Thunder v2.0

The block in my car is a TSP 347 with the LS6 block. The casting on the block reads 12561168. I have a set of 243s I'm going to put on, so I ordered the ARP 3609 head bolt kit. Its supposed to be for pre 04 blocks. However, comparing the bolts to the ones I took off the when we removed the heads, look totally different.



Do I have the wrong ARP bolts? Just doesn't seem like those will thread without bottoming out. Maybe its an optical illusion, hoping someone can shed some light for me

LS1-450

iTrader: (33)

If you have an LS6 block you need the post 04 bolts. They are the shorter bolts. The bolt on the right is a pre-04 bolt. An Ls6 block needs the 04 & later.

Thunder v2.0

It must be my block then? Cuz they are advertised to fit LS1/LS6.

LS1-450

iTrader: (33)

Yah, you have to be careful. I have both types of blocks, as well. The LS6 blocks that I have are all short & all different than the LS1's. Their advertising is confusing for this reason. That's not to say that there aren't a few odd ball LS1's out there. It's best to pull one of the center bolts before ordering, just to be sure.

Thunder v2.0

Lesson learned I guess *sigh*

joecar

So pre-2004 12561168 block = short bolts (ARP 134-3610)...?

NHRATA01

iTrader: (10)

I'm not so sure about that. I have an '01 that came from the factory with the LS6 block. When I did the heads I used the long ARP bolts, which matched the size of the stock GM bolts.

I thought I remembered in '04 when the GTO came out, all LS1's used the LS6 block, changeover might've even taken place for the '03 model year.

My guess is the OP's block was an '04+ LS6.

joecar

Ah, gotcha... (I'm still not quite awake).