Offset ground crank strength?

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Offset ground crank strength?

Post  bb429power on January 29th 2014, 10:51 pm

I bought a turnkey car a few weeks ago for a great price, the owner passed away and his friend was selling all the guys cars. Anyway, I don't have a spec sheet for the engine, I was told it is a 514. Apparently it ran 9's in another car but predicted 10's in this car because of weight difference. I got to thinking some more while at work and my boss and I are wondering if it's an aftermarket crank or an offset ground stock crank. Now it looks like the two ways to achieve a 514 combo are a 4.15 stroke/4.440 bore or a 4.30 stroke/4.360 (stock) bore. I haven't heard of an offset ground 4.30 but I have heard of it in a 4.14 stroke. I will have to measure it, but either way... Does anyone have an idea of how much power or rpm's an offset ground stock crank can handle? And could a setup like either of these been done with a stock rod or what length would be needed?

I can't wait to get this thing on the road!
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Re: Offset ground crank strength?

Post  res0rli9 on January 29th 2014, 11:41 pm

The first one I read about doing a 512 with an offset ground stock crank was Dyno Don.
So I don't thank you'll have anything to worry about.

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Re: Offset ground crank strength?

Post  IDT-572 on January 30th 2014, 7:18 am

I ran 6.20's on one @ 3200 lb.................. Forever with no problem
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Re: Offset ground crank strength?

Post  LivermoreDave on January 30th 2014, 11:42 am

As to strength concerns, the 4.3" and 4.5" stroke aftermarket crankshafts are popular. As Blake and res have replied you concerns should be uneventful considering normal assembly guidelines are followed. If your concerns are of overlap, I was told overlap is not a consideration until the math exceededs 4.0". Most math does although I'm not certain of the danger zone!

Overlap math as explained to me. Crankpin diameter + main journal diameter = overlap. (i.e., 2.2" + 3.0" = 5.2") Another result, 2.2" + 2.75" = 4.95". It seems in most BBF applications of size the math exceeds the "so-called" overlap concern. What's safe? Beats me!

It seems there are many 4.3" assemblies in service and I don't hear of much failure due to crankshaft concerns.

Dave.

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Re: Offset ground crank strength?

Post  Carl on January 30th 2014, 12:12 pm

bb429power wrote:I bought a turnkey car a few weeks ago for a great price, the owner passed away and his friend was selling all the guys cars. Anyway, I don't have a spec sheet for the engine, I was told it is a 514. Apparently it ran 9's in another car but predicted 10's in this car because of weight difference. I got to thinking some more while at work and my boss and I are wondering if it's an aftermarket crank or an offset ground stock crank. Now it looks like the two ways to achieve a 514 combo are a 4.15 stroke/4.440 bore or a 4.30 stroke/4.360 (stock) bore. I haven't heard of an offset ground 4.30 but I have heard of it in a 4.14 stroke. I will have to measure it, but either way... Does anyone have an idea of how much power or rpm's an offset ground stock crank can handle? And could a setup like either of these been done with a stock rod or what length would be needed?

I can't wait to get this thing on the road!

More than likely, it's a 4.140 stroke with a BBC dimension 6.800 rod. As you can see in the attached link, it's going to have the most journal overlap (and strength) of any cast crank. How much will it handle? I don't personally like to use them at more than ~650HP because upgrading to a forged piece isn't that much in the big picture, but they've been proven to handle 1000+HP. At the higher power levels, duty cycle is the better question, and state of tune will play a big role as well.

http://home.earthlink.net/~highflowdynamics/highflowdynamicstechnicalpages/id3.html


 Wink 

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Re: Offset ground crank strength?

Post  LivermoreDave on January 30th 2014, 12:51 pm

Thanks Carl for posting the link. Now I need educated as how the overlap is figured! Can you help, because my calculator isn't doing a good job of explaining!

Dave.

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Re: Offset ground crank strength?

Post  Bill Heard on January 30th 2014, 1:32 pm

My Good Old Girl engine is a 472 cubic in. off set ground stock crank with 4.00 stroke. My engine builder didn't like going more than 4 in. stroke. Motor is 15 years old, been through 3 cranks and still going. Don't remember all the numbers but I think the rods are four hundred long chevy rods .015 over bore. Seems like the guys going more than 4 in were breaking cranks (drag racing).
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Re: Offset ground crank strength?

Post  austin460 on February 1st 2014, 5:06 am

Carl wrote:
bb429power wrote:I bought a turnkey car a few weeks ago for a great price, the owner passed away and his friend was selling all the guys cars. Anyway, I don't have a spec sheet for the engine, I was told it is a 514. Apparently it ran 9's in another car but predicted 10's in this car because of weight difference. I got to thinking some more while at work and my boss and I are wondering if it's an aftermarket crank or an offset ground stock crank. Now it looks like the two ways to achieve a 514 combo are a 4.15 stroke/4.440 bore or a 4.30 stroke/4.360 (stock) bore. I haven't heard of an offset ground 4.30 but I have heard of it in a 4.14 stroke. I will have to measure it, but either way... Does anyone have an idea of how much power or rpm's an offset ground stock crank can handle? And could a setup like either of these been done with a stock rod or what length would be needed?

I can't wait to get this thing on the road!

More than likely, it's a 4.140 stroke with a BBC dimension 6.800 rod.  As you can see in the attached link, it's going to have the most journal overlap (and strength) of any cast crank.  How much will it handle?  I don't personally like to use them at more than ~650HP because upgrading to a forged piece isn't that much in the big picture, but they've been proven to handle 1000+HP.  At the higher power levels, duty cycle is the better question, and state of tune will play a big role as well.

http://home.earthlink.net/~highflowdynamics/highflowdynamicstechnicalpages/id3.html


 Wink 

I believe the 6.7 BBC rod can be used also depending on piston pin height.
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Re: Offset ground crank strength?

Post  bbf-falcon on February 1st 2014, 12:34 pm

I have one offset to 4.15 usung a 6.7 rod. The 4.14 generally uses the 6.8 rod.

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Re: Offset ground crank strength?

Post  68galaxie on February 1st 2014, 12:41 pm

I have been using a 4.145" offset ground crank (over 10 years now) with 6.535" Crower connecting rods and Venolia pistons.
A few pistons came close to crankshaft counterweights - and easily rectified.
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Re: Offset ground crank strength?

Post  Carl on February 1st 2014, 12:54 pm

austin460 wrote:I believe the 6.7 BBC rod can be used also depending on piston pin height.

Most commonly available pistons for 4.14 cranks are based around a 6.8 rod with a 1.420 compression height. I have no doubt a 6.7 rod (or 6.535) rod would work, it's just not as common.



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Re: Offset ground crank strength?

Post  bb429power on February 2nd 2014, 11:08 pm

Thanks for all the replies guys, I guess at some point I should pull the pan and see what's in there. I'd like to know how close it is to it's limit, how hard I can push it, and if I can add a little nitrous if it's too slow!
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Re: Offset ground crank strength?

Post  Bret Powell on February 2nd 2014, 11:26 pm

I think I'd personally rather have an offset ground Ford piece than a Chinese cast piece.

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Re: Offset ground crank strength?

Post  dfree383 on February 3rd 2014, 11:50 am

Bret Powell wrote:I think I'd personally rather have an offset ground Ford piece than a Chinese cast piece.

Bret

As long as the grinder does it properly with good fillets and tolerances.
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