Old question rehashed: Maximum bore

[Kevin Hawkinson]

We've had this discussion many times, but now, I'm phrasing the question a little differently.

If I have bore sleeves put in a redblock, what is the absolute maximum bore size that the bore spacing will accomodate?
Specifically, can I go up to 102.4mm? There is a huge range of off-the-shelf, flat-top, forged pistons in that size, and I'd like to be able to use those.

 

[isaac]

I think you might have to talk to a swede about "cementing" the block if you went that far. That sounds like crazy talk.

Then again, you'd be an inspiration to us all.

 

[own6volvos]

If the stock bore on a B230 is around 96mm... it sure as hell doens't look like the cylinder wall is more than maybe 3-4mm think. You would be boring right through the wall into the coolant passage.

 

[Kirby]

yeah but b230's suck....if you could bore it out that much without any problems that would be most excellent. Thinking of putting dry sleeves in the block?

 

[the poi]

well if you sleeve it, it doesnt matter if it goes into the water passage right? they would just be held in by the rest of the block... whats the possibility of a sleeved block like that having bore shift issues?

 

[stealthfti]

it's a bore center issue

the bore centers on redblocks are 4.125in C-C between #1 -#2 and between $3-#4; with the bore center between #2-#3 at 4.25in....IIRC.

to go the bore diameter you mention would require a siamese arrangement along the lines of that all aluminum two piece shortblock that was the subject of a topic not too long ago. And even then, I suspect that it would be tough to accomodate the size bore you want.

HTH

Thomas Fritz
...the stealth FTi

 

[mAydAy]

Customs pistons would be much safer, easier, stronger, quicker and much, much, much cheaper.

You can bore it out some but not have to deal with sleeves or anything, no rod modifications are required although if you are getting custom rods that shouldn't be an issue, you don't have to worry about trying to cement it and get it all to fit (If it even will) and also, if you frag the block, it'd be much quicker to chuck that assembly into another block than one where the block its self has a few thousand dollars in, and running those large bores even with sleeves you run a MUCH larger risk of fragging the block, especially if everything doesn't turn out juuuuuust right.

Sure, you'll probably pay $600-1000 for pistons, but its MUCH cheaper than testing the block, boring it, and sleeving it if its possible or a viable candidate, and then the $200-300 MINIMUM (Probably $4-600 if they're real strong pistons, I don't know if you're going N/A or turbo here) for your pistons. I'm not trying to burst your bubble, I love new ideas, I just don't think its a cost-effective option unless you are trying to get serious displacement out of it. My calculations say you'd get about 2.8liters using those pistons and a stroker crank but unless you need the displacement I would pursue other possibilities.

-Andy

 

[Kevin Hawkinson]

Yeah, I guess I just better put the crack pipe down for a while, eh?

 

[JohnLane]

So the question is still not answered.........
How big can one get in boresize assuming that it is going to get sleeved anyway?
With sleeves is 100MM doable?

Does anyone know how long a stroke can be fitted figuring on relieving the block to clear the big ends of the rods?

Kevin.......You going to mix an increase of stroke with this great big hole?
How about a deck plate so that you can give it some NICE LONG connecting rods?

Oh Boy!! I would get quite a kick out of making a really NAUGHTY motor.

Thoughts?
John Lane.

 

[740Weapon]

i think someone needs to refer to the aq171. and its largest bore size. because after that i think a v8 swap becomes cheaper.

 

[Morley]

Uhmm....if you have just won the lottery or somethin', why not shell out 4500$ for a B230R block? AFAIK that block has 10mm walls, and could easily take 102mm pistons.

Also, I'm pretty sure most Supernational cars here in Scandinavia run with 3-3,2 litre redblocks...I can check what rods, pistons, and blocks they use, and get back to it, if you want?

 

[JohnLane]

Uhmm....if you have just won the lottery or somethin', why not shell out 4500$ for a B230R block? AFAIK that block has 10mm walls, and could easily take 102mm pistons.

Also, I'm pretty sure most Supernational cars here in Scandinavia run with 3-3,2 litre redblocks...I can check what rods, pistons, and blocks they use, and get back to it, if you want?

Please do. I am curious.
The HornetKar may have to have more poke for next year if I win the prize money. Heehee.
John Lane.

 

[142T5]

Personally, I don't understand why you want to bother with such large capacity. Surely that's the last straw. It would surely be safer running a smaller piston and you can spend any money you would of spent on stroking, huge pistons on something more beneficial like a B234 head or a bigger turbo. Is it really that worthwhile? I guess though in the end you're going to be using some forged pistons anyway, so why not making them as big as you possibly can, cos big is better... right?

142T5

 

[towerymt]

yeah but b230's suck....

