How To Fix A Leaking 1992-1996 LT1 Intake

There was no question that this was still a small-block Chevy, but there were plenty of upgrades stuffed into this next-gen mouse motor. One of the biggest improvements over its predecessor was the redesigned intake that shortened the intake tract considerably and lengthened the legs on this new V8. Its penchant to rev allowed it to use a full sweep of the tachometer. This new design gave the second-gen small-block 20-percent more horsepower and a much broader torque curve. Yes, the L98’s torque could be a lot of fun, but coupling torque with high-revving horsepower will put a smile on anyone’s face.

Another deviation from the original small-block was a reverse-flow cooling system, which routed coolant to the heads first, and then to the block. This upgraded path of coolant helped cool the combustion chamber, which allowed engineers to bump the compression ratio – one of the first positive steps in drawing Bowtie performance out of the EPA-ladened dark ages.

This also meant the coolant no longer spent any time in the intake, although it still flowed through the throttle body. Even with a dry intake, there are still opportunities for leaks. As these engines rack up the months and miles, oil leaks from the front and rear China wall surfaces have proven to be the intake’s biggest issue. Just like many aspects of automotive maintenance, fixing that leaking intake is a great weekend task, and your driveway and engine bay will thank you for it.

Components Of The LT1 Intake

There are a few modern technologies attached to the topside of the LT1 engine. Components such as the Exhaust Gas Recirculation (EGR) system, a vapor control valve, and a Manifold Absolute Pressure (MAP) sensor all play an important role in how well the LT1 engine performs.

The EGR valve is a positive-backpressure valve that uses exhaust pressure to operate. It injects exhaust gasses back into the intake charge to help displace oxygen and decrease combustion temperatures under certain conditions. When the EGR system is working properly, it can be a great resource in limiting detonation within the higher-compression LT1 engine. But, too much of a good thing is still too much. Excessive exhaust gas due to a faulty EGR valve can cause surging, stalling, and a rough idle.

While disassembling the LT1 intake, it is always a great idea to inspect the EGR valve for proper operation and ensure there is no carbon buildup preventing it from moving or closing completely.

The vapor control valve is an often-misunderstood component of the LT1 engine’s operation. While there was a time when enthusiasts would “pull all that emissions junk” in the name of performance, the vapor control system actually benefits the way the LT1 performs. This valve connects a charcoal canister (which stores gas vapor from the tank) to the intake. While cruising, the car’s computer sends a signal to open the valve, improving fuel efficiency as the engine burns away vapors that would otherwise be wasted. It is recommended to not remove this valve, especially if you think tossing it will improve performance.

The MAP sensor is the highest profile sensor of the engine. It sits atop the intake, constantly reporting on the level of load the engine is experiencing at any given moment. It works on the pressure variations experienced inside the intake. A higher vacuum reading indicates the engine is experiencing low load, conversely, pressure increases (less vacuum) as more load is added through opening the throttle or going uphill.

It is imperative that the MAP sensor has a good seal and is operating properly to allow the PCM to know the burden put upon the engine at any moment of time. Be sure to check inside the sensor for any oil buildup, as this can skew the sensor’s input. Also make sure the seal is still in good shape and replace it if in doubt.

Even though it may not be necessary when changing the intake gaskets on an LT1 engine, it would be fuelish (pun intended) to not remove the fuel rail and injectors to inspect them. Also it’s a good idea to check every injector with a multimeter to see if they are shorted to ground. A good injector will have around 12.6 ohms of resistance. A reading of 11.5 ohms or lower means the injector is suspect and shorted internally. Removing the fuel rail also allows you to check for carbon on the injectors and inspect the fuel pressure regulator for leakage.

Removing The LT1 Intake

When removing the intake, it’s best to start at the front and remove the throttle body. There is a gasket between it and the intake and now is a great time to make sure that gasket has a good seal by replacing it with a new one.

We recommend removing the front and rear intake bolts first and working inward. Remember the placement of the bolts, as some are studs, and are there to hold certain components. Mark which holes used the studs so you aren’t swapping them while the intake gasket is curing. If you’re this deep in replacing your LT1’s intake gasket, you already know the importance of a good seal.

