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2 bolt main convert to 4 bolt main.

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Shawn_Watson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shawn_Watson Quote  Post ReplyReply Direct Link To This Post Posted: Feb/17/2019 at 3:50pm
I know, right?  I'm sure AMC racers have put plenty of nitrous squeeze on 360 blocks so you'd think there would have to be stories of them blowing up or fretting the caps at xxx hp but I can't seem to find any.


Shawn
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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Feb/17/2019 at 3:52pm
You would have to machine the caps flat for contact area, but a ridged cap girdle in conjunction with studs should provide more bottom end support with 2 studs on the thinner casting.
Girdles usually were not successful to prevent walk because they were just added.
 A properly machined and fitted girdle of higher grade steel should be stronger then 4 bolt mains.
Have not done the math on this.

So it turns out that math on this is not really possible. It's harmonics that cause cap walk and not direct force.
Have a read of this manufacturer:
I'm really not convinced that the aluminum girdle is best as it has greater expansion then steel and the different materials may cause other problems.
There are some that are using steel and running with 2 bolt mains up to 1000 HP with success, but they are nitro s drag racing and tearing down every 5 to 10 passes.  

For an AMC motor  you would have to have an engine on a dyno measuring the harmonics to determine the best girdle material and design. 1040 heat treated steel plate seems to be were most end up with the steel girdle.




Edited by Trader - Feb/18/2019 at 9:23am
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texasamx View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote texasamx Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2019 at 12:26pm
Like others have said, the 390's don't have enough metal for the second bolt and most engine don't rev high enough to justify the expense... studs will do fine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst390 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2019 at 1:11pm
I went 9.40's-145 @2950# with 2 bolt mains
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PROSTOCKTOM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2019 at 1:19pm
Here's the deciding factor to consider. Currently the 3 center caps are $379.50 plus $28 for shipping, for a total of $407.50 If you use all 5 caps the cost is $850 plus $35 shipping, for a total of $885. Plus you need to buy a set of studs for $150. Now add the machine shop cost to install the caps and align bore the block for $600 and you have anywhere between $1157.50 to $1635 to convert to 4 bolt main caps. I know this first hand because I just had 5 caps installed on a 401 and the $1635 did not include cleaning the block or boring it. So to prepare a 401 block ready to build with all 5 caps will set you back over $2000 not counting the cost of the block. This reason alone is why I wish someone would make an aftermarket iron block.

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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2019 at 3:17pm
I know I'm not in your league, but it would be interesting to have these people make a billet steel girdle up, and next engine on the dyno do a vibration monitoring with and without the girdle.
Everything I've read so far, Formula 1 to drag racing - Many are using separate or attached girdles with the main caps with better results then 4 bolt mains.  Even on the Honda's spinning 15,000 RPM.
I know, not my money either! Just my thoughts.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jcisworthy Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2019 at 6:25pm
Anything done to an engine causes a change. Installing a stud girdle will change metal frequencies but what does that mean or how does someone interpret it? 

It is easy to say just do this or that but in reality what you suggest "next time on the dyno" that is much easier said than done. On top of that, how many manufactures out there really care if an AMC engine blows up or not? 

It has been said by many the only thing a stud girdle does is contain parts better when the engine blows up. 
Specializing in dyno services, engine building, and cylinder head porting

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2019 at 8:26pm
Originally posted by jcisworthy jcisworthy wrote:

Anything done to an engine causes a change. Installing a stud girdle will change metal frequencies but what does that mean or how does someone interpret it? 

It is easy to say just do this or that but in reality what you suggest "next time on the dyno" that is much easier said than done. On top of that, how many manufactures out there really care if an AMC engine blows up or not? 

It has been said by many the only thing a stud girdle does is contain parts better when the engine blows up. 

This is a good point,
when Jeep added a main cap girdle to the 4.0L's in 1996 they didn't claim it was for strength at all,
they claimed it was done to reduce the engines NVH (noise vibration and harshness).

......too bad they didn't for-see all the NVH they'd get from worn out slipper pistons after 40k miles but that's another thread LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote motorhead_1 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2019 at 10:14pm
something like this could be copied to the amc block. seems to work for the oldsmobile stroker guys. 
i used this on a 496 olds stroker motor several years back. 

69 SC/Rambler tribute 401/th400, 68 Rebel SST LSA, 66 F100 460/c6, 88 Merkur Xr4Ti, 71 Jaguar XJ6 LS1, 08 Supercharged Tundra
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Post Options Post Options   Thanks (0) Thanks(0)   Quote motorhead_1 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2019 at 10:16pm
wouldn't let me attach all 3 pics

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