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Discussion Starter #1
i'm about to start building a 383 to drop down into a 63 chevyII and i was just wondering what y'alls preference was between a two bolt and a four bolt block. i've got both and as soon as i decide which block to use i'll be ready to send it to the machine shop. I was also wondering, and i know that i'm getting ahead of myself at this stage but what kind of ignition system would y'all also recommend? any info would be helpful.
thanks,
M
 

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Do you have the casting numbers?

Without knowing those I'd say go for the 4bolt block.
 

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i would say it depends how wild you want to go, eather will work if you just mess around with it, even the 2 bolt. when you start to get serious i would say a 4 bolt, and if you realy want to get wild get the 2 bolt and have splayed caps put on. some of the older guys here can probobly give you a guesstimate as what hp ranges are safe with each.

give us more details and the guys here can point ya in the right direction...
-Leo-
 

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I would say any thing less than 500HP a 2-bolt should be fine. If you are going to use a supercharger, turbo, or a big shot of nitrous I would go for a 4-bolt. If you want to go really wild use splayed caps or look into an after market block (eg. world,dart, ect.).
 

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All things being equal, I would go with the 4 bolt, but the 2 bolt would probably be fine. As far as an ignition system, I have had very good performance from an all MSD system. But pretty much any aftermarket ignition is better than points. Good luck....
 

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Pure American Muscle
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The question is two fold. 1 What is the use of the engine going to be? and 2 what condition are the blocks in.

If the 4 bolt is in the same or better condition then the 2 bolt I would use that.
If the 4 bolt is in worse shape and your not going to spin it to high RPM's or really pound it then the 2 bolt will be enough for you.
I know you will take it to the machine shop but are either block over bored already? The conditions of the cyd. walls any core shift. All that would effect my choice of block.
Since the 2 bolt will take most any N/A <500hp set up if it is in the better condition with less core shift and better overall it would be safe to use that. If your going to get crazy (over 550 or 600hp) you should start looking at after-market blocks not always needed but it is a major peace of mind +.


Hope that helps.


Chris
 

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killerformula said:
if one of them is a later one-piece rear main, by all means USE THAT ONE!!!
lol but killer, nothing wrong with a cheby marking his terrotory! ;)
 

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As stated above the two bolt will be fine for up to 500HP. The 4 bolt will handle more, but the cylinder walls will not last much past 500HP without at the least a short fill(grout). Chevy blocks will typically split a cylinder before cracking the mains if nothing is changed.

One thing that really has alot to do with durability is the RPM level of the engine. When you start passing the 6000RPM level with a long stroke engine, the parts and pieces start getting real heavy.

I would argue that a power adder on an initially lower HP engine would be easier on the block because RPM can be kept lower and still make the same power. RPM is a real parts killer. Just food for thought...or arguement.

Chris
 

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TurboS10 said:
Chevy blocks will typically split a cylinder before cracking the mains if nothing is changed.
Chris, that's <bad> news to me...I've spoken at great length with camaroman7d (Royce) about his build on his blown 388 and he's bored .060. I don't believe he has filled his block and he's making approximately 780 HP if I'm not mistaken. I used an early 2-bolt block, had it machined and installed Milodon splayed caps. I sure don't look forward to that kind of problem on the street.

Can you tell us more or maybe qualify that statement?

Thanks, Larry
 

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I am not saying that Royce does not know his poop, cause he does, but..........

I was told this by a machinist some years ago. He said that much over 500 HP and the cylinder walls just usually dont last long. I would imagine that this has to do with the amount of overbore, the original thickness of the cylinders, and the block material makup which is largely dictated by when it was made. Typically the early model blocks tend to have more nickel content from what I understand, which makes them somewhat stronger.

As with any failure, the block will last a while. If is is something that only gets beat on once in a while, it may last a long time. If it is a drag car that sees 5-10 full throttle runs a week, then failure will be much faster. This all has to do with material fatigue qualities. Kindof like running stock rods in an 8000RPM engine. They will last once or twice or twenty times......but they will let go eventually. To me, blocks are the same way if you start pushing the limits.

