General Motors LS and Gen-V LT engine swaps are popular for a reason: these engines are reliable and have massive power potential. LS swap kits abound, but once you get the engine into the vehicle, you still have to get all the plumbing done. Holley and their family of brands are here to help with that. There are no complete plumbing kits for LS or LT swaps, mainly because every install has different needs, so you are often on your own trying to figure out what works and what doesn’t.

There are several key areas that cause trouble for a lot of swappers. We are focusing on a few of these key areas: oil delivery, coolant, steam lines, vacuum, transmission fluid, and fuel.

Fuel

There are about a bajillion plumbing needs for LS and LT fuel systems, but we are focusing on the engine itself here. All stock fuel rails on LS and LT engines use push-connect fittings. There are couple of ways to tackle this- use a push-on adapter (p/n AT991966ERL) or use a semi-permanent adapter like the one shown here (p/n 751166ERL). The push-on style uses the factory method, but that also means carrying around a disconnect tool should you run into problems. The other style, which is also a lot cheaper, is a semi-permanent installation. The fitting has a threaded U-shaped nut that threads into the larger adapter. The adapter is sealed with an O-ring for leak-free operation, and it doesn’t damage the hardline.

GM push-connect fuel fittings are great when they don’t leak, which they often do.

That can be fixed with a thread-on adapter from Earl’s. The horseshoe nut slips over the hardline, below the flare.

Then the adapter threads on over the nipple, which is sealed with an O-ring. No more leaks, no special disconnect tool.

Oil

In order to maintain the safe operation of your engine, you need to monitor the oil pressure. On an LS, there are several options, the main one being the oil bypass cover on the side of the oil pan. All LS and LT engines have this feature. It is the simplest method of pulling oil pressure from the engine with an oil sending unit. The factory covers are not drilled and tapped for a port, though there is one factory cover that has a boss cast into it. Most swappers opt for an aftermarket cover like the one shown here from Earl’s. This unit (p/n LS0020ERL) is for an LS, LT pan require a different part number (p/n 1137ERL), they are not interchangeable.

If you need to use the bypass ports for something else, such as an oil cooler, dry-sump system or as an oil feed/return for a turbo, then you may need to locate another port. On the top of LS blocks, to the driver side of the cam sensor, is a large port that may be used for an oil pressure sending unit. Earl’s has you covered there too with p/n AT9919AUJERL.

Every LS and LT engine has a bypass port on the oil pan. This is the simplest way to get oil pressure from your engine to your gauges. LS and LT covers are different, they do not interchange.

The NPT port on the top is suitable for oil pressure senders or a turbocharger feed line.

This one fits any LS engine. Earl’s has these for Gen-V LT engines as well.

If you can’t use the bypass cover, you can use the oil port on the top of the block next to the cam sensor, you just need the right fitting.

This port seals with an aluminum washer. This could also be used for a turbo feed line.

Coolant

There are a few issues with getting the coolant in and out of an LS/LT swap, but the heater core plumbing is often the most frustrating because you probably didn’t realize it was going to be in the way until after your engine is in the car. No worries, as you can head that off at the pass with a set of these 90-degree swivel barbs from Earl’s. These are available in several sizes and work with the Holley mid-mount accessory drive OR a factory LS water pump. In order to use these on a stock water pump, you need to crush and remove the bonded-in barbs and tap the housing for the corresponding pipe thread.

The water pump coolant ports are often in the way on LS and LT swaps, these 90-degree swivel ports help alleviate that issue and can make routing the heater hoses nicer too.

The Holley mid-mount accessory drive system actually has two sets of coolant ports. The 90-degree fittings work really well here too.

Steam Lines

Likely the most needlessly confusing component of an LS engine are the steam lines. The problem is that only the LS engines used them. The Gen-V LT engines do not. The factory hard lines are ugly and don’t lend themselves to clean installs, so Earl’s has a bunch of cool options for cleaning them up. There are hardline kits and rubber hose kits, as well as several versions of block adapters. We like their super trick -3 or -4 AN machined aluminum blocks that swivel.

