Balanced Camshaft?


Fubar

Totally ****** Up
Mark II Lifetime
Le Mans 2010 Supporter
Aug 2, 2006
3,979
Dallas, TX
First a correction, they do not add a counter weight, it is actually a process of milling down the shaft to balance. I am told the gears and chain on the GT are a neutral issue, not being out of balance by more than a gram or two. The cam shaft themselves are typically out of balance to the tune of 45-55 grams each, so 200 gram of rotating mass out of wack on the cams. I have nothing to reference that against so I assume it is accurate (based on the source, I do not doubt it). Now, moving on to the necessity of the service, I am told that it will ‘add’ power, tho we can only guess at the figure because it has never been done as a sole modification. The main difference that was suggested, was the smoothness of the power band. I am very interested in that, because the GT’s typical Dyno graph is a very bouncy at higher rpms. Most graphs use a “5” on smoothing because they get so jumpy. I initially thought this was due to fuel supply or spark failure. This is the first mention that the valve train may play a roll in those fluctuations.

Money spent: waiting for pudding and proof.
 

soroush

Ford Gt Owner
Mark II Lifetime
Aug 8, 2007
5,050
ask me how I know bad things can happen if your cams arent balanced, actually the vibration in the motor was so bad that it broke not only the retaining nut for the rocker arm, but also the rocker arm and flattened the push rod at the same time :) I did balance the cam on my boss, but thats because we spin her to 8500 rpms ! I ve never had to do that on any other car, oh and I put a girddle on it just in case.



 

Fubar

Totally ****** Up
Mark II Lifetime
Le Mans 2010 Supporter
Aug 2, 2006
3,979
Dallas, TX
Was that the cam from your GT?
 

soroush

Ford Gt Owner
Mark II Lifetime
Aug 8, 2007
5,050
Was that the cam from your GT?
no boss 302
 

Indy GT

Yea, I got one...too
Mark IV Lifetime
Jan 14, 2006
2,390
Greenwood, IN
Let's be a little careful about mixing apples and oranges. The comments by Soroush are for a pushrod cam/valve arrangement. The FGT as we all know is a completely different architecture.

Rotating dynamics or shaft harmonics are very complex topics and misunderstood by most without actual hands-on or analytical modeling experience. In vogue today for most OE production vehicles is dual-plane tire/rim balancing whereby the outer side of the rim is evaluated for imbalance as is the inner side of the rim. Lead (or more "green" steel) weights are added to each "plane" for a "better" canceling effect of the assembly imbalances. This is now deemed necessary and appropriate for rim widths of 8-12". Interestingly the FGT does not use balance weights on the external rim for aesthetics so a single plane balance can work but I believe the spacing between the two planes is important.

My experience with high speed rotating engine hardware (rotation speeds greater than 10K) all use a design required dual plane balance to a low residual gram-inch callout. Our GT engine cams are approximately 20” long which would tend to favor a multiplane balance, though I see no discussion of balancing a cam shaft at different planes. A car wheel/tire has a much higher rotating mass than our cam shaft but more importantly, the weights are placed at a much higher radius (say 11” from the rotation axis) than a camshaft (maybe ½”). Camshafts spin within their mount bearings on a film of oil which provides inherent damping of any unbalance and thus are naturally damped. Any wheel/tire dynamics are attenuated by the shock absorber mounted remotely to the axle support structure so dynamic responses are more easily noticed by the passengers.

Mark, the “low” cam operating speed, very small radius to add or subtract balance weight and singular plane balance operation IMO makes little sense in spending the $600. In fact drilling holes or grinding off material may actually induce stress risers into the camshaft which might nucleate fatigue cracks. I agree with the comments of Flatrod.

As a guy that balances stuff all the time, I have never heard of balancing cams. I have however balanced cam gears in the past. I'll have to spin a cam up and see what is what with one. I just wonder how they do it. How do you take weight off or how do you add weight. Being so close to center line, I would think its not going to make much difference.
 

B.M.F.

GT Owner
Mark II Lifetime
Jan 29, 2009
1,260
Minnesota
Let's be a little careful about mixing apples and oranges. The comments by Soroush are for a pushrod cam/valve arrangement. The FGT as we all know is a completely different architecture.

Rotating dynamics or shaft harmonics are very complex topics and misunderstood by most without actual hands-on or analytical modeling experience. In vogue today for most OE production vehicles is dual-plane tire/rim balancing whereby the outer side of the rim is evaluated for imbalance as is the inner side of the rim. Lead (or more "green" steel) weights are added to each "plane" for a "better" canceling effect of the assembly imbalances. This is now deemed necessary and appropriate for rim widths of 8-12". Interestingly the FGT does not use balance weights on the external rim for aesthetics so a single plane balance can work but I believe the spacing between the two planes is important.

