Help me Armchair build a 'Goldilocks' 4.8L LS engine...

So a long time ago I bought a cheap 4.8L off of a friend/forum member, and it's been sitting around waiting for a donor car that I found.  I have since found a pretty straight E46 wagon that I intend to drop it in over either this or next winter. 

I have some knowledge of the LS-series engines, and know that the block is the same as the 5.3, but the internet is a great and terrible place, and there's just SO.MUCH.INFORMATION, that it's hard to decide what to do.  Enter GRM.  

What I want is reliable power  (300-400whp) without needing to sell a kidney, basically.  I am not interested in turbo, just because an E46 engine bay is already cramped. So that would mean cams, heads, intake, and upgraded valvetrain/timing chain.  But there's just so many parts/options/iterations available that I'm unsure of direct compatibility without purchasing a 4.8l specific "kit" for $3000.  

I already have access and base level knowledge of HP Tuners, so that's what I'll be using for the base tune, and will likely have a pro dial it in beyond that. 

So basically any guidance would be appreciated, so I can start accumulating parts and building the engine up as I have time.  The engine is disassembled and stored currently, so now would be the time! 

Shouldn't be hard to do, 295hp was stock in some of the later versions.

Cam, better flowing heads, intake manifold, and a tune should do it. Note it will be a rev'er not a torque'r.  

I always wanted to build one like this, 400hp and rev to 7500. Sort of a modern DZ302.

Instead of trying to build the 4.8 for 400 hp, sell it to someone who's read too many Hot Rod articles about 1000 hp turbo builds and just buy an LS3. Same size, same weight, 430 hp in bone stock form.

My first LS was a 5.3 that was built for "400 hp" with all the usual effort (cam, LS6 heads, headwork, tune) and it was supposed to be easy to drive because it was lower torque. Never saw it make over 350 on the dyno. Swapped in an LS3, picked up 15 mph at the end of the straight at HPR and learned that it's not hard to deal with torque.

Keith Tanner said:

Instead of trying to build the 4.8 for 400 hp, sell it to someone who's read too many Hot Rod articles about 1000 hp turbo builds and just buy an LS3. Same size, same weight, 430 hp in bone stock form.

My first LS was a 5.3 that was built for "400 hp" with all the usual effort (cam, LS6 heads, headwork, tune) and it was supposed to be easy to drive because it was lower torque. Never saw it make over 350 on the dyno. Swapped in an LS3, picked up 15 mph at the end of the straight at HPR and learned that it's not hard to deal with torque.

I respect your input on this, I just was hoping to keep the budget a little more 'grassroots' than this.  Cheapest LS3 I can find is $4k... Where I have a $300 LM4 in my garage, that's a pretty big gap to cover expense-wise... I'm not trying to make a world-beater or anything- just something more fun and spritely than the anemic 170k mile 2.5 in the car now... 

Fair enough. Just do the math on rebuilding and tuning a bucket of parts for more power versus buying some displacement that's ready to go :) Sometimes the grassroots option is to spend the money up front. It certainly would have been in my case.

Im watching with interest. 

Same kinda plan only with a 5.3 and challenge budget if possible. 

I know on the ls1 vette, longtube headers and bigger throttle body/intake tract really woke them up. Id ASSUME the same with our truck based engines. However, i see soooo much conflicting information with searching....

I do prefer displacement for torque, but I think a cheap 4.8L would be fine.  LS3s aren't cheap these days.  Properly geared it will be a hoot.

Step 1.... what heads are on it?  Last three of the casting number works.  They are most likely 862 or 706.  If they are one of those, don't stress.  You could swap heads, but there aren't many other LS heads with a small enough chamber to keep your compression up... at least none that are cost effective.  Both of those heads give you about 9.5:1 and have 200cc cathedral ports that are more than adequate for feeding 4.8L.  If anything you could do a wee bit of pocket porting and shave down the valve guides a bit, but I wouldn't for a 400hp build.

If you have room (and don't mind the ugliness) keep the truck intake.  By far the best bang for buck.  LS6 intake is a close second and offers more hood clearance.

Cam is your big thing.  Factory cams spec'd out at 191/190.  Your compression and head flow can support something more like mid 210s.  Narrow up the LSA as well.  Early factory cams were 115.5 LSA and later ones were 114.  Something 113 or 112 would wake up the torque a bit.  Wide LSAs make wider torque curves with a lower peak number.  Narrow LSAs will tend to make more peak torque at a lower RPM without killing the overall torque production.  Wider LSAs are an OEM choice to help them meet emissions (required by the gubmint) and NVH (preferred by most customers) so if you're going aftermarket cam, just squeeze those lobes together a bit.  

