Duramax Diesels Forum Truck of the Week
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Old 04-16-2017, 09:30 PM
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Default To AF or not?

So I have the motor out, head studding it along with porting heads, valve springs, and push rods. Running an ihi with s366 center section in it for Air. I plan to pull the motor again next year and do rods and more fuel. Currently still going to run stock fuel this year. Would I see any benefits with going ahead with a stage 1 or close to stock grind cam that's an AF or should I wait to do an aggressive cam when I do rods and have reliefs in pistons?
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Old 04-17-2017, 04:35 AM
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Wait and do it when you build. Replace your crank too at that time.


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Old 04-17-2017, 05:43 AM
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Not that this will mean much, but I am not sold on the AF cam. Failures have still occurred with AF cams. If it was me, I would look at upgrading the crank as stated above.

This is just my opinion.

Paul
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Old 04-17-2017, 08:53 AM
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The af cam is cool and theory looks good on paper. But I have seen power drops with them. A standard fire will make more power.
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Old 04-17-2017, 11:09 AM
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Originally Posted by JDPlowboy View Post
The af cam is cool and theory looks good on paper. But I have seen power drops with them. A standard fire will make more power.
Do you have dyno sheets/timeslips of cams with same specs standard firing and alternate firing to back this up? I think there is allot more that goes into making power in these trucks than firing order alone. I'm. It saying that it's the answer at all but there has been vibration analysis testing done that shows better harmonics with the af versus the standard firing order.
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Old 04-17-2017, 11:27 AM
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If the alternate firing order was better, why hasn't GM changed to it?

Why would they continue to risk broken cranks if the fix was that simple?

Why did they completely redesign the crank and lower end of the L5P if the fix was a simple firing order swap?

That would have been SO much simpler, and SO much cheaper for GM to do........ Hmmm....
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Old 04-17-2017, 11:49 AM
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If you read my previous post you will see where I wrote that I don't believe that it's an absolute solution. But the af cams have been proven to improve harmonics, in most cases guys are swapping the stock can out for a more aggressive grind anyways. Why not install something that is ultimately going to allow your engine to run smoother? To the OP if it were me I would wait for the full build then decide what grind af cam to better suite your build, goals can change between now and then.
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Old 04-17-2017, 12:07 PM
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Quote:
Originally Posted by boostwhore View Post
If you read my previous post you will see where I wrote that I don't believe that it's an absolute solution. But the af cams have been proven to improve harmonics, in most cases guys are swapping the stock can out for a more aggressive grind anyways. Why not install something that is ultimately going to allow your engine to run smoother? To the OP if it were me I would wait for the full build then decide what grind af cam to better suite your build, goals can change between now and then.


Who says it will last longer before breaking? You really think GM hasn't tested this??


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Best 1/8th, 6.93, 104.24MPH (Street tires, fuel only, single HX60 turbo) (2016)

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Old 04-17-2017, 01:05 PM
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Originally Posted by IOWA LLY View Post
Who says it will last longer before breaking? You really think GM hasn't tested this??


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Do you believe they have any benefit?
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Old 04-17-2017, 01:10 PM
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Quote:
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Do you believe they have any benefit?


I believe they might make the engine run smoother at idle and part throttle. Based on what a lot of people have reported. But there's so many variables involved in comparing before and after an engine build that I'm skeptical of even that.

But honestly I'm not the least bit convinced they help make the crank last any longer. I could be totally wrong, and I don't have a dog in this fight at all. But I've not seen any evidence that they actually help make the cranks live so me personally I wouldn't spend one dime to switch the firing order.


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Best 1/8th, 7.29, 98.6MPH (Street tires, fuel only, single Journal bearing GT42 charger) (2010)

Best 1/8th, 6.93, 104.24MPH (Street tires, fuel only, single HX60 turbo) (2016)

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Old 04-17-2017, 01:46 PM
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My original engine was built and balanced by the same machine shop as this engine with the AF cam. It is 10x smoother at idle than the first built engine or the two factory bottom ends I've had in the truck. My original built engine made it 5k miles with a brand new LB7 crank and stock cam. Was around 1000hp and I honestly wasn't that hard in the engine. Now this engine received an 80k mile used LBZ crank with a Socal AF cam. It has made it somewhere around 15-17k miles so far and I beat the hell out of it around 1,200hp. It may not be a fix all, but something has made this engine last longer.
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Old 04-17-2017, 01:53 PM
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Quote:
Originally Posted by Harbin_22 View Post
My original engine was built and balanced by the same machine shop as this engine with the AF cam. It is 10x smoother at idle than the first built engine or the two factory bottom ends I've had in the truck. My original built engine made it 5k miles with a brand new LB7 crank and stock cam. Was around 1000hp and I honestly wasn't that hard in the engine. Now this engine received an 80k mile used LBZ crank with a Socal AF cam. It has made it somewhere around 15-17k miles so far and I beat the hell out of it around 1,200hp. It may not be a fix all, but something has made this engine last longer.


Exactly. But there is also the guys out there that have broken brand new cranks with AF cams. And plenty of built motors that have tons of miles on the stock cam and crank and still going. Idk. Just not enough stories like yours Harbin to totally convince me.


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2009 ECI Diesel Truck Points Champion
2010 ECI Diesel Truck Points Champion
2011 ECI Diesel Truck Points Champion
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Big thanks to everyone who helps me.

Best 1/8th, 7.29, 98.6MPH (Street tires, fuel only, single Journal bearing GT42 charger) (2010)

Best 1/8th, 6.93, 104.24MPH (Street tires, fuel only, single HX60 turbo) (2016)

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Old 04-17-2017, 02:12 PM
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I would rather have the piece of mind that I gave it a solid fighting chance if I were building a new motor. The AF is not worth it IMO for just a cam swap on a crank that has already seen the original firing order harmonics since the stock cam has already proven to be more than efficient enough to break stock rods/pistons.

I would run an AF with a full build and a fresh crank though as I did on my first build. I used a new LML crank the first go around. The current build is getting a narrow rod Bryant crank from SoCal. There are a few high horsepower people out there than may speak up about their findings as well. The longevity at high horsepower definitely increased with less crank failures for a given time period in the same application. Obviously its not an end all, however, I do think it may help a little. There is really not enough solid evidence to prove one way or another, but its worth a shot to me if I am already swapping the cam for a build anyway. Its a very small cost compared to the total bill, why risk it...
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Old 04-17-2017, 02:18 PM
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personally id just go straight to a better crank and move on. you can pick up SF cams cheap now used or buy them new for a few dollars less than a AF depending on where you buy from. I sold my spare lb7 crank knowing that if/when mine goes ill be buying a callies crank and fingers pistons right off the bat. may throw a cam in it but whether its AF or SF will depend on if i really want the smoother idle or if i get a good deal on one or the other.
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Old 04-17-2017, 02:51 PM
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