GM balanced engine
Thread Starter
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
I knockout out the rods myself for the balancing using a press, but decided to have them put back together by a proessional. I don't know what they used to heat the rods.
I wrote a seperate thread on the crank balancing. A little debate concerning the technicallity of internal vs external balance....
of the rotating assembly. The low down was the crank with GM dampener and GM flexplate (plate had weights welded to it) when put on the balancer was 28.4 at the front and 10.8 at the rear of the crank. The crank was "GM balanced to their standards" and I would have to assume that the dampener and the flexplate were balanced. NASCAR standards are 3.0 at each end. When the balance was finished I had .01 at the front and .38 at the rear. It should run very smooth.
Do a search on "GM balance Part II".
I wrote a seperate thread on the crank balancing. A little debate concerning the technicallity of internal vs external balance....
of the rotating assembly. The low down was the crank with GM dampener and GM flexplate (plate had weights welded to it) when put on the balancer was 28.4 at the front and 10.8 at the rear of the crank. The crank was "GM balanced to their standards" and I would have to assume that the dampener and the flexplate were balanced. NASCAR standards are 3.0 at each end. When the balance was finished I had .01 at the front and .38 at the rear. It should run very smooth.Do a search on "GM balance Part II".
Last edited by John A. Marker; May 3, 2008 at 12:34 AM.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
GM balanced engine Part II
Thanks for the reply. I checked the "GM BE PII" thread but only found
values for the imbalance, not physical weights of the crank, flywheel
and flexplate components. All the same, your remarks there about the
process and findings are detailed and informative - worthwhile reading.
Sorry to see that your threads are attracting such unconstructive
feedback. You are dealing with it gracefully.
Good luck with the rest of the build.
.
Thanks for the reply. I checked the "GM BE PII" thread but only found
values for the imbalance, not physical weights of the crank, flywheel
and flexplate components. All the same, your remarks there about the
process and findings are detailed and informative - worthwhile reading.
Sorry to see that your threads are attracting such unconstructive
feedback. You are dealing with it gracefully.
Good luck with the rest of the build.
.
Thread Starter
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Sorry, didn't know that you were looking for the weights of the components. I have the weights of the rods, pin/piston combination, but did not weigh the crank, flexplate or dampener. I am not sure how much value these weights would be. The crank is steel, where as many are cast. Therefore different weights for different materials. I would also think that with the GM standards you would find that two GM cranks would not weigh the same after being balanced by GM ( it may be only grams ).
I used a 6" dampener instead of the usual 8" as recommended by several Forum members (found thru search) because of clearance issues on ZZ4 engines with the front cross member. I have everything to cut, box and weld the cross member and the skill, but why tackle a job like this when you just downsize the dampener.
I talked to Ed's Crankshafts Friday and they mentioned that they even get the Scat and Eagle cranks that are "balanced" and are still out as compared to what they perfer to leave their shop, which is to have the front and rear within .5 grams.
I used a 6" dampener instead of the usual 8" as recommended by several Forum members (found thru search) because of clearance issues on ZZ4 engines with the front cross member. I have everything to cut, box and weld the cross member and the skill, but why tackle a job like this when you just downsize the dampener.
I talked to Ed's Crankshafts Friday and they mentioned that they even get the Scat and Eagle cranks that are "balanced" and are still out as compared to what they perfer to leave their shop, which is to have the front and rear within .5 grams.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
I am interested in the weight of the ZZ4's steel crank and companion
pcs from the perspective of inertia and acceleration. For my purposes
production differences in weights will not matter. Some day, I hope
to find a source for these figures, along with measurements for the
circumferences of the OEM damper, crank weights and flex plate.
I understand your reasons for the choice in harmonic damper diameter.
Although it is not relevant in your usage, it may be interesting to know
that David Vizard has written about back-to-back tests which he states
have shown that an SBC with a heavier (larger dia) harmonic damper
displays more HP than with a lighter (smaller) damper.
This was contrary to what I had believed beforehand. In short, DV
claims the benefits of greater dampening trumps reduced rotating inertia.
.
pcs from the perspective of inertia and acceleration. For my purposes
production differences in weights will not matter. Some day, I hope
to find a source for these figures, along with measurements for the
circumferences of the OEM damper, crank weights and flex plate.
