4.1L bore size question??

[NCTURBOS]

OK, here is any easy one for some of you guys.

What is the bore size of a standard bore 4.1L stage 2? I thought it was 3.965, but a friend is saying that it's 4.00!

I see so many people with 4.00 bore or larger, is that because of finding pistons easier? Or that's the shape the block was in when found?


TIA,

K.

 

[TurboCrazy]

3.965" is virgin bore.

 

[NCTURBOS]

Originally posted by TurboCrazy
3.965" is virgin bore.

So, that's before the final bore/hone process correct? And that puts it at 4.00 ready for the pistons to be dropped in?


TIA,

K.

 

[Brutal Six]

Keith,

Turbo Crazy is correct. The standard bore for a 4.1 block is 3.965". The NEW blocks I've seen and used are typically 3.960" from the factory. Mine current block was 3.960" and we finished the cylinders at 3.965". Many of the used blocks you'll find are over 4.0" bore because of the displacement allowed by the sanctioning body they were being used in. 274" motors were pretty common. You can either have a 4.0" bore and a 3.625" stroke or 4.020" bore and a 3.590" stroke to get 274".

I hope this makes sense.

Neal

 

[NCTURBOS]

Originally posted by Brutal Six
Keith,

Turbo Crazy is correct. The standard bore for a 4.1 block is 3.965". The NEW blocks I've seen and used are typically 3.960" from the factory. Mine current block was 3.960" and we finished the cylinders at 3.965". Many of the used blocks you'll find are over 4.0" bore because of the displacement allowed by the sanctioning body they were being used in. 274" motors were pretty common. You can either have a 4.0" bore and a 3.625" stroke or 4.020" bore and a 3.590" stroke to get 274".

I hope this makes sense.

Neal

Neal,

It makes perfect sense, now.

What "typically" is the farthest you can bore these blocks?


K.

 

[750H.P.V6]

Keith,

I once had an Off center block that was 4.060". I know of several guys running On center blocks with a bore size that big. It seems to me I once talked to a guy that had a block that was 4.070". Personally at 4.060" I'd say that would be fine. Maybe Billy Anderson can chime in and give his 2 cents.

Neal

 

[EightSecV6]

For the Majority of the blocks out there, 3.965 usually wont clean up the bore enough to use it. Off center blocks usually have no problem going 4.070, I have run one late on center at 4.090 with no problems (no bigger gasket available), you still need to sonic check EVERY hole before you bore it.
Bill