4.8 into 74 3/4 ton 4x4
 

I have been given a 4.8 that probably needs a new rod to make it go. I just have concerns about if its enough engine for that truck? Was thinking about swapping out a 5.3 crank and rods and use the flat top pistons to make it snort a bit more. Then I looked up that the original engine only had 160 hp and the 4.8 is like 250 hp. another concern is that it has the np203 transfer case and I don't want to tear the chain out of it so I'm not worried about max hp. So my question is anyone done this and how is it going. my plan is:

4.8 with vinci mega torque cam
sm465
np203
4 in lift
35 in tires

it will be a DD and weekend hunting rig,

thanks for any input.

Chip

Re: 4.8 into 74 3/4 ton 4x4
 

I would be more concerned about the torque and at what rpm range rather than the hp. Also with 35" tires you will likely want 4.10 or lower gears. I could be wrong, but I believe that 4.8's torque range is going to be farther up the rpm scale than your stock 350.

Re: 4.8 into 74 3/4 ton 4x4
 

4.8's are good motors and are happy revving. Not so much lugging. Think 283 or even to some extent 327.

My 07 GMC rcsb with the 4.8. It got the same mpg at 2000 rpm as it did at 2700 rpm.

I would go 5.13's, and with 35's your at 2500 rpm at 65. This will make the engine happy, and let it work where it makes power.

The engine has less to do with mpg vs the vehicle it goes in.

Re: 4.8 into 74 3/4 ton 4x4
 

I agree...gear ratio is a bigger factor than engine size...although a 4.8 is proven I would use at least a 5.3 if it were mine...especially if your gonna have to build the 4.8...5.3s are fairly cheap for a good running engine...you didnt mention if the free engine came with everything you need...acc,comp,wiring,maf,throttle,manis...etc
Also no mention of the adapters you'll need to go LS to sm465

Re: 4.8 into 74 3/4 ton 4x4
 

the 4.8 is complete with all acc needed. I am planning to use a bellhousing from novak transmissions and a sachs1050 flywheel. it has 4:11 in it now and I was going to get around to asking about gearing, so thanks for the answer. The engine ran upside down after a roll over and locked up, so not sure if it is a rod or main bearing and that will direct me further when that is uncovered. I also have a 6.0 sitting in the shop that needs a full rebuild also but like I said earlier I'm worried about the np203. the truck is a bare frame right now and I am just massing a pile of parts and planning.

Re: 4.8 into 74 3/4 ton 4x4
 

With the sm465 at 1:1 4th gear,4.11 rear gear, and 35in tires...at 65mph you'll be turning 2565rpm...not terriblely high rpms but I try to keep mine around 2000rpms for extended highway cruise speed...
With a 6.0, you dont have to drive it heavy throttle (yeah right)...I cant...
Heres a rpm calculator that may help your decision...http://www.csgnetwork.com/multirpmcalc.html

Re: 4.8 into 74 3/4 ton 4x4
 

thanks Mongo! I will use that link and try and decide what the heck I am doing.

Re: 4.8 into 74 3/4 ton 4x4
 

Not sure if you have read this, but here’s some good info for manual trans LS swaps
https://ls1tech.com/forums/conversio...tml?styleid=32

Re: 4.8 into 74 3/4 ton 4x4
 

As far as enough engine;
If you take into account that in the mid 70's, the 400ci SBC only made 185hp - granted, the torque always stayed above 350ft/lbs, the 4.8 comes in between 270-300hp and the same torque. Even a mild cam and springs would add 30-40hp/torque to that without losing anything at the bottom end.

I've driven a long wheel base 4.8/4L80E van towing a 30ft car trailer (full of stuff for moving... not a car) over two mountain ranges... it could have used a little more grunt, but it is more than enough for daily driving, and blew my late 70's 350 in my truck (a SWB 80 C10) out of the water as far as performance. The 6.0 would be better, because who doesn't like more power? But the 4.8 will be plenty if you're not racing.

Re: 4.8 into 74 3/4 ton 4x4
 

This is what I am thinking as well. hopefully all I need is a rod and crank (maybe) and with the right gears it will be just fine for what I am going to be doing.

anyone with any experience with the vinci mega torque cams? info I have found says power range 1400-5600 and great power in a 4.8 -6.0

Re: 4.8 into 74 3/4 ton 4x4
 

...I'd call brain tooley racing...he'll hook you up

Re: 4.8 into 74 3/4 ton 4x4
 

While you're in there, complete sets of gen 4 rods and pistons are pretty cheap. Just make sure you get flat tops for your 4.8. Hopefully the crank is good - they're plenty strong in stock form, even in a boosted application shy of 800hp or so.


