to make the car go 70 mph. There is no way around that.
Speed is dictated by the motors RPMS and gear ratio, not load.
At least when it comes to a manual transmission.
My cruising RPMs on the highway should drop when I put my lightweight drag wheels on going by your theory. I can tell you that they do not. lol
HuskerGT
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LRS has, what looks like, a pretty complete package for sale: http://www.latemodelrestoration.com/item/LRS-4209FRB-K/Mustang-88-373-Ratio-Rear-End-Gear-Kit
The kit looks complete but the master install kit is made by Yukon not Ford Racing. I'd like to be safe & stick with Ford Racing, but don't know if makes much of a difference. I know Yukon has been around for years but does anyone have any experience with this kit?
LRS has their 3.73 gears on sale now for $139
AM has the Ford Racing master install kit that appears to have additional components.
Musturd
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Vermillions logic makes no sense at all the logger weight gets the revs up quicker that's it regardless of flywheels and driveshafts a motor is going to still turn the same RPM at the same speed .
Brian95SVT
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Basically his (incorrect) logic (based on what he said) would also mean that if you had the a set of wheels and tires, then replaced them with the exact same specs/dimensions but with lighter wheels that the RPMs would change.... which is false.
At the end of the day the flywheel is connected to the crank. The flywheel only spins at the rate that the crank does, meaning it doesn't matter that its lighter its still going to spin at the same speed it will just take less energy per rotation. If it spun faster than the crank that it's connected to, it would break off. Same thing applies to the wheel logic, it does not change RPM but uses less energy per rotation.
All of his replies basically prove our points which I found funny.
I'm interested to see what formula he's using....
At the end of the day the flywheel is connected to the crank. The flywheel only spins at the rate that the crank does, meaning it doesn't matter that its lighter its still going to spin at the same speed it will just take less energy per rotation. If it spun faster than the crank that it's connected to, it would break off. Same thing applies to the wheel logic, it does not change RPM but uses less energy per rotation.
All of his replies basically prove our points which I found funny.
I'm interested to see what formula he's using....
justinschmidt1
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Yea, my engine RPM equation doesnt incorporate the weight of the flywheel or driveshaft. lol
Only needs the trans gear ratio, rear end gear ratio, tire height, and speed.
I dont think his formula exists.
justinschmidt1
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Im gonna say it has far more to do with the fact that you can cruise at 1700 rpms at 70 mph with a 2.73 gear rather than cruising at 2600 rpms with 4.10 gears to get the same 70 mph.
I would imagine a 2.73 gear would actually use a lot more fuel getting to 70 mph than a 4.10 since the 2.73 will force the motor to work a lot harder to get there than athe 4.10
if you had a weed wacker for an engine.
HuskerGT
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Anyone care to get back on topic yet (LOL) and address my question about the Yukon install kit?
rz5.0
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Yes replace everything. There is also 3.55
justinschmidt1
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Its easier for the car to get moving at slower speed with 4.10s over 2.73s....it makes a big enough difference for people to report improved MPG in citys when they switched to 4.10s or 3.73s so it must matter.
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