This is my first post here, but have been posting on the Silverado Sierra forum.

I have a 2005 Silverado SS with a 406 stroker and forged internals with an s485.
I am running a TBSS intake, and spraying around 16gph pre TB. I had it tuned in 91 with the methanol.

I started hearing some knocking so decided to pull the engine. Cylinder 7 was trashed with a broken piston. It shared some stuff with 5 and beat it up too. My current theory is that meth couldn’t make it to the back cylinder and it got hotter than the other, pinched the ring a bunch and it found the weak spot in the piston which was the valve relief. I bought a 4 corner steam kit, and a sheet metal intake.

Does that theory sound plausible? Haven’t torn down the bottom end yet but I suspect a bearing too. I’m unsure if you can add extra fuel per cylinder in HPTuners, but what my biggest question was is regarding meth. Can I spray pre-tb to cool down the air and get a reading from the IAT sensor, and also spray on top in the middle or more of a port injection style for more fuel? Or will I just run into the same problem? I’m a VW guy and this is my first V8 so I appreciate the help. Thanks!

 

first off you should not tune for meth, tune for your 91 octane then add the meth as a supplement.. What is your current fueling set-up? The #7 piston is known to have issues should you get on the lean side.

 

You broke a forged motor. It’s because of -

1. Ran it lean

2. Cylinder overheated

3. Shitty tune

What do the plugs look like? That tells the real story. How much boost we’re you running and what is the fueling setup?

 

I’ve never heard of not tuning for meth. Straight water, sure, but all my other cars have all been tuned to account for the octane boost. Twin 450 pumps through -8 everything, 1000cc injectors. I didn’t build this motor, and the guy who had it before me also blew it, which is why they took it out .020.

 

the guy who built it skipped some steps and cheaped out on a few things. It was on 5 psi when I got it and he only had a 255 single in the tank. They were Summit flat top pistons and were definitely the weak point of the build.
I installed twin 450’s through Holley -8 lines. Was running around 14psi and was waiting for e85 tune to turn it up. I’d guess maybe 650-700 on butt Dyno.

 

I just got the rods out. The previous owner installed ARP main bolts and did not have it line honed. I don’t think that that was the main reason, but it definitely did not help. There is not a single bearing that I would consider throwing back into a stock truck. The crank catches my fingernail where every single bearing was, some less than others.

Compression was lowered with the rods, and all of the pistons have more wear than I would expect from a 2000 mile build. I saw paperwork confirming that everything was new, and mileage was confirmed from the invoice for the built 4l80. This engine never had a chance.

 

What do you mean by this?

 

Rods were made slightly shorter so the compression was lowered. It had a lot of piston slap and the skirts look like this 👇🏼because the piston was going really low in the cylinder.

 

That’s what I thought. That skirt wear does not surprise me with shorter rods intended for lowering compression. Any 4” stroke LQx is already going to encounter some decent piston rocking and skirt wear.

You need to pick the correct piston for rod length. A rod requires Z piston whereas B rod requires Y. I am sure you know this already but yes, that engine never stood a chance.

 

Just checked ring gap. .017 on the top of one of them 🤦‍♂️. Is there a preferred way way to lower compression on these? I think this block can be saved and I am not going to do it through the rods again. I usually do it with pistons on my serious builds, and headspacer on my not so serious ones on my VW engines. Leaning towards pistons on this too. Thoughts?