LLY - Cracked piston

[NevadaLLY]

Cracked an lly piston on flat ground towing my fifth wheel. EGT’s were 700ish, boost around 12psi. The #7 cylinder was “clean” when I opened it up so assuming injector #7 stuck open and popped the piston. There is some mild scoring on the cylinder wall, can run a fingernail and catch slightly. I want to keep the build cost down but at the moment the list is- mahle performance cast pistons, Carrillo/wagler rods, AF crank, 60% sticks. Is a keyed crank a must? With the AF cam, will that help out the one crank? All bearings looked good in tear down - never lost any oil pressure and only ran for maybe 60seconds after cracking the piston. I might try to get my machine shop to key it if the $$ isn’t too high. Nowadays, seems like any question starts at 1K lol

 

[gmduramax]

I would do 100% injectors. AF crank isn’t necessary I would just make sure the crank is balanced good.

 

[TheBac]

Yes, have the crank keyed.

 

[Chevy1925]

you will be into the machine shop 1500-2k if they do quality work. Ill bet your heads needs a work over too and you dont know it (stock valve guides wear out quickly and spring seat pressure is all over the place)

If you simply cracked the piston and didnt get blow through into the cylinder wall, a .020 bore should be plenty (yes, have it bored so proper piston to wall clearance is there on the new pistons). Judging by the large star pattern on the piston, it wasnt a stuck injector but a victim of high timing/pulse width, stock lips on the pistons, high cylinder pressure and the pistons just failing from all this.

AF cam might help, might not. guys have still broken cranks with them. will it hurt to use one? no but dont think its a guarantee. is it better than a stock one? i would say yes when using a stock crank but it can be debated. you need a different crank if you want a real fix in there.

 

[Bdsankey]

As others have said, a good machine shop will be $1500-$2500 depending on exactly what you want done. Depending on mileage (as James said) the heads will need an overhaul which is the unknown in the whole bill. Boring/honing the block, balancing the rotating assy etc all have set costs but it is unknown how many guides/seats/valves etc your heads will need.


AF cam also is kind of one of those things that isn't exactly proven to be a solution. The only proven solution is a narrow rod throw crank. I personally believe that AF cams do help on new cranks but I don't know if there has been much of a study or poll done on used cranks.


Mahle motorsport pistons, decent cam (I'm a SoCal 3388 or 6480 fan), key the crankshaft, good rod (SoCal/Carrillo/Wagler/Howards/Crower etc), better balancer and proper air/fueling is a reliable and fun build. Note - that's at a high level, there definitely are little odds and ends that aren't listed above but those are the big pieces. I personally would like a 100% injector in something like that unless it is a dedicated tow pig or you don't plan on going over the ~650-700whp mark. To me, 100% injectors have really become the new ~60% injector. With the advancements in tuning methods and technology to continually make injector nozzles more efficient there is really no major downside except for a little extra cost.

 

[NevadaLLY]

I would do 100% injectors. AF crank isn’t necessary I would just make sure the crank is balanced good.

Wont 100% injectors require a stroker CP3 or dual fuel??

 

[Bdsankey]

Wont 100% injectors require a stroker CP3 or dual fuel??

Realistically so do 60% to get more power out of them. The stock CP3 pumps stop usually around the 575-600whp mark depending on age/condition.

 

[NevadaLLY]

you will be into the machine shop 1500-2k if they do quality work. Ill bet your heads needs a work over too and you dont know it (stock valve guides wear out quickly and spring seat pressure is all over the place)

If you simply cracked the piston and didnt get blow through into the cylinder wall, a .020 bore should be plenty (yes, have it bored so proper piston to wall clearance is there on the new pistons). Judging by the large star pattern on the piston, it wasnt a stuck injector but a victim of high timing/pulse width, stock lips on the pistons, high cylinder pressure and the pistons just failing from all this.

AF cam might help, might not. guys have still broken cranks with them. will it hurt to use one? no but dont think its a guarantee. is it better than a stock one? i would say yes when using a stock crank but it can be debated. you need a different crank if you want a real fix in there.

This piston was really the only one with the significant star pattern. Also this cylinder was running a reman (replaced 6ish years ago) so I'm thinking the balance rate has been out for a while. I inspected the heads and they're flat and I didn't have any valve noise. You think heads should be done too? 180K on the stock heads and this is the second time I've had them out of the truck (ARP studs and Grade C gaskets in 2014).

 

[NevadaLLY]

As others have said, a good machine shop will be $1500-$2500 depending on exactly what you want done. Depending on mileage (as James said) the heads will need an overhaul which is the unknown in the whole bill. Boring/honing the block, balancing the rotating assy etc all have set costs but it is unknown how many guides/seats/valves etc your heads will need.


