'00 3.8 to 4.3 Build

[dstaff]

I figured the person balancing would have weighed and marked what bore each piston went into according to weight.

That's not really how it works. The first step is to weight match all the pistons and each end of the rods. Since he used aftermarket racing pistons and rods, they were likely already pretty close to matched out of the box. I'd be surprised if they varied by more than a gram. Once the weights of the rotating and reciprocating components were equalized, a bobweight was calculated, and that's what gets attached to each throw of the crank when it gets spun on the balancing machine.

 

[Markstang]

That's not really how it works. The first step is to weight match all the pistons and each end of the rods. Since he used aftermarket racing pistons and rods, they were likely already pretty close to matched out of the box. I'd be surprised if they varied by more than a gram. Once the weights of the rotating and reciprocating components were equalized, a bobweight was calculated, and that's what gets attached to each throw of the crank when it gets spun on the balancing machine.

So then as long as they were properly balanced, they all weigh the same and don't need to be on a specific part of the crank. The only 'problem' then is they're backwards.

 

[dstaff]

So then as long as they were properly balanced, they all weigh the same and don't need to be on a specific part of the crank. The only 'problem' then is they're backwards.

Yes, this is correct. When a crank is balanced, the same amount of bobweight is installed on each rod throw. Most machines will only tell the operator to remove/add weight from the front and rear counterweights, so having to install a rod/piston combo on a particular throw for balancing purposes is not a concern. Having said that, it's not all that uncommon on older engines with wide tolerances to match light pistons with heavy rod small ends and vice versa. If that is done, the shop should instruct you which rod needs to go with which piston, but it should still not dictate where on the crank it needs to be installed.

 

[vsixxer24]

Okay, that makes sense. I'm pulling the engine this weekend and rotating the Pistons. I'm going to keep the heads on and use my bore camera to check out the dish tops. Thanks for replying!

 

[davidcseifert]

9:1 compression ratio.. a little lower than the stock 3.8

That's nice to hear, they look to be the same dish size as the ones I bought, he wasn't exactly sure what they were

 

[vsixxer24]

That's nice to hear, they look to be the same dish size as the ones I bought, he wasn't exactly sure what they were
View attachment 158182

Weird that your pistons have two valve reliefs.. what is your CR?

 

[davidcseifert]

That's why I asked about yours, I wasn't sure lol

 

[vsixxer24]

That's why I asked about yours, I wasn't sure lol

Oh haha where did you get your pistons from?

 

[davidcseifert]

Bought them from a friend selling his stuff before going into the military

 

[vsixxer24]

Bought them from a friend selling his stuff before going into the military

Oh I see, haha.. But the comp ratio will still vary even if they look the same, I think it depends on the wrist pin location/offset along with rod length/stroke, bore size, etc.. What are you building?

 

[davidcseifert]

4.3 splitport with a MP3 blower on 12 psi, just looking for 400rwhp for right now is all

 

[plstktnkr2]

This is the same basic build I am doing but I am using a "Super Coupe" engine as a starting point. My blog on my build is at:
More than "just a six"