All of us have looked under a hood and felt confused. You see a block painted orange or silver, but you have no clue what is really inside the bay. Is it an old small block or the modern LS everyone talks about? It is a common problem for guys who buy used projects. Today I will show you exactly what to look for so you can stop guessing and start wrenching on your pride and joy.
You should start by looking at the coil packs. An LS engine will have individual coils on top of the valve covers. Old school Chevy engines use a single distributor in the back of the engine. Check the intake manifold too. Modern LS engines use a plastic intake while the older ones use metal. Look for a VIN code on the block, check the cylinder head bolt count, and you will have your answer quickly.
Why Does the Engine Type Matter?
Picking the right parts depends on knowing what you have under the hood. You need to know if you can swap heads or if you need a different oil pan for your custom build.
The Distributor Location
An old Chevy small block has a distributor at the back of the engine near the firewall. You will see a cap with wires coming out. If you see that, it is not an LS engine. LS engines use coil packs that sit right on top of the valve covers.
Valve Cover Shape
Look at the shape of the valve covers. Traditional Chevy covers are held down by four bolts in the middle. LS valve covers are different, they use a center bolt pattern. They look much flatter and have a more modern, rounded shape to them. It is a very easy way to tell.
Intake Manifold Material
Most original Chevy small blocks came with cast iron or aluminum intake manifolds that have a carburetor sitting on top. LS engines almost always use a black plastic intake manifold. This makes the engine look a lot different when you first pop the hood. It is a dead giveaway for an LS.
Bolt Pattern Differences
The bellhousing pattern is a big clue for any mechanic. While some LS engines fit older transmissions, the top bolt hole is different. If you see an extra hole at the top of the transmission, you likely have an LS engine block. This is a very common transmission adapter plate use case.
Water Pump Mounts
Check how the water pump attaches to the engine block. Older Chevy engines use a different mounting style than the LS. The LS water pump is more compact, and it does not have the same bolt holes as the older small blocks. It is a unique part that only fits the LS.
Oil Filter Placement
Look for where the oil filter screws onto the engine. On an older small block, it points down toward the ground. Many LS engines use a remote mount or have a different adapter near the pan. If you see a weird hose setup, you are probably looking at an LS engine block.
You should always verify your engine before buying expensive parts. A mismatched part will cost you time and money. Check these specific spots first:
- Check the coil packs
- Inspect the intake manifold
- Look for the distributor
- Count valve cover bolts
- Check transmission pattern
- Verify water pump mount
How to Tell If You’ve Got an LS or Chevy Engine
Identifying the engine is the first step before you start spending money on upgrades. Most people get confused because both engines share the same basic Chevy DNA and heritage.
The Coil Pack Setup
You will see big plastic packs on top of the valve covers if you have an LS engine. These are part of the ignition system. They send power to the spark plugs. Each cylinder has its own coil. Old engines use a single coil and a distributor. This is the biggest difference you will see. You might find a broken ignition wire on an older engine, but on an LS, you have many wires to check. If you see a mess of wires going to the top of the valve covers, it is an LS.
Valve Cover Design
Look at how the valve covers attach to the head. Older Chevy engines use perimeter bolts. These are around the edge of the cover. The LS uses a different center bolt design. The covers look very smooth and flat. You cannot swap them between the two types. If you try to force them, you will have a massive oil leak. Always check the valve cover gasket style before you buy new ones. It is a simple visual check that takes only a few seconds to finish.
Intake Manifold Look
The intake on an LS engine is usually black plastic. It looks like a complex piece of art compared to the metal chunk on an old engine. Some people swap them out for metal ones, but the shape remains distinct. The fuel rails are also very visible on the LS. They run along the sides of the manifold. If you see plastic, you are likely looking at an LS engine. This is a common engine swap trait that you will see in many modern hot rods.
The Transmission Bolt Pattern
This is where things get tricky for a lot of guys. The LS block has a different bolt pattern for the bellhousing. Most of the bolts line up, but the top hole is different. If you see a bolt that does not seem to attach to anything, it is a sign of an LS block. You might need a special bellhousing adapter to make your old transmission fit. Do not assume everything will bolt up easily. Check your patterns before you try to force the transmission into place!
Water Pump Mounting
LS engines have a very distinct water pump. It sits flush against the block. You will see pulleys that look very compact. Older small blocks have a pump that sticks out further. The cooling system on an LS is also different. It uses different hoses and thermostat housing locations. If you are struggling with a cooling system issue, compare your pump to photos of a stock LS engine. You will see the difference right away. It is a very reliable way to identify your engine platform.
Engine Block Casting Numbers
Every Chevy engine has a casting number on the back of the block. You can look these numbers up online. They will tell you the exact year and displacement of your engine. It is the only way to be 100 percent sure. You might need a mirror to see the number if it is tucked behind the engine. Use a wire brush to clean off the grime first. Once you have the number, search for a casting number database to get the truth.
You must be careful when buying parts for these engines. Take your time to confirm what you have, or you will end up with boxes of stuff that does not fit.
- Check for individual coils
- Look for center bolt covers
- Verify the intake material
- Look for the transmission gap
- Compare water pump styles
- Find the casting number
Does the Intake Manifold Always Tell the Truth?
