Forcefed86

iTrader: (4)

Not looking to set the world on fire power wise. Would like a highest compression possible for a snappy ITB build. This is mainly for the sound of a high compression engine. I'm told 13:1 is about max for E85.

I have a gen3 dished 5.3 as a base and some flat top 4.8 pistons available. What route would you go to get the most compression possible with the factory parts? What's the max attainable? Sacrificing lift with less than perfect valve events is fine.

truckdoug

iTrader: (26)

i did an "iron L33" with gen 4 4.8 pistons on gen 4 5.3 rods, gen 3 5.3 crank. i think the CR with some 806's milled .040 was around 11:1. 224/228 .56x/.57x 115+2 with a 69mm gt45 its was a ton of fun.

i think you could mill for smaller chambers but im not sure how far that'll take you. i think aftermarket pistons is the best way to get compression up that high

KCS

iTrader: (20)

I would bore it out for LS1 pistons, then weld up the chambers on whatever heads I plan to use. 13:1 should be easy.

Forcefed86

iTrader: (4)

Thanks, that sure sounds simple. Worried about cost a machine shop would cost to weld up the CC's. Not sure I'd be competent enough to do it myself. But 11:1 isn't going to do what we want. Sounds like I won't have much of a choice.

I'd like to stay away from machining the block in anyway. This is going in a 2800lb scca toy. Not too worried about power, but I'd like to keep the cooling requirements to a minimum and the reliability up. Also would like the ability to drop in another short block and go. 350hp at the wheels would be plenty. Do you think a "cam only" ls6 intake on a 5.3 could do it at 13:1? Sure seems like it would. The ITB setup is one of the cheapie china deals for $1300. May have to be put on hold if we need that money for the heads.

JoeNova

I've done 13:1 and thrown boost on top of it before with E85. Wasn't an LS, but you get the idea.

You won't be able to do it on dished pistons. Flat tops, thin gasket, and the right head will get you 11.5:1. Any higher, you're going to end up causing issues with the head, like overmilling, excess valve shrouding, bad intake alignment, poor PTV clearance.

The best way to get 12:1 or higher would be to redo the chambers on the heads without milling them. ~52cc or so will get you around 12:1. Any less chamber and you're sacrificing flow.

Forcefed86

iTrader: (4)

Sacrifiing a little flow is ok. Reason for all this is he heard a 13:1 ITB LS scream by at the track and fell in love with the sound it made. I told him I think we could make something similar on a smaller scale shoestring budget. Really looking for that raspy high compression sound. I think the power will be there regardless. May have even talked him into my spare 4.8 so we can rev it higher "reliably".

gagliano7

I know when Advanced Inductions (AI) ports 317 heads they will weld up the chambers to make the chambers smaller for a lower cc #. I think it cost $200 more for welding up the chambers.

JoeNova

Flat tops, .040 gaskets, and welded chambers sounds like the way to go. 12:1 is doable this way without messing up head flow too much. 13:1 is going to be pushing it.

Fishmasterdan

I called a well known LS retailer. I was told to buy +11 dome pistons made for your heads and 13:1 would be very doable without ptv problems.

NC_John

iTrader: (1)

Did you check what your dynamic compression is going to be?

mOtOrHeAd MiKe

iTrader: (8)

Putting the 4.8 pistons in the 5.3 is a good start. Then you will want to look into a set of smaller chambered 4.8/5.3 706/862 heads (and want to keep the small valves) and of course mill the heads down. Then look into a set of thinner head gaskets (making sure the piston doesn't smack the head).

All that being said I would worry less about getting an exact SCR, and look into influencing the DCR with cam timing. Which should provide the sound and characteristics you are looking for. You can also manipulate the duration/valve events to match the flow of the 706/862s between .400 to .550" valve lift, and this should keep you out of PTV trouble.

Just my thoughts.

JakeFusion

iTrader: (7)

I'd definitely bore to 3.9 and run some Wiseco shelf dome pistons... why weld the chambers when you can just run heads at 65cc and run the Wiseco 12cc dome for 13.1:1 with .040 gaskets? Same cost as any other Wiseco shelf piston. And that would work with the stock crank and some lower costs (like Scat I-Beam) rods if you're trying to keep cost down. I would def run an aftermarket piston with that kind of compression even on E85.

JoeNova

Because welding chambers is cheaper than buying pistons. And you still have to pay for block machining, rods, rings, bearings, etc.

mOtOrHeAd MiKe

iTrader: (8)

What about welding pistons?

Forcefed86

iTrader: (4)

Getting a little off track.

As the title states... Highest compression using factory rotating assy. That means no machine shop, or aftermarket pistons. Tearing into the motor defeats the purpose of a quick and easy high compression LS.

Filling the heads seems like the way to go hands down for what we are after. I can't see 13:1 being an issue on factory pistons/rods. Cyl pressure is cyl pressure... and I won't be making diddly compared to the turbo engines.

I'd be thrilled with 350whp and that seems well within the tolerance for a gen3 rotating assy. My last gen3 short block went 8's @ about 3000lbs. 350-400 crank HP should hold up just fine.