Advice on 400 sbc engine
03-31-2007, 03:21 PM
#41
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In any case if it came from a truck (the guy said it came out of a blazer but who knows if it was original) it may be a 4 bolt main. Gonna pull the pan this afternoon. I have a set of 5.7" rods (minus one) so if the block's ok, I'm off........so to speak.
04-01-2007, 08:45 AM
#43
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Heads and pan off last night. Looks good, turns easily. Looks like a std bore (no markings on piston top) with fairly deep dished pistons. The pistons have very slight valve depressions (factory) in the outer rim portions. Looks to be a pretty low compression engine. Doesn't matter though, Summit has what I need.
04-01-2007, 09:34 AM
#44
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Dave,
If it's a 78 engine, it WILL NOT have 4bolt mains------------------and that's good.
The 4bolt main SB400 blocks were ONLY 70-72 models. Then in 73, the 400s went to 2bolt mains, ONLY. Over the years, it has been concluded that the more desireable 400 blocks are the 2 bolt versions. If a person just has to have a 4bolt block, the most desireable solution is to have splayed 4bolt caps added to a 2 bolt block.
The next choice (and in my opinion, the best solution for a street/performance 400) is to simply replace the main cap bolts with studs for improved clamping force. In the past, I have built, and some of my existing 400s have, 4bolt blocks. But if I build any more SB400s, they will be 2bolt blocks with studs like this one.
If it's a 78 engine, it WILL NOT have 4bolt mains------------------and that's good.
The 4bolt main SB400 blocks were ONLY 70-72 models. Then in 73, the 400s went to 2bolt mains, ONLY. Over the years, it has been concluded that the more desireable 400 blocks are the 2 bolt versions. If a person just has to have a 4bolt block, the most desireable solution is to have splayed 4bolt caps added to a 2 bolt block.
The next choice (and in my opinion, the best solution for a street/performance 400) is to simply replace the main cap bolts with studs for improved clamping force. In the past, I have built, and some of my existing 400s have, 4bolt blocks. But if I build any more SB400s, they will be 2bolt blocks with studs like this one.
04-01-2007, 03:27 PM
#45
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Thread Starter
Dave,
If it's a 78 engine, it WILL NOT have 4bolt mains------------------and that's good.
The 4bolt main SB400 blocks were ONLY 70-72 models. Then in 73, the 400s went to 2bolt mains, ONLY. Over the years, it has been concluded that the more desireable 400 blocks are the 2 bolt versions. If a person just has to have a 4bolt block, the most desireable solution is to have splayed 4bolt caps added to a 2 bolt block.
The next choice (and in my opinion, the best solution for a street/performance 400) is to simply replace the main cap bolts with studs for improved clamping force. In the past, I have built, and some of my existing 400s have, 4bolt blocks. But if I build any more SB400s, they will be 2bolt blocks with studs like this one.
If it's a 78 engine, it WILL NOT have 4bolt mains------------------and that's good.
The 4bolt main SB400 blocks were ONLY 70-72 models. Then in 73, the 400s went to 2bolt mains, ONLY. Over the years, it has been concluded that the more desireable 400 blocks are the 2 bolt versions. If a person just has to have a 4bolt block, the most desireable solution is to have splayed 4bolt caps added to a 2 bolt block.
The next choice (and in my opinion, the best solution for a street/performance 400) is to simply replace the main cap bolts with studs for improved clamping force. In the past, I have built, and some of my existing 400s have, 4bolt blocks. But if I build any more SB400s, they will be 2bolt blocks with studs like this one.
Yes DZ, it is indeed a two bolt main. I need to get one 5.7" Power Metal rod though, to match the 7 on my other block (1st post) 'cause it's bent. If I can find one all I'll need is a set of .030 pistons and rings and I'm off to the machine shop.
Question; the .030 400pistons using the 5.7" rods have the wrist pin hole moved so the piston doesn't protrude out the cylinder right? Seems a stupid enough question seeing as this is done regularly, just curious. 
04-01-2007, 05:25 PM
#46
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Dave,
Back in the VERY early 70s when I built a 400 for the first time using 5.7 rods, there were NO off the shelf pistons available for that configuration. Yes, you could ORDER pistons with a custom pin hole location-------------------------and they were so expensive that it was beyond the budget of the average guy who has to pinch every penny.
So, what we did was use STOCK 400, dished, low compression pistons (either .020-.030-.040 over), and have the piston tops milled. This would result in a nearly flat top piston and when used with 76cc heads, this would produce something in the range of 10 to 10.5:1 compression. I know of one specific engine that I built like that about 1975 that is still going (but probably ready for another rebuild). Today, there are multiple off the shelf piston configurations available for the SB400. And for example, a .030 over SB400 piston with the wrist pin hole positioned for using a 5.7 rod is VERY close to the same price as a normal .030 over 350 piston.
I have ZERO experience with the powered metal rods, I've always used run of the mill forged rods with zero failures or problems. But, apparently the powered metal rods are satisfactory because a lot of people seem to use them so I won't knock them.
I am certainly familiar with the damage, such as a bent rod, that liquid (or anything else) inside a cylinder, can do to an engine. Here is a bent rod that was in #6 cylinder of my 420 boat engine (got some water in the cylinder). The block was cracked, and since I had a few spare blocks, I simply gutted the boat engine and took the rods/pistons and another block to my machinist and had him machind another block to put all the guts back in. The engine is together and running fine but hasn't been lake tested yet.
Back in the VERY early 70s when I built a 400 for the first time using 5.7 rods, there were NO off the shelf pistons available for that configuration. Yes, you could ORDER pistons with a custom pin hole location-------------------------and they were so expensive that it was beyond the budget of the average guy who has to pinch every penny.
So, what we did was use STOCK 400, dished, low compression pistons (either .020-.030-.040 over), and have the piston tops milled. This would result in a nearly flat top piston and when used with 76cc heads, this would produce something in the range of 10 to 10.5:1 compression. I know of one specific engine that I built like that about 1975 that is still going (but probably ready for another rebuild). Today, there are multiple off the shelf piston configurations available for the SB400. And for example, a .030 over SB400 piston with the wrist pin hole positioned for using a 5.7 rod is VERY close to the same price as a normal .030 over 350 piston.
I have ZERO experience with the powered metal rods, I've always used run of the mill forged rods with zero failures or problems. But, apparently the powered metal rods are satisfactory because a lot of people seem to use them so I won't knock them.
I am certainly familiar with the damage, such as a bent rod, that liquid (or anything else) inside a cylinder, can do to an engine. Here is a bent rod that was in #6 cylinder of my 420 boat engine (got some water in the cylinder). The block was cracked, and since I had a few spare blocks, I simply gutted the boat engine and took the rods/pistons and another block to my machinist and had him machind another block to put all the guts back in. The engine is together and running fine but hasn't been lake tested yet.
Last edited by DZAUTO; 04-01-2007 at 05:27 PM.