100% agree here. BTR, Texas Speed, or even the Summit LS cams for a budget option, all have produced amazing results. I'm building a 5.3 for boost and it will get a summit cam.


I've never heard of that specific LS cam... in a lot of digging for cam options.

Re: 4.8 into 74 3/4 ton 4x4
 

I wouldn't get too hung up on keeping a np203. np208's can be had for $150, and np205's for not much more if you look around a bit. From what I read of the np203, it's going to hurt your fuel economy a bit if using it as a daily driver.

The holy grail for ls-powered transfer cases is a np205(strong) or np241(lightweight) with passenger side drop and a vehicle speed sensor already installed. Only available in Blazers and Suburbans in 89?, 90, and 91.

What 4.8 engine are you planning to use? Gen 3 or 4? I'd caution away from doing a manual swap on a Gen 4. Should be quite doable(I hope!), but a bit more research.

Re: 4.8 into 74 3/4 ton 4x4
 

it is a gen 3 4.8l I already have the kit to do the full to part time conversion for the 203. I think I am going to do the 5.3 parts swap with btr truck torque cam part time 203 and drive the thing and love it. I have a 70 c102wd hat is going to be the hot rod. thank all of you for the input and I will post updates soon I hope.

Re: 4.8 into 74 3/4 ton 4x4
 

thanks for the link :metal: very good info there

Re: 4.8 into 74 3/4 ton 4x4
 

Love both engines, but if your not going to keep this truck forever the 6.0 would have a better resale value.

This was a family truck from new (at least the chassis) and I plan for this to be my kids truck when I am gone some day! It will be known as Pete’s 74. Long story but given to me by my cousin after I saw it sitting in a hedge row as a pack rat condominium! Body was trash but chassis was in good shape and I have a 83 sitting in the driveway ready for donation. So here we go
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Re: 4.8 into 74 3/4 ton 4x4
 

The swap is pretty easy too, you don't even need the novak bellhousing. The original bellhousing will work fine, use the original style BBC clutch kit, it'll fit the nfw 1050 flywheel.

Re: 4.8 into 74 3/4 ton 4x4
 

I need to go look at the bell housing I have but can a person drill the 12 o'clock position to mate the gen III bolt pattern? I'm not sure I want to be minus two bolts in the housing.

Re: 4.8 into 74 3/4 ton 4x4
 

it works fine I'm running the oe bellhousing in my truck and plenty of others have done the same without issue.

Re: 4.8 into 74 3/4 ton 4x4
 

thanks for the info! any way to save some cash is a great thing

Re: 4.8 into 74 3/4 ton 4x4
 

I think you made a math goof. With a non-OD trans like the sm465, you'll be turning 3200 at 65 with those gears and tires. If you have a .75:1 overdrive, like in a 4l80e, you'll bring your rpm down to 2400 at 65.

If the OP intends to run a sm465 long term without installing a OD unit, I'd advise going with 4.11 gears.

Re: 4.8 into 74 3/4 ton 4x4
 

Buddy has an 03 or 04 with the 4.8, tho stock, NOT IMPRESSED. At ALL. I'm not sold on the LS's just yet. Naturally aspirated I don't get the infatuation. Yeah the run smooth, fast ECM, but they have **** for torque inless you run them to 10K RPM. Guess I'm just old school, I'll take a big block any day....

Re: 4.8 into 74 3/4 ton 4x4
 

If the OP intends to run a sm465 long term without installing a OD unit, I'd advise going with 4.11 gears.[/QUOTE]

I'm planning on 4:11 which is already there and seeing what happens. This truck's longest trips might be 100 miles at the most, I do plan on cruise, but mostly an intown driver. Just for FUN!!

Re: 4.8 into 74 3/4 ton 4x4
 

trust me I hear you I had an 83 swb 4wd that I put a 454 in and it was awesome! now I want fuel injection and no cold weather carb crap and cruise, maybe I'm getting lazy in my old age, but this is the route I'm going so trying to plan the best route to go.