Pay close attention to your final drive ratios.  What trans is going in?  Huge difference between a 4L60E and a T56.  Just for reference, a 4L60E with 3.08 rear is numerically about the same overall ratio spread as a T56 with 4.10 out back.  Your final drive ratios will have a huge impact on the cam selection.

If someone makes headers that fit, I would do it.  The basic hierarchy of exhaust manifold performance goes basically like this: stock manifolds usually suck, shorty headers are a mild improvement, full-length headers are best.  LS manifolds will do in a pinch, but it will take more duration on the cam to make the same torque/power as proper headers.  Hooker makes a "blackheart" manifold that is a fair compromise.  It looks like a combination of a log-style manifold and a shorty header and they packaged it as tightly as they could for swaps.  The best factory manifolds are the GTO style and the LS6 corvette style.  That's a cheap way to get a modest improvement for not much cash.... if they fit.

Having said that, the 4.8L is like a slightly displacement-handicapped 5.3L.  Good head flow and good compression means you are basically a cam and exhaust away from glory.  Don't stress about big-dollar parts.  Much about the LS architecture is already waiting for a few goodies to make power.  Far cry from the traditional small block that often needed darn near everything to make power.

Thanks for the input thus far, everyone!  I have a T56 already, and the nice part about bmw's is that there is no shortage of drive ratios for rear diffs, so I can somewhat tailor those as needed.  Current rear in the car is 3.63, but I plan to pull it and put in an LSD at some point, so again, I'll do some calcs and figure out the best way to appproach it, performance value-wise.

The Tupperwear Hot Rod is getting a 5.3 with a cam and a thinned out factory harness and controller. The only mod is going to be a cam advocated by the "sloppy mechanic" on Youtube. Nothing radical. The goal is all done for under 2k canadian bolted to a powerglide.

If the 5.3 runs as well as it did for 200k miles in the truck it came from, everyone will be happy. Once all the bugs are out of the project after a year or three of driving, any extra power needs can be addressed to suit driving and chassis requirements. Trying to anticipate everything ahead of time was just going to lead to analysis paralysis.

To keep it simple, I think having the heads milled ~0.030" to get the compression over 10:1 and grabbing an LS6 cam and would give you the most bang for the buck. Beyond that, I'd just do reliability stuff (lifters, LS9 springs, MLS head gaskets, etc.) which can add start adding up to real money pretty quickly too...

If swapping internals, heads, and aftermarket cams are on the table, the options are endless.

golfduke said:

Thanks for the input thus far, everyone!  I have a T56 already, and the nice part about bmw's is that there is no shortage of drive ratios for rear diffs, so I can somewhat tailor those as needed.  Current rear in the car is 3.63, but I plan to pull it and put in an LSD at some point, so again, I'll do some calcs and figure out the best way to appproach it, performance value-wise.

 

3.63 wouldn't be too bad with a T56 but with a small-displacement mill I'd consider something lower (ratio... higher numerically, of course.)  Do you have a tire size in mind?  And what's the curb weight?

Many of the Impala SS guys who swapped a T56 always debated 3.73 vs 4.10.  3.73 is a good economy choice on a stock cam.  4.10 was the street performance choice with a wee bit of cam, but lots of guys went 4.56.  It made first gear a little low, but even 4.56s with that 0.50 OD made the gears act like 2.28s on the highway.  It's hard to go too far with a T56.  The problem we SS guys discovered was finding a shop that could balance the driveshaft at a high enough RPM.

I have no idea what the best way is to get these parts, but what about 6.0 heads and intake on the 4.8 short block?  Grab the stock cam as well and tune it?  Is this doable?  I have no idea!

If you're going to cam it, I'd recommend one that can use factory valvetrain parts - even if it's a set of the blue LS3 or yellow LS7 springs (which, IIRC, are basically identical). I had a set of "upgraded" billet rockers break on me while tootling down the business loop at about 30 mph and 5% throttle. Also had a set of high dollar CNC ported heads vent the cooling jacket into the intake ports on the first session of a two-day Laguna Seca event, which made that 2000 mile tow completely pointless.

GM has a lot of resources. I'd use as much of their development as possible.

I've wanted to do a high rpm 4.8 for eons. I love the LR4 in the wife's truck. 