Once you remove the intake, check the gasket surfaces for any evidence of why the gasket failed. Age and numerous heat cycles have a cumulative effect on gaskets and at some point, they are destined to fail. Pay particular attention to any compromised areas throughout the gasket surface.

Removing the old gasket can be done several ways, but be mindful of a few things. You don’t want to prevent the new gasket from sealing by damaging the surface, and you REALLY don’t want anything foreign going into the engine! Those abrasive wheels on a dremel or grinder work fast, but the dust and small chunks from the process can be death to your engine. Elbow grease and patience is the safest way to a clean surface.

Before you start removing any gasket material, line the inside of the valley cavity with clean rags or shop towels. Using clean ones help prevent any outside debris from winding up in your engine’s oil pickup screen and you’ll see exactly how much stuff came from the gasket removal process.

This is also a great time to clean the bolt threads and chase the threads in the heads. Those rags you just put down will help catch the old thread sealer and crud that will come out of the threads. The inner holes are open at the bottom and need thread sealer, while the outer holes are blind holes and should never see any coolant or oil.

"Yes, even if you think the surfaces are clean enough, go ahead and clean them one more time..."

To remove the gasket, a Matco (Lisle) carbide scraper is ideal for aluminum surfaces and removes gasket material effectively without gouging, but they are not recommended for iron surfaces, such as the LT1’s block. No matter how you tackle removing the intake gasket, take your time, paying close attention to the front and rear block sealing surfaces.

Clean all the surfaces often with a fresh shop towel and alcohol to check for any remaining residue, and if you see any discoloration or oil on the towel – keep cleaning! The trick to keeping oil inside your engine is a good seal on both the heads and block, which you can’t get if there is already oil on any of these surfaces. Yes, even if you think the surfaces are clean enough, go ahead and clean them one more time and don’t touch the sealing surfaces once you’ve cleaned them. The front and rear surfaces where the block meets the intake are especially important to get clean.

Installing the LT1 Gaskets & Intake

Before you begin installing gaskets and sealant, take a minute and test-fit the gaskets to make sure everything is in place. It’s also recommended to prepare all the bolts in advance, so you can begin the tightening procedure immediately after placing the intake onto the engine.

The bolts that will go into the open holes in the center of the head and intake should get a light coating of thread sealer. The blind holes will get a small dab of never-seize. That said, it is NOT recommended to use never-seize on bolts with open holes where the messy stuff could potentially wind up inside your engine.

You’ll notice we used Permatex® oil resistant Ultra Black gasket maker for the front and rear surfaces of the intake. We began by putting a solid bead across the front and rear block surfaces. Then, the intake gaskets went on the heads, held in place by their small pins. Once the head-to-intake gaskets were in place, we added another dab of Ultra-Black to the corners where the gaskets meet. This gives another layer of protection at the corners, where oil likes to wait for an opportune time to leak.

With the gaskets all in place, quickly, but carefully lower the intake into position. Don’t let the Ultra Black skin over or you’ll have to redo the entire process, or learn to live with a leaking intake. It can only take about seven minutes for the gasket-in-a-tube to skin over, so be ready. If you install the intake and see a spurt of Ultra-Black shoot out like a Play-Doh press, it has skinned over and you might as well start over.

We like to install the end bolts first to prevent the intake from shifting around. Remember which holes got the studs! Once all the bolts are in place, begin the torquing sequence, as described in the service manual for your engine. Torque all the fasteners in sequence to 71 inch-pounds for the first pass and then cinch them down to 35 lb-ft on the second pass.

The clock stops ticking once you’ve got the intake properly torqued. You can continue installing the rest of the components, but we recommend letting the gaskets cure overnight before you start the engine. Besides, years of leak-free service is well worth the few hour wait to hear your engine roar back to life. Sleep on it and we think you’ll agree.

As mentioned, this task could easily be done in a weekend, and if you’ve got some friends who don’t mind helping clean parts, all the better. One thing is for sure, with that intake leak fixed, your engine will be much cleaner every time you open the hood!