Difference Between 305 And 350 [Explained]

The key difference between 305 and 350 engines that set them apart from each other is the bore size of the two engines. Other differences between the two engines include the heads, combustion chamber, horsepower, harmonic balancer, and crankshaft.

Keep reading this article to find out about these differences in detail. We’ll also answer some common questions related to the 305 and 350 engines. Let’s jump right in!

Difference Between 305 And 350 [Known A-Z]

There are a lot of similarities between the 350 and 350 engines. They have the same connecting rod and stroke. The 305 and 350 chevy engines look identical when they’ve been mounted on a vehicle.

The stroke size in the 305 and 350 engines is 3.4 inches. A lot of the parts are interchangeable in the two engines. So, is there any difference between 305 and 350 engines?

The main point of difference between the two engines is in their bore size. The difference in the bore size has led to some other differences between the two engines. Let’s have a look at these differences:

Difference Between 305 And 350 Bore Size

The 305 engine has a 3.760-inch bore. The 350 engine on the other hand has a 4-inch bore. It’s the main difference between the two engines. 

The bore size of the 305 engine is much smaller than the 350 engine. The combustion chambers and intake valves are smaller in the 305 engine so that it doesn’t overheat easily.

Difference Between 305 And 350 Heads

The cylinder heads between the two engines are different. The space between the holes on the cylinders is much higher in a 305 engine than in a 350 engine. That’s why the 305 engines break more easily compared to a 350 engine.

As the 305 cylinder heads have a smaller bore, you can put them on a 350 engine. But you can’t do it the other way around.

Difference Between 305 And 350 Combustion Chamber

The 350 and 305 chevy engine look the same in dimensions but the combustion chamber size is different in them.

The 350 head has a 76cc combustion chamber. The 305 head on the other hand uses a 58 cc combustion chamber. The 305 head has a smaller combustion chamber as it has a lesser cylinder volume.

Many people take the chamber heads of a 305 engine and put them on a 350 engine to increase the compression. It’ll increase the compression but there will be a reduction in the airflow as it has smaller valves.

The end result will be that the performance of the engine won’t increase. You’d get the same Horsepower with the 305 combustion chamber. That’s because reduced airflow will balance out the increase in compression.

HP Difference Between 305 And 350

You’ll get more horsepower from the 350 engine as it has a bigger combustion chamber and larger bores. You’ll get a difference of about 120 HP as the 305 engine horsepower won’t match the 350 engine horsepower.

Difference Between 305 And 350 Harmonic Balancers

The harmonic balancer in a 305 engine is hollow and 6 inches tall. The one on the 350 could be hollow 6 inches or solid 8 inches tall. There’s not a notable difference between them and you can use them interchangeably.

Difference Between 305 And 350 Crankshaft

The crankshafts in the 305 and 350 engines are almost identical but there’s a small difference between them. The counterweight on the 350 engine is heavier as the pistons of this engine are also heavier.

How To Tell The Difference Between 305 And 350 Engine?

Since there’s no visual difference between 305 and 350 engines, a good idea is to look at the casting numbers. A 305 engine has a 5L engine and a 350 engine has a 5.7L engine.

Find the casting number and check it online. The 305 engine will read gm 5 and the 350 engine will read gm 5.7. The components can be changed but the casting number is a sure-shot way to tell which engine you’re looking at.

Can You Bore A 305 To A 350?

It is possible to bore a 305 to a 350 engine. But doing it makes no sense as it’s cheaper to get the 350 engine block. You shouldn’t think of boring the 305 to 350 just because they have the same stroke.

The bores in the 305 are too small to work well with the 350 engine. The balance will be off as the weak crankcase won’t be able to balance well with the heavier pistons of the 350 engine.

What Side Is The Dipstick On A 305?

The location of the dipstick on a 305 engine can be either on the passenger side or the driver’s side. It depends on the model of the engine and the year it was made.

If the engine was made in 1979 or earlier, the dipstick will be on the driver’s side. Since then, the dipsticks have been moved to the passenger side. You can always look under the car and locate the oil pan to know where the dipstick is.


Now you know the main difference between 305 and 350 engines. This article has busted some common myths about increasing your HP on a 350 engine with a 305 cylinder head.

We hope this guide has helped you better understand both these engines and the key differences between 305 and 350 engines. Leave a comment below if you have any questions about any of these two engines.

Note: You can also read Top 5 diesel engine oil brands in 2023.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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