I need help deciding what to do...4.1 built or 3.8 built

[Nasty Wendy]

4.025" is 65 thousands over bore. You'd be begging for trouble.

I called Jegs and got a price on the Hypers and then called Summit and had them beat it.

 

[boostingbuick]

So what am I doing??? Mine is at 4.030 at making big power. Full weight car running 128 on pump gas. If it's sonic check and has enough meat on it will be just fine. Its the bore size that kills motors, its not having enough meat left and not found until your scraping parts up with a shovel. Measure twice and cut once.

 

[coldair85GN]

Well....I've been tossing this up in the air for the last couple hours trying to decide which way to go on pistons. The machine shop that cleaned up my block told me initially when I dropped off the block that it looked pretty grim, then after doing a quick bore cleanup they told me that once I honed it that it would just barely clean up to a .030 which shocked me. So...the question is do I buy .030 pistons and count on it working good or should I order .040 pistons so there is no doubt? I'm ready to purchase..so thats my dilemma. I'm also wondering if I should buy bearings at the same time or should I let the machine shop do it when they have the block? Enginekits.com has the pistons in any size I want from .020 over all the way up to .060 and they also have rings from sealed power and hastings.

 

[87GNSteve]

I would buy the .030 pistons let your machinist bore and fit each cylinder marking the pistons as he goes. Just dont put them on the rods.
If you need .040 just return them and the rings and start again.
Once the block is finnished, you can send the rotating assembly out to get balanced ( if you are planning to do so, [I hope]).

 

[coldair85GN]

Opinion on rings? Hastings are moly and the Sealed Power are cast?

 

[Nasty Wendy]

So what am I doing???

Rolling dice. I'm glad to hear you are winning though.
You are right on about the sonic check but remember these are production blocks that were never meant to be highperformance builds. Do you think the majority of them will bore out to 4.030 without problems? Keeping as much meat on the cylinder walls as you can is a good idea.

 

[coldair85GN]

Rolling dice. I'm glad to hear you are winning though.
You are right on about the sonic check but remember these are production blocks that were never meant to be highperformance builds. Do you think the majority of them will bore out to 4.030 without problems? Keeping as much meat on the cylinder walls as you can is a good idea.

There's an awful lot of em that are doing it. If I dont have to go that big I won't..and it looks like I won't have to, but its nice to know I could if I had to. I'm sure Buick never intended for the 3.8 block to go 9's either but I think it was figured out over the years that it could do so when properly done. Hell I only wanna go mid to high 10's.

Your sig is something else..little strange..but most of the people here are

 

[dlafont]

Just to be clear... The standard bore size of the 4.1 can be bored out to 0.035 to get to the 4.000" bore size. So don't you need 3.995" hyper pistons for 0.030" overbore of the standard 4.1 block?

In this link they say that the maximum bore for the stock 4.1 block is 4.000" or 0.035" overbore:

4.1 Recipe

D

 

[coldair85GN]

Well I went ahead and ordered the .030 over Speed Pro Hypers and also ordered the .030 over Sealed Power rings. Now I just sit and wait for all the parts to start rolling in.

 

[boostingbuick]

Not all the blocks are casted the same. They all some slight to medium difference in thickness and movement of holes and passages. Some may only have enough room to go .035. I would think you would be safe at that size. I just know what mine is go to. And it is safe at .065 over.

 

[Philv6]

Not all the blocks are casted the same. They all some slight to medium difference in thickness and movement of holes and passages. Some may only have enough room to go .035. I would think you would be safe at that size. I just know what mine is go to. And it is safe at .065 over.

Using what minimun wall thickness?

 

[boostingbuick]

I wish I could remember the number for a fact. You will need to contact an engine builder and they can give you that number.

 

[dlafont]

I found a nice Video of a 4.1 build up. Very good. Turbo Buick Engine Build -- Part 1