Spencer Ducharme

Hi guys. I was wondering if i could get away with a 3.903 bore in my 4.8 LS block and still reliably run boost without blowing out the cylinder walls? The motor retains the stock crank and i have forged rods in hand for it. Just trying to decided on piston bore before i give the machinst the ok. Planning on turbos and around 8-900hp crank. I dont plan on turning it up in the future.

Forcefed86

iTrader: (4)

Lots have done it. But not all blocks are created equally. They *should* be sonic checked when you go that big. But when your talking $300 long blocks I question if that's cost effective or necessary. IMO you don't need the bigger bore to make your power goals, So I don't see the reason to bore it out that big personally. Machining a 4.8 at all for those goals seems counter productive. For the cost of a machine shop visit and forged internals you could just buy gen 4 4.8... possibly 2 or 3. They will handle 900 crank "as is".

That said if your gonna do it, do you really need to go to 3.9"? Are pistons just that much cheaper? OR can you run go say .060 over for the same cost? Are you going to run the 5.3 crank and rods?

Just for comparison i'm going 8.80's at 158 on a mild 4.8 S480 combo. Untouched short block.

Spencer Ducharme

Wow. That awesome. I was planning on forged rods and pistons while getting the 4.8 crank polished and reusing it. If i keep the 4.8 bore and stroke the same though, i think i can just tell the machinist to clean the block up a bit. Thank you for your knowledge!

Forcefed86

iTrader: (4)

Forged 4.8 stuff is usually big $ as it's not common. Last I looked anyway! You'd be better off getting a 5.3 crank and rods if you went forged. Plus youd get more displacement.

And it does have to be a GEN4 internals 2005+ engine. The older engines had wimpy rods. If its apart and at a machine shop. Source some stock gen4 5.3 internals (crank/rods/pistons) and drop them in. Or just nuy a 5.3! lol. engines are the cheap parts!

AwesomeAuto

I tried to convince him over on Corvetteforums to run a stock 4.8 bore, be he said he already had the block and pistons to match and there wasn't anything he could do about it

Old Geezer

iTrader: (3)

^^^ That's because you didn't provide him with the answer he wanted to hear.....

01CamaroSSTx

iTrader: (3)

Forcefed86 steer'd OP in the right direction but my question to OP's would be "Are we talking daily driven engine or racing engine?"

A machined block with engine block filler could probably handle some abuse.

Forcefed86

iTrader: (4)

I agree! And depending on the application a 3.9" bore may be desirable. I was looking at doing the same for a high compression NA build and wanted the cubic inches as cheaply as possible. 3.9" bore hyper pistons are pretty darn cheap, so that was my reasoning.

But a 900hp turbo build isn't anything to sneeze at... I'd want the block as strong as possible if doing that. No to mention time/money wise you're just better off cycling $300-500 short blocks as necessary IMO. Build everything in mind of quick/easy disassembly. Forged or not... crap always goes wrong. And if your waiting on machine shops constantly it gets old fast. I'd rigid mount the turbo and plumbing in a way that you could literally leave most of it installed when putting engine in/out. Same with the cooling system and wiring. Going on my 4th season with this 8 second "temporary" $500 4.8 I threw in to get me by. Have a spare alum 5.3 sitting here waiting. Jus tpick up deals when they pop up and have a spare... or two!