Planning the build.

[ZZZero]

The block I'm planning on using for my sbc conversion in my 300zx,is a aluminum dartblock,having a 4.125 in bore,and 9.5 inch deck height.

Through research I have found that one can safely over bore this block to 4.250 in,without going past a .200 cylinder wall thickness.I plan on using a 4.125 stroker crank.My current goal is of literage,One way or another i would like to acheive 8 liters,first way of doing this would be to compromise cylinder wall thickness and bore the cylinders out to a whopping 4.34in,wich with the 4.125 crank would give me almost exactly 8 liters of displacement,but it would be of concern to me becuase I would like to turbo charge this engine,and would not like to be afraid of having the cylinder walls crack. On the other hand I could have a custom 4.250 in crank made and with the 4.250in bore would give me about 7.9 literes but I fear,I would have major space issues on the bottom end,and ideas? and or input? I would really like to have 8 liters,but if its not feesable then its not fessable.

 

Edit:Actually after more searching I have found 4.250in cranks for sale,and would not have to have one custom made.So that brings me to this,with the 4.250 crank AND a 4.28 bore I will reach my 8 liter mark,but will .030in overbore

really cut down on strength of the cylinder walls (walls would only be .170in thick)

 

Thanks all.

[grumpyvette]

the first thing ID point out is that reaching 8 ltrs (aproximately 488 cubic inches) is not going to get you a single thing "except bragging rights,"but a great deal more clearanceing work,head gasket sealing issues, and a lower safe peak rpm level that can mostly be avoided on a turbo engine at little or no cost in hp by dropping back only slightly to a 4.25" bore and 4.125" stroke 468 displacement.

 

next Id point out that the ability to effectively seal the cylinders with the sbcs 4.40 inch bore spacing leaves on a high cylinder pressure turbo application, very little effective area between the cylinders at even THAT 4.25" bore size at the 0.15" tangental area the head gasket must seal.

 

next Id point out that dropping back still further to a 4.185 bore and 4.125 stroke (454 displacement) is the route ID take for both the improved cylinder deck strength and head gasket seal potential if I was going the turbo sbc route.

but BEFORE you start, you may want to think this thru.......you can buy a BBC ALUMINUM BLOCK and easily and safely build a 4.5" bore 4.5" stroke 572 displacement engine that will totally destroy any sbc combo and have both far better heads (keep in mind youll jump from 2.05 intake valves to 2.30 valves and perhaps 230-245cc intake ports that might flow 300- 320cfm to 345cc ports that flow 400 plus cfm,and much stronger internal components in that turbo engine....think about it!) AND an all aluminum bbc will weight less than the sbc engines most guys install ,combined,those are a HUGE ADVANTAGE

a sbc 468 turbo combo that makes 2 hp per cubic inch of displacement will have about 940hp, but a bbc with the same 2 hp per cubic inch of displacement will have about 1150hp and both a much better life expectancy and stronger components, and the cost won,t be all that much higher, (your talking about spending easily $15,000-$18,000 plus with EITHER choice by the time its up and running

 

http://www.worldcastings.com/docs/05_cat_pg7.pdf

 

summit sells these for about $3700

 

http://www.worldcastings.com/docs/05_cat_pg23.pdf

 

match these to some forged flat top pistons and a decent forged crank with the correct rods and twin turbos and youll have a killer turbo combo

 

btw, in the real world an intercooled turbo sbc combo like that should produce 1100-1200hp, a big block easily exceeds 1500-1800hp

[ZZZero]

The reason for wanting 8 liters,is becuase the cylinders would have a larger output of exhuast gases,more exhuast gases means a larger turbo can be pushed and more psi= more happyness.

 

Somewhere you mentioned me using a 4.40 bore?

That would be ungodly safe as the cylinder walls would be extremely thin between cylinders,I planned on going,with a 4.28in bore and a 4.250 in crank. wich would get me right at 8 liters.

 

I have thought about the bbc route but all in all,even though higher hp numbers can be reached it seems to me that the added weight of the bb,would outweight the benefits,220lb iron bb vs the 95 lb aluminum sb?

Seems like in the end you would have an overall lower power to weight ratio.I would also like my car to be able to take corners moderately,and with all the weight of a bbc that ability to control the car at speed would decrease.

 

Unless im missing the fact that there are companies that produce aluminum bbc blocks.but I have had yet to find any.

[grumpyvette]

"Somewhere you mentioned me using a 4.40 bore?"

"220lb iron bb vs the 95 lb aluminum sb?"

 

seems OBVIOUS you skimmed thru vs read my post, I suggested an ALUMINUM block for the BBC and even posted a link

no I MENTIONED that the BORE CENTERLINE on a SMALL BLOCK is at 4.40" not the BORE size,meaning any bore size over about 4.185 starts to compromise the cylinder sealing area between the cylinders, even the 4.25 bore is slightly less than MINIMAL in my opinion, yeah ,it CAN be done, but its not ideal

[ZZZero]

Sorry you confused me up there with the 4.40 bore center line.

I'm at school at the moment and those links are blocked by websense so i couldnt check them out.

 

I was told though that as long as the cylinder walls are .200in thick all the way around there should'nt be any problems,with cylinder walls cracking etc, even on a turbocharged apllication?

 

Thanks for all the info it's been VERY helpful.