The mechanic that is doing the work is a high school buddy. I do not know what you define as old guy but he is pushing 50. He is the mechanics instructor at local school. That is why I do not have to pay for labor.
Engine Swap Advice
- Thread starter Cruck
- Start date
The engine that is in it now is not functional at all. It is a 350.
Sorry, I misunderstood. I still think I would try to find a good running SBC and just get it tuned up right and possibly swap the gears in the rear end if the ones it already has aren't ideal.
I'm confused too. You said in your first post that it's a great engine, it just gets horrible MPG. What do you consider to be horrible MPG?
Now the engine is not functional at all. Is that the assessment of your mechanic instructor friend? Unless it suffered some catastrophic failure, it might not be hard to get back to running condition.
An LS swap could potentially get you more MPGs, but at a much higher expense even if you use a junkyard engine. There are lots of extra costs associated to the LS swap, new engine mounts, converting the truck to EFI (new fuel lines, electric fuel pump), adding the ECU and required wiring to make the EFI work correctly. Then the transmission will need a controller, if you are using the modern electronic overdrive. The costs will add up and it may go beyond the skill level of your friend and his shop class.
On the other hand, keeping it a 350 could get you good MPGs with some tune-up work and upgrades. First off, the carburetor is a huge factor. Swapping to a well built Rochester Quadrajet will help. They could get MPGs on par with the old EFI TBI systems. They are hard to find good cores today so an alternative would be a Edelbrock AVS2 650, which if tuned well will get very good MPGs. A head swap to bump the compression can help too. Summit makes an economically priced iron cylinder head (non vortec) that works well with a low compression 350. Then making sure you have a properly tune distributor and strong ignition system will allow you to tune the carb to run very efficiently. Adding in a TH700-R4 transmission would also be a big help as well, but you need know your rear axle ratio. To find out the rear axle, check the RPO sticker, which should be in the glove box. It will have three letter codes that will tell you all the equipment your truck has.
Doing the above you could yeild near 18 MPG and do it more cost effectively than an LS swap. The LS might be a bit better on MPGS but it will be more expensive and much more complicated IMO.
On the other hand, keeping it a 350 could get you good MPGs with some tune-up work and upgrades. First off, the carburetor is a huge factor. Swapping to a well built Rochester Quadrajet will help. They could get MPGs on par with the old EFI TBI systems. They are hard to find good cores today so an alternative would be a Edelbrock AVS2 650, which if tuned well will get very good MPGs. A head swap to bump the compression can help too. Summit makes an economically priced iron cylinder head (non vortec) that works well with a low compression 350. Then making sure you have a properly tune distributor and strong ignition system will allow you to tune the carb to run very efficiently. Adding in a TH700-R4 transmission would also be a big help as well, but you need know your rear axle ratio. To find out the rear axle, check the RPO sticker, which should be in the glove box. It will have three letter codes that will tell you all the equipment your truck has.
Doing the above you could yeild near 18 MPG and do it more cost effectively than an LS swap. The LS might be a bit better on MPGS but it will be more expensive and much more complicated IMO.
Ok, it sounds like you have a non-running truck with a 350 (?) (everyone knows every SBC is a 350... as long as you don't look inside, it must be). An LS swap with the unloved 4.8 might be a low cost way. No AFM. I think latter ones may have had VVT and that may complicate things, as I'm not sure how far you want to go--full EFI conversion?
If you just want to pick an easy path and keep costs low, I'd find a running 350 and drop it in. Leave it carb'd. Transmission and rear end will need to be sorted out before any hopes of mpg. Building an engine may be loads of fun but if it was me, the endless thinking about what I could do (which heads, what cam, what compression) would quickly escalate. As would the bill.
IMO doing a full swap to an EFI drivetrain is a lot of work. Really cool to see done, but I have to wonder, if you haven't done anything like this before, if it's better to start small and work your way up.
I wouldn't turn down a good running cheap 305. I don't think it'd make much more mpg, but if cost is a factor, then it's not a bad motor. Just not a good one.
Once you learn how to swap an engine once, it should be all the easier the next time.
If you just want to pick an easy path and keep costs low, I'd find a running 350 and drop it in. Leave it carb'd. Transmission and rear end will need to be sorted out before any hopes of mpg. Building an engine may be loads of fun but if it was me, the endless thinking about what I could do (which heads, what cam, what compression) would quickly escalate. As would the bill.
