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Horsepower limits of a Service Block?

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jpnjim View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Feb/10/2018 at 8:13am
good information!
Thank you to all so far!
71 P-code 4spd Javelin/AMX
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Lyle View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lyle Quote  Post ReplyReply Direct Link To This Post Posted: Feb/10/2018 at 8:14am
Yes jpnjim, that's the picture.
Did some math this morning on the centrifugal force of just 5 lbs material removal from a 401 crankshaft at 8000 RPM (a lot I know). Came up with a not so insignificant 36,000 ft lbs.
My math could be wrong - did it twice as I thought the number was way too high.
Then did the same calculation at 5000 RPM and got 14,000 ft lbs.
A stock crankshaft at 5000 RPM was 27,000 ft lbs total and 8000 RPM was a whopping 69,000 ft lbs! 
I agree with the 4 bolt mains and can also now see why a crankshaft would flex.
Reducing the weight of a crankshaft in any way seems to reduce forces dramatically especially rotating it faster.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Feb/10/2018 at 1:30pm
An old tool and die maker one said "When you take a step you move the Earth".
He was over emphasizing that all things move and or bend with load.

A running engine is alive with movement, no engine block is with out some flex with temperature or movement.

Everything in that motor is bending, none more highly stressed than the valve train.

AMC Blocks are pretty good. 

Hurst390 is 100% correct.
I had a 1970 390 that had obvious main cap fretting with 2 bolt mains.
It was a sub 7,000 rpm motor that made in the neighborhood of 450HP.
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shootist View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shootist Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2018 at 4:37pm
For the record, I wasn't arguing that 4 bolt mains are not needed. If building for big horsepower it would definitely be wise to go 4 bolt mains. I was more just trying to point out the native strength of the service blocks aka 390/401 blocks. Anyway, they are good blocks for sure and not too excessively tough to build big power. Smart money spends money on the mains as Hurst mentioned.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2018 at 6:09pm
I am pretty sure the stock caps with ARP studs would tolerate
more than a stock set of bolts. But if 2 hp per inch is the goal
then IMO a set of 4 bolt cap with studs is a good idea.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2018 at 8:46pm
Thanks,
that makes sense Boris,
since others have mentioned main journal distortion by running studs without line honing it,
I think I would go right to the 4 bolt caps and get it line bored at that point.

The biggest problem with building an 800-1200 HP AMC (besides the oiling setup) is there's no viable plan B if you build more power than the block can handle.
The Aluminum Indy block has prioritized oiling, but doesnt have motor mount bosses.


So is there any kind of consensus?

Do we think a 4 bolt Central Forge 401 is good for 700-800hp if the walls arent too thin,
and a 4.125" Service Block can take 900+?

For the sake of argument assume it'll be a Turbo build,

At what horsepower level is it worth going with the harder to find service block and giving up .060" bore (4.125 vs 4.185) for cylinder wall thinkness?

500, 600, 700, 800? 
 






Edited by jpnjim - Feb/19/2018 at 8:49pm
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shootist View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shootist Quote  Post ReplyReply Direct Link To This Post Posted: Feb/21/2018 at 1:24pm
Do we think a 4 bolt Central Forge 401 is good for 700-800hp if the walls arent too thin,
and a 4.125" Service Block can take 900+? 

I believe both could make 900+ with no more than .020" over but I would sonic test them to rule out any thin spots.

At what horsepower level is it worth going with the harder to find service block and giving up .060" bore (4.125 vs 4.185) for cylinder wall thinkness?

I think once you start breaking the 1,000HP mark the thicker cylinder walls would be desirable.

Ghinmi or 401AMX1969 on the forum have both built 1000+ HP 401s using boost either SC or Turbo. My build with boost is only making around 800HP on 14lbs of boost. I am bored .030" over, using two bolt mains on a 73 401 block.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lyle Quote  Post ReplyReply Direct Link To This Post Posted: Feb/21/2018 at 2:58pm
If sonic testing shows and thin spots you can always put a liner/sleeve in that cylinder. Melling makes them, don't know the cost but on a 900 to 1000 HP build - cheap.
Like stated before many race engines are sleeved right from the start - no guessing on cylinder wall failure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Feb/21/2018 at 5:46pm
Sleeve all 8 and use a 4.25 bore :-)

"There ain't no replacement for displacement"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shootist Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2018 at 2:57pm
"There ain't no replacement for displacement"

Unless your running boost.......  Big smile
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