I understand your reasons for the choice in harmonic damper diameter.
Although it is not relevant in your usage, it may be interesting to know
that David Vizard has written about back-to-back tests which he states
have shown that an SBC with a heavier (larger dia) harmonic damper
displays more HP than with a lighter (smaller) damper.
This was contrary to what I had believed beforehand. In short, DV
claims the benefits of greater dampening trumps reduced rotating inertia.
.
Thread Starter
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
With this logic of using a bigger dampener, would it not also follow that a flywheel (100% balanced of course) would provide more power than a flexplate because of the weight?
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
A flywheel is generally a single mass and has no provision for absorption
and dissipation of harmonics. A harmonic damper is designed in one
of several ways, all intended to reduce peak frequencies of crankshaft
torsional oscillation.
Also, the flywheel is mounted at one end of the crankshaft. The
torsional problems occur along the length of the crank extending away
from the flywheel and the damper is located at the other end for control.
Steve Dinan
Dinan BMW
"Every time a cylinder fires, the force twists the crankshaft.
When the cylinder stops firing the force ceases to act and the
crankshaft starts to return to the untwisted position. However, the
crankshaft will overshoot and begin to twist in the opposite direction,
and then back again. Though this back-and-forth twisting motion
decays over a number of repetitions due to internal friction, the
frequency of vibration remains unique to the particular crankshaft.
This motion is complicated in the case of a crankshaft because the
amplitude of the vibration varies along the shaft. The crankshaft will
experience torsional vibrations of the greatest amplitude at the point
furthest from the flywheel or load."
Mr Vizard's message wasn't that heavier (without limit) is better. MyDinan BMW
"Every time a cylinder fires, the force twists the crankshaft.
When the cylinder stops firing the force ceases to act and the
crankshaft starts to return to the untwisted position. However, the
crankshaft will overshoot and begin to twist in the opposite direction,
and then back again. Though this back-and-forth twisting motion
decays over a number of repetitions due to internal friction, the
frequency of vibration remains unique to the particular crankshaft.
This motion is complicated in the case of a crankshaft because the
amplitude of the vibration varies along the shaft. The crankshaft will
experience torsional vibrations of the greatest amplitude at the point
furthest from the flywheel or load."
interpretation is that he found in a test of the OEM elastomeric
dampers available at the time, the heavier damper was better suited
for the test engine and that this manifested as more HP on the e-dyno.
The test also included what later came to be known as the Fluidampr
and I think but can not be sure, that the TCI 'Rattler' was included.
IIRC, the aftermarket dampers were discussed separately.
.
Thread Starter
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
I am by no means an expert on this aspect of the balancer. Shade tree logic. If the rotating assembly was not fully balanced, then the balancer would do its job to eliminate vibration. Therefore, a larger balancer may or could be more efficient eliminating the vibration in the crank than a smaller balancer. If this was true, then a smoother rotating crank could put out a little more HP. But I don't think it would be much.
My logic tells me that if you balance the rotating assembly, there will be less vibration and the balancer would be a value added part that would not come into play until the higher RPM's. The less than balanced engine would require the use of the dampener at a lower RPM and would work harder to keep things from flying apart at the higher ranges.
My logic tells me that if you balance the rotating assembly, there will be less vibration and the balancer would be a value added part that would not come into play until the higher RPM's. The less than balanced engine would require the use of the dampener at a lower RPM and would work harder to keep things from flying apart at the higher ranges.
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Thread Starter
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Fred, I only run agains myself. Like last year, my son and I both ran the car, but did not stay for the bracket racing.
The only major thing is a fresh engine (pistons and rings with good compression) and a different cam. Compression ratio I think will drop a small amount L98 bock vs the ZZ4. We will see, the track is the final test.
I feel like I am in a different league any way. Can't make 1985 plus a little newer technology compete with cars that are a year or two old. The only thing I can say is that I enjoy the car and it is paid for. There is the personal satisfaction of building this engine from what ended up being a bare block up. It will be better than what I started with.
Looking forward to seeing up in Sacramento.