My experience with high speed rotating engine hardware (rotation speeds greater than 10K) all use a design required dual plane balance to a low residual gram-inch callout. Our GT engine cams are approximately 20” long which would tend to favor a multiplane balance, though I see no discussion of balancing a cam shaft at different planes. A car wheel/tire has a much higher rotating mass than our cam shaft but more importantly, the weights are placed at a much higher radius (say 11” from the rotation axis) than a camshaft (maybe ½”). Camshafts spin within their mount bearings on a film of oil which provides inherent damping of any unbalance and thus are naturally damped. Any wheel/tire dynamics are attenuated by the shock absorber mounted remotely to the axle support structure so dynamic responses are more easily noticed by the passengers.

Mark, the “low” cam operating speed, very small radius to add or subtract balance weight and singular plane balance operation IMO makes little sense in spending the $600. In fact drilling holes or grinding off material may actually induce stress risers into the camshaft which might nucleate fatigue cracks. I agree with the comments of Flatrod.
Great read thank you. I believe John is grinding on the side of the lobes if my memory serves me correct.
 

Flatrod

GT Owner
Mark II Lifetime
Jan 29, 2008
145
Anchorage, Alaska
I am going to have to back up. There may be something to balancing the cams. I spun up a 5.4 intake cam today, it was off 56.3 in the front and 17.4 grams in the back. At 1/2 radius there is no way I would be able to correct the front, just to much weight to remove. Even the back would be a problem. I fear if this is done the cam would break somewhere at the correction point. When I have more time I may try to play with this a little more.
Being as the intake and exhaust cams are tied together with the small chain, I have to wonder if they cancel themselves out when running. 56 grams is a lot of weight. I can see the need, but don't see the answer.
 

Flatrod

GT Owner
Mark II Lifetime
Jan 29, 2008
145
Anchorage, Alaska
ask me how I know bad things can happen if your cams arent balanced, actually the vibration in the motor was so bad that it broke not only the retaining nut for the rocker arm, but also the rocker arm and flattened the push rod at the same time :) I did balance the cam on my boss, but thats because we spin her to 8500 rpms ! I ve never had to do that on any other car, oh and I put a girddle on it just in case.




Soroush
It is not uncommom to break a poly lock where you broke them. Most of that is caused by rocker arm flex. By adding the gridle that should not happen again. Nice to see someone running a mini plenum. Do you run that on the street?
 

Accufab

Well-known member
Mar 14, 2006
142
Here's the answer I have for cam balancing specific to this application. The valvetrain in these engines is very sensitive. Far more sensitive than anyone really understands as a practical matter of discussion. Every cam profile I have developed over the years one of the most important attributes is to remove instability. First in the grind itself then the parts attached. Fortunately I have a Spintron in house to test all of my theories and cars to apply those theories on. In Mark's specific case while I cannot say exactly what the horsepower gain would be, it would be better to explain it differently. It is not really power that is gained, it is power that is not lost. I would not be surprised to see a 20 hp difference or more at 8000 rpms specific to this application. The stock GT cams are appx 44-48 grams each out of balance and ours are normally 51-54 out of balance simply because the lobes are larger and thus more out of balance.

This is not a topic I regularly discuss unless I am specifically building an engine for someone. I know the benefit specific to what I do and it's not my job to educate the general population on my dime. As a matter of reference back some 10 years ago or so I tested this back to back on my own race car. We were running 200 mph in the quarter and after balancing we instantly were running over 205 mph. Based on our weight and mph that application would calculate to over 100 hp. Given that performance gain and the place where I found it, as a racer, would you tell everyone what you learned or just keep it to yourself and kick their ass at every opportunity? That is one of the many reasons why we are the very best at what we do and hold just about every record related to modular engines in the country.

Turbo cars specifically benefit more from balanced cams because the energy that drives those turbos is a direct result of cylinder pressure. If you are losing cylinder pressure due to loss of valve control, whether it's poor lobe design or rotational imbalance, then you are losing the force that drives the turbine. The power potential loss can be huge.