IMO doing a full swap to an EFI drivetrain is a lot of work. Really cool to see done, but I have to wonder, if you haven't done anything like this before, if it's better to start small and work your way up.
I wouldn't turn down a good running cheap 305. I don't think it'd make much more mpg, but if cost is a factor, then it's not a bad motor. Just not a good one.
Once you learn how to swap an engine once, it should be all the easier the next time.Iron duke!?
I would ask what he wants to do. I assume he doesn't want to spend dozens of hours figuring stuff out to put an unusual engine swap in, or maybe not even add FI?
I think you need to look at total cost.
Cost of gas
Cost of the engine
Cost of time*
Fix the running condition of the truck, even swap in another 350 if this one is tired, then call it good, spend a bit more on gas.
Ultimately cheaper, for you and everyone else, than a complex swap.
*I get that this is your buddy, but making the task complex and difficult is imposing on him.
Cost of gas
Cost of the engine
Cost of time*
Fix the running condition of the truck, even swap in another 350 if this one is tired, then call it good, spend a bit more on gas.
Ultimately cheaper, for you and everyone else, than a complex swap.
*I get that this is your buddy, but making the task complex and difficult is imposing on him.
I’m confused. Why not just rebuild what’s in the vehicle now? That avoids the extra cost of a junkyard engine which you’re going to completely rebuild anyway.
Post some pictures of what is in there now. That may help some of us figure out what is exactly going on.
I'm sorta surprised (and Sorta not considering where I am) that y'all want to make this an economic decision when that doesn't seem to be what it is.
He wants to get his dad's truck running and make it reliable and more pleasant to drive.
Now I do agree depending on what's wrong with it some improvements to what is there could be made, but if you're gonna swap engines LS is the way to go IMO.
He wants to get his dad's truck running and make it reliable and more pleasant to drive.
Now I do agree depending on what's wrong with it some improvements to what is there could be made, but if you're gonna swap engines LS is the way to go IMO.
His principal complaint seemed to be MPG.
But it will cost a lot more to fix that than the cost of additional gas in a truck that isn’t driven often.
Trying to make a silk purse out of a sow’s ear is futile no matter the resources behind the effort.
Seems like a lot of work for a car that doesn't get driven often.
Exactly, keep it simple. A decent running 350 with a good carb and ignition can get decent mileage. I know, I have a low compression 350 with QJET in one of my old vehicles that gets good mileage. The LS swap is not as easy as people make it out to be. It is an engine conversion not just a simple swap and it will require lots of little modifications and extra expenses to make it work right.
As @Astro14 said, the primary complaint in this story seems to be the MPG factor, which is economic. Swapping in anything that could dramatically improve the MPG is going to be expensive, and labor intensive.
The reality is that nothing will dramatically change the MPG.
It takes a certain amount of power to move the old truck. Any engine that's in there will be producing the same output to move the truck at his desired cruising speed, and will be using close the same amount of fuel to do so. Modern trucks can get a bit better MPG than an old '77, but there have been incremental improvements over nearly five decades to the entire vehicle to get there.
Looking at Fuelly for the average MPG that owners report for their modern trucks, the reality is there's not a huge difference between a gas powered '77, and a '24 equivalent. Yes, yes, someone will report their incredible MPG stats, but neglecting to mention that they're only including driving downhill both ways to school to get it...
Then there's the Instructor friend. Has he done any engine swaps? How complex were they? Will this be a class project for his students? Hopefully they don't burn it to the ground, like one auto shop class did to a project vehicle, when I was in Highschool...
I'm here to throw some cold water on your idea 
. 1st, I'm a GM guy, an LS fan and a big fan of square body trucks....but hear me out. I've got some experience with LS engine swaps and it isn't as straight forward as it seems.
The $5-20k you'll spend on an engine swap will go a loooooooooooooong way towards buying fuel for the SBC.
As you can see...this is going to add up fast! My vote is to stick with the 350 and stick an overdrive transmission in it. Have it built with more modern parts and it will have plenty of power and will increase your MPG considerably.
Air Flow Research 195cc Enforcer "As Cast" aluminum cylinder heads.
New pistons to give you a ~9.5:1 compression ratio
Edelbrock Performer RPM intake
660 CFM carb with vacuum secondary's
Comp Cams XE262H Hydraulic Roller cam
1.5:1 or 1.6:1 roller rockers.
