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Old 01-07-2003, 10:30 AM   #1
CNGBrick
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Does anyone have any information on the minimum practical cylinder wall thickness (thrust and non-thrust side) for a turbocharged red block? Has anyone split cylinders and what was the wall thickness at the split (and was detonation suspected)?

Thanks,

Richard Thomas
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Old 01-07-2003, 11:45 AM   #2
volvo88
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Richard,

Ugly duck gave me a number of 0.125" as the minimum wall thickness to go by. I'm having my B23FT bored 0.008" over and then sonic checked, by the way I found a really good test lab for sonic inspections!

Brad.
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Old 01-07-2003, 12:07 PM   #3
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Just as a side note, Madcap engines in Denver (for those who are local) will sonic check a V8 for only about 45.00. I'd bet a 4cyl would be less.
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Old 01-07-2003, 02:12 PM   #4
CNGBrick
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Thanks guys.

Brad: do you know what peak combustion pressures are assumed for that .125"wall thickness? So far the thinest part of the cylinder I was able to measure was .130" on the non-thrust side. Thrust side came in at .160".

Thanks again,

Richard Thomas
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Old 01-07-2003, 07:17 PM   #5
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Richard,

Give me a day to work on the combustion pressure issue. How are you checking wall thickness? Where was the 0.130" measurement taken (cyl. no., bottom/top, side/front back)?

Brad.
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Old 01-07-2003, 10:49 PM   #6
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Richard are you positive about those numbers? How are you mesuing them? The #1 & #2 blocks I have, have (non thrust) .81 and .104 patches respectively. I was thinking this was normal and that I'd play with a couple things- repositioned bores and block fill- to get my .040+.
If better blocks are out there maybe I should keep looking...

The rule of thumb suggested to me is starting at .100 for street perf Na, going to .125 for serious turbo, as minimums. With a slightly smaller bore like we have, a little less thickness is acceptable than for big bore V8's. If you were buildng a BBC .125-130 would be more your rule of thumb, apparently.

The most common spot mentioned for breakage is the front of #1, near the water pump area.
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Old 01-08-2003, 06:28 AM   #7
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Two years back, developing the 16V Ovlov.net turbo racecar I did a lot of sonic testing of B23 and B230 blocks, and talked at length to Mike Aaaro about these things. I can now confidently say that my early problems with splitting bores (No 1 in particular) were primarily associated with detonation around 5,000rpm - a function of my particular 16V head, cam grind and volumetric efficiency (my VE peaking at around 5,000rpm). That detonation problem was finally cured with water injection.
For any normal turbo application, up to 18psi boost at standard bore or first oversize (+0.3mm or 12 thou) almost any block will do if detonation is controlled.
There is some core shift in all Volvo block castings, but it is not the death knell as some have suggested - I have sonic tested about 10 blocks, and found wall thickness (4 points measured around each bore) varying from 2.8mm (112 thou) to 5mm (200 thou). Maximum core shift in any one bore was 2.8mm min to 4.7mm max - a B234F block, not my favorite, I use B230 blocks from '89 exclusively now. The best I measured was a B21 standard bore with 3.9mm min, 4.9mm max over the 4 pots.
For any hi-po Volvo I would recommend sonic testing (4 points per bore) at a cost of around US$80 by a specialist. Provided you have minimum 3mm, go for it.
My engine builder (a V8 race boat specialist) says many successful 1000HP V8's have only 110 thou wall thickness.
I hope this helps. Nothing like some facts to spoil a good argument.
Dick Prince Ovlov.net
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Old 01-08-2003, 10:21 AM   #8
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[quote:de02298d24]I have sonic tested about 10 blocks, and found wall thickness (4 points measured around each bore) varying from 2.8mm (112 thou) to 5mm (200 thou). Maximum core shift in any one bore was 2.8mm min to 4.7mm max - a B234F block, not my favorite, I use B230 blocks from '89 exclusively now. The best I measured was a B21 standard bore with 3.9mm min, 4.9mm max over the 4 pots. [/quote:de02298d24]

Ok, sounds good, especially that you've proven to your satisfaction that the walls aren't actually that troublesome. I'm still surprised that my two blocks are the worst out there- just seems my luck must be bad...??

My b23ft block, still sitting a few steps away, was bored .040 before sanity took over and I had it sonic checked. After boring, but before final honing, it had an area of .066 thickness. It can happen. I believe Calgary Richard recieved the pics I have of the aftermath of a Ford 2.3 breaking a wall. It's ugly... I also was in corespondence with another Canadian using Buick forged pistons, who cracked his bores. We went over every detail we could think of, and saw no assembly or other fault.
I think we can agree that the b21ft in std was the all time best for thickness. Just stands to reason. Volvo 'used to' cast some very thick walls- my 1963 b18 is .207 nominal over, and ran a supercharger for a summer, through a lot of tuning problems, and showed no problems. Still, my 'better' b23E/f NA block has the between cylinder area very consistently around .105, with the front cylinder too close to the front with a .104/.160 shifted bore. If I use this block overbored .040, I will have thickness somewhere in the low .080's
Sounds like the shop I am dealing with (they have several low 7 second cars) and Richard Prince agree that .110 would be the minimum in general. I'm think bore the #1 moved so I only lose .005 at the front (down to .099-ish) and set the block at an angle facig down to the rear and use block fill up to about the half way point for #4 and up to the water pump hole for #1. then I can add N20 or an Eaton M90 in a few years without worry.
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Old 01-08-2003, 02:29 PM   #9
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Hmmm...

I'll have to get some more measurements to make sure I don't have any weak spots...

I looked at some typical cylinder pressure curves for high-pressure turbo systems. Most curves show that by 35 to 40 degrees ATDC the cylinder pressure dropped to less than half of peak cylinder pressure (assuming no knocking). At that point the piston is about 12mm down from TDC. The pistons I have have the rings close to the top of the pistons so I'm assuming that the deck thickness plays a role in stiffening the cylinder walls at that height.

I guess I'll be pulling the pistons and getting a sonic check done for peace of mind.

Richard Thomas
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