Min dependable cyl wall thickness ??

[my way]

What is considered adequate cyl wall thickness AFTER boring ? Have a block here I have been measuring through frost plug holes and thermostat opening. Going to have it sonic tested too. Am tempted to go down to .100+ to get an available piston from Silvolite to work. This would be a naturally aspirated high performance-racing-application. Opinions and or experience requested-thanks
My way

 

[drag-200stang]

What size bore are you wanting to use?

 

[xctasy]

Don't cut more than 40 thou, with 20 or 30 better. You can cut to 70 thou oversize, but its really risky. Some have 70 Thou over bores for 3.75" Jeep pistons, but even with a sonar ray checked block, its a risk, and stock 3.68" bore US Fords often have less than 120 thou wall clearance when new at the thrust faces before a 40 thou over bore. It's nothing to have even less than 90 thou wall thickness after a little aging or core shift.

In the 60's, Ford pinioned thin wall shell molding cast iron blocks, with egg shape wall section. That means in only a few instances are there any Ford blocks anywhere that are going to get more than 90 thou at the thrust face after just simple bare minimum clean up and cylinder true-up boring. In an American setting, plenty of blocks have suffered a freeze thaw injury, and the front water pump stud often bottoms out if the head has been re-planed in its life. That's why I advocate using stock or smaller than stock shallow deck pistons, and use the common and bullet proof 22R Toyota or GM 4200 or other Clevite sleeves, and then use that short deck, modern piston with a more modern forged steel conrod.

Each thin wall 200 or 250 US Ford I6 block is designed as an econo engine, and needs a modern belt and braces approach to safeguard it's future durability. In a similar way, Ford I6 blocks get ruined when the conrods bolts come loose or the cast rods fail, then they take out the camshaft as they then become like interference engines like some double overhead cam multi-valve engines do when the cam timing slips. The FoMoCo cylinder bores are the same kind of risk. Just because you can put 70 thou overbores on the block for Jeep 3.75"pistons in your 200 or 250 and get away with it doesn't mean everyone can do it.


For a 11;1 compression ratio, you NEED the sort of durability of the best factory 010 Chev 350 blocks....180 thou at the thrust faces. The only Ford blocks after the mid sixties that meet the criteria are the 385 Big blocks, some 335 351M's and 400 Fords, all the FE's, US 144/170, EAO Pinto 2.0 liter and Lima 2.3 liter blocks, Aussie 188/200/221/250 and some NASCAR XE code Cleveland 335 blocks meet that criteria. World blocks, and aftermarket SVO blocks are also great. With the exceptions above, Ford never again built in any excess metal in even the seasoned Boss 302 or 351 engines, and our I6 engines aren't even as good as AMC/Jeep and Chevy Small Blocks and L6's regarding wall thickness. We need to deal with it, and work around cost effective solutions. The solution is to treat an iron block like an Alloy Buick Olds Pontiac/Rover 215 or any alloy LS Chevy engine, and use good American sleeve and cheaper piston/rod combos.





Should be a minimum of 90 thou for a thin wall Ford block, but with age and rusting, any thin wall Ford 200 or 250 shouldn't be taken out past 40 thou.
The Clevelands are the worlds worst and post 1969 to pre 1985 Windsors were almost as bad.


viewtopic.php?f=5&t=71410&p=549719#p549719

But......will they be able to bore the block .230 w/o turning it into garbage?

Yes. I know for a fact that in a production block 250 with a liner, that will work fine. The Australian Geelong plants made there own versions of the US Cleveland engines, AND THEY categorically used to have liners attached from the factory at greater wall thickness than that. GM England's Vauxhall division used to have a recommendation with the four bearing L6 3.25" 2651 cc and 3.625" bore 3294 cc engine that a standard sized bore be used with a 3.375 or 3.875" overbore. This was a 125 thou wall thickness liner. That's 250 thou over.