Once you have the lines themselves sorted, you need a port to vent them into. You have a few choices, such as the radiator, which is the factory method. The problem is that most radiators do not have an available port for the steam lines unless it is an LS-swap specific unit. The easiest and cleanest is to port the lines into the water pump. You can drill and tap a stock water pump, but if you have one of Holley’s Mid-Mount accessory drives, there is a port already threaded for steam lines built into the housing.

Steam lines are an LS-only thing, and they have to be dealt with. There are several options from Earl’s, but we like these trick swivel jobs.

There are 2 styles- single and double output in -3 and -4 AN thread. You can use 2 or 4 fittings, depending on if your rear steam lines are blocked or open.

They seal with O-rings and give you a lot of options when the time comes to build your steam line system.

These factory steam lines are ugly, but functional. Most aftermarket heads do not come with any lines at all, so if you don’t have the factory ones, you need the Earl’s units.

We used a double and a single on this LM7 that is currently being rebuilt. The rear steam lines had the factory block-offs installed.

The Earl’s 25-550 kit comes with a pre-terminated hose that fits and looks good.

The double output side runs to the radiator or water pump to complete the circuit.

If you want extra fancy, then the stainless steel hardline kit is the one you want. This is a -3 AN kit.

With the intake off, you can see how the lines are routed. This is perfect for a high-end LS build.

The Holley Mid-Mount Accessory Drive system features this port on the back of the water pump housing to connect to the steam lines.

Vacuum

There are multiple vacuum ports available on LS engines, so we are focusing on LTs here. There are no factory vacuum ports on LT engines at all. You will have to make one, unless you have an aftermarket intake. There are two options that do not require much work- the EGR valve and the fuel tank evaporation port, just behind the throttle body. The EGR valve is on the passenger side, the fuel evap port is on the driver's side. We could delete the EGR and plug it, but the port is very large and it is tricky to find a plug that has a threaded port. Meanwhile, the fuel evap port is right there, easy to access.

Once you remove the evap valve, you can tap the intake to ¼-inch NPT and thread in a hose barb adapter or get fancy with AN fittings. Just make sure you seal the threads with some liquid thread sealant. This port has a very small hole into the intake, but the fitting size is large, so you can drill out the restriction inside the intake if you need a lot of vacuum, like for power brakes.

This is the fuel evap port on an L83 LT intake. We had already threaded it, the bore is smooth from the factory.

After tapping the port to 1/4-inch NPT, a regular old brass hose barb nipple seals the deal. This can be used for any non-metered vacuum application, such as power brakes. If you use this for PCV, your engine will not run right, as it is not factoring in the extra air. It is quite literally a huge vacuum leak.

PCV

LS and LT engines are bit different in terms of PCV systems. In LS engines, the PCV ports are build into some factory valve covers, but not all of them. If you have aftermarket valve covers, then you need to get that pressure out of the crankcase. These two pieces work together to provide you with an easy PCV port in any LS valve cover. The oil fill cap (p/n 3434122ERL) is hollow and threaded for the PCV adapter. You can use this for more than just PCV, but that is the main purpose. The cool thing is that it is baffled, so you won’t end up with oil being sucked out of the engine.

The other main option for this part is for a catch can system. LS engines can use them, but these are quite necessary for any LT engine, swap or factory-installed. LT engines do not have any fuel running through the intake as they are direct-injected. This leads to carbon build-up on the stem side of the intake valves. After 50k miles, your intake valves are likely to have a significant build-up, and by 100k miles, your valves are sticking. The main reason for this build-up is not just the lack of fuel to wash them down (that’s why it builds up), but the main reason is because LT engines do not have good PCV systems...in fact they are absolute garbage, with no filtering ability at all. What happens is that you get a lot of oil vapor, as well as trash and actual liquid oil being sucked into the intake. Many LT-series owners report 1-2 quarts of oil loss per 5k miles, and this isn't isolated to the Gen-V LT engine - this actually goes for ALL GM GDI engines, including the V6s.

The solution to this is adding a catch can inline with the factory system or bypassing the factory system altogether. Earl’s catch can kits gives you just about everything you need to build a functional catch can system and eliminate the issue altogether.

