How much more power can a 5.3L make without hurting road manners or gas mileage?

Termite_Delight said:

If you insist on a 5.3, start with a L33, Aluminum block 320hp stock.

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Since cost isn't a huge factor here, maybe the 6.0 would be the better choice since it gets me closer to the goal from the beginning. Ricko19 is right those were weird numbers I threw out there. What I should have said is that I'd like to get close to 400hp and 400 torque.

And I'd like to preserve the road manners and fuel economy. So maybe 6.0 is the way to go in this case.

Ricko1966 said:

Oh yeah the NA aspect of that motor was way overkill,and way over spent. A turbocharged mostly stock 305 with a turbo would do. But boost is going to make anything better,and what I think is most bang for the buck. Just my opinion.

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You are so right, and I'm the old timer that proved it! But as already stated, you need to keep your foot out of it for good fuel mileage. (very hard to do)



Except for the carb, bone stock 305 with a Rajay turbo.

Oh great @Turbo4whl tell us more because I am so kicking around a mild 305 build with a turbo for my truck. Anything you want to share would be appreciated,but let's figure out a way so we don't distract from O.Ps post. Maybe start a build sheet for that truck for us. Thank you

Turbo4whl said:

You are so right, and I'm the old timer that proved it! But as already stated, you need to keep your foot out of it for good fuel mileage. (very hard to do)

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Except for the carb, bone stock 305 with a Rajay turbo.

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How much power did you get outta that set-up?

Ricko1966 said:

Oh yeah the NA aspect of that motor was way overkill,and way over spent. A turbocharged mostly stock 305 with a turbo would do. But boost is going to make anything better,and what I think is most bang for the buck. Just my opinion.

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I don't disagree with you about boost. I love boosted stuff.
Durrty Thurrty? Boost. LowBurb? Boost. Busa? Boost. Merc S55 I sold in December? Boost. Car I'll buy next? Boost.
I have a forced induction problem...

PhotonFanatic said:

Since cost isn't a huge factor here, maybe the 6.0 would be the better choice since it gets me closer to the goal from the beginning. Ricko19 is right those were weird numbers I threw out there. What I should have said is that I'd like to get close to 400hp and 400 torque.

And I'd like to preserve the road manners and fuel economy. So maybe 6.0 is the way to go in this case.

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6.0 gets pretty bad fuel economy. Turbo + small displacement will work, but kits are pricey. The guys who do it cheap have some fab skills.

Now smaller displacement, higher compression, the right heads, cam and a proper tune can make great power and economy. It will need more expensive fuel though.

Are your intentions with the truck fairly light duty, ie commuting, moving the occasional couch in the bed, etc?

@618Syndicate

Never on a dyno, no real numbers. I did need to add a waste gate, not in the picture. Ran 7 lbs of boost, tuned old school reading plugs and adjusting jets and timing.

I also added a water injection system with a trigger switch set at 3 PSI and a temperature switch. Water injection not needed on a cold engine. Winter time 50:50 mix, water and denatured alcohol. This allowed for the most amount of spark advance.

About the power, seat of the pants proved the improvement. My brother-in-law dubbed it my Sleeper

Frankenchevy said:

6.0 gets pretty bad fuel economy. Turbo + small displacement will work, but kits are pricey. The guys who do it cheap have some fab skills.

Now smaller displacement, higher compression, the right heads, cam and a proper tune can make great power and economy. It will need more expensive fuel though.

Are your intentions with the truck fairly light duty, ie commuting, moving the occasional couch in the bed, etc?

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Yeah moving the occasional couch. It's kind of a nice resto mod truck. One of those where you don't want to damage the paint. But since I won't own a truck that can't be used as a truck, it still does most truck duties. And the old 350 is worn out.

I've heard people say the 5.3L fuel economy isn't much different from the 6.0L. I guess we could tell by the injector size and how much fuel they're actually spraying.


From a google search:

"To answer your question, a 5.3 will on average get about 4 mpg better than the 6.0. Yes gearing, tires, how you drive, tune or not, all makes a difference in any of our trucks, but it still comes down to about 4 mpg not matter what anyone says."

Sounds like the 6.0L will probably keep my wore out 350 MPG. While the 5.3L will improve it some.

Grit dog said:

@PhotonFanatic, your best bet would be to do a 6.0 Uhaul swap.
Buy ya a running 4.8 junker engine for cheap, rent a Chevy Uhaul van for 2 days. Swap the 6.0 in the van for the 4.8 laying on your floor. Return Uhaul van with a full tank of gas!
Presto, low buck 6.0 for your squarebody!

