Havent posted here in a while since the days of the 350 GRENADE motor and im at it again with a LS motor. Im giving my high school 71 chevelle a much needed restoration and am planning on a twin turbo LS motor built very similar to the Hot Rod magazine 4.8 that made 1200 hp except i want to do it with a 6 liter block.


My question is what does it take to balance the 4.8 crank to the heavier OEM 6 liter pistons? The counterweights are so thin they arent very user friendly to add mallory metal. Im thinking a short stroke big bore LS should make a hell of a fun turbo motor and the extra cubes should make more power with less boost than the hot rod build. I also scored a set of fully CNC ported 5.3 castings with Ferrea valves to use on the buildup.


This is what i have so far

STD bore 2004 6 liter block and pistons (same wrist pin dia. as the 4.8 rods) non floaters
4.8 crank
TSP 228R cam on a 112 L/C
CNC heads with 2.00-1.55 valves (unknown chamber size but im guessing 61-62cc)
Edelbrock single plane EFI intake
Intake elbows.com fabricated elbow
60 lb siemens injectors
twin T76 godspeed hairdryers with a .96 A/R housing (same as the hot rod buildup)
Double roller chain
Home ported stock 6 liter oil pump with a better relief spring
New moly rings and bearings, MLS head gaskets
Cheapie Procomp head studs

It should wind up at 328 cubes and technically be a 5.3 again that revs to the moon! Compression should land somewhere around 9.5 to 1 if i figured it right. Of course its all used stock stuff in really good shape so lets see what it can do. Im looking for suggestions, ideas, balancing issues etc that have to do with the build so fire away guys! Thanks in advance.

 

Its a cool build. Not many do it but there was a guy that did it and he used ls3 heads on it I think. I would use the cathedral ports for sure like you are though. Im interested to see what others say.

 

I would think your best best would be to try to get an aftermarket piston/pin/ring set of about the same weight as the stocker. I know it's more money and probably would be more than the whole build just for pistons, but it would definitely be a stronger build. Wiseco Junkyard Dog K0045XS pistons would be a drop in, and with a .051 gasket and 62cc heads would put you at 8.99:1 and .010" in the hole.

My goal is to do a forged 4.8, stock crank, stock bore, and some piston swapping trickery to get it since nobody makes anything for that application.

 

Yeah 4.8's are definitely the bastard child of the LS family. Its too bad because the rod length, rod ratio and lightest weight pistons in stock form make it the best motor to push to HUGE power numbers on stock junk. I do have a 5.3 block that i could just grab and go but i really want to use the 6 liters 4.00 bore and pistons. The 2004 pistons i have are a bit odd that they do have coated skirts yet are not full floaters like 2005 newer stuff.

Unfortunately the full floater pistons use a wrist pin thats .002 different then non floater stuff and ruins the interchangeability of parts. I really dont see a problem making 1000 hp with stock LS stuff as long as i stick with the 4.8 stroke with less piston speed and cyl wall friction. Hell the stock rod bolts would probably even work.

 

ls3 block is a 4.03 not a 4 inch block ... tech u can use the heads but I don't think they would make good power on a 4 inch block

 

Who said anything about a ls3?

 

he did

 

LS3 has nothing to do with LS3 heads. L92/LS3 heads bolt right onto a 4.00" bore 6.0 no problem, so I'm not sure why you even mention it.

 

And they've been proven to make power just fine, as well as lsa and ls9 heads

 

An LS3 block is actually a 4.065" bore. I only said that I saw where a guy used a 6.0l block with a 4.8L crank and he used LS3 heads. I was only saying that some had done it.

 

And I have LS3 heads that work just fine on a stock 6.0l 4" bore motor. GM did it from the factory with an LY6 and L76.

 

Got it balanced fairly easy. The 6.0 pistons are around 97 grams heavier so the crank needed 42 grams added to both front and back to balance right. We had to drill the counterweights for a 1/2 dia tungsten insert then welded the piss out of them. Technically if somebody was a hacker, 6.0 pistons on a 4.8 crank is barely out of the factory 30 gram tolerance and it would probably run smooth with no balancing at all. If your digging deep into the junk pile to build a time bomb, have at it! Ha ha.

 

Did you happen to weight a stock piston/pin/rings/lock while you had them out? Just wondering if an aftermarket lighter weight piston could be used right out of the box, but would need to know for sure what the factory ones weighed.

 

No kidding 97 grams is a hell of a lot of weight, pin options may be able to knock a nice chunk of that down too depending.

 

Cool idea as i have both motors laying around lol do you think the piston speed difference will make that much more power than a stock 6.0 will?

 

Destroked motors always sound fun, alot of work to get it right though. I don't see the OEM parts/fastners lasting long in the "moon" rev range. Awesome of you to find out for us though!

Doubt it will make anymore power, it will just having a larger power band to play in. I know of a couple 4.8 turbo guys taking the rpms to 7500 or so with aftermarket fastners on the OEM long blocks.

 

My logic on this build is Hot Rod extracted 1200 hp out of a stock 4.8 so why not bore it out to the 6.0 bore size? Plus for a budget build the strongest stock stuff would have to be the short stroke crank with awesome crankpin overlap and the 1.9 rod ratio that minimizes rod stress. Plus the reduction in piston speed will let it crank some more RPM's safely. You cant argue with 1203 hp from the Hot Rod buildup and the bonus may be better gas mileage to boot!

One other benefit over a 4.8 or 5.3 is better head flow due to the larger bore size unsgrouding the valves. Thats my logic in building this thing and the fact i can build it out of mostly good used parts means if its a fail im not out much of anything. What do you guys think?

 

I think let it rip. Even if the whole shitbag flies apart in spectacular fashion, you're really not out much.

 

Also if you check out truckin magazine they did the same thing with 2003 5.3 and made over 1300hp..

http://www.truckinweb.com/tech/engine/1213tr_vortec_5_3l_big_bang/viewall.html

My post was directed to the average Joe doing "bolt-on" builds in their garage. To them I say if you can make 1200hp on an OEM rotating assy, why bother doing any machine work? By the time I paid to have all the parts machined for a destroked 4" bore motor, I could have bought another junk yard LS or two!

Don't get me wrong, more power to you for experimenting! Sounds like a badass idea. If I had the ability to machine parts cheap and easy I'd do all kinds of similar projects. I'm in for results!

 

Man I can't wait to see how this turns out.