8.1 Vortec VS 383 Stroker VS 6.0 Iron LS

[Bextreme04]

If you want MPG and reliability with EFI, I still think the factory stuff is going to be better than any aftermarket, so long as you have a decent tune done (which is needed either way).
There has been testing done before, I think the final conclusion is that a carb, when properly tuned for a specific point, gets better power and efficiency. But the really big caveat to that is that the tuning would need to change every time the air pressure changes from elevation, or the temperature changes, or the engine is warming up, or the fuel quality changes from tank to tank, or any other parameter changes by a small amount. At that point, you would need something like a computer that could handle all of those variations, probably some type of sensor in the exhaust to make sure the changes are right, and a way for the computer to adjust how much fuel is being added/injected, and I think you see where I'm going...
Good EFI on an older engine is better than a carb on a newer engine for 99% of the stuff out there, but there's a bit more to be had with a newer engine that has inherently better efficiency (like modern heads and bearings).

All that said, I'm liking the 8.1...

No. Testing conclusion is that you will make more absolute power with a carb properly tuned for the exact circumstances being tested. Efficiency is not even close. The EFI will beat out the carb hands down for efficiency in every situation.

You don't go for EFI with the intention of more power. You go with EFI so that you know it will get it's best efficiency and power in EVERY situation without you needing to mess with it. Cold out? Cranks right up and runs good. Hot out? Cranks right up and runs good. Top of a mountain? Cranks right up and runs good.

It also has the added bonus of being able to monitor and protect the engine under heavy duty conditions. A carb will let you wash the cylinder walls from being way too rich or burn a hole in a valve or piston from pulling a heavy load up a steep grade with your foot to the floor. A properly set up EFI system will keep it from detonating, melting pistons, burning up the trans, etc... without you needing to stare at the gauges all the time.

Run an L29(7.4L) or L18(8.1L) and keep the factory P01 or P59 ECU. Get it tuned by someone competent and you'll have all the power you need and still get 12-14mpg when you can manage to keep your foot out of the skinny pedal.

 

[Hunter79764]

I stand corrected on the efficiency, although we aren't in any disagreement about the whole idea. A carb has a VERY narrow tuning window of being optimized, so narrow that it doesn't exist in the real world. Everything else is a compromise and a high tech bandaid (power valves, idle circuits, the whole concept of secondaries, etc are all created to cover inherent issues with carburation). EFI, when done properly with full engineering behind it, will work much better in essentially every situation that a normal vehicle goes through in normal driving. And while the Holley stuff is easy to tune, I really don't think it is better than factory EFI for most stuff. GM spent millions of dollars creating the systems and algorithms and tables to adjust to everything from idling in Antarctica to WOT for hours in Death Valley. I don't think most of us give them the credit they deserve.

That said, plastic heater hose Tee's, the Cadillac Cimmaron, and 2000's era EVAP systems suck and should disappear from the face of the earth.

 

[Ricko1966]

The bearings in an LS are no better than the bearings in plain old 350. Better heads will improve performance and efficiency,but there are better heads available for an old 350.And the better efficiency isn't in flow it's in fast burn, like vortecs,tbi heads, lt1 heads. Equal power with less timing means less trying to push the piston down on its upstroke. The extra timing has the engine fighting itself for a few degrees every rotation. The new rule is MBT,( minimum best timing) ( maximum best torque) not,give it as much timing as possible without detonation. You can port the block(yes the block) for even more efficiency.That and improved fuel management and ignition management are part of the path to better efficiency.

 

[TheClassicRed]

If you want MPG and reliability with EFI, I still think the factory stuff is going to be better than any aftermarket, so long as you have a decent tune done (which is needed either way).
There has been testing done before, I think the final conclusion is that a carb, when properly tuned for a specific point, gets better power and efficiency. But the really big caveat to that is that the tuning would need to change every time the air pressure changes from elevation, or the temperature changes, or the engine is warming up, or the fuel quality changes from tank to tank, or any other parameter changes by a small amount. At that point, you would need something like a computer that could handle all of those variations, probably some type of sensor in the exhaust to make sure the changes are right, and a way for the computer to adjust how much fuel is being added/injected, and I think you see where I'm going...
Good EFI on an older engine is better than a carb on a newer engine for 99% of the stuff out there, but there's a bit more to be had with a newer engine that has inherently better efficiency (like modern heads and bearings).

All that said, I'm liking the 8.1...

