Suppose 5 liters and a 3.90:1 axle, versus 7.5 liters and a 2.60:1 axle. the latter should be heavier, but how about everything else? Acceleration, emissions, mileage?
If valid, then the most torque per displacement should be the wisest choice?
Like a Vortec 454 makes good torque, but not good torque per displacement like an LS3, for instance.
Is this any way to try to choose a swap?

 

Choose a swap according to your skills and budget.

 

Exactly. The first numbers you should be looking at when planning a swap is $ figures. If you can't get the work done why start? Plus you have to factor in what your actually planning to do with your car. Like, why have 7.5 liters just to putt around town? A lot of fuel for nothing. Why have 3.08 gears if you plan on drag racing a lot? (though gear all depends on the rest of the drivetrain more than intended purpose)

 

go with the 454, but keep the 3.90 gears...
it'll be moar fun...

 

gears don't compensate for a lack of power. There's no gear set in the world that would make me want a 305 more than a big block.

 

The potential for both is undeniably obvious where in stock form the 454 might be de-tuned to reach emissions levels and the 5.3 in stock form not so much.

Certainly in matched tune levels the 454 has a better VE.That is not to say that gas mileage would be better because the shear size difference and consumption.

The one and only way to compare VE's is to have like type engines.In this case it's the old apples to oranges comparison.

 

Why a 305? Why not a '69 DZ302 vs a peanut-port, and assume no further mods. Still choose the big block?
Let's zoom the scale. How about a 4.8L with 3.42:1 against a 5.3L with 3.08:1?

 

Can't dispute that, but in that vein it was apples to oranges choosing between a 135 horsepower 2.8L with 3.42:1 against a 145 horsepower 305 with 2.73:1. At the time I would have taken the 305, but now I'm wondering about an Ecotec 4 with a 4.56:1 axle.

 

What exactly are you driving at? Displacement is only a partial factor on choosing gear ratio. The factory choices were dependent often on mileage/emissions concerns, and torque band. A 350 that revs peak @7200 is not going to have the same band as a 350 that revs to 4800. 2.73 gears are going to be terrible with the 1st 350 but be streetable with the second. So why are you so displacement driven?

 

The only time I would ever own a DZ302 would be in a numbers matching z/28. I'm not a fan of tweaked out small cube high rpm motors. I like torque.

 

There must be a scientifically-best swap, and it must be math and formulas that will determine it. Looking at the 4.8 vs 5.3 I just used, the carburetor selection would be the exact same, so air consumption would be the same, thus MPG. But instead of multiplying cubic inches by gearing, try rated torque. Then the 5.3 has the expected advantage, and another 10-15 HP. ( OE stock SAE ratings ) So when you actually use the thing, real-world MPG should be less than the 4.8L, I think.
I'm not committing to any engine or any gearing yet.
I have a 135 horsepower 2.8L I'm not happy with. Serious candidates for my car include the 160 horsepower 3.4L, a 200 horsepower 3.8L, a 200 horsepower 4.3L, a 270-275 horsepower 4.8L, a 230 horsepower 5.0L, a 285 horsepower 5.3L, a 308 horsepower 5.7L, a 325 horsepower 6.0L, and a 290 horsepower 7.4L, though it looks the 7.4 is eliminated by several factors.

 

Best swap for what? What are your goals? No equation can determine human expectations. If mileage is your main/only concern I would think you'd want the smallest displacement with the best VE, then the gearing that works best to that engines torque band. I cannot prove or disprove that but it would be my thinking. The driver has the next largest input on mileage. Car weight, wind resistance, drivetrain efficiency are all factors ignored by your current thoery. There are probably several factors that I'm missing too. Lastly why would a 4.8L and a 5.3L with the same carb have the same air consumption? A 5.3L would still try to draw 5.3 liters worth of air, would it not? I assume the VE would be different between the two engines though if all else is comparable. I'm sure someone on here has more or better knowledge to set us both straight.

 

Because the 4.8 with 3.42:1 is running more RPM than the 5.3 with 3.08:1 gearing. Not everything can be equal at the same time. Give both engines the same gearing, the outcome becomes easily predictable. We can't learn anything new from that.
I'm here to learn.
Sure I could do a 350 in a weekend and have cheap smiles. Or do the 6.0L and have real power in a month. Or keep tweaking the 2.8L and have 40 MPG in a year.

 

It all boils down to power to weight ratio. Gears aren't going to terribly hinder any car. An Lt1 with 2.73 gears and an auto is still going to beat an L98 with a 3.42 gear.

 

I already have the 3.42:1 axle, and I've found a complete '01 4.8L with 59K miles and a 90-day warranty for $350. Tempting. Or do the 5.3L now for $435, then swap to 3.73:1 gears with a future 4.8L swap? (The 6.0L is out, the best deal is $800 for one with 168K miles and cranks 150-155 psi in all cylinders.)

 

If nobody has the answer, then I'll throw in a 350 while getting ready to swap in a 4.8

 

You got your answer. You're trying to pseudo-measure things that aren't measurable. There is no "best" swap. Best for who? For what power levels? Efficiency? Gas mileage? Cost? The list is never ending.. You're selectively looking at certain variables and completely excluding many other critical factors. There is no scientific way of deciding what "best" is.

 

Believe it or don't-GM does a pretty fair job of engineering in stock form for the the big picture/overall.

 

The best of those deals is the 6.0.

Other than the engine, the rest of the cost of the swap will be the same for any of those engines. The cost of the engine is miniscule.

Getting as much performance out of the 4.8 as you'd get out of the 6.0 will cost a LOT more than $450.

 

I grant that the 6.0 is going to offer more torque per displacement, but is a stock 6.0 with 2.73:1 gears going to give more MPG and cleaner emissions than a 5.3 with 3.08, or a 4.8 with 3.42 gearing? How can you know for sure?
I also grant that the 6.0 offers more results per dollar spent on upgrades, but I'm not looking at cams or intakes or TBs, though the headers seem halfway necessary.
As far as I'm concerned, this thread can be ignored for the next several months, until I have some results to post. Starting with the 4.8 means the least time with the car unable to be driven.
While I'm gathering the mounts, the front accessories, and whatever else, I'll drop a 350 in.

 

Pick which is most important to you - acceleration, emissions, or mileage.

If emissions is a requirement regardless, given the conditions under which emissions are measured, any one of them can be made to meet the requirements.

If acceleration is most important, hands down it's the 6.0.

If mileage is most important, depends upon your driving conditions. If lots of hills, the larger engine may come out okay. If around town, the smaller will probably be best.

If you say all 3 are equally important, you'll be getting a 5.3.