Pro Tip: Keep your intake valves clean with an intake-valve cleaner treatment at least every other oil change. Available at any parts store, these cleaners are injected through the air intake system (AFTER the MAF sensor!) into the throttle body. Most treatments require two people: one to operate the throttle through a varying rev range, while the other administers the treatment. A single treatment on an engine that has not been treated before can increase performance and fuel economy.

Crankcase pressure has to be vented, otherwise you can run into all kinds of problems. LS valve covers don’t always have PCV ports, and LT engines have lots of issues with their PCV system, this valve cover oil cap is actually a baffled PCV port.

When used with the thread-in PCV adapter, you can make your own system. The cap has -10 threads, so it can be used with the catch-can kit as well.

This catch can kit comes with several fittings and a oil filler port, so you can vent your engine and store that oil away from the intake.

Transmission Fluid

This isn’t the most complicated, in fact it is fairly easy on most swaps, but if you are using one of the newer GM automatics, such as the 6L80, then the old ways won’t work. The newer transmissions use a bolt-on block to carry the transmission fluid to and from the trans cooler and the transmission case is not threaded for individual fittings. If you have the original lines, you can use them, but that isn’t super clean and requires flaring the lines and using hardline adapters or plain hose. Instead of those ugly options, Earl’s Plumbing offers an adapter fitting (p/n 1128ERL) that replaces the chunky aluminum hardline block with a streamlined O-ring adapter with -6 AN ports so you can plumb your transmission as you choose. Of course if you have a 4LXX or other GM transmission, Earl’s has those adapters, too.

For GM 6LXX transmissions, this aluminum fitting block is the easiest way to plumb the trans cooler lines. It features O-ring seals and -6 AN threads for leak-free service.

The factory line block is huge. By the time you get exhaust under the car, there is very little room to access the cooler lines, and if you didn’t get one with your donor transmission, then you would have to pay for the full line set.

The Earl’s adapter is considerably smaller, and you can use hardline, rubber, or even Teflon lines. You just need a -6AN fitting.

Power Steering

If you are running power steering, then you will need some adapters in pretty much any LS or LT swap. GM vehicles need either SAE or metric gearbox adapters to get the fluid in and out of your pump, depending on your application. These are commonly referred to as “bump tube adapters” because they “bump” the sizing of fitting. These are hard to find locally and most parts stores will have absolutely no idea what you are talking about. Earl’s has you covered though, with multiple sizes. Most GM vehicles require inverted flare O-ring fittings, which look a little funky. 1979 and older vehicles typically feature 5/8"-18 and 11/16"-18 thread, whereas newer GM vehicles have 16mm and 18mm metric threads. This goes for gearboxes as well as rack and pinion steering units. The other side is -6, which mates up to the output of most GM type-II power steering pumps.

Depending on the accessory drive you are running, you may need a long-stem output fitting for your pump as well. Earl’s p/n 961961ERL is a long -6 adapter that replaces the entire output fitting on Type-II pumps so that you can run a -6 fitting and clear the pulley. We have used this one several LS and LT swaps, and it is a godsend for clearance.

This is a bump tube adapter for power steering units. The inverted O-ring flare is unique to power steering systems.

Air Intake

The last part of our plumbing is air intake. Unlike an air breather on top of a carb, LS and LT engines have specific requirements for air flow and MAF sensors placement. For LT engines, the MAF needs to be at least 10” before the throttle body in a straight section of tubing at least 6” long. This is not always feasible, but that is the GM spec. The pipe itself needs to be 4” in diameter, which is also really tough to accommodate in most muscle cars. The Flowmaster universal air intake kit (p/n 615400) solves all of these issues, ensuring that you can get the air into your engine. This is a really cool kit...you just need a bandsaw, reciprocating saw, or even a hacksaw to the cut the tubing and it comes with a conical air filter, mounting tabs, and even a MAF mount (late-style LT design). If you are careful and buy an extra filter, you can actually make two intakes with one kit.

We love the Flowmaster universal intake kit! It looks great, fits anywhere, and has a super cool filter to boot!