That's why if I do go twards the 383 id be using the holley sniper, automatic tuning with a O2 sensor to make sure your not running lean or rich. And works when going up and down in elevation. Especially with a hyperspark distributor your spark timing would be perfect everytime

 

[Bextreme04]

That's why if I do go twards the 383 id be using the holley sniper, automatic tuning with a O2 sensor to make sure your not running lean or rich. And works when going up and down in elevation. Especially with a hyperspark distributor your spark timing would be perfect everytime

You're gonna spend more for a holley sniper system than you would to just get an 8.1 or 7.4 with the trans, wiring harness, and computer included... Just saying. Also, the sniper system has it's limitations. Most of the really efficient head designs don't have a heat crossover and the TBI style fuel injection has issues with cold starting and running in cooler temps without something to heat the manifold up. They do OK and are a mild improvement over carb for daily driving, but can be temperamental. If you needed a new carb anyways, then it makes sense. If you are only trying to improve MPG... you would need to drive A LOT of miles to make up the cost of a sniper system. $1700 for the basic kit with the fuel pump you would need buys a lot of MPG, and a semi-tuned carb is going to be getting 10-12mpg.. you'll maybe gain 2-4mpg tops(more realistic numbers would be 1-2mpg in most situations) unless you are also getting a lockup transmission(which the sniper WILL NOT CONTROL). Maybe the best cost thing to do if you insist on a 383 would be to find a donor 3/4 or 1 ton GMT400 with an L31. Then you can strip it for the fuel system, engine/trans/wiring harness and get an LS 0411 computer to run it. Then if you want to stroke it in the future, you can keep running the stock computer and tune it cheaply and easily. Mild cam in an L31 is good for 300hp at the wheels pretty easily and there are guys on the GMT400 forum running some mild builds in vans and trucks getting 16-18MPG's with a mild 383/4L80 combo running 0411 computers and marine MPFI setups.

 

[CountKrunk]

Marine MPFI?

 

[Shorty81]

THERE IS NO REPLACEMENT for DISPLACEMENT!!

 

[yevgenievich]

There are aftermarket mpfi intakes for a bbc that will run on 411 ecu if going away from l29 intake manifold. Or 8.1l with stock intake will work well for most uses.

 

[AuroraGirl]

The 383 would basically be a new rebuilt engine. The stock fuel , and ignition system would work well for the 383. I would add long tube headers. A hydraulic roller cam, carb, and good dual plane intake. If you could afford a set of heads, I would do that also.

The 6.0's have some issues with the head gaskets leaking water, the front cover gaskets burn out , depending on the year the TPS sensors give you the dreaded Engine Reduce Power mode. These are all repairable, but can add to the cost. The fuel system and ECM add complexity to the build.

The 8.1 would be interesting. It would also require a fuel system and all the electronics. I might consider an older GEN 4, or 5 BBC. It could run the stock style fuel and ignition system.

For the transmission you would need a stand alone controller for the old school SBC, or BBC. The FI engines should run it, may require some programming. All it takes is time and $$$.

also knock sensors tend to die, and the cam sensor wiring pigtail eviddently isnt the best. im hoping my cam sensor just needs a new pigtail but a new sensor would be quicker lol

 

[TheClassicRed]

You're gonna spend more for a holley sniper system than you would to just get an 8.1 or 7.4 with the trans, wiring harness, and computer included... Just saying. Also, the sniper system has it's limitations. Most of the really efficient head designs don't have a heat crossover and the TBI style fuel injection has issues with cold starting and running in cooler temps without something to heat the manifold up. They do OK and are a mild improvement over carb for daily driving, but can be temperamental. If you needed a new carb anyways, then it makes sense. If you are only trying to improve MPG... you would need to drive A LOT of miles to make up the cost of a sniper system. $1700 for the basic kit with the fuel pump you would need buys a lot of MPG, and a semi-tuned carb is going to be getting 10-12mpg.. you'll maybe gain 2-4mpg tops(more realistic numbers would be 1-2mpg in most situations) unless you are also getting a lockup transmission(which the sniper WILL NOT CONTROL). Maybe the best cost thing to do if you insist on a 383 would be to find a donor 3/4 or 1 ton GMT400 with an L31. Then you can strip it for the fuel system, engine/trans/wiring harness and get an LS 0411 computer to run it. Then if you want to stroke it in the future, you can keep running the stock computer and tune it cheaply and easily. Mild cam in an L31 is good for 300hp at the wheels pretty easily and there are guys on the GMT400 forum running some mild builds in vans and trucks getting 16-18MPG's with a mild 383/4L80 combo running 0411 computers and marine MPFI setups.

