I currently run a 4.063" bore in with my combo. I am dropping off my block this weekend to get a line bore, honed and cleaned up.

So I am talking with my dad who used to have a engine rebuilding business. He swears up and down that you can bore that motor to 4.125" and not have any issues if you don't plan on boosting the motor/big shot of n2o. He has sleeved a lot of motors, including many LT1 blocks, so he knows how much has to come out to get a sleeve in.

I have to get a set of custom pistons anyways, so why I thought if it would work, put a 3.875" crank in also and get 414"?

Also, would not a big bore help the valve shrouding?

I asked about sonic checking the block and he flat out said that is what people used to do with 30 year old blocks but the newer stuff is fine for the most part.

Any thoughts?

 

One of the seemingly knowledgable people who used to post on CZ28.com a few years ago detailed the steps he had to take to bore an LT1 block to 4.090". It included a detailed sonic thickness check, and actually recentering the bores to leave the meat on the thrust side. Given that description, I'd assume it was approaching the limit. That particular engine was a 420.4 with 4.000 crank.

There is someone else who occasionsally posts here who did a sleeved LT1 427 with a 4.125" bore.

 

This is just my opinion, and it's worth exactly what you paid for it; but trying to go that big is probably well over the line into diminishing returns.

BTW, I'm up in Ashtabula, having just moved here last year. I noticed you're in the A/C area.

Are there any particularly good machine/engine shops in our region?

 

I am curious to as how thick the cylinder walls are stock though LT1 though? People always say it is bad to overbore...it gets thin...so give me some numbers or are am I being told what people are just reading on the internet?

 

im not trying to insult ur dad or anything but u can not make an lt1 block a 4.125 bore.....a regular sbc like dart block but not an lt1

 

The shop that built my engine measured the wall thicknesses, and recommended that we limit the overbore to 0.020". Probably not a bad idea when thinking about a 300-shot of nitrous. The shop had substantial experience in building 1,000+HP LT1 engines, so I respected their judgement. I suppose I could find the actual measurements if I went to the shop and dug out the file folder from 5 years ago.

 

I don't have an issue when comes to correcting my dad...in fact, I asked him if he is talking about an older SBC and not the newer LT1 blocks...I am sure if GM could save a buck or two, they would. Hence the reason I posted here.

I would really like to get some more cubes out of the motor...I will keep it to getting it thru a larger stroke and just hone the current block.

 

The gen1 400 SBC had a 4.125 bore. To accomplish this, GM had to siamese the cylinders together witout any coolant passage gap between them.

The LT1 block is basically the same as a GEN1 block internally / structurally. I'd imagine that boring a LT1 block out to 4.125 would involve major rework of the block. Is that even possible? The LT1 block does not have siamesed cylinders.

Even with this siamesed setup, 400's were notorious for having paper thin cylinder walls. I just dont see how a LT1 could be made that big.

 

I spoke with my dad. He told me that boring out .0625" a side leaves .1875" still cylinder wall thickness. That would make the initial thickness .25".

I really want to verify this.

 

http://www.grandsportregistry.com/im...lt4asm-400.jpg

How thick do those walls look?

 

I have a bit bigger pic of that...

http://imageevent.com/robshawk/laaut...=1&n=1&l=0&z=9

 

i see this alot at more performance and they have a few LT4 blocks that were bored and stroked to 427s. And if i recall correctly they were sleeved. I'll be there tomorrow(maybe) so I'll find out. Personally if you ask me, if you want to see how thin the walls are just get some tin foil and make a 4.125 inch tube out of it...yes I'm serious thats how it looks. But i will check to see if it was sleeved or not.

 

Assuming the cylinder bores have not been recentered, you can infer that the minor thrust side is equally as thick the major thrust side showing.

That wall seems to be as thick as the spark plug wire, which appears to be
in close proximity for scaling.

The question is, what is the outside diameter of that spark plug wire?

 

Nice cutaway, however..... I question that being representative of oem casting(s) of various components, that make up a complete engine, that is/was actually sold to the general public. I know the manifold ports don't look like that shown. If only oem (manifold) ports were really like that. So, therefore, I have my doubts, regarding other 'features' of display, as well. Certainly doesn't look 'right' to me, and it's got nothin' to do with what is in the piston ring grooves, either.

 

Another issue with the larger pic, the cut away through the cylinder wall is not in the center and does not appear to strike through the centerline of the bore. This would make the material appear thicker than if you were to cut perpendicular through the centerline of the bore.

Mike