putting in a new engine

[christine]

I just got a 78 chevy s/b stepside and made a deal with my father that i could get it if a new engine was put in (luckily paid for my him). He wants to put a newer(like 99 or newer) 4.8L V8 as I am a student and the 454 thats in there right now is going to kill me for gas. Has anyone heard of someone doing this with an older truck, it seemed a little weird to me but i was willing to make any agreements to finally getthe truck, or does anyone have any better ideas of an engine to put in? all help would be appreciated

[jeefsilverado]

I would go with a 5.3 or 6.0 liter if you are going to do the swap.

[beaterC10]

I would slide a carbed 350 in that truck and avoid all the extra work.

[christine]

What would be the gas differences in putting in 5.3 or 6l compared to the 4.8?

[piecesparts]

Gas mileage is in the eye of the beholder. first of all the 4.8 is a good small block engine, kinda like the original 327 small block of the early years. I have a buddy that has one in his 99 Chevy and he can get 23 MPG. I also have friends that have the 5.3 in their trucks and they get around 20 to 21 MPG on them. What I would caution you in this endeavor, is that there will be some differences in what you build compared to what GM put out in the late 90s and now. You will need to consider your gear ratio in comparison to what is on the market. Most trucks are getting either the 3.42 rear end or the 3.23 rear end, depending on the build sheets, with th 3.23 being a most popular choice. What do you have? The truck weight will be different, the tranny may be different. The wind resistance is definitely different in the models.
The 6.0 liter motor is just that---a big puller motor and can be a gas guzzler. Everyone would love to have one--UNTIL you gas up. I have a mid eighties truck with a 385 stroker motor in it and I can get 15 MPG with it using a 700 R4 tranny and I feel good that it does that well. I know guys that only get 12 or 13 with their standard 350/350 setup in their truck. Before you go to far, look at everything---gears, tranny, and engine combination, as well as what size tires you are going to use---it all fits together. Don't fall for the idea that the lower the RPMs, the better the gas mileage. There is a breaking line there, where you will loose efficiency for driving and start to gobble gas by going to low. We actually improved the gas mileage on my son's truck by putting in lower gears to get his RPMs up into the power range and not lugging the motor.

[Captkaos]

I would say go for it. I am waiting on my 6.0L to get here for one of my trucks.

[Ric83]

From what I have heard from actual 4.8 and 5.3 owners, the power diff. between them is very noticeable not to justify getting the 4.8 over the 5.3 for the 1-2 mpg gain.

[eagle23]

I think it's one of those "it depends" questions

If you can provide some more info, we might be better able to help sort some things out with you. You won't find this board lacking in opinions

How far is school, and how often would you be making the trip? The cost of the 4.8 engine over a regular 350 may take years to recover, especially when you add in the cost of adapting new engine technology to our old trucks. For example, you can get a brand new GM 350 crate engine with a 100,000 mile warranty for ~$1400US.

Do you know what rear axle ratio the truck has? It might be on the glove box door, and still might be right if any previous owners did not swap in another axle. The axle ratio can make a big difference in mileage.

Would you and your dad do all the swap work, or have it done by a local shop--that adds big money fast.

If fuel mileage is the real concern, you might do well with a simple 350 swap, then work out gas costs, e.g., you pay 2/3, he pays 1/3. I'll bet the dollar cost savings in using a standard 350 over the newer engine adaptation costs might fund a lot of fuel.

And the comment above about the barn-door aerodynamics of our trucks is true vs the new ones...that and fuel injection are a big part of their better mileage.

See what I mean about "It depends"?

Keep us posted.

Brian