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Old 04-22-2013, 11:31 PM
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638 vs. the 880 block

I haven't seen any recent threads on these two blocks so I'm assuming this is old news, but I wanted to bring it up again for those who are planning on building a roller cam'd 383. I had read that the 880 blocks were some of the strongest Chevy made so I naturally had to have one. I'd been buying parts for my 383 build for some time and got a good deal on a set of new KB135-.040 and had to buy a set of 5.7" rods. Thinking how sweet this was going to be I did some more searching on the 880 block and found that the bore length was shorter on these?? Sure enough I grabbed my digital caliper and went to measure, 5.6". OH! Wait lets do the math: 5.7" rod + 1.433" compression height +1.875" (1/2 the stroke) totals 9.008". Now minus the std deck height of 9.025 gives another .017" to take from the 5.6" bore length which gives 5.583" of cylinder bore to work with. If you add the 1.433" compression height with the 3.75" stroke gives a 5.183" (BDC) where the center of the pin will be in the bore and if you add the other half of the pin diameter .4635" totals 5.6465", hmmm? This puts .0635" of the pin outside the cylinder along with .8665" of the piston skirt ??? I can see why some guys have piston slap along with busted skirts. Looks like 6" rods only with the 880 blocks.
I swapped my 880 block for a 638 out of a 95 3/4 ton truck. The 880 blocks began in mid 95 with the ending of the 638's. Is there actually any metallurgical benefits of the 880 over the 638?

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Old 04-23-2013, 12:53 PM
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Quote:
Originally Posted by Kal81 View Post
I haven't seen any recent threads on these two blocks so I'm assuming this is old news, but I wanted to bring it up again for those who are planning on building a roller cam'd 383. I had read that the 880 blocks were some of the strongest Chevy made so I naturally had to have one. I'd been buying parts for my 383 build for some time and got a good deal on a set of new KB135-.040 and had to buy a set of 5.7" rods. Thinking how sweet this was going to be I did some more searching on the 880 block and found that the bore length was shorter on these?? Sure enough I grabbed my digital caliper and went to measure, 5.6". OH! Wait lets do the math: 5.7" rod + 1.433" compression height +1.875" (1/2 the stroke) totals 9.008". Now minus the std deck height of 9.025 gives another .017" to take from the 5.6" bore length which gives 5.583" of cylinder bore to work with. If you add the 1.433" compression height with the 3.75" stroke gives a 5.183" (BDC) where the center of the pin will be in the bore and if you add the other half of the pin diameter .4635" totals 5.6465", hmmm? This puts .0635" of the pin outside the cylinder along with .8665" of the piston skirt ??? I can see why some guys have piston slap along with busted skirts. Looks like 6" rods only with the 880 blocks.
I swapped my 880 block for a 638 out of a 95 3/4 ton truck. The 880 blocks began in mid 95 with the ending of the 638's. Is there actually any metallurgical benefits of the 880 over the 638?
No, both blocks use a shorter cylinder bore spigot which can be a problem with skirt slap when not using a piston with an offset pin or with loose clearance as required by non-hypereutectic castings or 2618 low silicon forgings. High silicon materials found in hyper-eutectic castings and 4032 forgings have lower rates of thermal expansion/contraction which allows them to run tighter skirt clearance which reduces the thrust-over slap with direction reversal coming around BDC, so they are quieter and less likely to sustain skirt damage, especially when combined with an offset pin.

Bogie
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Old 04-23-2013, 03:09 PM
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I found this same issue some years ago when I did some measuring.
I have two 880 Vortec blocks. The first is a 1996 block, the bore length is stock. The next block is from 1998 and the bores are in fact shorter.
I'm not sure when GM brought on this change or if there was a time lag between engine plants when the change was made.
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Old 04-26-2013, 04:47 PM
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The 638 block was used from 87-95
880 From 1995-2000


GM Performance :: View topic - Stroker Engine 880 vs. 638 Block Casting # Problems?

I see that the 2013 Chevrolet Performance pArts Catalogue lists the 350 blocks that are machined for the 3.800" stroker crank clearance for the GM ZZ383/HT383/HT383-E engines as p/n 88962516. But there is no direct cross refernce that they are indedd 638 blocks.
It does say that they use 638 blocks for the 350 cube crate engines.

From the 2001 GMPP catalogue, it states that bare block p/n 10105123 wighs 197lbs and could be either casting number 10243880 or 14093638.

I wonder what a 2013 Mercruiser 350 engine would have as a block casting number?

peaee
Hog
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