Flywheel weight options

Gunner:

First off in a perfect world the weight of the Flywheel by itself has little to do with the torque output of the motor..........although one could rational that the total weight of the package including flywheel, disc's and Pressure plate "IS" directly connected to the the total amount of torque and horsepower the motor may create. Surface area for friction materials ( clutch disc's ) must be matched to the anticipated torque and Horsepower that it is attached to.......In racing we do that by adding another disc or two with floaters between them and or use a higher coefficient of friction material to make the clutch bite harder...the flywheel is merely there either to engage a clutch disc as a form of transferring energy and or for a means of starting the motor via the ring gear..........

Getting back to the 4 cylinder motors there firing pulse is every 180 degrees of crankshaft rotation or twice during one complete 360 degree revolution............hence the need for "Inertia" or induced weight to carry the little motor through to the next firing position. Compare that with a V8 motor which fires every 90 degrees of crank rotation or 4 times per 360 degrees and it becomes clearer that one has to be treated differently than the other.

Now introduce a Buick Odd fire V6 motor that truly started it's life as a V8.........when GM decided to build the little V6 back in 1961 or 1962 they took a V8 block an essentially cut off the rear two cylinders , the crankshaft was also just bobbed off in the casting leaving a 3 throw crankshaft.............hence the Odd-Fire arrangement.
Look at the chart below and that should help you see where the Odd-fire sequence comes from...........the odd fire V6 is firing on a 90 degree to 150 degree pulse while the Even Fire V6 is firing every 120 degrees of rotation. The reason that had to happen is because the crankshaft as mentioned above only had three throws on it with two connecting rods per throw.............the Even Fire on the other hand had a new crank built that had split throws on the same journal 15 degrees apart in either direction making each cylinder 120 degree's apart.............so in order to cover up that Odd Fire sequence the heavy Flywheel was introduced. In realty I don't think that Willys nor Buick had intended for that change to be anything other than a mask to calm that un-even pulse down a little........although for most folks with a Odd Fire 225 in a Jeep the extra flywheel weight seems to be the ticket to get the little motor to idle over a rock or climb a hill.

That chart did not come out as drawn but you should get the point

Angle 0° 90° 180° 270° 360° 450° 540° 630°
Odd firing 1 6 5 4 3 2
Even firing 1 4 5 6 3 2

 

Oddfire and evenfire GM engines have the same firing order. 165432. The 200, 229, and 262 (4.3 V-6) Chevrolet engines also had that same firing order.
Not sure where that other firing order came from but it's not a 225 or 231 unless possibly reverse rotation marine application but that doesn't make sense either.
GM when they reacquired the Buick V-6 and modified it to the oddfire 231 used the light car style flywheel which is balanced different than the evenfire 231. The oddfire 231 was used from '75 to early '77 as far as Ive been able to pin down although some sources say '74. I cannot confirm or deny this.
Late '77 the evenfire design that Tarry99 talks about above was introduced and produced into the '90's in various forms. I have seen both evenfire and oddfire 231's that were produced and used in the '77 model year GM line.
The 231 oddfire also used softer rubber engine mounts to try and soften the inherent vibrations produced In A 90* V-6. These were carried on into the later applications for the engine.
Like Tarry99 said the weight if the flywheel does not change the torque output if the engine. The heavier components will however increase the inertia produced to help carry the crankshaft rotationally to the following firing pulses. It doesn't matter if it's a one cylinder or V-16 engine, basic physics still apply. Ever seen a 1 or 2 cylinder steam engine with the huge flywheels? How about a Johnny Popper John Deere tractor? Same idea applies. The inertia of the flywheel helps carry the engine to the next firing pulse. A lighter flywheel is less effective doing this as there is less inertia produced or available.
Sent from my iPhone

 

I just wanted to make sure I understood oldtime. Yeah, it's straightforward with a flywheel for the most part.

Here are some of the questions I faced:

1. what bell to use
2. which starter to use (3 different types)
3. use starter which bolts to block or to bell?
4 if starter bolts to block, which flywheel to use (differs between 153 tooth and 168 tooth)
5. if 153 tooth, where to get one
6. if 168 tooth, get another one or use the one I have
7. if I use the 168 tooth I have, should I have it drilled to accept a 10.4" disc?
8. if I don't drill it, will I be all right with a 11" disc? ie will it be too big?
9. how about a 10.4" disc in a 11" pressure plate?
10. what weight of flywheel, disc and pp is optimum?
11. cost?
12. what parts do I already have and so on

a. how does this all affect acceleration?
b. how is driving in stop-n-go traffic affected?
c. what about off pavement use?
d. mpg?
e. pedal pressure?

And on it goes. Lots of things to consider- surprisingly, much of this had to do with the starter motor and flywheel combination, which the Chevy guys routinely deal with. The 153 block is only compatible with a starter motor for a 153 tooth flywheel if the starter is bolted to the block. In the end, it sounds like a larger and heavier set up is not only acceptable, but probably preferable for the 4 banger. From my research, I suspected that to be the case, but I had no direct experience with it. I've wrenched for over 40 years, but am now just getting into mods like this.

I'll go with:

1. 168 tooth chevy nodular flywheel I have on hand
2. cast iron truck bellhousing with tapped holes for 3 bolt starter- have on hand
3. 3 bolt chevy starter- gotta buy
4. 11'" Astrovan clutch kit- gotta buy
5. 10.4" Summit disc if the 11" proves too big
6. hydraulic slave cylinder

 

Before you spend any money make sure the block is drilled for the starter that is for the 168 tooth flywheel.
I have nine of these engines from DJs and Mercruiser boats (including the 181 ci)...ALL are drilled for the 153 tooth flywheel/starter combo.

 

The block is drilled for only the starter to mesh with a 153 tooth flywheel. It's not drilled to accept the 1698 tooth flywheel.

The cast iron bellhousing is set up for the 3 bolt starter motor. That starter motor meshes with the 168 tooth flywheel.