Hey guys after a bit of advice little 4.8 upon inspection needs a bore , so I've read it's possible to fit 5.7 pistons in it as im Australia it's alot easier and cheaper to find 5.7 forged pistons for it as its a gen 3 i will put a set of gen4 rods in at the same time.This engine will be running a single gtx42 turbo with fast lsxr intake with 862 heads with full port and polish with 1.95 valves and a summit pro ls truck cam.i was wondering with the piston side /bottom end is there anything else I can do to gain any else whilst doing the rebuild ? Car weighs 2400lb

 

6.098” rods and oem 5.7 pistons won’t work with the 4.8 crank. You’ll need to get a 3.622” crank too.

what is the available compression heights of the forged pistons there? It’ll take a pretty tall piston to make up the difference in crank stroke.

 

to be honest I'm yet to look into piston height sizes yet ,i didnt realise id have to change crank etc makes me wonder if im better off putting a cple more pound of boost in it to make up for the cubes .The car is very light but was just exploring ideas whilst i have to have the block rebored.

 

4.8/5.3 use the same piston height so you either need gen 4 4.8 rods or a 3.622 crank and standard 6.098 gen 4 rods.

 

So slow ride your saying it is possible to use the gen 4 4.8 rods with a 5.7 piston providing I can get the piston heights the same ? Or completely go with the 3.622 crank etc is that the ls1 crank BTW?

 

The piston height is the same for 4.8, 5.3, 5.7, 6.0 and 6.2 (4.8/5.3 pistons are basically the same thing GM just changed rod length and crank stroke between them) If you have floating pin 4.8 rods and floating pin 5.7 pistons (which are more rare towards the end of 5.7 cycle) you can do it(also some aftermarket companies like Silvolite make a floating pin 5.7 piston that fits on a stock rod). The floating pin on a stock rod is 0.943" for all gen 4 stuff I listed other than oddball stuff like ls7/9 etc. It all depends on what you have access to parts wise thats easy for you to get.

 

That's awesome slowride that clarifies it for me I will order through summit more than likely if I can't get it here in Oz! Also with those 5.7 pistons would it make the 4.8 around 314 cubes ?.....cheers for the help to

 

These are the list off summit pros pistons .

 

I don't believe the Summit 5.7 pistons come with piston pin locks cut I could be wrong. You can use a 0.945" floating pin piston given it has locks/groove on a stock gen 4 rod, but the rods will need a slight pin fitting hone to take it from 0.943" to 0.945" etc. The WS6store also sells a lot of ICON stuff that will work in the the FHR or Premium levels for 5.7 sizes that would work well also.

 

I have some summit LS forged 5.7 pistons and mine came with lock grooves cut. If I remember I'll post a pic tonight.

 

I remember when they came out I mentioned that to Brian as it would interest people using stock gen 4+ rods on them. Not much reason to use a gen 3 press fit rod anyway.

 

I just found a local guy in my area has a 3.905 bore 4.00.stroke crank -4cc pistons hbeam rods all forged stroker kit for a really great price .Can this be a good option do away with the 4.8 and go for a 383 provid that is stroke okay ?

 

Prob cheaper/easier/better to go with another 4.8 block? Are they that hard to come by? What is the goal for the car et wise? Do you have a 7.50 cage? Are you sure you need a large overbore? You can get a single .020 3.78 piston cheap and run it?

What you are doing is polishing a turd IMO. The best part of the 4.8 is its cheap and strong with plenty of cyl wall thickness and less stroke and side loading. At 2400lbs you should be able to run pretty dang quick “as is” with a gen4 4.8. talking 7s easy. By the time you throw all the machine work and parts at the 4.8 (not to mention down time) couldn’t just grab another 4.8… or 2?

When you over bore it to 3.9x you weaken the hell out of it. It is done quite a bit, but depending on the block casting and if you get lucky, you could be pushing it on wall thickness between the cyls at that bore. Which is less than ideal on a turbo build IMO. Then adding stroke and additional side loading as well? Why? You don’t need it at your weight. Focus on rpm and the top end and keep the 4.8 bottom end as is.

At that weight why do you want a bigger motor that is 5x as expensive and 5x more likely to break?

Don't get me wrong bigger motors will make more power quicker and if its in your budget to play with go for it. But I wouldn't bore and stroke a stock block that far personally. If I were to use good parts I'd want a good block I knew wouldn't crack and shift under big loads. Otherwise the gen4 factory rotating assy is pretty well matched for factory blocks. Best "bang for your buck" IMO anyway are factory long blocks. I as going 158 at 3200lbs with a cam/springs 4.8. Cheap S480 china turbo on 21ish lbs. At 2400lbs my other setup went 5.50's on 15lbs without an intercooler. So I'd think with a nice intercooled setup a cam only 4.8 could go 4's and 7's "easy" @ 2400lbs.