rkreigh

I have a few 4.8 iron short blocks. 2 have stock bore, and nice stock rotating assembly, one block is .040 over has forged pistons, but the block is scored on number 7

and I have a new lunati 4.0 forged crank and h beam rods

I'm looking to do 2 turbo short blocks that will handle upwards of 1000 hp

my questions are, for a 1000 hp build, what is the safe limit I should bore these blocks? can they go as big as 3.905?? or is around 3.8 the way to go to have very thick piston walls

I have both stock LS6 and AFR 225 heads that I will be using in my builds and would like to stay with those heads

I'm also curious about your thoughts of going with a stock, short stroke crank and 4.8 displacement, vs the 4.0 lunati stroker crank

the turbo kit on one car is a ttix twin turbo 127 injectors

the turbo kit on the other car (*68 vette*) is twin T60 turbos currently with 80 lb injectors

I'm trying to sort all this out and freshen up a couple of engines this winter

like to hear any tips on turbo iron block builds!!

also considering burtonsville machine, I'm in alex VA

thanks

JoeNova

Personal preference, but I would NEVER overbore a block for a turbo build unless it is because the block has scoring and needs it or you can't find pistons available in the size you need. There are 2 liter 4-cylinders making upwards of 1500 HP now. There isn't much need to increase the displacement by thinning out the cylinder walls. Maybe I'm not as old-school as everyone else here, but I've had daily driven 4-cylinders that make more power than 95% of the N/A LS1 builds on this website.

As for the 4.8, do you know what year/generation they are? The stronger 4-th generation internals can take a severe beating. There have been bone stock 4.8s, stock cam/valve springs, stock rings/gap, headgaskets, etc that have put down serious HP to the wheels. I can think of one that made more than 800 to the wheels. Even with the weaker gen 3 internals, someone made over 1000 HP to the wheels on a 4.8. They are, in theory, the strongest factory shortblock, and they will rev to the moon thanks to the small bore and short stroke.


In all honesty, if you already have the parts, what is stopping you from using them? If you already have the 4" crank and AFR heads, can you think of a reason to let them sit and collect dust?

Forcefed86

iTrader: (4)

From what I’ve read, 3.9” is as high as you should go. (mostly NA guys doing this) Even at 3.9” some blocks are questionable and all need sonic testing. I sure wouldn’t push a 3.9” 4.8 block to 1000+ HP, at least not one I had any money in.

With a drag car, the only reason to go with a 4.8 I’m aware of would be the bore/stroke ratio and stronger block. Building a 4.8 is cool and all, don’t get me wrong. If you go that route, I’d leave the small bore and short stroke. Then use a big stall and rev the **** out of it to make up for the displacement losses. I’ve always looked at big RPM motors as the more expensive route.

If you’re going through the trouble of machining and using aftermarket parts, why not start with a 4” bore block? Then just clean up the bore leaving as much wall thickness as possible. If your stuffing the block full of aftermarket parts, the 6.0 makes much more sense for a drag car IMO. In the end I’d guess it would be cheaper than a motor you had to rev to the moon.

Just a thought… either way keep us posted.

rkreigh

I'll check the casting numbers, from what I understand it's the 2004 4.8 and up motors that have the good ls2 rod?

I need to fill in some missing pieces to the plan

yes, I kinda have a hodge podge of parts. only reason I'm not using the afr heads is that they are on a currently functioning motor (*ls6 ttix forged rods & crank) that engine has got a tap in it so I'm weighing alternatives on what to do to replace it. might even keep the alum block and stay with it if the the pistons are Ok and it just needs to be freshened up

the other turbo engine for sure has a scored block. might just bore it to 3.905 if it sonic checks and build a NA screamer

for the turbo builds the small bore makes sense

yes, I've been looking for deals on 6.0 iron blocks. can the bigger 4.0 + bore size work ok with the AFR 3.9x heads??? can the chambers be worked a bit?

that would work as I could use the crank and rods and buy the larger pistons.

for the c3 "resto mod build" I've certainly been tempted to just run a stock bottom end as 800 is all that car will handle (and I need a beefed rear and tranny even at that level) car currently has a 350 auto and the 68 rear has weaker spindle bearings/shafts

so here's the plan, tear into the alum block ls6, find out what's wrong, but have a forged short block ready ready. I definitely agree with much of what's said about NOT boring the block. for sure I'll use these engines in one turbo build or the other.

for the c3 with the skinny tires, limiting low end torq and a top end charge has some appeal on the street as I'm trying to hook it and go boost by speed with a Haltech computer should be a fun experiment

also looking for haltech geeks out there!

thanks for the great advice and help!!!

quadriplegic

good info here. I want at least 700rwhp. A 5.3 will probably do this correct?

Forcefed86

iTrader: (4)

700 is very possible with either small bore LS motor. Just went 9.1 @150 19 lbs on my 4.8. Trapped 159 on my 5.3, and many others have gone faster.

quadriplegic

Forged stuff?

dirty_old_chevy

The general consensus seems to be: if the factory valley cover bolts have a 13mm head and the exhaust manifold bolts have a 13mm head, then it has the stronger rods.

Forcefed86

iTrader: (4)

No. All stock block JY stuff. Cam and head studs basically. Builds are in the link on my signature.

VTC_WS6

iTrader: (9)

Well since the 5.3L I just put together has decided to generate no oil pressure, I too am going to use a 4.8L I have laying in the garage. I'll carry over the PRC stg 2.5's, but I'm wondering if there is a more advantageous cam to use or should I just stick to the LS9? I know the 4.8L gives you the option of stretching the revs a little bit, but is there a preferable boost-happy cam that'll take advantage of the extra revs?

2muchboostNY

iTrader: (8)

No personal experience but there is some good info on this thread.

https://ls1tech.com/forums/forced-in...4-ls9-cam.html

JoeNova

Isky triple 12 is an excellent boost cam for the 4.8.

AlterEgo

iTrader: (9)

Does anyone have a part number for this Isky triple 12 that is a good cam for a boosted 4.8??? Might work well with my twin setup...

I watched a video on youtoube with a 5.3 with a triple isky 12, it seemed like it had a nice lope to it... I always thought FI did't work well with a lopey cam.... idk??

Forcefed86

iTrader: (4)

The trip. 12 is not lopey at all. Idles like stock. PM stock48 for the cam. You can contact isky and buy it directly, but most go through him. Mine was labeled HR-740.

dirty_old_chevy

It don't take much of a cam to make a 4.8 lope a little....

Forcefed86

iTrader: (4)

Suppose I should say neither my 4.8 or my 5.3 had a noticeable lope with this cam. I also don't really idle under 900ish rpm due to my huge 160lb injectors.

dirty_old_chevy

Ya, 900 is pretty high. I can see why you didn't experience any. I've listened to some idle vids on pt.net with that cam and they had a noticeable sound, but the idle speed was way lower.