LS vs SBC mpg calculations

[Billett]

Couldn't sleep so I decided to do a fun little exercise. My truck is getting some pretty terrible mileage with the stock 350 and np435 and I've been thinking about doing a swap to an ls. I wondered, is the initial cost worth it? How long will it take to break even on fuel savings? Well I did some calculations based on some mpg recordings I've gotten from swaps on this site. Here's how it went.

Starting with my current 350 I get about 11 mpg. That's about .09 gallons per mile. Given a gas price of $3.50 it costs me $0.318 per mile. I pay 30 cents a mile!!! That's insane! Anyway, cost to swap is $0 since it's already in there, but I have the feeling that this thing is going to crap out on me within a few years. Also, just for comparisons sake, it'll cost me $15,909.09 to go 50k miles.

If I were to swap in an LQ4, which I'd really like to do, I'm hearing an average of around 17 mpg. This gives me 0.05 gallons per mile, $0.206 per mile and a savings of $0.112 every mile I travel. That's a third of my current cost so it sounds pretty good so far. Cost to swap, (being conservative and not doing anything other than a rebuild), I'll say is $5000. That means I could travel 44,523.8 miles in my current setup for the cost to swap. Thing is, I doubt my 350 has that many miles left in it anyway before a tear down is in order. Oh, and this would cost me $10,294.12 for 50k miles.

Keeping up? Good, it gets better. Let's say I went for a 5.3 instead. Personally I like the cool factor of the 6.0, but as far as mileage goes the 5.3 should get closer to 20 mpg from what I've seen on here. Also, the 4.8 has been damn near the same so consider these numbers the same for both engines. 20 mpg gets me 0.05 gallons per mile, $0.175 per mile, and a savings of $0.143 per mile. That's almost half of my original cost, for you folks following along at home! From what I've seen this cost to swap is cheaper due to the price of the engine itself so I put it at $3000 to swap. That will get me 20952.4 miles from my 350. It's dead even at $8750 for 50k miles.

In regards to the 50k mile price, that's a $1544 difference. I thought it would be higher, but still, that's a good chunk of change. Personally I think $1500 is worth the price of having the extra power and cool factor, but either way you're saving a minimum of almost 6 grand over the sbc. These numbers pretty much made the decision to swap for me. It's a no brainer.

Also, for those of you who haven't fallen asleep yet, I did another set of calculations for my motorcycle just for the fun of it. I have a Yamaha xv535 cruiser that get's 45 mpg or so, but you could pretend it's a civic hybrid or something as well. I bought my motorcycle specifically with fuel economy in mind because I knew the truck was so bad, so in the summer I tend to use it much more than my truck when going back and forth to work. The 78 mile round trip would cost me just shy of $25 PER DAY in my truck vs $6 on the bike. Now then, back to numbers 45 mpg gets 0.022 gallons per mile, $0.078 per mile saving $0.24 every mile. Initial cost was $2500 for my bike. That would have gotten me 10,399.2 miles in the truck. Money well spent believe me. This thing will cost me $3,888.89 at the end of 50k miles.

Here's a quick and dirty, figure that a BBC or 305 will get roughly the same as my 350, and the 4.8 is the same as the 5.3:

Engine - MPG - Cost per 100 miles
350 sbc - 11 - $31.82
6.0L - 17 - $20.59
5.3L - 20 - $17.50
Motorcycle - 45 - $7.78

Moral of the story: Need a cheap way to get better mpg's? Buy a motorcycle!

In all seriousness though, I really hoped this has helped some of you guys as well. I have the actual spreadsheet I did this on if anyone wants it, and I can do more calculations if people request it. If you feel some of the mpg estimates are off I can tell you what the changed calculations would be, but I really just wanted to give an idea for just how much these things save over the Gen I engines.