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in the planning stages of a new sbc 15 deg build...not sure if i wanna go with 4.155 or 4.185 bore..i will be using 3.875 stroke crank.

any opinions on wich is better with 15 deg heads and 8500 rpm?
 

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in the planning stages of a new sbc 15 deg build...not sure if i wanna go with 4.155 or 4.185 bore..i will be using 3.875 stroke crank.

any opinions on wich is better with 15 deg heads and 8500 rpm?
Go 4.155 so you have room to go bigger in case of cyl damage. If you start at the 4.185 you have very little room to go more. Howard
 

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If you don't have the block yet do the 3/8s head bolt threads and go 4.185" you will have tones of room left for the future. Make sure you get the biggest cam bore and lifter bore you can afford.
 

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bigger is better,,,,:wink:
 

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I have heard you can max. bore them to 4.200" per some engine builders.

We have machined quite a few of the GM Bowtie blocks that the cup guys have run and have taken them up to 4.195 and some 4.200.

Biggest thing is to bottom tap all the holes and use a .950 reach stud and bottom out on a ball beaing which seems to kee the cylinders rounder.

Trying to use a .750 reach and bottom it on the top of the deck is quite a challange to keep the cylinders round when torquing.
 

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I personally like to keep it 4.155 in case something goes wrong you have room to bore a little bigger.With that being said I know people that have bored 4.185 and not had issues.For the extra couple of cubes i would rather have a little safety net.
 

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4.155 is fine, never see the difference over a 4.185.....
 

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Bore her out hell if it hurts a cylinder put a sleave in it, Mines 4.200 I have also seen one 4.250 but real thin in between cylinders but no leaks N/A !!!!!
 

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cnc blocks, that's a really cool idea. do you have a part number for those studs, and what size ball bearing do you normally use .250?
 

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It's simply a question of your priorities - max power or durability? The extra displacement is only part of the benefit for going bigger. The larger bore allows for bigger valves and/or combustion chamber work that will make the heads work better too...but that might be splitting hairs for what you need. Max effort engines most always have maxed-out bores for that reason.
 

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cnc blocks, that's a really cool idea. do you have a part number for those studs, and what size ball bearing do you normally use .250?
Those studs are available through ARP and the we use a .175 ball bearing and the holes must be bottomed taped!!!
 

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if you go 4.155 bore with a tall deck block, I have some nice rods and pistons for you. changing my combo and already ordered new ones. they have about 30 passes on them. pm me for details if your interested.

thanks
 
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