AF cam also is kind of one of those things that isn't exactly proven to be a solution. The only proven solution is a narrow rod throw crank. I personally believe that AF cams do help on new cranks but I don't know if there has been much of a study or poll done on used cranks.


Mahle motorsport pistons, decent cam (I'm a SoCal 3388 or 6480 fan), key the crankshaft, good rod (SoCal/Carrillo/Wagler/Howards/Crower etc), better balancer and proper air/fueling is a reliable and fun build. Note - that's at a high level, there definitely are little odds and ends that aren't listed above but those are the big pieces. I personally would like a 100% injector in something like that unless it is a dedicated tow pig or you don't plan on going over the ~650-700whp mark. To me, 100% injectors have really become the new ~60% injector. With the advancements in tuning methods and technology to continually make injector nozzles more efficient there is really no major downside except for a little extra cost.

Truck is 80% used as a tow pig, other times just for bad weather and the usual drive to pick up materials and such from the hardware store. Otherwise not a DD. Although I love this truck, I'm tempted to move up into the latest models as there are so many other random issues popping up with this rig (windshield wiper motor quit, etc).

On the 100% overs - fill me in on the supporting mods. Can the stock CP3 with the lift pump fuel them? I guess I had always heard the 100's were difficult to tune and to keep the truck running clean.

 

[Bdsankey]

Truck is 80% used as a tow pig, other times just for bad weather and the usual drive to pick up materials and such from the hardware store. Otherwise not a DD. Although I love this truck, I'm tempted to move up into the latest models as there are so many other random issues popping up with this rig (windshield wiper motor quit, etc).

On the 100% overs - fill me in on the supporting mods. Can the stock CP3 with the lift pump fuel them? I guess I had always heard the 100's were difficult to tune and to keep the truck running clean.

So what makes you want to run 60% overs? What is your end goal with the truck? A stock CP3 and lift pump can technically fuel any injector properly, it just depends on the desired HP goal. IE a bone stock CP3 in good health is going to stop not long after the OEM turbocharger.

 

[NevadaLLY]

So what makes you want to run 60% overs? What is your end goal with the truck? A stock CP3 and lift pump can technically fuel any injector properly, it just depends on the desired HP goal. IE a bone stock CP3 in good health is going to stop not long after the OEM turbocharger.

60 over for lower pulse width, lower cylinder pressures. I'm running all the supporting mods to take this as far as I want but think I want to stop around 800RWHP on the race tune - hoping for 500 ish for reliable tow tune.

You'll see I'm running compounds so air isn't an issue.

 

[Bdsankey]

60 over for lower pulse width, lower cylinder pressures. I'm running all the supporting mods to take this as far as I want but think I want to stop around 800RWHP on the race tune - hoping for 500 ish for reliable tow tune.

You'll see I'm running compounds so air isn't an issue.

If your goal is ~800whp then you will definitely want 100% injectors. Can you make it on 60%? You sure can, but IMO the motor will be significantly happier on 100%. I also don't think you're 75/96 will be up to the task of 800whp. Depending who built it you may get close but you will always make less size for size in compounds vs a single. IE a single S475 will make more power than a compound setup with a S475 as the atmospheric charger. For the same goals you're after (my tow pig is getting a similar makeover) I went with a S364.5/480 compound setup, more specifically a S480/96/1.15 T6. In my opinion the 80mm comp wheel's flow is really needed to crest the 800whp mark in compounds. 100% injectors also are not the bear they used to be, the technology on both the manufacturing side and the tuning side has GREATLY advanced. They easily can be clean, extremely controllable, and tamed down to make the power you're after while offering realistically no major drawbacks.


A stock CP3 also will never fuel your goals, with or without a lift pump. You will need realistically a 12mm CP3 or dual stock pumps (personally I prefer a 12mm as a single pump is far easier on plumbing and less items to potentially fail). A 10mm may do what you're after but I prefer to not size the fuel system to barely meet my goals, I'd rather be air limited than fuel limited.

 

[NevadaLLY]

If your goal is ~800whp then you will definitely want 100% injectors. Can you make it on 60%? You sure can, but IMO the motor will be significantly happier on 100%. I also don't think you're 75/96 will be up to the task of 800whp. Depending who built it you may get close but you will always make less size for size in compounds vs a single. IE a single S475 will make more power than a compound setup with a S475 as the atmospheric charger. For the same goals you're after (my tow pig is getting a similar makeover) I went with a S364.5/480 compound setup, more specifically a S480/96/1.15 T6. In my opinion the 80mm comp wheel's flow is really needed to crest the 800whp mark in compounds. 100% injectors also are not the bear they used to be, the technology on both the manufacturing side and the tuning side has GREATLY advanced. They easily can be clean, extremely controllable, and tamed down to make the power you're after while offering realistically no major drawbacks.