As for the other benefits, they can be as endless as you'd like to discuss, for example, on my own car, we still are running the same valve guides that I installed 4 years ago as well as the same springs and valves. Hundreds of passes and we are running it to 9800 rpms. Specific to Marks car a big benefit will be cooling the exhaust valves during road racing. The valve is closed only several milliseconds at 7000 rpms. It uses that time to transfer heat from the valve back to the head. If there is any instability (and there is) that time does not cool the valve and the egts go up as does the temp of the valve. At some point you will either drop a valve or the valve seat will fall out. Either is not a good option.

So the original question is as to the value, that is for each person to decide. For me, quite frankly it's a pain to do. I know the value and that's why we offer it on our engines. The only way for a person to fully appreciate it's value is to completely understand its potential specific to this engine. This is what I do all day every day so it's easy for me. How this is relevant in other applications has zero to do with a modular 4 cam engine. I have seen it done on pushrod stuff and I'd question the real value on some of those applications because typically since all lobes are on the same cam statically it should be neutral, however dynamically it is not. It would completely depend on firing order and lobe placement.


See this for further questions

www.youtube.com/watch?v=CNPNxbEQX8Y

Or this www.youtube.com/watch?v=4W_7Ivt_XKI

Or this www.youtube.com/watch?v=7EP_sQ50ORM

Or this www.youtube.com/watch?v=oROLe_Ns590

Or this www.youtube.com/watch?v=6c7hWcQRQAc

Best regards,

John Mihovetz
Accufab Inc
 
Last edited:
H

HHGT

Guest
Great details as always John. Thanks for sharing.
 

DBK

The Favor Factory™
Staff member
Le Mans 2010 Supporter
Jul 30, 2005
14,614
Metro Detroit
Here's the answer I have for cam balancing specific to this application. The valvetrain in these engines is very sensitive. Far more sensitive than anyone really understands as a practical matter of discussion. Every cam profile I have developed over the years one of the most important attributes is to remove instability. First in the grind itself then the parts attached. Fortunately I have a Spintron in house to test all of my theories and cars to apply those theories on. In Mark's specific case while I cannot say exactly what the horsepower gain would be, it would be better to explain it differently. It is not really power that is gained, it is power that is not lost. I would not be surprised to see a 20 hp difference or more at 8000 rpms specific to this application. The stock GT cams are appx 44-48 grams each out of balance and ours are normally 51-54 out of balance simply because the lobes are larger and thus more out of balance.

This is not a topic I regularly discuss unless I am specifically building an engine for someone. I know the benefit specific to what I do and it's not my job to educate the general population on my dime. As a matter of reference back some 10 years ago or so I tested this back to back on my own race car. We were running 200 mph in the quarter and after balancing we instantly were running over 205 mph. Based on our weight and mph that application would calculate to over 100 hp. Given that performance gain and the place where I found it, as a racer, would you tell everyone what you learned or just keep it to yourself and kick their ass at every opportunity? That is one of the many reasons why we are the very best at what we do and hold just about every record related to modular engines in the country.

Turbo cars specifically benefit more from balanced cams because the energy that drives those turbos is a direct result of cylinder pressure. If you are losing cylinder pressure due to loss of valve control, whether it's poor lobe design or rotational imbalance, then you are losing the force that drives the turbine. The power potential loss can be huge.

As for the other benefits, they can be as endless as you'd like to discuss, for example, on my own car, we still are running the same valve guides that I installed 4 years ago as well as the same springs and valves. Hundreds of passes and we are running it to 9800 rpms. Specific to Marks car a big benefit will be cooling the exhaust valves during road racing. The valve is closed only several milliseconds at 7000 rpms. It uses that time to transfer heat from the valve back to the head. If there is any instability (and there is) that time does not cool the valve and the egts go up as does the temp of the valve. At some point you will either drop a valve or the valve seat will fall out. Either is not a good option.

So the original question is as to the value, that is for each person to decide. For me, quite frankly it's a pain to do. I know the value and that's why we offer it on our engines. The only way for a person to fully appreciate it's value is to completely understand its potential specific to this engine. This is what I do all day every day so it's easy for me. How this is relevant in other applications has zero to do with a modular 4 cam engine. I have seen it done on pushrod stuff and I'd question the real value on some of those applications because typically since all lobes are on the same cam statically it should be neutral, however dynamically it is not. It would completely depend on firing order and lobe placement.