That's kinda why I made the thread to pro and con it. The 383 would be the most expensive choice of the three. The only reason im considering it is i already have a block that is bored 30-60 over and some racing heads that came with it, i dont know if they're usable, i still have to take them to the machine shop and have them check em out. with the sniper but I could find them second hand pretty cheap in comparison. And with the mpg the lower it is with a normal carb the more important the 1-2 or 3-4 mpg really counts. Could be 10-40% more gas. And I do plan to drive it alot alot, I am very against the idea of a garage truck.

The only way I'd be 100% on the 383 is if I got a preditor carb. One of those old monster truck carbs mannnn that'd be sweet to put on the truck.

 

[Bextreme04]

That's kinda why I made the thread to pro and con it. The 383 would be the most expensive choice of the three. The only reason im considering it is i already have a block that is bored 30-60 over and some racing heads that came with it, i dont know if they're usable, i still have to take them to the machine shop and have them check em out. with the sniper but I could find them second hand pretty cheap in comparison. And with the mpg the lower it is with a normal carb the more important the 1-2 or 3-4 mpg really counts. Could be 10-40% more gas. And I do plan to drive it alot alot, I am very against the idea of a garage truck.

The only way I'd be 100% on the 383 is if I got a preditor carb. One of those old monster truck carbs mannnn that'd be sweet to put on the truck.

Sooo... best case, you have a poorly tuned carb and you are getting 10mpg. If you drive your truck 20,000 miles in a year(not likely), you burn 2000 gallons of fuel in that year. If you spend the $1800 on the sniper(not including any engine work... which is going to be A LOT for a 383) you MIGHT get it up to 14mpg without doing anything transmission related(VERY unlikely, probably closer to 12 without trans work that the sniper will not help with). So, 20,000 miles at 14mpg gets you down to 1428 gallons in that same year. If you are paying $4/gallon on average, that would save you $2288 per year in gas.

Now, the reality is that you are probably going to be closer to $5-6000 to do the 383, 4L80, Sniper, and stand alone controller for the trans. Probably another $1-2k in other parts to support the combo, maybe more depending on if you are paying someone else to do the work or doing it yourself. Basically the $6k is gonna be in parts and labor that requires specialty tools, if you aren't doing the majority of the work yourself, double it. That would get you into that 14mpg range more solidly.

The 6.0/7.4/8.1 combo with a 4l80 is going to be a factory swap over. You can get the engine/trans/harness/pcm combo from junkyards or donor cars in good condition with reasonable miles for $1500-2500 depending on mileage. Less in some places and if you are willing to wait for the right deal. Another $1K for random fuel supply and swap bracket stuff you will need to get it all installed and running. Any one of those setups is going to get you right into the same MPG as your 383 straight from the jump.. stock.

So, to build the 383 the way you say you want it.. you'll maybe pay that back in MPG in 1-4 years depending on how deep you go and how many miles you drive. 20k in a year is a whole lot of miles in a square.

6.0/7.4/8.1 combo would pay you back in 1-2 years tops, depending on how much you drive it.

The reality is, you aren't likely to drive it 20k a year. If you drive it 5k miles a year, then you would need to quadruple the number of years to pay back the upgrade in MPG. So for the 383, you'd pay back the MPG in 20 years or so... maybe. Same for the LS or BBC swap, 5k miles a year would take you 4-5 years for it to pay it back.

Not trying to dissuade you from doing it.. just pointing out you seem really focused on MPG but also seem very set on doing the worst option for MPG

I'm doing the 7.4/4l80 in my K25, but I only use it for truck stuff around the house and hunting a few times a year. I have a little 93 Honda Civic coupe that I use for 90% of my daily driving and it gets ~25-30mpg and has at least 300k miles on it. Family vacations and camping with our trailer, we use my wife's 2011 Suburban, it gets 15-20mpg with the 5.3 and ~10mpg towing our trailer. I'm swapping in a 6.2 that I got for $1500 locally, which will probably drop the regular driving MPG, but should help a lot with the towing power and MPG, since it won't have to work so hard.

 

[Mogulmasher]

It WAS a 350. lol
I tried to get it to pull in any gear, but it would only go in 1st. I got it home, but I'm pretty sure it's toast.

I'd take the other side of that bet. The 5.3s get good milage from the modern engine management. Compare a factory 5.3 pickup and a factory 5.7 vortec pickup not a big difference mpg wise because they both have way better engine management than a carbureator and mechanical distributor.

I've owned a couple vortec 350 in a 98 Yukon and a 00 2500, yukon got 3-4 mpg less than a 99 Tahoe 5.3 I owned. I managed a fleet of trucks at work around vortec 350 to early ls trucks timeframe and same result, 5.3 always got better mileage. Just my real world experience.

But again, you don't own a square for mpg. Although it is nice to save a buck here or there if it happens to work out that way....