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

[Hunter79764]

Good advice in here, I'd say that you could touch up the heads a bit if you wanted, it would add a little without much downside as long as you are just talking basics. Opening up the cam timing can gain quite a bit, but a good tuner can keep it very civil at idle, and will get the most performance out of it at the same time.
How much power you want really dictates what you should do. Really, a modern 300 hp 327 is a pretty good engine (i.e. a stock 5.3). a stage 1 cam will add a little to it, especially in the upper RPM range, with very little tradeoff. Call any of the "truck cam" manufacturers and get their recommendation on specifics. If you want significant gains, boost on a stock engine will get you near 500 pretty easy, and keep your smooth idle and MPG when you aren't leaning into it, but obviously it steps things up a fair bit on the cost and complexity for the install. Your call.

 

[PhotonFanatic]

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.

No way to get a 6 speed? Or maybe it's not necessary. I like doing 85 on the highway at low rpm's so I don't have to listen to as much engine noise.

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.

But you'd be spraying less fuel if you're turning lower RPM's... right?

 

[TotalyHucked]

But you'd be spraying less fuel if you're turning lower RPM's... right?

Correct. On the highway, as long as you have the torque to keep it in high gear, you're correct. Anywhere else but steady state cruise though, the truck is working much harder with taller gears. Think of it as trying to get a tight bolt out. 2.73s are like using a stubby ratchet, can hardly turn the bolt. 3.42s are like a 12" ratchet and 4.10s are like a 4ft breaker bar. Not to mention, LS's don't make torque in the same low RPM range that small blocks do. LS's like to rev, they make peak torque much higher. "Don't fear the gear" is definitely true of an LS. Gear ratio will make much less of a mpg difference than aero will in these bricks. I get 20-22mpg if I keep it below 80 but I get 14mpg at 90 lol

Since you like running 85+ with lower RPMs, you either need more than 4 gears or you need a good middle ground rear gear. My truck with the cam/stall/4L65/3.90s runs ~2500 at 80 and 3k at 90. Since you'd have a less aggressive cam and likely a stock converter, I'd recommend 3.42s or 3.55s. They'll get you much better acceleration than 2.73s without making it spin high on the freeway. Now, if you go with a 6L90, the rear gear recommendations would be different because of the ratios in that trans.

Picking a rear gear/cam/stall is a complicated process and needs to be thought out ahead of time before buying parts. It all has to play nicely together. I decided on my tire size and rear gear first, that way I knew where I'd be at cruise RPM. Then picked my cam and then my stall converter.

 

[GTX63]

Just swapping out the typical 5.3 for the old 350, without any modifications, is going to make a pretty noticeable difference. This is coming from an old school, gen 1 sbc diehard fan who also happens to be able to critically think. Reading about what it is you are wanting, and some of your driving habits, just throw any thoughts about mpgs in the trash can. A bone stock 5.3 in a squarebody with a ie L460E and 2.73 gears is going to give you around 13-14 mpg on average. A 6.0 is going to net about 11mpg no matter what.
I have known several guys who dropped 5.3s into their old Scottsdale or Bonanzas, with turbo 350s and 3.73 gearing and were more than happy with the performance.
If you have a lot of questions and concerns, I would start from scratch. You can always cam and do head mods, etc after the fact.

 

[Craig Nedrow]

Ok, ok. The old 350 in good shape got 13 mpg. The 355 circle track motor got 11 really fun MPG. The 454 gets about 10-11, puts the other two motors to shame. Wife's 6.2 gets constant 14.5, hauling our 21 ft Imagine trailer it gets between 7 and 9 MPG, has a 6l80. All real numbers from rigs I own. The truck is an 1973 K20, 4:10 with 33" TA, 350 trans 3100 rpm at 70. Swap the 2:73, listen to the input 3:43, or 3:73, (would be my choice). The 4L80e is relative simple, proven, tough, cheap, light years better then the 700R4, (350 with OD, can be built strong.) I have an LS type motor two actually 5.7, 6.0 cast iron. 5.7 can make tons of power, had to get rid of the 98 Camaro, B-4 I killed myself,. 6.0 is the boost queen. Motor cost, is it an issue? Wa St has the highest price for gas in the nation, yeah gas milage is important now. Soooo just remember, any motor you boost will need to be torn down, rings gapped. I build for reliability, motor efficiency, cause an efficient motor gets the best relative gas mileage, not the same as good gas mileage, but the best for the application. Here are 5.3 specs.
https://help.summitracing.com/app/answers/detail/a_id/4818/~/chevy-lm7-engine-specs
How much more power can a 5.3L make without hurting road manners or gas mileage?
I build motors at a local machine shop, Lessons I have learned go big or go home. Get a 6.0 4l80e setup (got mine for $1500 143000 miles Portland OR.). then go see Richard Holdner, and pick a combination.

 

[Camar068]

note to add, drive your 5.3 as if it was a stock 350 and you'll get 15-18. It's the foot that gets ya.

 

[Sgt Gus]

Nice read over a cup & 1/2 of coffee.
Y'all would be great Goin fishing and listening to talk shop over the camp fire. Or at the local dinner anytime.
I'll put my daughter's build in the construction thread once the client donations come in, lol.

 

[Turbo4whl]

That build has over 2k in parts before he even boosted it. Bang for the buck you can't beat an LS. Sure, you can do other stuff, stuff that might even be cooler than an LS, but in terms of HP/$ a modded LS will win every time.

The way I see it, you need more HP for your road rally race car, but you want more torque for your truck.

You don't need that bumpy cam or fancy porting if you are boosting. Blow that air and fuel in and you are making torque.

 

[Turbo4whl]

Nice read over a cup & 1/2 of coffee.
Y'all would be great Goin fishing and listening to talk shop over the camp fire. Or at the local dinner anytime.
I'll put my daughter's build in the construction thread once the client donations come in, lol.

I have a feeling that the client's funds are from your pocket....

 

[idahovette]

^^^^^^^^SO TRUE!!!!!

 

[Sgt Gus]

I have a feeling that the client's funds are from your pocket....

Yeppers! Gotta close jobs to get paid and have enough extra to fund the truck project. Such is life.