Lachata

I'd really like the advise from those who have built a iron ls1,

so I got my 5.3 block back from the machine shop bored out to 5.7,
new ls1 pistons pressed to the 5.3 rods, the stock 5.3 crank was polished

i did Not get rotating assembly balanced, some people say it has to be balanced some say it doesn't, It's going to have a mild cam ported 243 heads the goal is 400whp.
I would like the input of anyone who built a iron ls1 and Did Not get it balanced to see if it worked without problems??

im on a tight budget that's why I didn't get It balanced, if it will work like this without self destructing that would be awesome. Thanks in advance

KCS

iTrader: (20)

I know that the difference between a dished 4" bore LQ4 piston and a flat top 4" bore LQ9 piston is about 15g. You're going from a dished 3.780" bore piston to a flat top 3.898" bore piston, I'm sure that the weight is much greater. You need to balance the crank IMO.

Aaron at SDPC

I agree with KCS the setup needs to be balanced.

A.R. Shale Targa

iTrader: (2)

And furthermore the crank might need Mallory slugs to rebalance which tends to escalate the cost exponentially
A 3-400 dollar balance charge is not unlikely here unless your machinist is creative with a hand grinder

nine8ss

iTrader: (5)

With the weight difference in pistons, you are in for a world of hurt. Boom...

boostified

iTrader: (1)

The 5.3 crank is heavier than a ls1 crank too

GtoProject

iTrader: (2)

Even if you are putting an engine together with stock parts that you know will "work" it should always be a priority to get a rotating assembly balanced before installation. Proper balancing procedures, as well as numerous other seemingly small details during assembly, are what can make the difference between a engine that'll take a beating for 50,000 miles and an engine that'll put up with the same abuse for double or triple that time. Never skimp on your short block, a few hundred saved now is a few thousand lost later on.

jimmyp3353

iTrader: (3)

Why would you not balance the rotating assembly? Most shops charge like $200. that's nothing.

A.R. Shale Targa

iTrader: (2)

CORRECT !!!!! A typical make bob weights up after matching all the rods for big end and total weight, plus matching all the pistons, with pins and clips/rings etc. and then spinning a crank plus drilling counterweight holes is in the 175 to 225 range
As the OP stated he is going from lighter weight dished 3.78" pistons to flat top 4" bore pistons.
this adds a bunch to the bob weight gram total. So either the crank counter weights need to be drilled and heavy metal slugs (mallory) BTW $45 each get installed or said balancer fella needs to be an artist with a hand grinder by removing a bunch of weight off the rod throw sides. VERY time consuming either way and much more costly.
The OP's best option would be to find a decent 6.0 crank that can take a polish and have a touch up balance....IMO cheaper than trying to UP balance a 5.3 crank

truckdoug

iTrader: (25)

how about just getting a stock 5.7 crank?

at 7000 rpm 15 grams becomes something like 200lbs





I have run engines with a 1-2gm. imbalance with little repercussion. I'm sure the bearings did not appreciate it very much.

But 15 grams will hammer the bearings to **** in short order.