This combo will give you an easy 350hp and 415 lb-ft of torque and will be a good daily driver with good street manners. Add a 700R4 four speed transmission (no electronics) with a 2000 rpm stall converter.
If you are feeling spendy and want a bit more modern convenience consider Holley Sniper2 EFI. It is a Throttle Body Injection style fuel injection that bolts in place of a carburetor and requires very little wiring. It is self-tuning and self-learning and will run great and efficiently! It will give you those quick cold-starts and modern driveability like modern EFI.
. 1st, I'm a GM guy, an LS fan and a big fan of square body trucks....but hear me out. I've got some experience with LS engine swaps and it isn't as straight forward as it seems.The $5-20k you'll spend on an engine swap will go a loooooooooooooong way towards buying fuel for the SBC.
- Motor Mounts. If you were to even go down the road of an engine swap...keep it LS. The motor mounts are different but LS swaps are common enough that adapter motor mounts exist. For the 3.6 V6 you'd have to fabricate new mounts.
- Headers. LS swap headers exist. The V6 "manifolds" are partially cast into the heads so there will be no adapter headers. If things don't fit you will be fabricating ways to move the interfering parts around the cast manifolds.
- Cooling. The inlet/outlet hoses are on different sides for the LS vs the SBC. You'll need a specific LS swap radiator and need to figure out the hoses.
- Transmission. What transmission do you have now? For 1977 it is probably a TH350 or TH400 three speed or big heavy cast iron manual. Either way they don't have overdrive...which is going to kill your MPG. You will also need to buy an adapter to go from the LS to older transmission and a new torque converter with a dual bolt pattern.
- Engine Control and wiring. Are you going to get the full engine harness out of the donor vehicle or go aftermarket like the Holley Terminator X? You'll need to integrate the new harness into your vehicle somehow.
- Fuel. You will need a new fuel system to handle the high pressure. That includes a new electric fuel pump, fuel lines and filters...and a return line which you probably don't have.
- Gauges. Your oil pressure and water temp gauges won't work with an LS swap. You'll need to plumb those sending units to a new location.
As you can see...this is going to add up fast! My vote is to stick with the 350 and stick an overdrive transmission in it. Have it built with more modern parts and it will have plenty of power and will increase your MPG considerably.
Air Flow Research 195cc Enforcer "As Cast" aluminum cylinder heads.
New pistons to give you a ~9.5:1 compression ratio
Edelbrock Performer RPM intake
660 CFM carb with vacuum secondary's
Comp Cams XE262H Hydraulic Roller cam
1.5:1 or 1.6:1 roller rockers.
This combo will give you an easy 350hp and 415 lb-ft of torque and will be a good daily driver with good street manners. Add a 700R4 four speed transmission (no electronics) with a 2000 rpm stall converter.
If you are feeling spendy and want a bit more modern convenience consider Holley Sniper2 EFI. It is a Throttle Body Injection style fuel injection that bolts in place of a carburetor and requires very little wiring. It is self-tuning and self-learning and will run great and efficiently! It will give you those quick cold-starts and modern driveability like modern EFI.
A smaller engine may get worse mpg as it's working harder than a larger engine.The current engine is not running. I understand the lack of aerodynamics and that it is not a 1:1 thing here. The idea is to be as fuel efficient as I can under the circumstances. Understanding that it might not be cost effective I will probably just go with some sort of V8.
I have done tons of reading, I am much farther along than I was before deciding to do this. HAHA so I am getting there.
It is funny you mention that, one of my first ideas was to take an L92 from an escalade or denali. When I realized how bad the mpg would be I went down the rabbit hole of could I use a smaller engine to get similar results. I even looked into some sort of ev conversion.
I will purchase a junk yard engine and do a complete rebuild. Looks like I will be going with LS power.
only 50 lol
This is what I was thinking.
Since the truck originally had an I6, it probably has the higher gears to get moving with the smaller engine.
I need to go back and see if this is driven a lot of miles.
Unless the OP just wants to learn and try some stuff, take time to work smart.
It seems like the OP needs to learn a few things before tackling an engine swap.
Do nothing approach with a running frankstein driveline truck that goes 2k-3k/year. You won’t save a penny and might get something unreliable .
Good luck.
Good luck.
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