2011 Apex motor

[machzrobbie]

My buddy Stone's motor came apart on the ice earlier in the year, I figured a Rod went through the block from running higher boost then the rods could handle. I bought a used motor and am getting the parts together to install rods, and new head shim along with cam timing. I was going to wiegh the stock rods out of the broken motor to compare them to the new ones and when taking the piston off the rod I noticed the web on the bottom of the piston was cracked. After inspecting the 3 other intact pistons they were all cracked. I am now thinking that maybe the piston failed and went sideways and broke the rod. What do you think?

 

[machzrobbie]

piston crack

 

[kviper]

Hi Robbie! Did the head have damage? thinking if the piston turned and impacted the head there would be damage. If the rod broke there may not be head damage? In either case the pistons sure must have had stress!

 

[machzrobbie]

Head is destroyed

 

[kviper]

I think you are right!

 

[sorenson1610]

Ouch!

 

[stingray719]

Strange that looks like a vibration crack to me.

 

[Agman 57]

How much boost was he running in that motor, that it came apart like that?

 

[machzrobbie]

We trail ride at 12-13 pounds and turn it up on race gas to 20. Sled has been pushed hard on the asphalt running 8.2 @159 mph as well. New motor is almost back together with rods. Decided to go with stock pistons and head shim again.

 

[Climbmax]

did you add fuel when you upped the boost? The OEM injectors can't handle that much boost as they are almost maxed out @ 290.

 

[machzrobbie]

It's not a fuel problem, we've had both sleds we tune in the mid 10's a/f at 19lbs of boost with the stock injectors on the 11/12 with the fuel pressure regulator MCX supplies. Pistons and plugs show nice burns

 

[mbarryracing]

It's not a fuel problem, we've had both sleds we tune in the mid 10's a/f at 19lbs of boost with the stock injectors on the 11/12 with the fuel pressure regulator MCX supplies. Pistons and plugs show nice burns

It might not be an AFR problem, but that doesn't mean it's not a fuel problem. You can have a good AFR and still detonate and damage components like that due to poor fuel octane quality...
Even fuel right from a can or drum can be crap, then add elevated intake air charge temps and combustion pressures and you'll rattle cast pistons apart.
We've had stock engines run at higher boost then 20 lbs with good fresh race fuel last the whole race season without coming apart like that.

 

[machzrobbie]

It's not a fuel problem, we've had both sleds we tune in the mid 10's a/f at 19lbs of boost with the stock injectors on the 11/12 with the fuel pressure regulator MCX supplies. Pistons and plugs show nice burns

It might not be an AFR problem, but that doesn't mean it's not a fuel problem. You can have a good AFR and still detonate and damage components like that due to poor fuel octane quality...
Even fuel right from a can or drum can be crap, then add elevated intake air charge temps and combustion pressures and you'll rattle cast pistons apart.
We've had stock engines run at higher boost then 20 lbs with good fresh race fuel last the whole race season without coming apart like that.

I guess I should have said it different - its not a A/F problem - someone stated that the stock injectors could not flow enough fuel and I was commenting that they flow eoungh fuel at 20lbs to keep A/F in the mid 10's. Fuel that was used was fresh race fuel from a sealed can, and there's no sign of deto on the tops of the pistons - only flaw on the other pistons is the crack in the pictures. Opinion seems to be that there was too much timing probably rattling the pistons, causing the stress cracks. I'm going to take my motor apart and inspect it over the next couple weeks and install rods. This motor has doulbe the miles mine has, so it will be interesting to see what I find.

 

[onestopjim]

stock piston will only last so long we ran them for years but also change them a lot we have since then make our own piston and have had no more issues.

I think I may still have a set of stock bore , all our new engines are big bore... let me know if you want them..

also keep in mind the 2011 motor is different if your looking for any used parts any way... (head) and your header will not fit older heads

 

[mulot30th]

Agree with Jim on that one, changed a few stock pistons on high boost (outlaw) sled.

engine were still runing strong and well, but pistons get cracks under at same place on machzrobbies picture.

I like stock pistons on stock bore engines, but need change more often before bad things happen.