Chevy LS pistons are 96 mm (3.78) and replacements are only $40 each. ( includes pins) times 12 is under $500 . Stock the V12 is 90mm ( 3.543)
If I bore the Jaguar sleeve out big enough to handle the Chevy piston I only have .080 wall which would normally be thinner than it should be ( recommended is .100 wall). However the sleeve is backed up by the aluminum block.
Not only that but the wall thickness at the top of the sleeve ( unsupported portion ) is .245 thick and that step section goes down 1.800 to where the sleeve is backed up by about .200+ thick aluminum.
What would the hive do? Just do it? Chance it? Make custom sleeves and bore the block?
What's wrong with the V12 pistons?
In reply to frenchyd :
Shhhh.... The block is sleeping.
Sorry, I'll show myself out.
If you have spare blocks and/or spare blocks are easy and cheap to come by, risk it. It is only worth the trouble of making a dozen sleeves and custom machining the block if the block itself is worth the effort.
If I follow the math right, stock sleeve is about .200" and you'd be getting them machined down to .080". I wonder if you'll run into an out of round condition resulting from the thin wall.
Rigante
New Reader
10/10/21 2:40 p.m.
https://www.summitracing.com/parts/uem-s3442h-1-0mm/make/chevrolet
what about the Chevy 4 cylinder pistons. You can buy them in 91mm and they are 60 for 4. Idk if they work just a thought.
Opti
Dork
10/10/21 3:04 p.m.
On this setup would a half fill help with block and bore strength?
Driven5
UltraDork
10/10/21 3:34 p.m.
The Ford 4.6 V8 has a 90.2mm bore and the current 5.0 V8 has a 92.2mm bore. Both should have good availability of cheap pistons too. Might pose other issues for your application though.
Brotus7 said:
If I follow the math right, stock sleeve is about .200" and you'd be getting them machined down to .080". I wonder if you'll run into an out of round condition resulting from the thin wall.
Since the iron sleeve is backed up by the aluminum block I'm thinking it "should" remain round.
cdowd (Forum Supporter) said:
https://www.summitracing.com/parts/uem-s3442h-1-0mm/make/chevrolet
what about the Chevy 4 cylinder pistons. You can buy them in 91mm and they are 60 for 4. Idk if they work just a thought.
That gets me .040 overbore. I doubt the extra .040 would Net me more than a few horsepower. Not a lot of reward for the extra machine work required. I've looked pretty hard for a 93 or 93.5 mm piston that I can afford.
Opti said:
On this setup would a half fill help with block and bore strength?
Filling a block is OK for drag racing but not road racing where you are hard on the throttle for 30 minutes or more.
matthewmcl said:
If you have spare blocks and/or spare blocks are easy and cheap to come by, risk it. It is only worth the trouble of making a dozen sleeves and custom machining the block if the block itself is worth the effort.
Right now I have 3 complete engines. One nice block, several sets of heads,etc. Sometime this winter a 4th promises to show up. While all an aluminum engine it Seems like it should be expensive. However if you check the junkyards they almost never sell. I had 50 complete engines at one point and only sold 1 engine a year on average. Towards the end I was offering them for $500 each with a complete check out including a compression test. And a 1 year warranty. Most of the rest I took apart and sold the metals for scrap.
obsolete said:
What's wrong with the V12 pistons?
They are fine. Seldom ever worn enough to justify discarding. With the short stroke (2.75) piston speed even at 7000 rpm is very slow. The factory ran a stock engine to 8300 RPM before any valve float and there was no strain on the engine. Massively over built since the factory designed this engine to go out to 500 cu in from the stock 326
Again you ask, why new pistons? Well there are 2 different heads. The first set (from 1971-1980) are the best heads they are designed to make a lot of power. Like the LS Chevy heads, When the valve opens there is no shrouding until the charge hits the cylinder wall and the flow direction has started the swirl.
The combustion chamber is in the piston and it's a proper shallow Hemi head with the spark plug in nearly perfect center.
But stock, the US compression ratio is a miserable 7.8-1
The 1981- until end of production is a smog head. Like the Chevy 350 the intake valves are shrouded. While that has 11.5 compression. The pistons can't be used with the earlier head.
In reply to frenchyd :
Sounds like another block is easier to get than even just the material cost for custom sleeves. Bore the block and find out if it works. If it doesn't, worry about custom sleeves then.
Indy "Nub" Guy said:
In reply to frenchyd :
Shhhh.... The block is sleeping.
Sorry, I'll show myself out.
Funny! ;-) I did write Sleeving but darn spell check thought I meant sleeping. Hey, spell check look at where the V that I typed is and where the P you put in is?
Driven5 said:
The Ford 4.6 V8 has a 90.2mm bore and the current 5.0 V8 has a 92.2mm bore. Both should have good availability of cheap pistons too. Might pose other issues for your application though.
I sorta need a dish piston. Or one that I can mill into a dish. The good Head is a completely flat head and a flat piston and a flat head won't provide the swirl and squish needed.