The only major thing is a fresh engine (pistons and rings with good compression) and a different cam. Compression ratio I think will drop a small amount L98 bock vs the ZZ4. We will see, the track is the final test.
I feel like I am in a different league any way. Can't make 1985 plus a little newer technology compete with cars that are a year or two old. The only thing I can say is that I enjoy the car and it is paid for. There is the personal satisfaction of building this engine from what ended up being a bare block up. It will be better than what I started with.
Looking forward to seeing up in Sacramento.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
If the rotating assembly was not fully balanced, then the balancer would
do its job to eliminate vibration. Therefore, a larger balancer may or
could be more efficient eliminating the vibration in the crank than a
smaller balancer.
My logic tells me that if you balance the rotating assembly, there will
be less vibration and the balancer would be a value added part that
would not come into play until the higher RPM's. The less than balanced
engine would require the use of the dampener at a lower RPM and
would work harder to keep things from flying apart at the higher ranges.
do its job to eliminate vibration. Therefore, a larger balancer may or
could be more efficient eliminating the vibration in the crank than a
smaller balancer.
My logic tells me that if you balance the rotating assembly, there will
be less vibration and the balancer would be a value added part that
would not come into play until the higher RPM's. The less than balanced
engine would require the use of the dampener at a lower RPM and
would work harder to keep things from flying apart at the higher ranges.
loads imposed by the intake, compression, power and exhaust strokes
of an Otto Cycle engine.
An even-fire V8 has what is called a 'fourth-order' harmonic - at 3,000
RPM, a V8 crank experiences 200 pulses per second (200 Hz); at 6000
RPM, the frequency is 400 Hz.
.
Thread Starter
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
SALOM4ME - You are way above my head in this area. Are you an engineer? Is this vibration something that has been addressed by the aftermarket parts companies? Different balancers etc?
I know that with valve springs you get this vibration in the spring which is why there is a inner dampener spring (ofter not made of round material but flat) that goes inside the main spring and the coils are the reverse direction of the main spring. This inner spring reduces the vibration at various levels of the main outer spring.
I know that with valve springs you get this vibration in the spring which is why there is a inner dampener spring (ofter not made of round material but flat) that goes inside the main spring and the coils are the reverse direction of the main spring. This inner spring reduces the vibration at various levels of the main outer spring.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Originally Posted by John A. Marker
Is this vibration something that has been addressed by the
aftermarket parts companies? Different balancers etc?
aftermarket parts companies? Different balancers etc?
balance of the rotating assy (and as with other OEM parts), there are
manufacturing tolerances and other contraints.
There are aftermarket vendors of dampers that are modeled after the
common OEM design w/ inner and outer sections separated by an
elastomer ring. There are also mfr's of other styles such as Fluidampr,
ATI and TCI.
Which Fluidamper to buy? (Includes citations for Mr Vizard's remarks)
Harmonic Balancers?
24502534 (Courtesy of GMPartsDirect)
"These dampers are specially tuned by GM engineering for up
to 9000 rpm usage. They are used on all small-block V8 engines with
standard size crankshaft hub diameter. These dampers employ 70
durometer O-rings to dampen harmful crankshaft vibrations. The black
outer ring is fully degreed with contrasting white marks to simplify
ignition timing and valve lash adjustments. The hub is drilled and tapped
for standard pulleys and accessory drives. The dampers are 7.74" in
diameter and weigh 8.95 pounds (4.5 pounds intertia weight)."
to 9000 rpm usage. They are used on all small-block V8 engines with
standard size crankshaft hub diameter. These dampers employ 70
durometer O-rings to dampen harmful crankshaft vibrations. The black
outer ring is fully degreed with contrasting white marks to simplify
ignition timing and valve lash adjustments. The hub is drilled and tapped
for standard pulleys and accessory drives. The dampers are 7.74" in
diameter and weigh 8.95 pounds (4.5 pounds intertia weight)."
John A. Marker, I introduced the remarks about Mr Vizard's findings
simply for the sake of interest on this journey of discovery. IMO,
if your OEM balancer is in good shape, it will be more than adequate
for your purposes. I became interested in alternatives when I was
on a program to reduce rotating weight and was surprised when I
learned that lighter is not always better in this regard.
.
