2003 4.8L Tahoe performance?

[TexasYahoe]

So I got my Tahoe a few years ago, always wanted one. It got the base model, cloth seats, 4.8L, etc. I've been happy with it ever since. But it was super slow. Didn't really matter because I had other performance cars to play with.

But now I'm trying to use the truck for towing.. and it's pretty sluggish. It also has 135,000 miles on it.

So, my question is, what basic mods are the best?

Do Cold Air Intakes really free up that much power on these motors?
Do long tube headers & high flow cats make lots of power like on other motors?
How restrictive is the factory exhaust?
I did some searching and I wasn't able to find much info on the 4.8L engine..

I'm thinking a CAI and long tube headers (since I have an exhaust leak at the manifold anyways), then a tune. That combo seems pretty tried and true for everything else i've touched in the past... thoughts? Thanks!!

 

[blueflamed03]

same thing I have, add gears, and a Black Bear tune. CAI helps minimal if any at best, but headers on a 4.8 will kill the low end even more. Gears, tune, and maybe a small converter.

 

[TexasYahoe]

I agree, gears do wonders... my tach broke a few months ago (stuck on redline, bah), when I get that fixed I'll have to check the RPMs in overdrive, etc, and see if it's right for me. What gears are stock on the base models? I don't even know if mine is called an LS or LT, I never researched this beast lol.

What size headers is everyone losing low end power with? Are they making different sizes to chose from? Also, what about shorty headers? Those shouldn't kill low end too much if it really is that much of a problem..

Any dyno graphs of the BB tune on a stock engine? I'm really really curious to see the low end torque gains...

Also, it feels like my converter is taking a crap.. barely takes off from a red light on flat ground it's so worn out.

 

[TexasYahoe]

I did the Seafoam treatment yesterday evening (http://www.tahoeyukonforum.com/forum/showthread.php?t=29672)

And noticed why I have that loud exhaust leak at the exhaust manifold.... check out the pic:


The darn bolt is completely missing on the far left I wonder how long it's been like that. At least it should be an easy fix though. Anyone know what size bolt & threads it is? I didn't want to remove any other bolts cause they are pretty rusted on... all i know is it's a 10mm (metric?!?! why GM, why!!)

 

[blueflamed03]

makes ya wonder if the engibe isnt sensing a knock, so its retarding the timing with that exhaust leak.

Run the RPO's in the glove box, it will tell you what gears you have.

Stall, a simple, cheap start is a Trailblazer I6 converter, it will help low end sense.

The tune and gears were HUGE for me...best mod was the tune, hands down best money spent.


What size is your tires, then search what gears you do have, and go from there.

headers, stay small primaries, 1 5/8"...no 1 3/4" on a 4.8...too huge.

 

[TexasYahoe]

Good point on the knock sensor.. it very well may have been pulling timing, especially with how rough it was running.

I'll check the RPOs for my gear ratio, thanks for the heads up on that. What brand gears do most people run in their GM trucks? GM, Richmond, or other?

I might try the corvette servo and tune first, and see how much that helps. I will at least do the tune for sure. I have access to Diablo and soon EFI Live, which is what I believe Black Bear uses, so I'll have to play around in there or see if I can purchase an editable file for my truck from him. Oh also, I think i like the way the Flowmaster Delta 40 mufflers sound on the 4.8, I might have one of those welded in too. (The original 40 series are just a little too loud/raspy for me, at least coming from under a Tahoe, IMO)

Thanks again for the advice, very much appreciated!

 

[ezdaar]

By the time you mod out that lil 4.8, change gears, install a TQ, headers,, etc. you could buy a 5.3 long block and swap it in, save money and be alot better off.
The gains would be far superior to modding that lil 4.8.
Just a thought..

 

[yukon2004]

TexasYahoe,

Keep us updated on what you decide to do performance wise. I've got the 4.8 as well, so I'm curious.

 

[blueflamed03]

4.8's can be made to run pretty decent...gears, I chose Yukon brand, ordered the whole kit from Ron's Machine, best deals.

 

[TexasYahoe]

By the time you mod out that lil 4.8, change gears, install a TQ, headers,, etc. you could buy a 5.3 long block and swap it in, save money and be alot better off.
The gains would be far superior to modding that lil 4.8.
Just a thought..

I appreciate the advice, but honestly that's pretty far from reality (an FYI for others reading this)

The 4.8 with just a cam, tune, and gears would walk all over a stock 5.3 truck. It's not like they use extremely different engine technology like going from a bump stick to dual overhead cams or something. Size isn't an issue with these 2 engines, unless you're shooting for over 500HP. And isn't the 5.3 rated at only 10 more HP than the 4.8 from the factory? See what I'm sayin..

My plan for performance upgrades is still up in the air, as I found out today that i'm not just missing an exhaust manifold bolt; someone broke it off in the cylinder head. So I may do shorty headers or long tubes now, since I have to drill & tap that hole anyways. I also have an exhaust leak in the top center of the passenger side manifold that looks pretty bad, so that will be taken care of at the same time.

So, my list of mods, in order, should be something like:

1) SeaFoam for 100k+ carbon buildup removal - done.
2) K&N drop in or some type of CAI kit - using drop in now.
3) Headers - TBD based on research (I do NOT want to sacrifice low end torque at all)
4) Tune. that's the most important part for me. Coming VERY soon.
5) Corvette servo in the trans for the shift kit.
5) Flowmaster Delta 40 muffler (for sound quality)
6) Gears - if the above list doesn't put the performance where I need it, the Gear swap will take care of that problem with out a doubt.

For the record, just a gear swap in a 4.8 tahoe and you can beat a Corvette in the 1/4 mile. Or at least the 1/8th lol. Because Yes, it makes that big of a difference. I can't imagine what I would think if I heard that someone swapped engines before rear end gears.