See this for further questions

www.youtube.com/watch?v=CNPNxbEQX8Y

Or this www.youtube.com/watch?v=4W_7Ivt_XKI

Or this www.youtube.com/watch?v=7EP_sQ50ORM

Or this www.youtube.com/watch?v=oROLe_Ns590

Or this www.youtube.com/watch?v=6c7hWcQRQAc

Best regards,

John Mihovetz
Accufab Inc
I love everything about this post :lol :thumbsup
 

BlackICE

GT Owner
Nov 2, 2005
1,412
SF Bay Area in California
John, thanks for the post. No doubt that I, and many others here, view you as the guru of the mod Ford.
 

Flatrod

GT Owner
Mark II Lifetime
Jan 29, 2008
145
Anchorage, Alaska
John, I too thank you for your post. At first I didn't see anything in it, but after spinning up a cam I do see it now and do understand the benifits. And as you say its the power that is not lost that makes the most grains wether it is cam balancing or in other places in the engine.
 

Fubar

Totally ****** Up
Mark II Lifetime
Le Mans 2010 Supporter
Aug 2, 2006
3,979
Dallas, TX
Heh, that's my guy right there. He gotz my motor and I when I getz it back... I'm coming for you! All of you!! (but especially you Chip!)
 

Indy GT

Yea, I got one...too
Mark IV Lifetime
Jan 14, 2006
2,390
Greenwood, IN
Thanks John very much for the behind-the-scenes education. As I stated there is no substitue for hands-on experience of which you have a great deal. Thanks for sharing this experience with us!

Mark - Go get um.....
 

soroush

Ford Gt Owner
Mark II Lifetime
Aug 8, 2007
5,050
Soroush
It is not uncommom to break a poly lock where you broke them. Most of that is caused by rocker arm flex. By adding the gridle that should not happen again. Nice to see someone running a mini plenum. Do you run that on the street?
very observant :) yes I run it all the time its never been off the car since it was installed 14 years ago be the previous owner,, I have had the car for 11 years now.
 

B.M.F.

GT Owner
Mark II Lifetime
Jan 29, 2009
1,260
Minnesota
Here's the answer I have for cam balancing specific to this application. The valvetrain in these engines is very sensitive. Far more sensitive than anyone really understands as a practical matter of discussion. Every cam profile I have developed over the years one of the most important attributes is to remove instability. First in the grind itself then the parts attached. Fortunately I have a Spintron in house to test all of my theories and cars to apply those theories on. In Mark's specific case while I cannot say exactly what the horsepower gain would be, it would be better to explain it differently. It is not really power that is gained, it is power that is not lost. I would not be surprised to see a 20 hp difference or more at 8000 rpms specific to this application. The stock GT cams are appx 44-48 grams each out of balance and ours are normally 51-54 out of balance simply because the lobes are larger and thus more out of balance.

This is not a topic I regularly discuss unless I am specifically building an engine for someone. I know the benefit specific to what I do and it's not my job to educate the general population on my dime. As a matter of reference back some 10 years ago or so I tested this back to back on my own race car. We were running 200 mph in the quarter and after balancing we instantly were running over 205 mph. Based on our weight and mph that application would calculate to over 100 hp. Given that performance gain and the place where I found it, as a racer, would you tell everyone what you learned or just keep it to yourself and kick their ass at every opportunity? That is one of the many reasons why we are the very best at what we do and hold just about every record related to modular engines in the country.

Turbo cars specifically benefit more from balanced cams because the energy that drives those turbos is a direct result of cylinder pressure. If you are losing cylinder pressure due to loss of valve control, whether it's poor lobe design or rotational imbalance, then you are losing the force that drives the turbine. The power potential loss can be huge.

As for the other benefits, they can be as endless as you'd like to discuss, for example, on my own car, we still are running the same valve guides that I installed 4 years ago as well as the same springs and valves. Hundreds of passes and we are running it to 9800 rpms. Specific to Marks car a big benefit will be cooling the exhaust valves during road racing. The valve is closed only several milliseconds at 7000 rpms. It uses that time to transfer heat from the valve back to the head. If there is any instability (and there is) that time does not cool the valve and the egts go up as does the temp of the valve. At some point you will either drop a valve or the valve seat will fall out. Either is not a good option.

So the original question is as to the value, that is for each person to decide. For me, quite frankly it's a pain to do. I know the value and that's why we offer it on our engines. The only way for a person to fully appreciate it's value is to completely understand its potential specific to this engine. This is what I do all day every day so it's easy for me. How this is relevant in other applications has zero to do with a modular 4 cam engine. I have seen it done on pushrod stuff and I'd question the real value on some of those applications because typically since all lobes are on the same cam statically it should be neutral, however dynamically it is not. It would completely depend on firing order and lobe placement.