You can certainly re-bore some of the older non siamese cast iron Ford and GM engines 230 thou without a cylinder liner, and get an engine to survive. The standard Detroit thinwall non linered rules have always been 60 thou over is the most, with 20 to 30 thou the suggested maximum if its a Cleveland 351, Windsor 5.0, or iron block Chevy 305/350. With a liner, Ford and Chev generally said take it back to stock bore, with a 125 thou thick liner the suggested minimum. Factory Cleveland 302 and 351 Aussie engines were partly linered from the factory from 1972 to 1979; the whole of those short deck 335 engines had way to much core shift in there production processes and failure in service ment Ford Australia had to recoup the scrapage rate, and so until a landmark case in 1979 which ruled the process unacceptable from a consumer perspective after Ford Australia got taken to court by a 1978 XC Fairmont V8 owner, you'll constantly find many reports of production RPO blocks reworked with liners in them.

A thin wall iron block Chevy V8 under a high load drag or circuit racing situation certainly won't cope with as much overbore as an iron blocked i4 or I6. Strongest thin wall engine ever made was the 180 thick cylinder walls of the early 3.875" 283 and then the better low core shift 350 Chev cylinder blocks. The early 283 ones could take a 125 thou over bore and survive in a hardfill drag race engine, but the later 350 blocks would break with just 60 thou over, but they were in 12:1 compression engines under extreme duty.

Eg 1. X Flow Ford Kent 4 cylinder found in early Pintos, Cortinas, rear drive Escorts and Fiestas could be taken out to +153.5 with 80% reliability in stock 711M blocks to +212 thou with 80 % reliability in an South African AX blocks from a stock 1500 or 1600 cc 3.19" bore size. They used to furnace braze old Ford production iron blocks for BDA racing engines before the HART blocks.
Eg 2. The 3 liter 60 degree Ford Dagenham 'Essex' engines could be taken out to 330 thou to 4" from a stock 3.672" bore size with 80% of blocks so bored becoming scrap. They used those in 450 hp quad cam GAA racing engines.
Eg 3. The thick wall 1948 to 1958 and Holden 132.5 cubic inch I6 Grey Motors . +187.5 thou from an un-rusted early 3.00" bore block without bore distortion, and +247.5 with quite a lot of distortion.

Eg 4. Linered iron Nissan 1985 to 1996 RB24, 26, and 30 blocks converted to Skyline GTR spec can make 900 to 1000 hp turbo charged, and can cope with 103 thick liners from a stock 85 mm bore with perfect reliability.

As soon as you add a liner with a bare minimum of interference fit, you get a great deal of strength back.

 

[my way]

First-thanks for the info and the links.
Have a 68 170 short block out in the shed I have been wondering what to do with and maybe watched that 170 falcon racing video from down under one to many times. So a little bench-internet brainstorming here
Would be shooting for a class F, under 183.99 enough to be safe at tech from wear etc.--around 180 or so. With stock stroke that's around .125 over. Now before I get spanked here, let me give some numbers
between cyl walls through the frost plugs mid height on the cyl I get around .233. metal between cyl from top is about .595-.233=.362 divided by 2=181. I know third place measurement in this area is dicey, but this is what I got.
At the front thermostat bore measuring to bore and subtracting measurement to water jacket, I got about the same, around .180
Know I need more checking, but at this point if things bear out taking .065 er so would seem OK ??
Suns shining in Iowa and gotta make hay so gotta go fer now, but I will be back-got some measurements on a 68 200 for comparison
My way

 

[CNC-Dude]

We found that anything less than .125" thick on the thrust side was likely to cause problems in performance setups. You will also get a lot of cylinder wall distortion if it's thinner as well. The walls are typically thinner between the cylinders because they are barrel and cam shaped around the exterior, so sonic checking is the best solution to plot the cylinder wall thickness. Also, the thrust side of the cylinders is the most important area to check, so don't confuse this with the part of the cylinders that is in between the cylinders.

 

[my way]

More thanks.
All info kind of adds up. Have a 68 200 on an eng stand apart with frost plugs out. Using the same measuring approach which only shows thickness in the wall on the cyl to cyl area not the thrust or 180 from the thrust, I came up with .130+. Now if they are cast a tad thicker-egg shaped -that would support the .030 over recommendation for the .125 er so wall thickness needed after boring-Give er take some :roll:
Factor in the additional .050 wall (.180) for the 170 block and the .125 or a little less overbore doesn't sound out of reason.
Not gonna order pistons yet , but will sonic test soon as I finish my other projects--maybe sooner. Thanks to all again
My way