The least painful way to get LS power into an early Chevy
Editor Steven Rupp traced a line in the sand; “What’s the cheapest LS swap you could do?” It was a challenge we had to accept.
Spending money is easy. The simple route for an LS swap is to just plunk down your credit card on a complete, new LS3 crate engine and a pile of extra parts and bolt it all together. But, if you’re like us that just isn’t a realistic option. On the other side of the coin, a used iron LS engine out of a truck is dirt cheap.
Our approach to Rupp’s test would be to look for the smallest and least desirable—and most plentiful—LS engine on the market. That brings us to the early Gen III 4.8L or 5.3L truck engines. For those who may not be aware of these powerplants, they are the workhorses of the GM lineup. You can think of the 4.8L as the 283 of the LS engines and the 5.3L as similar to the old 327. The 4.8L stroke at 3.268 inches is shorter than a 5.3L at 3.622 inches and the 4.8L is accompanied by flat-top pistons with the same 3.780-inch bore as the 5.3L. GM doesn’t build the 4.8L anymore, which is one reason why nobody wants them. If you can find a 5.3L LS for cheap run with it, but for this story we found a 4.8L for $200. And yes, that’s not a typo.
We will focus this story on swapping this little truck engine in an early Chevelle because that’s what we have sitting in the shop. The approach for other cars will vary slightly but for the most part the same details will carry over to most Bowtie car lines. The other half of this budget approach is the transmission. In this case, we’re going to use a TH350 as our cheap trans of choice. These gearboxes are common on the used market for less than $500 and will bolt up to an LS engine with a simple hub adapter.
Our approach here is strictly minimalistic. If we don’t need any extra (read expensive) parts, then we’re not going to deal with them. We’ll start with the induction system because that decision affects other items you have to figure into the budget. In some cases, it might appear that a carburetor and spark box would be the least expensive way to go. For example, in the case of a ’60’s or ’70’s car like a Chevelle, a carburetor conversion is less expensive because you don’t have to invest in a high-pressure return style fuel pump and delivery system.
However, you will need some kind of electric fuel pump because there is no provision for a mechanical fuel pump on an LS block. There are a few budget pumps like the Holley red pump that doesn’t need a fuel pressure regulator that will also keep the cost down. A fully baffled EFI tank is best, but if you need to make due with a modded stock tank then make sure to keep your fuel level up to avoid starvation issues. Our sidebar shows the price breakdown of a carb conversion versus EFI, using the Edelbrock Pro-Flo 4 as an example. As you can see, the prices are very close, depending upon which direction you choose. If you have access to a used Holley carburetor for roughly half the price of a new one, obviously that helps, but it may need a rebuild kit which then drives the price back up.
On the EFI side of the street, we selected Edelbrock’s Pro-Flo 4 EFI package combined with a used LS1 intake, and slightly larger 5.3L flex fuel injectors. Edelbrock has completely updated this over the previous Pro-Flo 3 while reducing the price (sans manifold and injectors) to just under $900. This includes the EFI, harness, oxygen sensor, and the wireless tablet. The system is incredibly powerful, self-learning, and very easy to operate. Load the engine-relevant data into the tablet and then it can also be used like a digital dashboard if so desired. It’s pretty cool and very affordable. Another recent entrant into the affordable LS EFI swap is Holley’s new Terminator X system, which starts just under a grand for the kit.
A stock LS truck ECU with stock harness would also work, but would need custom software tuning to make it work and the price often will end up higher than what we’re projecting for the Pro-Flo 4. This OE approach is useful as long as the engine remains stock. Any change that requires tuning will likely require the services of a tuner.
Additionally, there are several small items that end up costing much more than anticipated. As an example, let’s take the approach of bolting an LS1 intake on a 4.8L/5.3L and using the Pro-Flo 4 EFI. One hidden roadblock is that the water pump on the truck accessory drive crashes into the throttle body. The truck EFI manifold is OK, but it’s taller and won’t fit under a low hood line of an early Chevy II, for example.
So this means converting to an F-body style water pump, but this demands a different harmonic balancer because the serpentine belt drive pulley is integrated into the balancer. An F-body replacement balancer is not expensive, but this further requires a specific factory accessory drive. One alternative is Kwik Performance, which offers an alternator-only bracket system that will mount the stock truck alternator. If power steering is also on the list, there are several options offered by various manufacturers, like Holley, which is a story all by itself.
There are literally a dozen or so companies making flat plate conversion mounts to convert the four-bolt LS engine mount to adapt to the more common small-block Chevy three-bolt pattern.