Many people assume a plastic intake means an LS, but some people put plastic intakes on older engines. You have to be careful with these custom builds. Look at the block itself if you are really not sure. The mounting holes for the heads are a better way to check.
The block markings are the final word for any engine identification. If someone swapped the parts, the intake will lie to you. Check the block casting number. It never lies. A quick search on your phone can save you hundreds of dollars in incorrect engine parts.
Check the starter location too. On older blocks, the starter is on the passenger side. On an LS, it is on the driver side. This is a very reliable way to confirm what you have. Do not ignore the simple stuff when you are deep into a project.
- Check the starter mount side
- Look for block casting numbers
- Verify the oil pan shape
- Check the dipstick location
- Look at the alternator mount
- Compare the exhaust ports
Is the Crankshaft Sensor Important?
Yes, the crankshaft sensor is a massive clue. Old engines do not have one. An LS engine must have one to run its computer system. You will find it near the back of the block on the passenger side. It is a small sensor with a wire sticking out of it.
If you see a plug for a sensor near the bottom of the block, you definitely have an LS style engine. Old Chevy blocks are totally flat in that area. They use a mechanical fuel pump instead. An LS engine uses an electric pump in the tank. This is a major fuel system difference.
Look for the sensor wire. If you find one, do not waste your time looking for a distributor. You will not find one. Stick to the modern parts for your build and you will be fine.
- Check for crank sensor plug
- Look for electric fuel pump
- Find the computer harness
- Check for distributor hole
- Inspect the block casting
- Verify the sensor position
Can You Use Older Parts on an LS Engine?
You can use some parts, but most will not fit. The head bolts are totally different sizes. The intake ports are shaped in a way that makes them impossible to swap. You need to buy parts made for your specific block or you will fail.
I have tried to swap parts before and it was a mess. You end up with vacuum leaks and engine fires if you are not careful. Use the right parts. It is worth the extra cost to get the correct performance parts for your engine build.
If you are building a budget engine, check the classifieds for take-off parts. Many people upgrade their LS engines and sell the stock parts for cheap. It is a great way to keep your costs low while building something fast and fun.
- Verify head bolt pattern
- Check intake port shape
- Look for oil pan clearance
- Match the flywheel size
- Check accessory drive kits
- Ask for engine history
Will a Chevy Small Block Fit Where an LS Was?
It will fit, but you will need new mounts. The LS mounts are different than the old school style. You also need to change the transmission or get a fancy adapter plate. It is a lot of work for a simple swap.
Most people prefer to keep the LS because it makes more power. It is lighter and handles better than the old heavy iron blocks. If you have an LS, keep it. You will spend less money making it fast compared to an old small block. Look into a modern engine mount kit to make the install easier.
Take your time with the wiring. That is where most people quit. If you stay organized, you can make it work. Just keep your goal in mind and stay focused on the task at hand.
- Buy custom engine mounts
- Get a transmission adapter
- Plan your wiring harness
- Check oil pan clearance
- Upgrade your fuel pump
- Keep your cooling system
Final Thoughts
I hope this helps you figure out what you are working on. It feels good to know exactly what you have under the hood. Take your time, look for those key signs like the coils or the intake, and you will be set. Building a car is hard work, but getting it right makes every bit of the effort worth it. Good luck with your project and enjoy the ride.
| Feature | Old Chevy Small Block | LS Engine |
|---|---|---|
| Ignition | Distributor | Coil Packs |
| Intake | Metal | Plastic |
| Valve Cover | 4 Bolt Edge | Center Bolt |
| Fuel Pump | Mechanical | Electric |
| Crank Sensor | None | Yes |
| Starter | Passenger Side | Driver Side |
| Block | Cast Iron | Iron or Aluminum |
| Oil Filter | Downward | Remote or Pan |
| Water Pump | Large | Compact |
| Bellhousing | Standard | LS Pattern |
Frequently Asked Questions
Is It Easy to Tell the Difference?
Yes, it is very easy if you look at the right spots. The coil packs and the intake manifold are the two things that stand out the most. If you see those, you have an LS.
Can I Swap an LS Into an Old Car?
You can do it, but you need the right parts. You will need new engine mounts, a new transmission adapter, and a custom wiring harness to make it run like a new car.
Are LS Engines Better Than Old Ones?
They are much more efficient and usually make more power. They are also lighter because they use aluminum blocks. For a daily driver or a fast street car, the LS is the king.
Do All LS Engines Have Plastic Intakes?
Almost all of them do. There are some aftermarket ones that are made of metal, but they are built to replace the plastic ones on an LS engine. Check the bolt pattern.
Should I Keep the Old Engine?
That depends on your goal. If you want a classic restoration, keep the old engine. If you want more power and reliability, swap it for an LS engine right away.
Will My Old Headers Fit an LS?
No, the exhaust port pattern is totally different. You need to buy headers that are specifically designed for the LS engine block. Do not try to drill new holes.
Does the VIN Tell Me the Engine?
The VIN can tell you what the car came with from the factory. If it is an old car, it will tell you the original engine. It won’t tell you if someone swapped it.
Will the Engine Last a Long Time?
Both engines are very tough if you take care of them. Change the oil often and keep the cooling system clean. They will run for a long time if you maintain them.
