Prove it to me....Camshaft Gear Drive is a HP Killer

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Prove it to me....Camshaft Gear Drive is a HP Killer

Post by Jeff Lee »

Ok, I have this Milodon 3-gear brand new. Came with some horse trading. I’m seriously thinking of using it. Why? 1,000#+/- spring pressure on Super Stock engine, I have a 55mm cam core by LSM that has the keyway in the wrong position. Basically, have to retard the cam 8° to be 1.5° advanced.
A MAJOR pain in the you-know-what to degree and not something you really want to change once you arrive at an ICL.
The Milodon has what looks like an easy method of changing the ICL once you establish a straight up ICL.
The old “increase in camshaft harmonics = loss in HP”. According to Milodon, this is absolutely not true. Of course they are the salesmen.
The 4-gear assemblies apparently are the culprit for HP loss.
I have searched the internet hi and low and I can not find substantive evidence (real dyno numbers or before / after track times) that support this.
So I’m somewhat thinking that the “facts” (or wives tale) just keep repeating themselves across the internet.
Or am I wrong? I’d like to hear from somebody that can support this HP loss. Timing belt is not an available option with AMC. Thanks.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by allencr267 »

Offset key on the cam AND crank for the 8?
Sorry, no help on chain vs gear drive loss.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by Jeff Lee »

So far I believe this is a good cam, other than the key issue. So I want to keep using it.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by Tom68 »

viewtopic.php?t=65719&start=15

Well it ca\n't be a power killer, there's a gazillion factory gear drives been made over the last century and a half.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by Jeff Lee »

Tom68 - Can’t believe I didn’t find that. Thanks!
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by GARY C »

Jeff Lee wrote: Wed May 10, 2023 11:18 pm Ok, I have this Milodon 3-gear brand new. Came with some horse trading. I’m seriously thinking of using it. Why? 1,000#+/- spring pressure on Super Stock engine, I have a 55mm cam core by LSM that has the keyway in the wrong position. Basically, have to retard the cam 8° to be 1.5° advanced.
A MAJOR pain in the you-know-what to degree and not something you really want to change once you arrive at an ICL.
The Milodon has what looks like an easy method of changing the ICL once you establish a straight up ICL.
The old “increase in camshaft harmonics = loss in HP”. According to Milodon, this is absolutely not true. Of course they are the salesmen.
The 4-gear assemblies apparently are the culprit for HP loss.
I have searched the internet hi and low and I can not find substantive evidence (real dyno numbers or before / after track times) that support this.
So I’m somewhat thinking that the “facts” (or wives tale) just keep repeating themselves across the internet.
Or am I wrong? I’d like to hear from somebody that can support this HP loss. Timing belt is not an available option with AMC. Thanks.
Your mind is set on running it, so run it and see if the "wives tales" or wrong!

But you will only know if it looses power if your willing to test one vs the other, no one could convince you of that even if they posted dyno numbers.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by rebelrouser »

I always thought the big HP advantage of gear drive over chain was the chain stretch and cam retard at high rpm's. Not apples to apples because of the rpms run, but scores of diesel engines have gear drives, they do it for the accuracy of cam and injection pump events. I don't know how to scientifically prove it, but it seems a roller chain would just also have to have less friction loss compared to a straight cut gear. As mentioned only true way would be to switch on a dyno and see. But could it be more than say 5HP loss with the gear drive?
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by GARY C »

rebelrouser wrote: Fri May 12, 2023 8:06 am I always thought the big HP advantage of gear drive over chain was the chain stretch and cam retard at high rpm's. Not apples to apples because of the rpms run, but scores of diesel engines have gear drives, they do it for the accuracy of cam and injection pump events. I don't know how to scientifically prove it, but it seems a roller chain would just also have to have less friction loss compared to a straight cut gear. As mentioned only true way would be to switch on a dyno and see. But could it be more than say 5HP loss with the gear drive?
Some engines because of design gears are the only option, some tests have shown loose belts will only retard the cam at higher rpm increasing top end power.

The biggest loss in power I have seen reported was 7 hp but I don't remember what system or engine combo.

Here are several articles talking about them, my personal experience with a Pete Jackson type was big fluctuations in timing and breaking the front main web out of my block on a 7000 rpm SBC.
https://www.bing.com/search?form=MOZSBR ... power+loss
Last edited by GARY C on Fri May 12, 2023 9:28 am, edited 1 time in total.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by Walter R. Malik »

We tested the Milodon three gear drive in the early 90's against a chain drive, (a belt drive was not legal in Trans-Am racing).

There was no apparent loss of power on those roller cammed, 310 cid Chevrolet small block engines; the rules had a rev limit of 8,200 RPM.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by ClassAct »

GARY C wrote: Fri May 12, 2023 8:47 am
rebelrouser wrote: Fri May 12, 2023 8:06 am I always thought the big HP advantage of gear drive over chain was the chain stretch and cam retard at high rpm's. Not apples to apples because of the rpms run, but scores of diesel engines have gear drives, they do it for the accuracy of cam and injection pump events. I don't know how to scientifically prove it, but it seems a roller chain would just also have to have less friction loss compared to a straight cut gear. As mentioned only true way would be to switch on a dyno and see. But could it be more than say 5HP loss with the gear drive?
Some engines because of design gears are the only option, some tests have shown loose belts will only retard the cam at higher rpm increasing top end power.

The biggest loss in power I have seen reported was 7 hp but I don't remember what system or engine combo.

