Jay Gadsby

iTrader: (3)

Hey Ladies and Gents,

I am doing a budget build for my swap into my 240SX. I picked up an LS1 for a song, and come to find out the block was cracked. Oh well. I found a 5.3 LM7 block for a great deal with heads and all, but it lost oil pressure due to what was thought was a spun cam bearing. I pulled the engine apart today, the cam bearings are worn, only one is clocked a tiny tiny bit off 12/6 position. Like 1130/530 position. I am going to have them all replace and checked out by a local engine builder.

When I pulled the rods and pistons out, I was happy to find the new style rods in there (floating wrist pin, beefier construct). I was toying with the idea of running 4.8L pistons to bump the compression. Not sure if that will cause the compression to skyrocket and explode the engine into tiny fragments.

And for more information, I have a Comp 228R Cam with 114+4, LS6 Intake, All GTO accessories etc to run this with. Still need to replace springs and retainers to support the bigger cam. They are 706 heads btw. Would the 228R (.588/.588) cause PTV issues with flat top pistons assuming they are able to be run, and how to hell does one find flat top 96.010mm floating wrist pin pistons. I appreciate any help you guys or gals can give me. I hope this isn't too noobish, searched for a while, but may be a little high on bondo and other chemical fumes from the day in the Man Cave.

chrisfrost

iTrader: (8)

hello , how are You today ? You can safely run the 4.8L pistons in a 5.3L as long as They go from 1 rod design to the same rod design . The early gen3 piston pins are .0945" and the gen4 2005-present piston pins are .928 or right around there . As far as compression is concerned , the 5.3L non HO compression is 9.45/1 and using the 4.8L pistons will bump comp to I believe 10/1 . Go to Wallace Racing and on Their home page somewhere is a link to Their engine/automobile calculators .They have at least 150 dfferent calc from static and dynamic comp to camshaft calc to 1/4 and 1/8thmile calc gear change calc hp/weight=et blah blah blah ,,,,,,,for free . Go to Summit and search 4.8L pistons and narrow for 2007-pres . I bought 1999 4.8L Speed-Pros for $180 for the set . The newer 1's are something like $260 set or pretty close.

chrisfrost

iTrader: (8)

I don't know if You are aware of the problems with 706's but the 1's with a c between 2 of the rocker boss's have had problems with cracking and coolant leaking . I guess the company that made/molded Them screwed up

redtan

iTrader: (5)

4.8s have a different stroke than 5.3s, so if you plan on using the 4.8 pistons with a 3.622 stroke you're going to have to get a shorter rod otherwise the pistons would come out of the hole too much.

Jay Gadsby

iTrader: (3)

The rods I would use are the 5.3L rods. I was just looking for the bump in compression. I have looked on Summit's site, Jeg's, and a couple others, every time I put in 96.010 bore size, it ends up with a press fit wrist pin. I am just going to call them.

Heads- I have an "A" and an "X" cast in between the rocker boss. I am assuming these are in the free and clear.

The car is a 98 240SX, so with a full swap into it, even with the iron, it should still be sub 3000lbs. I am not using it for professional drag race, just the occasional trip to the strip and as a daily driver. Assuming with the little bump in compression, cam, ls6 intake, headers, and a tune, I can achieve 350rwhp, then that would put me sitting happy, happy, happy. What do we think, 350 doable? Or should I get some TEA heads, bore it out to LS1 specs, and have at it?

T/ALT1

iTrader: (3)

Well it would cheap to bore the block and just toss a set of stock LS1 pistons/rods off the classifieds for cheap and have the compression plus more cubes. JMO

Jay Gadsby

iTrader: (3)

I just may do that. I have 6 good shape pistons and rods out of the LS1. Had a destroyed piston on one, and a bent rod on another. I need to take it to the machine shop anyhow.

Bilster

iTrader: (21)

4.8 pistons will work because they are the same compression height as the 5.3. While the 5.3 does have a bigger stroke as you indicated, it also has a shorter rod length than the 4.8 creating the same compression height for both motors.

Bilster

iTrader: (21)

LSx GM engines have fantastic bore wear capabilities. Unfortunately, that's because the cylinder bore is like granite. It's hard to machine so most shops charge a premium to bore to LS1 size. Then there is the fact that you must re-balance the motor because of the increased weight of the piston. So while it's a great idea if you have the money, it's not an idea that I would call "budget".

Just an FYI, not all aftermarket 4.8 pistons are flat-top. Silvolite and Engine Tech are a couple of companies that actually are.

RezinTexas

for the cost of that you could buy a bare 6.0 block and have a bigger bore. ask me how I know

chrisfrost

iTrader: (8)

Also worth noting , I have a 5.3L that I had bored .030" over . The stock pistons came out of the hole roughly .010" and I bought Speed-Pro cast hyperutectic 4.8L flat tops which They list the compression height as being the same or .001" different . The set was $180 . When I mocked up a cpl pistons/rods with crankshaft in the engine They were between .005"- .010" under the deck so for quench and My desired compression ratio I'm using the LS1 gaskets that are .041" thick and removing .011"-.012" from the block deck . I have no complaints about the pistons , They have coated skirts, are pretty stout looking and price was right but that is quite a difference . Back at the time I posted My dilema here and I got 1 or 2 responses suggesting that the manufacturer does this to keep the static compression ratio the same as stock .
To the OP , when You're searching in Summits' online catalog there is a further refine search criteria for years so just put in 2007 or ? before the bore size and You'll be good to go

kacivic

iTrader: (2)

So if not milling the deck, would there still be any real benefit to using those pistons? Add in the cost of rings (another ~$120 or so), and I'm just wondering if there's any real benefit here.