The 305 and the 350 chevy engines are identical in terms of their outer physical dimensions. The two engines also have the same stroke. So, we frequently get the question – can you bore a 305 to a 350?

The short answer is that you can’t do it because of the difference in the bore widths of the two engines. But if you want to know the detailed answer with a proper explanation, stick around and complete reading the article.

What Does Boring A 305 To 350 Mean?

The bore size of a Chevy small block 305 engine is 3.736 inches. On the other hand, the bore size of a Chevy 350 engine is 4.00 inches. It means there is a 0.264 difference in the bore size of the two engines.

By boring a 305 to a 350, it means can we increase the bore size of the 305 engines to match the bore size of the 350 engine. It means increasing the 3.736-inch bore size to 4.00 inches. Now, let’s see why it can’t be done.

What Is The Difference Between 305 And 350 Chevy?

The main difference between 305 and 350 Chevy is the bore size. A 305 Chevy has a 3.760” bore size, which is pretty smaller than the 350. On the other hand, the bore size of the 350 Chevy is 4”. 

Secondly, the heads are also different on the 305 and 350 Chevy. The 305 head has a 58cc chamber. In contrast, the 350 head has a 76cc chamber. Compared to 350, the 305 is much smaller. They make the 305 chambers smaller because it has less cylinder volume. 

Can You Bore A 305 To A 350 [Explained A-Z]

The 305 and 350 engines have a lot of interchangeable parts. Even the cylinder heads of the two engines have the same physical dimensions. So, why is it that you can’t bore a 305 to a 350?

1. Difference In Bore Width

You can increase the bore size of any engine by 0.06 inches without causing any significant damage to it. So, if you increase the bore size of the 305 engine from 3.736 inches, you can get it up to 3.796 inches. That is how much can you bore a chevy 305 when you push it to its maximum limit.

But the 350 engine has a bore width of 4 inches. There’ll still be a gap of 0.204 inches in the bore size of the two engines even if you push it to the highest limit. So, you cannot bore the 305 to a 350 if you want to stay safe.

But there’s an exception to this rule. The earlier 305 engines were made with a lot of material and the cylinders were thick. But the manufacturing companies wanted to reduce the cost and started using less material.

The best way to know if you can bore the 305 engine to match the bore size of the 350 is to get a sonic inspection done. You’ll know the exact information of your engine and whether you can bore it to a 350 or not.

Even if you fit this exception, it’s still recommended that you do not bore the 305. Because once you’re done with the boring, the 305 will be extremely thin. You’ll also have to rebalance the whole thing and it’ll bring up your cost.

Getting a 350 block will be cheaper than boring the 305 to a 350. So, there’s no wisdom in trying to bore a 305 to a 350 and you should get a 350 block instead if you love the 350 engines.

Note: Read to know if you can bore a 305 to a 327 or not.

2. Difference In Valve Sizes & Port Flow

There’s another aspect you need to consider to complete this discussion. As the 305 and 350 engines have interchangeable parts and you can swap the cylinder heads with one another, many people use 305 heads on a 350 engine thinking that it’ll increase the horsepower.

But does that truly happen? Does swapping the heads of a 305 and a 350 engine actually increase the power of the engine? You need to take a look at the valve sizes and you’ll know the answer to this question.

The stroke and crank of the 305 and 350 are the same. The dimensions of the cylinders are also the same which is why you can swap one with another. But the size of the valves is not the same for the two engines.

The 350 engines have bigger intake and exhaust valves for proper airflow. But the 305 engines have smaller valves as it has a smaller bore. The 305 engine has a smaller combustion chamber of 58 cc and the 350 engine has a higher combustion chamber of 76 cc.

So, will the compression increase by swapping the chamber heads of a 305 engine with a 350 engine? Yes, the compression will increase but there is a major problem that occurs when you do that.

The port flow of the 305 engine is smaller and it has poor airflow. While you can bump up the compression by switching the heads, you won’t get any horsepower gain because of the reduction in the flow of air.

So, you should steer clear of changing the heads of the two engines to generate more power. It wouldn’t work. Stick to your 350 as it is and save yourself from wasting your time and energy.

Can You Put 350 Heads On A 305 Block?

350 heads will physically fit and work on 305 heads. The 350 heads are similar in combustion chamber size and intake valve size to the 305 heads. However, in most cases, it will give the 305 less performance because the compression will drop significantly. 

But, you will get better performance at higher ramps due to the bigger intake valves. And the downside is- it will also make it burn more fuels. 

Keep in mind, that no compression loss occurs if you find the older 305s that used 434 casting heads, which had 63cc chambers. Unfortunately, you can hardly find that type of head these days. We recommend you go for the L98 aluminum 350 Vette heads with the 58cc chambers if you want to get better performance.

Can You Bore A 305 To 383?

The 383 engine has a bore size of 4.030 inches and a stroke size of 3.75 inches. The difference between the 305 and 383 bore sizes is much more than the difference between the 305 and 350 bore sizes.

You cannot bore the 305 to the 383 for the same reasons you can’t bore a 305 to a 350. Boring out a 305 to a 383 is not possible because you’ll get nowhere near the bore size of 4.030 inches of a 383 engine.

Can You Bore A 350 To A 400?

The 350 and 400 engines have different sizes of bores, strokes, and rods even though the block design is identical. The bore width of the 350 engine is 4.00 inches whereas that of the 400 is 4.125 inches.

The stroke size of the 350 engine is 3.48 inches and the stroke size of the 400 engine is 3.75 inches. You can get the bore size of the 350 engine to 4.06 inches but unfortunately, you can’t bore a 350 to a 400.

What Is A 305 Bored 40 Over?

A 305 bored 40 over means that you’re increasing the bore size of the 305 by 0.04 inches. If we were to bore a 305 40 over, the new bore size will be 3.776 inches.

FAQs:

Conclusion

Now you know what to say if someone asks can you bore a 305 to a 350. We hope that you can clearly understand how much you can bore an engine by reading this article.

Use this information for your next engine build and consider the pros and cons of boring an engine. Generally, it’s good if you’re against it as it can cause many problems. Drop a comment below if you have any questions.