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Shortest rods? #2997670
12/22/21 07:41 PM
12/22/21 07:41 PM
Joined: Jan 2003
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Frostbitefalls MN (Rocky&Bullw...
gregsdart Offline OP
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The only reason to consider this is to use some valuable parts in a new application.
I am going to use the crank and intake from the 550 megablock motor in a new BMP Aluminum block.
So what I want to do with the heads, valvetrain , pistons, rings and block left over from previous build is to put a stroker crank in it and lower the compression to a liveable level for the 440-1 heads. My Cp pistons have a pin height of 1.662.
To get compression down to 11/1 with all this I would need to run a 6.700 rod on a 4.5 crank a friend has for sale. That ends up at 1.4888 rod ratio. Not too terrible, but there is also a 4.75 crank available which would need a 6.535 rod, which is 1.37. since this motor will be aimed at a power band of under 6500 rpm, maybe even below 6,000 rpm side loading will be somewhat less than a 7500 rpm race motor.
So let's hear what you think. By being able to reuse the original heads, pistons, rings, and block the cost of this build would be pretty low. And the 4.75" crank would make good use of the fully ported -1 heads I have also, and at low rpm

Last edited by gregsdart; 12/22/21 07:43 PM.

8.77 153 mph best, 3055 lbs 528 indy 440-1 alky
Re: Shortest rods? [Re: gregsdart] #2997678
12/22/21 08:31 PM
12/22/21 08:31 PM
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Posts: 620
Central TEXAS!!!!
sr4440 Offline
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I think that you may have counter weight clearance issues with a 6.53 rod and a 4.75 crank.


Joe


Without Data, you’re just another guy with an opinion.
Re: Shortest rods? [Re: sr4440] #2997701
12/22/21 10:37 PM
12/22/21 10:37 PM
Joined: Jan 2003
Posts: 9,444
Frostbitefalls MN (Rocky&Bullw...
gregsdart Offline OP
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gregsdart  Offline OP
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Originally Posted by sr4440
I think that you may have counter weight clearance issues with a 6.53 rod and a 4.75 crank.


Joe
Maybe, Not sure how to do the math.


8.77 153 mph best, 3055 lbs 528 indy 440-1 alky
Re: Shortest rods? [Re: gregsdart] #2997746
12/23/21 12:55 AM
12/23/21 12:55 AM
Joined: Jan 2003
Posts: 29,672
Oregon
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AndyF Offline
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AndyF  Offline
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Originally Posted by gregsdart
Originally Posted by sr4440
I think that you may have counter weight clearance issues with a 6.53 rod and a 4.75 crank.


Joe
Maybe, Not sure how to do the math.


You can't do the math unless you know the size of the counterweights as well as the shape of the piston skirts. Most likely you'll need to mock it up. I'm pretty sure it won't work but if you have the parts sitting on the bench it will only take a couple of minutes to swing a piston and rod on the crank to see for sure.

Re: Shortest rods? [Re: AndyF] #2997754
12/23/21 01:15 AM
12/23/21 01:15 AM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart Offline OP
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gregsdart  Offline OP
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Looks like the longest stroke I could use would be a 4.5 with those pistoñs. I figured longer might add value since the cranks would all cost the same. But after penciling it out adding stroke eats up clearance in a hurry.


8.77 153 mph best, 3055 lbs 528 indy 440-1 alky
Re: Shortest rods? [Re: gregsdart] #2997821
12/23/21 10:56 AM
12/23/21 10:56 AM
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Missouri
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jwb123 Offline
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Missouri
You mentioned rod stroke ratio so you understand the concept. I like the longest rod I can stuff in the engine, will not see a performance increase, but the longevity is what I am after. My last engine is a 4.25 stroke 4.5 bore with a 7 inch chevy rod, it makes tons of torque, and just over 800HP and revs to 7000 like a smallblock. very happy with the combination.

Re: Shortest rods? [Re: gregsdart] #2997893
12/23/21 02:36 PM
12/23/21 02:36 PM
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Posts: 16,644
Western NC
440Jim Offline
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Western NC
I made a quick change to an old calc I did years ago on a low deck idea. I haven't double checked it yet.
But is this what you are looking for?
The distance under the piston pin can be a tight spot hitting the crank counter weight.

MaxStrokeClearance1.JPG

1993 Daytona, 1973 Cuda 440, 2009 Challenger 5.7 Hemi, 2015 RAM 1500 5.7 Hemi 8-speed auto, Link to 572 B1 - Part 1
Re: Shortest rods? [Re: 440Jim] #2997916
12/23/21 03:59 PM
12/23/21 03:59 PM
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Posts: 9,444
Frostbitefalls MN (Rocky&Bullw...
gregsdart Offline OP
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Jim, I wasn't far off on my assumptions. Rod c/cc - 1/2 stroke , - .495 (1/2 pin dia, - .190,- .060 clearance= Max radius of crank cw.


8.77 153 mph best, 3055 lbs 528 indy 440-1 alky
Re: Shortest rods? [Re: gregsdart] #2997959
12/23/21 05:52 PM
12/23/21 05:52 PM
Joined: Jan 2003
Posts: 16,644
Western NC
440Jim Offline
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440Jim  Offline
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Western NC
As Andy mentioned, if the piston skirt is not well designed for this application, it could hit the counterweight before the piston pin boss.
My new B1 pistons are 0.205" below the pin, maybe for more strength then those 0.190 ones I had back then. And these B1 pistons are designed for 7.100" rods, 4.500" stroke, so there is plenty of room.







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