Differences in N/A Block

darud35 · 02-06-2012, 06:09 AM

Can someone explain the difference between a late and early NA engine block?

As a background, I have an 86 turbo engine that has some cylinder scoring. What I'd like to do is take a good NA block and use my internals. I was told a late engine (87+) would be easiest. My understanding is it's easier to drill and tap for the oil passage to the turbo, This could be completely incorrect though.

Any info would be really appreciated. I'm itching to rebuild my engine!

9FF · 02-06-2012, 06:41 AM

iirc sump, belt tensioner, oil housing & oprv are different 86na to 87na. Can you not hone & lap your existing block? It probably would be more cost effective and less troublesome that swapping internals. Also bear in mind if you are putting existing pistons in a different block you have to pick a block with a tolerance group matching your existing pistons.

darud35 · 02-06-2012, 07:14 AM

Thanks 9FF. I've heard mixed reviews on the "home" hone and lap of the Alusil block. The guy I bought the engine from buys and sells them frequently and said he's willing to get me a good block. So I figured I'd go that route.

I can bring a bore gauge and calipers to check it out. I'm assuming the block would only be in a different tolerance group if it had been rebuilt previously? Not entirely sure how that works.

Since I've already ordered belts and rollers (along with a complete rebuild kit) I'm assuming I should keep with the late block? Is the oil pan the same?

nynor · 02-06-2012, 07:16 AM

Quote:

Originally Posted by 9FF

iirc sump, belt tensioner, oil housing & oprv are different 86na to 87na. Can you not hone & lap your existing block? It probably would be more cost effective and less troublesome that swapping internals. Also bear in mind if you are putting existing pistons in a different block you have to pick a block with a tolerance group matching your existing pistons.

this sounds about right. why not just get a turbo short block and call it a day? i suppose that turbocharging a 2.7 liter would be fun....

nynor · 02-06-2012, 07:17 AM

i think that if the head is off the engine, the pistons are stamped with the tolerance group.

9FF · 02-06-2012, 07:44 AM

The tolerance group is set at the factory on new blocks. They match the pistons to the block dimensions. I think you are confusing tolerance group with oversize pistons, not the same. One is set at the factory, one is for a bored block.

darud35 · 02-06-2012, 08:13 AM

Quote:

Originally Posted by nynor

this sounds about right. why not just get a turbo short block and call it a day? i suppose that turbocharging a 2.7 liter would be fun....

Indeed it would! Not really part of our deal unfortunately.

I will check out the specs. I guess I'm somewhat confused, i dont think my rings are for a certain tolerance group, and i'll be using my turbo pistons. Is the cylinder wall spec different or is it something with the piston? Basically id like to use my turbo pistons and rods, etc.

krystar · 02-06-2012, 08:40 AM

on the piston face, there's a number stamped. 0,1,or 2. on the block, there's a number stamped on the top deck. same 0,1,2.

they correspond to different diameters of cylinders. i think 0 was 99.98mm, 1 was 99.99, and 2 was 100mm.

9FF · 02-06-2012, 08:54 AM

You can use your turbo pistons and rods, you just have to match the tolerance group. If your pistons have a "1" stamped on the top just make sure the block you get is a tolerance group 1 block. There are 3 groups 0,1&2.

darud35 · 02-06-2012, 12:59 PM

Ok thanks a lot guys.

Is the consensus to use a late block too?