thewhizkidnumerouno

I have a '78 chevy stepside with a TH-400. I was thinking about swapping in an LS engine. My goals for the truck are good gas mileage(which is why I'm going with a fuel-injected engine), good drivability and between 350 and 400 horsepower. This is a daily driver, so I don't need a whole lot. I am also doing this on a budget for the engine of no more than $2,000.

I have narrowed it down to the 5.3 and the 6.0.

I know that the 6.0 will give me slightly worse gas mileage than the 5.3, but I will be at my power goal. It will also be slightly more expensive.

The 5.3 will cost less and get slightly better mileage. With the money I will save, I think that I could get to my power goals fairly easily.

What engine do you guys think that I should go with? Thank you!

kornboy

iTrader: (13)

What modds are you planning? Is the 2k for motor and speed parts?or just motor?

thewhizkidnumerouno

I can only afford to save $100 a month towards this, so the 2k is for the motor and all speed parts, if I can afford any. Since I is a kollege stoodent, I'd like to spend as little as possible. I will be selling my old 350 to pay for the fuel system. Any extra money I have from that will be put into speed parts.

The mods that I am planning on are headers and possibly a cam as long as I don't have to get new springs. I am a computer science major, so I figured I might also tweak the computer a bit.

garys 68

iTrader: (1)

5.3s are almost free. You'll probably pay more to buy a harness or have one modified and computer reprogrammed. They will get better milage and still do have the torque to move a relatively large vehicle. They're in full size chevy pickups. I just bought one to go in a 72 cutlass for a DD.
While you can "hot rod" a 5.3, the 6.0 is a much better platform. Also, the TH400 is a pretty big trans that eats mor hp than a TH350, making the 6.0 a better choice.
What's your rear end ratio? If it's over 3.30, you're just going to be revving the 6.0 for no reason. The 5.3 with a higher ratio will be fine. A 2.73 ratio might be better off with a 6.0.

speedtigger

iTrader: (16)

I would say that a really honest assessment of what is motivating this swap is key here.

What is your primary motive? If it is fuel economy, then the 5.3. If it is performance, the 6.0.

I personally, have always preferred torque in a pickup. The 6.0 will have more.

Jim85IROC

iTrader: (6)

If fuel economy is of any concern, I'd strongly look toward another transmission. Nothing is going to get good mileage in front of a TH400. Not only does it lack overdrive, but it's inefficient.

A 5.3 with a 4L65E would be a great combination.

ghettocruiser

iTrader: (17)

I agree...TH400 might be simple, but its not going to help your MPG. Are you def against a manual? Sixth gear is a MPG blessing haha.

With a good trans set up and proper gearing you can see good MPG Im sure.

I would go with whatever motor you can more easily afford and find. Either one will offer you with good performance with the right parts. For a truck Ide be looking at the 6.0 though. Torque is your friend.

J.

thewhizkidnumerouno

My rear end is a 12-bolt, 3.55 posi.

My main motive for the swap is basically just to get better economy than the carbed 350 would have. Either the 5.3 or the 6.0 should give me better mileage than the carb.

I was planning on swapping in a o/d tranny when I could afford it. Wouldn't I have to reconfigure the speedo for it to work? I'd like a stick, but I don't think I have the cash for a swap, unless I can get a takeout assembly.

Pop N Wood

iTrader: (1)

You're sort of wasting your time asking which one will be cheaper. The only way you are going to answer this question is to start shopping for deals and buy whichever unit you can get the best price on.

And +3 on the transmission and gearing choice being your #1 way to better fuel economy. My project went from a 2.4L 6 cylinder to a carb'd 6.0L LS2 V8 and the MPG actually improved with the bigger engine. I attribute this to the steeper gearing. The V8 car pulls 2400 RPM at 70 mph. I just finished swapping out the rear gears to drop this to 2300 RPM at 70 mph, so hoping for slightly more MPG.

If I were in your position I would look for a complete pull out including the trans, harness, ECM and all accessories. Minimizing the unknowns is generally the cheapest way to complete a swap.

One last thing, properly set up carbs don't give up much in the way of MPG. So I wouldn't look there for economy.

garys 68

iTrader: (1)

A 3.55 would be a great rear end to use with an OD trans. Do yourself a favor and get a 5.3 or 6.0 (if budget permits) already connected to a 4L60e or 4L80e. You'll end up spending extra time and money to get the TH400 to work, only to find out you're not happy with it. Then you'll spend more time and money to add the OD trans that the motor originally came with.

chuckd71

iTrader: (23)

If you are going for "economy" then making this swap is throwing away dollars to save dimes.

01ssreda4

iTrader: (96)

I agree.....No logic here what-so-ever. Just run what you got until you get out of school.

thewhizkidnumerouno

The reason that I am considering an LS swap is because my truck hasn't run in 10 years. I am going to get it running, but I have yet to do so. I probably should have said that in my original post. I apologize, that's my bad. I am asking these questions to see if it would be worth the effort to spend basically the same money to get equal horsepower and better economy with an LS over my 350. I'm just trying to get the best band for my buck.

I figured out much it would cost to rebuild my 350 and around how much it would cost to swap in an LS. That's the reason my budget is $2,000: that's how much it will cost to rebuild my current engine. I was just wondering what engine you guys thought I should go with.

What I've gotten out of this is that I need to find a 5.3 or 6.0 with a tranny attached for this to be worth it and that this combo should be relatively easy to find. So, I'll look for a 6.0 and an attached tranny over Christmas Break. Thanks for all of your help guys. I'll let you know what I find.