I'm in the choose RPM range you want your torque to come in, buy cam to match. Run stock timing chain, springs to suit the lift on your cam but odds are a stock style spring will work unless you go silly with lift, stock GM lifters, I wouldn't bother with aftermarket heads on a 4.8. Intake, truck intake if it'll fit really any stock LS intake for your head port if it doesn't.  Remember to measure your pushrod length and I'd toss in a new LS2 timing chain if yours has miles on it but that's optional. The 4.8 won't be a DoD engine so stock valley cover and lifters should work.

pres589 (djronnebaum) said:

I have no idea what the best way is to get these parts, but what about 6.0 heads and intake on the 4.8 short block?  Grab the stock cam as well and tune it?  Is this doable?  I have no idea!

It's doable, but not advisable.  Most of the cathedral port heads use the same basic port but different size chambers, so you would be tanking compression and not gaining much flow.

For instance, the LQ4/LQ9 6.0L heads are functionally the same as LS6 heads, but they just have bigger chambers.  This is partly because the LQ9 is larger displacement but also because GM wanted lower compression.  On my LQ9 I swapped for fully ported LS6 heads and I now have 11.3:1

pres589 (djronnebaum) said:

I have no idea what the best way is to get these parts, but what about 6.0 heads and intake on the 4.8 short block?  Grab the stock cam as well and tune it?  Is this doable?  I have no idea!

I think some of the 6.0 heads (at least the Gen 4 ones) may not work with the smaller bore of the 4.8/5.3.  Best to make sure before buying any of them.  I could be wrong, but I would assume most truck 6.0 cams would be no more aggressive, and possibly less, than the cams on a smaller engine.

In reply to bobzilla :

What is the recipe for a high rpm 4.8/LSX, and what is the first limiting factor to rpm on these engines?

dannyp84 said:

In reply to bobzilla :

What is the recipe for a high rpm 4.8/LSX, and what is the first limiting factor to rpm on these engines?

The main limiting factor on RPM is valvetrain on these motors.  The short stroke of the 4.8 can allow for some desirable metrics in some regards for high engine speeds but is not the limiting factor in most cases. The LS7 had the largest factor stroke and highest factory rev limiter of the LS family.

You can spin the stock rotating assembly well into the 7XXXrpm range with a good cam and good valvesprings

In reply to RacetruckRon :

I've always wanted to see someone build a high rpm Gen III on a budget, but also figure out how to switch the firing order back to 18436572 like a traditional small block so that it sounds better, I've never loved the LS noise.

In reply to dannyp84 :

The firing order change reduces a lot of stress on the crank and helps the engine rev.  Muffler and crossover choice is critical on the LS sounding good.  I'm a big fan of the Corvette H pipe sound, 4th Gen Fbody Y pipe is a close second to me.

A 4.8 with mild cam and headers will make 300whp through an auto transmission.  You don't need heads, you don't need an intake although those things will help.  

Watch Richard Holder on YouTube a few hours. He does tons LS dyno testing. Most of his "400hp" combos are a cam and good tuning. I second using as many Factory parts as possible, and the LS3 comment for that matter...

RacetruckRon said:

In reply to dannyp84 :

The firing order change reduces a lot of stress on the crank and helps the engine rev.  Muffler and crossover choice is critical on the LS sounding good.  I'm a big fan of the Corvette H pipe sound, 4th Gen Fbody Y pipe is a close second to me.

Why do the newer Camaros driving around always sound way too raspy and sharp? Just not enough muffler?

You said LM4. I think that's a aluminum 5.3 if that's what you have that's great.

If it's a 4.8 I'd assume it's a LR4 which is an iron 4.8.

Do you want this thing to Rev high or have more of a stockist powerband.

If all you care about is cheap and hp. Ls9 cams are very cheap, not a great setup for a low comp 4.8 and will have to rev it pretty hard. 211/230 and built for a larger motor with a PD blower on it.

If you'll spend a little more you could get a 300 dollar set of 243/799s and gain some of your power from heads and not have to go so big on a cam. I think the 243s flow about 40cfm more on the intake side than the 862s. GM did this on the Gen 4 4.8s. Problem is you'll lose some compression and at 9.4 it doesn't have a bunch to begin with. You can always shave them, but you could do that with 862 and gain compression. I generally like OE cams but unfortunately they are all designed for much bigger motors than a 4.8. If you had to go OE the LS1/LQ9 cam is a small step up, and shouldn't have to be revved super hard.

For intakes NNBS intakes are good and cheap, if you want a car intake the Dorman setup is a knockoff of a lower early FAST and Ls6 style upper, and cheap. 

If you are willing to spend a little more have one of the LS cam guys spec and grind you something, with correct valve timing for the 4.8.