Some guys on another forum suggested I come to this site with questions regarding my '99 Sierra, so here I am.

I have a 1999 GMC Sierra, regular cab/short box with a 5.3/auto. I've been told this is a rare or desirable configuration but don't know that to be true. Other than a Flowmaster muffler it's stock.

I've had the truck since 2000, it has almost 250k miles on it. Suffice to say I'm somewhat attached, but I know it's getting long in the tooth so I'm weighing my options regarding the next engine, mods, etc.

Not looking to make a 900hp race truck, just a fun cruise and commute rig. A few ideas I'm considering:

1. Rebuild the original engine. Maybe upgrade heads/cam.
2. Buy a 5.3 crate engine
3. Swap to a LQ4 or some other engine

So what suggestions do you guys have? Please advise if I'd need to change the transmission up.

I would also like to add a limited slip to the differential. What's involved with that on a GM rear end?

Thanks!

 

I'd swap in a 6.0 of some kind either a LQ4 or LQ9 for the easiest bump in power and torque.

If it's the stock transmission, it might not be the best option for a more powerful engine, you can get a mildly built 4L60e to handle the bump in power.

For the rear end you can buy just the limited slip diff and swap your ring gear on to it or you could buy the diff with new gears if you want to change ratio's.

I'd do a gear swap if it has 3.23's or 3.42's, go to some 3.73's or 3.90's for a nice gear and still keep decent cruise rpm for mpgs.

 

Thanks. So is the 6.0 a better or easier swap than a 6.2?

Also, what's the best factory head for a street 6.0?

 

Yes, a 6.0 either being a lq4 or lq9 will be easier than the newer 6.2 engines. The stock heads on them are pretty efficient as they come for most builds, but the best budget head you could put a mild 6.0 is a stock 243 casting. Ported is better obviously, but not necessarily needed unless you want a decent bump in power. From the sounds of your plans, a stock head would do just fine. If you cam the engine then keep the lift under or around .570ish duration on both intake and exhaust. 220ish duration on both sides should suit it just fine and make plenty of down low torque. There's not a lot to gain on any more lift after that point unless you have a intake and heads set up for 6500rpm plus and the stock intake even with ported heads will start leveling out or begin to fall off there almost every time. Plus the 4l60e isn't a big fan of rpm with thr slide pump design it has, and even built unit would be much happier with the rpm kept down around that area which is plenty of rpm for most trucks. Power under the curve is what you want in these heavy trucks if you're looking for some get up and go. Keeping the Int/exh duration around that area will help make a nicely balanced powerband for a truck.

 

So I did some reading and am considering the following:

LQ4 long block
LQ9 pistons
Comp Cams 54-542-11

• 212/216 @ .050"
• 0.520/0.524 lift
• 115° lobe separation

8.1L (31lb) Injectors
ECM Tune


Does this sound about right? Do I need to look at headers or a different intake or throttle body for this type of setup?

 

That is a tiny cam for a 6.0! I would go with more duration and a small stall.

224r or 228r with a 3000-3200, 243 heads and a TBSS intake would be a decent low dollar combo, then throw some 373,390, or 410 out back and you would have a really fun truck.

 

Don't forget to upgrade the transmission! Even a stock, high-mile LQ4 will jellify your 250K mile 60E.

What is your budget? That will really help determine things. And what kind of drivability are you after?

 

What kind of mods are in order for the transmission?

I haven't nailed down a budget; let's call it $5,000. This is still gonna be a daily driver.

 

Transmission mods should include a full rebuild with bw or alto clutches and some sort of shift kit and vette style servo, and a higher than stock stall, but depending on the cam wouldnt go too much above about 2800 for a dd.

 

My vote is for a good used 80E, I hate 60Es.