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Lol! While you're at it might as compare tires. Maybe score a free upgrade.

Camar068 said:

The easiest increase in power is going to be a cold air intake. If you decide to go headers, make sure you go long tube. Short tube headers are just as good as stock manifolds....so your paying for looks when you go shorty.

hopefully I'll be building a 5.3 from the ground up. Be about $2,200. I've got the Brian Tooley Racing Torque cam on my list because it increases HP/TQ below 2,500 rpm's. I don't need a thumper cam as I don't spend much time over 5,000 rpms.

For the BTR torque cam you need to upgrade your valve springs, but your stock converter will be fine. I've not done springs but watched enough videos to see that it's easy.....that and I stayed at a Holiday Inn last night lol.

What's your gear ratio and trans?

Of course, in the end....gas mileage is all up to your foot. I can get 17 mpg's out of my swap if I want to, but I don't

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Cold air intakes are great but must be done right.
The usual cheap ones hurt power and mileage as they suck in hot under hood air instead of getting it from the outer fender.
Make sure they get their air from outside the engine bay or you are paying to hurt your performance.

In last months issue of Hot Rod magazine there is Part 1 "Project Groundhog" of a 5.3 they are building up to be driven on the street with not buckets of horse power. And this months issue of Part 2 where they finish the engine. I haven't looked at it yet, I've got it but haven't got to that part yet, but what they've done looks pretty good so far. I'm to that part tonight, but check it out and compare to what you are doing to yours. A couple of three months ago they had a buildup of a hemi they got out of a wrecking yard and what they did to it is kinda the same as this issues GM. It seems these new engines, I'm not familiar with, can handle a lot of horse power without using hardly any high performance internals. This 5.3 build is doing a bit of machine work and mostly all stock parts and should make decent hp numbers and street manners.

Haven't see anybody mention that any boosted engine will need more ring clearance, requiring teardown, and file fitting the rings. You hear about it all the time, but believe ime, it is a bit tedious. At the shop, we use many different brand pistons, each comes with it's own clearance. Within that set, there are different clearances if it is for example, a marine engine, stock, or boosted. So think what is involved....Remove engine, teardown, ring dissemble, file, reassemble, (hope you don't break a ring.) gasket sets are expensive, as is time. Your rig will be down for a month, (yeah right, more like a year,) and I can see an easy 5000 $ spent. If you do that, trans of choice would be a 4l80e, not the 6l80.

Id say turbo if you want the mileage and idle quality to stay the same. The turbo will suck down more fuel when you are close to boost or in boost while driving but when driving lightly with traffic and idling it should be the same for you. IMHO never change the cam unless you want that choppy idle.

Albrigap said:

Cold air intakes are great but must be done right.
The usual cheap ones hurt power and mileage as they suck in hot under hood air instead of getting it from the outer fender.
Make sure they get their air from outside the engine bay or you are paying to hurt your performance.

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Hot air doesn't hurt milage it hurts power and vice versa. Cold air is more dense so you can get more oxygen and fuel into the same space..it's that old expansion contraction deal..Oldsmobile like 1967-70 used a crazy heated air cleaner system for maximum fuel milage Un the turnpike cruiser edition cutlass. The hyper miles use preheated air to increase their fuel milage.Lots of manufacturers back in the day ran cowl hoods,shaker hoods etc. On the performance models. Those were functional no decorations.

I've got an LH6 5.3 (Envoy Denali's and certain Trailblazer's got them, they've got a goofy oil pan with a hole through it for the AWD/4WD axle). They're all aluminum, flat top pistons and have 243/799 heads and are rated for ~310-335hp depending on who you talk to. I slipped a BTR stage 4 truck cam in mine (224/230 .553/.553 109+0) that's definitely rowdier than you're looking for but I figure I gained 90-100hp with that and minor head work (messaging the bowls, valve job, etc). That paired with a 2800-3200 Circle D stall converter and a 3.90 gear makes for a hell of a fun truck. But it does shake the truck alot and tries to surge through the converter if you're not on the brakes hard enough at a stop light.

For what you're looking for, I'd probably stick with the stage 2 truck cam and a valve spring upgrade. You can keep the stock converter and mild manners that way. Either that or look for a LQ9 6.0 or one of the non-DOD 6.2s and leave it alone. Any of those should hover around the 375-400hp mark. With any option though, I would certainly change your rear gear. A 2.73 sucks for fun and also zaps fuel economy cuz the engine is gonna work so hard. If you want a highway flyer, stick some 3.42s in it. Or a good middle of the road would be a 3.73.