See this for further questions

www.youtube.com/watch?v=CNPNxbEQX8Y

Or this www.youtube.com/watch?v=4W_7Ivt_XKI

Or this www.youtube.com/watch?v=7EP_sQ50ORM

Or this www.youtube.com/watch?v=oROLe_Ns590

Or this www.youtube.com/watch?v=6c7hWcQRQAc

Best regards,

John Mihovetz
Accufab Inc
I was hoping the vids were of the spintron :D Very interesting on the heat of the valve and such...Also I seen the cams Roush were doing and they actually had counter weights made into the cams.
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
3,546
Turbo cars specifically benefit more from balanced cams because the energy that drives those turbos is a direct result of cylinder pressure. If you are losing cylinder pressure due to loss of valve control, whether it's poor lobe design or rotational imbalance, then you are losing the force that drives the turbine. The power potential loss can be huge.
John, thanks for your contribution to enlighten us as your experience and reputation with the modular Ford is without peers. In your (racing) business every friggin' detail that can help differentiate you from your competitors is gonna help you maintain the leadership position. Start putting together all of these small differentiators and they can to add up and give you a significant, consistent advantage. That said, I'm not sure to understand your statement, above. In fact, I wouldn't think that the turbos themselves give a rat's behind about cylinder pressures since really they are driven exclusively by the exhaust stroke. In other words, I wouldn't think that turbos care if the engine is a 9.0:1 compression or an 11.0:1 compression. Now, of course, "losing cylinder pressure" can be detrimental to the engine's HP and overall output -which of course is helping to drive the turbos but I guess I just don't get the emphasis on "Turbo cars specifically" regarding the issue of balanced cams. If you were so inclined, I for one would really love to see or learn of the magnitude of difference that can be attained. Is it something akin to the small but ultimately meaningful "race-environment" change or is it something that can be easily measured and felt on a real dyno (or a butt dyno)?
 

Accufab

Well-known member
Mar 14, 2006
142
Specifically about the turbo engine, the turbine is spun by the volume and velocity of air forced through the turbine. A lower compression engine just by nature makes less cylinder pressure thus less BANG when it fires. So the turbo is slower to respond and ultimately cannot make as much potential boost. A case in point will be the voice of Chip Beck when he gets his car returned. I spoke to the tuner and he told me that it was the smoothest GT he had ever tuned on the dyno (balanced cams) and the boost came in instantly ( changed cam timing to increase cylinder pressure). As some on here have experienced with their turbo cars the lag is slow to make power. Now if you can spool it up 1000 rpms faster then the gain in power in that window can be enormous. Right behind that is how rpm and shift point come into play. A typical car shifted at 7000 rpms will enter the next gear and have some lag. An engine that we build will drop in the next gear and lag will be much less if any under the same conditions.

So cylinder pressure and valve control is more important on a turbo application above all others. Another critical link about valvetrain stability particular to turbo cars is charge contamination. Obviously there is backpressure in the exhaust at all times under boost. If the exhaust valve bounces and lets spent gases back into the cylinder then the intake charge of fresh air is contaminated and its oxygen content reduced. No oxygen = no power.

Some of the above weak turbo response is cured by using smaller (more restriction) exhaust housings. Less power potential again. So for what we do that doesn't work. Any type of exhaust pressure just by nature will cause some form of reversion particularly in high boost engines. Usually we will raise the compression, move the cams and run a larger exhaust housing. We have faster response, more efficient engine that requires less boost to meet the customers power requirement. Win all the way around.

A typical GT 8.5 to 1 engine will have 160 lbs of cranking compression. Our typical 10 to 1 engine will have 200 psi and our typical 12 to 1 engine will be around 260 psi. It is always difficult to talk our customers into higher compression stuff. Largely I am sure from their past experiences or fear. The engine is going to detonate typically at "X" cylinder pressure regardless of how you get there. The difference being that the higher compression is always more efficient and will always yield more power at the same threshold of detonation. The low compression engine will always require more timing as well. The high compression stuff typically needs 10 degrees less timing so the result is more force is exerted on the crank in a forward motion and less is consumed trying to stop the crank before TDC. The end result shows more power on the dyno and the car will accelerate faster. Also it does NOT require more fuel, it simply produces more power with the fuel it has. We have had brake specific numbers as low as .30 and BMEP above 550 on the dyno with our high compression turbo engines. Can't even come close to that with low compression.

Hope this helps

John
 

Mullet

FORD GT OWNER
Le Mans 2010 Supporter
Oct 21, 2008
2,461
Houston Texas
I feel smarter.