A B230 is the only way to get that large of a bore (w/o sleeving)..the R block, which is quite expensive. It can handle at least a 100mm bore.

How thick are the sleeves, and can they handle the load as the only divider between the piston bore and the water channel? If not, 100mm+ won't work, because the wall thickness just isn't there. At OEM overbore sizes, there may be only ~0.100" (2.54mm) in some places.

Using the numbers provided by StealthFTi, I believe there is approximately 8.72" from the edge of bore #1 to the edge of bore #4. That is to say, the total length across all 4 bores, less the bore size of #1 and #4 (using 96mm). Can you fit your 102.4mm bore within 110.7mm of space (8.72"/2)? That's assuming you were to bore #1 and #4 off center of the existing bore, perhaps well into the water channel. I think you would pick up about 2mm additional space per bore from a B21 (92mm bore). More questions than answers.


I've heard of a 103mm stroke using a Penta crank. Not sure if that's useful info.

 

[245gti]

Somewhat related to this discussion.....

http://www.forums.turbobricks.com/showthread.php?t=25981

Yeah, I know. It's my thread. I just thought the timing was rather convenient....

 

[Kirby]

really? This is useful information then as I was under the false impression that the b230 cylinder walls were thinner then the b23 series. Thanks for the clarification

 

[growley]

Oh Boy!! I would get quite a kick out of making a really NAUGHTY motor.

Heh, that made me laugh for some reason.

 

[Kevin Hawkinson]

The reason for the question is the new US GroupF rally class, which does not allow turbos. But, for my car's weight (about 2800lbs) my displacement limit is 4000cc. Also, "The engine is unrestricted, but must be derived (at least the engine block) from a product line offered by the manufacturer of the vehicle." IOW Volvo engines only.
That's why I'm thinking about a big displacement, NA redblock. The V6 is also a possibility, but I think there is a very large knowledge base for the redblock, there are fewer parts (translation: cheaper), and I am traction limited, since it's 2wd only. That means it's pretty pointless to go past 250HP (no offense John) unless I want to spend a lot on tires.

The SBC stuff is pretty attractive because its WAY cheap. Forged flat-top pistons can be had for about $500 for a set of 8, and weigh about 350g each. Forged H-beam rods are about $400 for 8, and weigh less than 650 g each. Compare that to stock B23 at about 850g for the piston and 850g for the rod.
The geometry is good too. If I use a piston with 1.125" compression height with a 6.25" rod and 86mm crank, the total height is only .040 less than the stock setup, and then I can just deck the block. The rod/stroke ratio for this setup is 1.85, and that ain't bad.

But, it's looking like all the money I save on pistons and rods will have to go into the block and crank. Sleeve the block, possible move #1 and #4 holes outward, and weld up the crank and regrind it to locate the narrower rods.
Sounds like too much work to me. 100mm or 3.9" pistons would make things less complicated, but they're also not as common.

 

[stealthfti]

Michael,
I think you misunderstood my point; or I did a poor job in making it....most likely the latter.

between #1 and #2 cylinders, the distance between the center of the bore for #1 and the center of the bore for #2 is 4.125in....[104.775mm].

which means that the maximum radius of a circle for each of those cylinders....with the circles touching each other would be 2.0265in....[52.3875mm]. Those circles touching each other would be the thickness of a pencil line. That pencil line would be a pretty thin cylinder wall, would it not?

The question then becomes how thick would the cylinder walls have to be in order to survive in a running engine. Take that thickness, and subtract that value from the max radius of 2.0625in; and then you would know the max radius of the piston diameter that you could use....IF you were to go with a siamesed cylinder arrangement. If you could not do the siamesed arrangement, and had to go with 'sleeves', then you would have to double that wall thickness value, and then subtract that amount from the radius value of 2.0625in.

Another way to see it is to think of the bore center dimension as the maximum piston size with pencil line cylinder wall thickness; then shrink the piston diameter the amount of wall thickness you have to have.

With a siamesed cylinder arrangement, you might be able to go with 100mm diameter pistons [possibly 102mm]; but that would mean some pretty thin material between the two cylinders. Doable, true; but the block would have to be cast with the siamesed cylinders.

Rather than going to all that hassle; I think a stroked motor with the 96mm bore and the 86mm stroke is very worthwhile. I would offer a variation that few would consider: do the 86mm stroker, but use the 145mm rods [actually they would have to be aftermarket rods, for the smaller rod journals on the 86mm stroker crank]. The rod stroke ratio would be more conducive for a boost motor. [and yes, that is heresy.....heeheehee]

TF

 

[n xntrx volvo]

for that price and displacement, how bout putting out the feelers for the new v8? it would be less streesed, and get you through more races w/o needing a tear down. btw, if a redblock is the way you're going, theres also a supermarine block (sim to r )that can be bored to 99mm.
-Aaron