After hearing this news about the blocks I started paying attention when I saw block failures on the web and such. Most of the time it seems to be cracked cylinders, but that has just been my observation. So many people get caught up in the main bolt style and count, but I personally have seen alot more cracked cylinders than cracked main webs.

That information is what prompted me to tall fill my block on my turbo engine. Everyone screams about the mains on a 400 being weak, but if you do some research you will find that RPM is the key component in making things go boom more than the power output. In NA engines the two are sortof the same, but forced induction engines can make alot of power in low RPM range. What this added power does is add alot more cylinder pressure and stress. Under those stresses the cylinders begin to "walk" around a little bit. Eventually this will cause a crack, but the grout can prevent this. But the good news is that by keeping RPM down, you will likely have worry about the mains or the crank letting go.

Kindof comes down to this.....When you double or triple the intended power output of an engine, something WILL break. It is just a matter of keeping it together as long as you can.

If I were you, I would at the very least have a short fill done to limit the movement of the cylinders. With a short fill you can still run on the street without cooling issues. This will also help stabilize the main web area. The whole deal with things cracking is because of movement. Making it as rigid as possible will help.

I dont run a machine shop and I have never had either one of these failures. I am just offering what I have been told and have observed since coming upon the information

Chris
 

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It is all kindof common sense, but sometimes it helps if someone spells it out. Until it was explained to me, I never really gave it a thought. Then I started reading an paying attention.

Most of the heat from combustion is in the top few inches of the cylinders and the heads. What I have been told is that you will loose alot of oil cooling by not having water circulating in the bottom of the block which makes an oil cooler manditory. I am going to be monitoring oil temp on my turbo engine in the pan when I get it back together so I will know something soon. I have a thermostatic controlled oil cooler on mine so I think it will be fine, but I am not taking any chances.

Chris
 

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block alloy

you can tell what some of the sb chevys block alloys are by looking under the timing chain cover. their can be two numbers one for tin and one for nickle. tin helps the block heat and cool more evenly, and the nickle hardens and polishes the bore surface. the numbers are near the cam bore, and are one on top of the other, like 10 over 20. 10 would be tin 20 for nickle. if their is only one number its the nickle percentage. if their is neither 10 or 20 that means only trace amounts are in the block..... (info taken out of an interchange manual)

-Leo-
 

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if its going in an early ChevyII & thinking about using a 1 piece rear main seal block...make sure an aftermarket oil pan is available...or you have the ability to modify your own.
It may have changed now, but about 10 years ago neither Milodon or Moroso, or Hamburger made an oil pan for that application. & I know you cant get a pan for 1 piece rear main for Vega/Monza right now.
 

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Discussion Starter #17 (Edited)
i just wanted to say thanks everyone for their comments and suggestions. and i appoligize for the amount of time that has passed before i could respond to suggestions. But as far as my block selections, i believe that i am going to go with the late '70's 4 bolt. So ive already started making clearance for my 6" rods. but my question now is Turbos10 mentioned,
"One thing that really has alot to do with durability is the RPM level of the engine. When you start passing the 6000RPM level with a long stroke engine, the parts and pieces start getting real heavy."

I just wanted to say thanks everyone for their comments and suggestions. and I appoligize for the amount of time that has passed before i could respond to suggestions. But as far as my block selections, i believe that i am going to go with the late '70's 4 bolt. So ive already started making clearance for my 6" rods which i'm bolting to a internally ballanced scat crank. But my question now is Turbos10 mentioned,
"One thing that really has alot to do with durability is the RPM level of the engine. When you start passing the 6000RPM level with a long stroke engine, the parts and pieces start getting real heavy."
But i've heard tell that these motors could easly spin 6500 almost 7000, but what was done to them i am not sure. how would i calculate the peak rpm range of my motor? if you have any questions, just ask.
thanks again,
M
 

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Of course you can spin them to higher RPM. All I am saying is that the chance of breakage goes way up when you do. With big heads, cam, intake, carb you can get 7500 out of a 400 with ease. The problem is that if you are doing this, you are going to be putting alot of stress on everything and you likely dont need that kind of power or can afford the type of parts to make it stay together. If you are wanting to use a stock block, make all the power you can in the 6000RPM range.

Chris
 
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