Here are several articles talking about them, my personal experience with a Pete Jackson type was big fluctuations in timing and breaking the front main web out of my block on a 7000 rpm SBC.
https://www.bing.com/search?form=MOZSBR ... power+loss
So you have used a junk gear drive and now condemn them all? Bad policy. Mostly belt drives are used for convenience. They are easier to degree (the gear drive isn’t hard, just different and you can’t line it up “dot to dot” to start” and it is easier to move cam timing on the dyno or even at the track.

Cup cars, Pro Stock, probably Comp Eliminator and maybe some Super Stock guys (I’d have to look to see if belt drives are legal is SS because I don’t remember) are about the only ones I can think of who would do that.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by GARY C »

ClassAct wrote: Fri May 12, 2023 10:32 am
GARY C wrote: Fri May 12, 2023 8:47 am
rebelrouser wrote: Fri May 12, 2023 8:06 am I always thought the big HP advantage of gear drive over chain was the chain stretch and cam retard at high rpm's. Not apples to apples because of the rpms run, but scores of diesel engines have gear drives, they do it for the accuracy of cam and injection pump events. I don't know how to scientifically prove it, but it seems a roller chain would just also have to have less friction loss compared to a straight cut gear. As mentioned only true way would be to switch on a dyno and see. But could it be more than say 5HP loss with the gear drive?
Some engines because of design gears are the only option, some tests have shown loose belts will only retard the cam at higher rpm increasing top end power.

The biggest loss in power I have seen reported was 7 hp but I don't remember what system or engine combo.

Here are several articles talking about them, my personal experience with a Pete Jackson type was big fluctuations in timing and breaking the front main web out of my block on a 7000 rpm SBC.
https://www.bing.com/search?form=MOZSBR ... power+loss
So you have used a junk gear drive and now condemn them all? Bad policy. Mostly belt drives are used for convenience. They are easier to degree (the gear drive isn’t hard, just different and you can’t line it up “dot to dot” to start” and it is easier to move cam timing on the dyno or even at the track.

Cup cars, Pro Stock, probably Comp Eliminator and maybe some Super Stock guys (I’d have to look to see if belt drives are legal is SS because I don’t remember) are about the only ones I can think of who would do that.
Where did I condemn them all? I simply stated my experience with the one style I have used and would not recommend to anyone.
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THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by amc fan »

In the early 80’s the multi position crank sprockets for AMC we’re in the wrong place… not enough advance.
I used Dumont broach and made my own.
I put the cam where I wanted it without crank key marked it and scribed the position broached it and presto exactly where I wanted it.
Any competent machinist / mechanic can do it.
All that is needed is an arbor press.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by hoffman900 »

ClassAct wrote: Fri May 12, 2023 10:32 am
GARY C wrote: Fri May 12, 2023 8:47 am
rebelrouser wrote: Fri May 12, 2023 8:06 am I always thought the big HP advantage of gear drive over chain was the chain stretch and cam retard at high rpm's. Not apples to apples because of the rpms run, but scores of diesel engines have gear drives, they do it for the accuracy of cam and injection pump events. I don't know how to scientifically prove it, but it seems a roller chain would just also have to have less friction loss compared to a straight cut gear. As mentioned only true way would be to switch on a dyno and see. But could it be more than say 5HP loss with the gear drive?
Some engines because of design gears are the only option, some tests have shown loose belts will only retard the cam at higher rpm increasing top end power.

The biggest loss in power I have seen reported was 7 hp but I don't remember what system or engine combo.

Here are several articles talking about them, my personal experience with a Pete Jackson type was big fluctuations in timing and breaking the front main web out of my block on a 7000 rpm SBC.
https://www.bing.com/search?form=MOZSBR ... power+loss
So you have used a junk gear drive and now condemn them all? Bad policy. Mostly belt drives are used for convenience. They are easier to degree (the gear drive isn’t hard, just different and you can’t line it up “dot to dot” to start” and it is easier to move cam timing on the dyno or even at the track.

Cup cars, Pro Stock, probably Comp Eliminator and maybe some Super Stock guys (I’d have to look to see if belt drives are legal is SS because I don’t remember) are about the only ones I can think of who would do that.
Cup guys had issues with the NextGen and packaging the steering rack, which resulted in overheating belts / breaking.
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Re: Prove it to me....Camshaft Gear Drive is a HP Killer

Post by Warp Speed »

hoffman900 wrote: Fri May 12, 2023 12:23 pm
ClassAct wrote: Fri May 12, 2023 10:32 am
GARY C wrote: Fri May 12, 2023 8:47 am
Some engines because of design gears are the only option, some tests have shown loose belts will only retard the cam at higher rpm increasing top end power.

The biggest loss in power I have seen reported was 7 hp but I don't remember what system or engine combo.

Here are several articles talking about them, my personal experience with a Pete Jackson type was big fluctuations in timing and breaking the front main web out of my block on a 7000 rpm SBC.
https://www.bing.com/search?form=MOZSBR ... power+loss
So you have used a junk gear drive and now condemn them all? Bad policy. Mostly belt drives are used for convenience. They are easier to degree (the gear drive isn’t hard, just different and you can’t line it up “dot to dot” to start” and it is easier to move cam timing on the dyno or even at the track.

Cup cars, Pro Stock, probably Comp Eliminator and maybe some Super Stock guys (I’d have to look to see if belt drives are legal is SS because I don’t remember) are about the only ones I can think of who would do that.
Cup guys had issues with the NextGen and packaging the steering rack, which resulted in overheating belts / breaking.
That was mainly due to belt size and material.
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