Ls3 shortblock

[JDopirak]

Hello,

So the same guy I bought my 243heads from "who owns a local ls junkyard" has a freshened up ls3 shortblock for sale bored .05 over , new bearings and pistons for $2500. I'm thinking about buying it and slapping my top end on it. My top end is cnc ported 243 heads and my stock truck intake manifold. I'll have to buy a new cam.

I think $2500 for a ls3 shortblock is good but I want to hear your thoughts.

 

[JDopirak]

Hello,

So the same guy I bought my 243heads from "who owns a local ls junkyard" has a freshened up ls3 shortblock for sale bored .05 over , new bearings and pistons for $2500. I'm thinking about buying it and slapping my top end on it. My top end is cnc ported 243 heads and my stock truck intake manifold. I'll have to buy a new cam.

I think $2500 for a ls3 shortblock is good but I want to hear your thoughts.

Idk how to delete post but I bought the shortblock.

 

[kbuskill]

Just saw this post. Not terribly familiar with the LS engines as far as the amount that can be bored.

I know on the the old SBC .060" over bore was pushing the limits and could potentially cause cooling issues.

.050" seems like a lot to me but maybe the LS has more meat to sacrifice.

Keep us posted on your swap.

 

[Ilikemtb999]

Wouldn’t 243 heads be a choke point on a 6.2?

 

[992dr]

.005 or .050?

 

[JDopirak]

Wouldn’t 243 heads be a choke point on a 6.2?

So I got the short block home it has been bored 20 over. It measured 4.085 cylinders.

My heads are cnc ported so looking at the flow charts my heads flow almost exactly the same on intake side off by like 4cfm and they flow 25ish better on exhaust side. So they will act like stock ls3 heads.

The big issue is it has flat top pistons and if I did the math right" I suck at math sooo most likely wrong" but with 243 heads with 64cc my compression will be like 11 to 1 using stock head gaskets. I dont kmow much when it comes to engine building sooo anyone who does care to chime in??

 

[JDopirak]

 

[iamdub]

So I got the short block home it has been bored 20 over. It measured 4.085 cylinders.

My heads are cnc ported so looking at the flow charts my heads flow almost exactly the same on intake side off by like 4cfm and they flow 25ish better on exhaust side. So they will act like stock ls3 heads.

The big issue is it has flat top pistons and if I did the math right" I suck at math sooo most likely wrong" but with 243 heads with 64cc my compression will be like 11 to 1 using stock head gaskets. I dont kmow much when it comes to engine building sooo anyone who does care to chime in??

The only mod to the heads were having the runners CNC'ed? Did they check the chamber volumes? GM heads commonly have larger than advertised chamber volumes. If you're not gonna boost it and are fine with running 93 (and you should be with any performance setup), 11:1 SCR is a good thing.

Are the pistons stock dimensions, just .020" oversized? I'd still check to see how much they come outta the hole. Once you know that and your actual chamber volume, you can calculate your SCR.

 

[JDopirak]

The only mod to the heads were having the runners CNC'ed? Did they check the chamber volumes? GM heads commonly have larger than advertised chamber volumes. If you're not gonna boost it and are fine with running 93 (and you should be with any performance setup), 11:1 SCR is a good thing.



Are the pistons stock dimensions, just .020" oversized? I'd still check to see how much they come outta the hole. Once you know that and your actual chamber volume, you can calculate your SCR.

I already run 93 daily as that is what my truck was tuned on. My heads where the stage one porting from texas speed so I'm basing my numbers off there charts. And no boost. I'd love to break 400whp tho.

As far as I know stock dimensions other then 20 over and I'm going to buy a bridge and dial indicator and see if I can get exact measurements. I was basing it off of .007 out of the hole which came up a few times on fourms when looking up ls3 stuff. Also using .051 gasket for cr calculator.

 

[swathdiver]

Wouldn’t 243 heads be a choke point on a 6.2?

For more than 6000 rpms yes, they'll make more torque down low and is a great combination in our trucks if the cam is right.

So I got the short block home it has been bored 20 over. It measured 4.085 cylinders.

That is the max overbore for a 6.2, good to go. Put a 3.9 crank and you'll have a 409! Get one of those adjustable pushrods so you can measure for the length you'll need. That's one method of determining what you'll need anyway. Math works too!