A stock CP3 also will never fuel your goals, with or without a lift pump. You will need realistically a 12mm CP3 or dual stock pumps (personally I prefer a 12mm as a single pump is far easier on plumbing and less items to potentially fail). A 10mm may do what you're after but I prefer to not size the fuel system to barely meet my goals, I'd rather be air limited than fuel limited.

I want to keep this build decently low on the cost side but do it right. Stroker CP3 isn’t on the list this round. I’m ok not hitting 800 right now but want the bottom end to support the heavy towing, low end grunt (why I went compound). I just don’t want to go to 100’s and have tuning issues or flow rates that are difficult to control for a reliable rig. I’m not doing the tuning so that’s a plus. How have the injectors changed? Aren’t they the same P/N for going back in with different nozzles?

 

[Bdsankey]

I want to keep this build decently low on the cost side but do it right. Stroker CP3 isn’t on the list this round. I’m ok not hitting 800 right now but want the bottom end to support the heavy towing, low end grunt (why I went compound). I just don’t want to go to 100’s and have tuning issues or flow rates that are difficult to control for a reliable rig. I’m not doing the tuning so that’s a plus. How have the injectors changed? Aren’t they the same P/N for going back in with different nozzles?

That's like comparing a fuel injection system from a 1990 to a 2020, sure it does the same job but one is a hell of alot more advanced. Also, the methods behind tuning has greatly changed. IE timing tables, injection tables, compensation tables etc are all greatly improved over tuning even 5 years ago. Look how many stock bottom end trucks we're now seeing making big numbers on the strip and still surviving. We couldn't do that a few years ago.



How have they changed? Well, each company injection uses a slightly different spray angle, different internal modifications/clearances, some use coatings, twe now have the ability to run higher pressures to promote a more efficient fuel burn. At the end of the day, you asked for an opinion and I gave it. My experience has shown that for your goals a 100% nozzle would be a great choice, especially on a set of compounds and a built motor like you are talking about building.


Personally, I'd do below to go with your S475/stock setup. It won't reach your 800whp goal with the 475/96/1.15 but it'll be a reliable and fun setup. It would be an atmospheric turbo change away from your goal. You can do the motor build now and add fuel when your budget allows. The key here is to do things once.

100% overs (buy a quality injector)
12mm or dual stock pumps
SoCal rods (almost 1/2 the price of Carrillo/Wagler)
Mahle motorsport pistons without reliefs in 0.020" overbore
SoCal 3388 cam
Manton springs and 7/16" pushrods
ARP hardware everywhere
Good aftermarket balancer
Flexplate (BD is a nice upgrade over OEM and nowhere near the cost of billet)
Pinned/shimmed oil pump
Change the press in oil galley plugs to threaded NPT plugs (eliminates them pushing out)
Keyed stock crank

 

[NevadaLLY]

Whats the smallest pulse width you can run on the 100's? I don't want my tow tune being too hot.

 

[S Phinney]

You need enough fuel to drive the turbos. 60 minimum and I wouldn’t go larger than 100 overs. You need a 10mm pump minimum and a 12 if you go with 100 overs or two sportsman pumps. To drive your turbos smallest of tunes with the 100 overs would be in the 1300-1400 range on the big end.


Sent from my iPhone using Tapatalk

 

[darkness]

Don’t forget to save some money for oil cooling. That should be done sooner than later especially with twins. Looks like you have some already but a 2020 cooler would be nice.

 

[Chevy1925]

Whats the smallest pulse width you can run on the 100's? I don't want my tow tune being too hot.

ive ran down to 900uS and had no issues, you will be in the 1100-1300uS range, my guess. perfect place to be. you will notice that in the 1000-1500uS range, 100uS changes make a decent difference in power. beyond that, its a diminishing return as efficiency starts falling off.

 

[Bdsankey]

ive ran down to 900uS and had no issues, you will be in the 1100-1300uS range, my guess. perfect place to be. you will notice that in the 1000-1500uS range, 100uS changes make a decent difference in power. beyond that, its a diminishing return as efficiency starts falling off.

What pulse were you running on your tow file with the compounds on your LB7? Those were 100% if I recall? It's been awhile.

 

[Chevy1925]

What pulse were you running on your tow file with the compounds on your LB7? Those were 100% if I recall? It's been awhile.

i played with a few different ones but yes, 100%'s. i think i finally settled on 1000uS for summer. it was like 480-500hp (felt neutered compared to before ) as i was tired of starring at the coolant temp. i could just put my foot to the floor and go. There was a fine line in enough fuel to light the 483 and not like Shane says. the 900uS i used at one point coming back from a trip would hardly get the 483 to do anything, 475 should work off that but not much lower. i never tried it but ive heard going under 800uS can be hard to tune part throttle.