930 Engine Balancing Results - Page 2

350HP930 · 01-17-2005, 06:58 PM

Here is my modifiled flywheel.

350HP930 · 01-17-2005, 06:59 PM

Here is a pic that shows the notch in the pulley.

350HP930 · 01-17-2005, 07:03 PM

Here is a pic of the whole balancing apparatus.

350HP930 · 01-17-2005, 07:08 PM

Here is a screen capture from the balancing PC.

snowman · 01-17-2005, 07:30 PM

So ya only got it to 0.64gm instead of 0.00000000gms. Now you will have to limit the RPMs to 30,000 or less.

Very nice equipment.

Brother · 01-17-2005, 07:43 PM

How much would your shop charge to have this done?

350HP930 · 01-18-2005, 02:52 PM

A 'race balance' that gets all rods and piston sets within 0.1 grams of each other and the crank-flywheel-pulley combo within a 0.3 oz-inches costs $462.

We also have a 'street balance' for $381 but its likely that most porsche motors would already be within that balance spec from the factory.

snowman · 01-18-2005, 07:41 PM

0.1 grams vs 1 gram is a TOTAL WASTE of money on an all out RACE CAR, even 1 gram is questionable. For example just how much difference in force at 9000RPM is there with 1 gram unbalance in pistons? Or how about 1 gram cm for crank balance?
The number can be calculated, but the answerr is still fly sh itt.

350HP930 · 01-19-2005, 03:11 AM

One could argue that balancing a porsche motor is a waste of money since its already 'good enough'.

A one by one inch piece of paper weighs about 0.1 grams so that should allow one to put into perspective how much weight we are talking about.

I guess the next time I am doing some machine work perhaps I shouldn't bother being accurate to 0.0001 +-0.00005" because getting to within 0.0005" of the target is 'good enough' and anything else is a waste of time and money.

dean · 01-19-2005, 03:59 AM

Thanks for posting the pics.

afterburn 549 · 01-19-2005, 06:20 AM

Please lets not get into pissing contest about this.....if you want to shoot for "0' grams thats ok with me and we all can learn from your exp.-If you want to shoot for something less,Fine. I think this is a good place to learn and help ea other.
I have noticed that in the last few months that the members here have aspired to be dignified and respectifull while helping,correcting and apoligizing for stuff.....NOT like other places.....where rude is the rule.
My 2c

350HP930 · 05:03 PM

Quote:

Originally posted by snowman
For example just how much difference in force at 9000RPM is there with 1 gram unbalance in pistons? Or how about 1 gram cm for crank balance?
The number can be calculated, but the answerr is still fly sh itt.

Well, that was a good question and I suspected that it would add up to more than fly **** so I decided to make some quicky calculations using some of that old school physics stuff that is still bouncing around inside my head.

The following caculations use F=ma for linearly accelerating mass such as imbalances between the reciprocating sets and F=mv^2/r for the rotating mass like the crank and big rod ends.

A porsche motor spinning over @ 7K RPMs is going to see max piston and rotating mass speeds of 27.5 m/s (61.5 MPH).

Since the pistons accelerate and decelerate twice per revolution this means that there will be 466 accel/decel events per second where the approximate acceleration is about 12,815 m/s^2

Using these numbers for each 0.1g imbalance between reciprocating weight there will be an applied force of 1.28 N (0.288 lbs) to the motor.

For each 0.1g of imbalance in the rotating mass there will be a resulting 2.02 N (0.454 lbs) force.

If you arrange several of these of these 0.1g imbalances in the right configuration we could be talking several lbs of buzz inducing force applied to a motor at its max RPMs.

I think it would take a lot of fly **** to amount to a large fraction of a pound, let alone several.

snowman · 08:19 PM

For imbalance, anything less than hundereds of lbs is fly s....t. Thats why Porsche uses numbers like 15gm cm to be good nuff.

Actually there is another reason as well. Oil.

Oil weighs a lot. How much oil is there on each piston, each part of the crank at any one time? It varies, a lot and we are talking about numbers ranging from 5 to 25 grams. every time an oil squirter hoses down the bottom of the piston is adds a lot of weight, not exactly uniformly, the crank is being splashed with oil and retaines varying ammounts both internally and externally.

I suspect thats the main reason even the ANAL types, and most really good Porsche machinests fit that discription, who like perfection, usually stop at one gram.

Even so its really nice to have equipment that can do 0.1gm and if you don't have to spend to much time doing it , its always nice to have perfection as in the fully finished undercarriage of a concours car, not practical at all but nice.

Rbialkin · 01-20-2005, 06:17 AM

This is a great discussion, guys. I think everyone can learn something from it, and it's just one of the great things about these boards.

al lkosmal · 01-29-2005, 05:41 PM

350HP930,
I will be in Tampa, for business, the third week of February. Any chance I can stop by and drool on your motor????

350HP930 · 01-29-2005, 06:01 PM

Well, about half of it is at home and the other half work, but we do give tours of the machine shop if you would like to stop by.

Blanco · 02-01-2005, 06:04 AM

Tampa aint too far from Atlanta.

JohnJL · 09-03-2005, 07:19 PM

I'll share mine too...will pick up the rods tomorrow, but I was able to get my pistons, rings, locks and pins to within .8 grams of each other and a reciprocating mass zero imbalance across the banks. Here are the total mass of each piston + rings + pins + locks. I didn't remove any material, just mixed-and-matched. I'll scan and post my balancing worksheet later.

Piston Mass (g)
1 576.8
2 576.8
3 576.8
4 576.0
5 576.8
6 576.0

I'll install piston # 4 and #6 the #1 and #4 cylinders, so that there will (at least until the rods come in) be a perfect balance out to 1 dec place grams across the banks.

john

Aircooled4evr · Aircooled4evr's Garage

Quote:

Originally Posted by JohnJL

I'll share mine too...will pick up the rods tomorrow, but I was able to get my pistons, rings, locks and pins to within .8 grams of each other and a reciprocating mass zero imbalance across the banks. Here are the total mass of each piston + rings + pins + locks. I didn't remove any material, just mixed-and-matched. I'll scan and post my balancing worksheet later.

Piston Mass (g)
1 576.8
2 576.8
3 576.8
4 576.0
5 576.8
6 576.0

I'll install piston # 4 and #6 the #1 and #4 cylinders, so that there will (at least until the rods come in) be a perfect balance out to 1 dec place grams across the banks.

john

Good info thread, that deserves a "renewal"