The valve reliefs in a lot of Chevy pistons provide a thick enough head to mill into to achieve what I need.
Few people understand how easy it is to use a router and a wooden guide to modify pistons.
Then use a simple balance beam scale to match weights and Bob's your Uncle
Some Ford v6 have 93mm pistons. Summit has 6 of them for just over 100 dollars. Might be worth getting a set to see if you could put enough relief in them.
Have you looked at the compression hight of the LS pistons as compared to the Jag's? I haven't but, I seem to recall (perhaps erroneously) the the Jag's is relatively high.
It's one of the things I'm hoping for. It's nice to know a lot about a subject enough so you can play Lego's with internals.
Got an idea of what I'm doing?
APEowner said:
Have you looked at the compression hight of the LS pistons as compared to the Jag's? I haven't but, I seem to recall (perhaps erroneously) the the Jag's is relatively high.
That would allow you more stroke with the same rods, or longer rods.
As far as wall thickness goes, 351Cs would have cylinder wall thickness as low as .100" or so on the sides (not thrust) with stock bores, with nothing supporting the other side but coolant. Gut instinct says you'd probably be fine thinner than that, but this is an area I don't have much picking-up-the-shrapnel experience with.
It does explain why Clevelands didn't tolerate much overbore. And why Aussie blocks were popular to import for NASCAR, when they weren't boring the cylinders completely out and furnace brazing thickwall sleeves in place. The 351Cs cast in Australia had much, much thicker cylinder walls.
The cylinder heads were also so thin casting-wise that, between flexing from combustion pressure and flexing from valvetrain motion, they would set up resonances in the water jacket that would act as anti-pumps. The band-aid fix for that was drilling and tapping the rocker pedestal mounts all the way through and running all-thread down to lock the top of the combustion chamber down ("posting"). And the people with shaft rockers sat back and laughed 
Well, except for the part that any small block with shaft rockers also came with really crappy cylinder head flow...
.080" na would be totally fine, boost I would sleeve it
Pete. (l33t FS) said:
APEowner said:
Have you looked at the compression hight of the LS pistons as compared to the Jag's? I haven't but, I seem to recall (perhaps erroneously) the the Jag's is relatively high.
That would allow you more stroke with the same rods, or longer rods.
As far as wall thickness goes, 351Cs would have cylinder wall thickness as low as .100" or so on the sides (not thrust) with stock bores, with nothing supporting the other side but coolant. Gut instinct says you'd probably be fine thinner than that, but this is an area I don't have much picking-up-the-shrapnel experience with.
It does explain why Clevelands didn't tolerate much overbore. And why Aussie blocks were popular to import for NASCAR, when they weren't boring the cylinders completely out and furnace brazing thickwall sleeves in place. The 351Cs cast in Australia had much, much thicker cylinder walls.
The cylinder heads were also so thin casting-wise that, between flexing from combustion pressure and flexing from valvetrain motion, they would set up resonances in the water jacket that would act as anti-pumps. The band-aid fix for that was drilling and tapping the rocker pedestal mounts all the way through and running all-thread down to lock the top of the combustion chamber down ("posting"). And the people with shaft rockers sat back and laughed Well, except for the part that any small block with shaft rockers also came with really crappy cylinder head flow...
Sorry but stroke is only affected by the crankshaft. Piston pin height can affect compression though. Or in my case a shorter pin height will allow a longer stroke without the piston going past the top of the block.
However a longer stroke will increase piston speed. Dirty rough calculation each 1/4 inch of stroke will gain something like 250 Ft. per sec. with production piston speed to around 3000 ft. Per sec. unless cast and then 2500 ft. Per sec is about the upper limits that are safe. Hyperthoratic (sp) are almost like forged though.
Paul_VR6 (Forum Supporter) said:
.080" na would be totally fine, boost I would sleeve it
Does Alfa use a iron sleeve in their aluminum block ?
Based on a quick search it looks like the stock Jag pin height is 1.560" while the stock LS height is 1.33". Assuming that's correct you're going to need to need either different rods or a different crank (that may or may not clear the stock block). I would think that either would quickly eat up the potential cost savings of using the LS pistons.
The Jag sleeves are interesting. They're a wet sleeve but roughly the bottom two thirds are a slip fit into the aluminum bores in the block while the top third is a larger diamater and clamped between the cylinder head and the top of the bore in the block.
The sleeves are different thicknesses in different areas and the original design would have considered at least to some extent how the heat was carried away from the cylinder and what needed to happen to keep the bore roughly the same diameter from top to bottom at operating temperature. I don't know how much, or even if, going over the recomended spec. would effect that.
Another factor to consider is the clamping forces between the cylinder head and the top of the block. The clamping loads are going to cause the cylinder wall to want to bulge in the thin area between the top of the cylinder and the flange that sits on the block. Normally that bulge would be insignificant but as the cylinder wall gets thinner at some point it's going to become an actual measurable factor. I have no idea what that point might be. I have no actuall experince with sleeves of this type so this is all speculation on my part but personally I wouldn't mess with an over spec. bore in this application in a budget build.
