200ci connecting rods
- Thread starter Bayrunner
- Start date
'68falconohio
Well-known member
Only the crankshaft stroke and cylinder bore affect the cubic inch of an engine. Simply swapping to a longer or shorter connecting rod in and of itself doesn't change the cubic inch of an engine in any way. Now if by using a particular rod requires you to alter/or allows the cranks stroke to be changed to able to use it, then yes, a cubic inch change has been made, but only by what was done to the crankshaft itself, and not by the rod you use.
The 200 rods in a 250 is for the Australian Crossflow only. Since both crossflow engines used the same block, they have the same deck height; the US 200 and 250 have different deck heights.
The Aussies use the 200 rods with a special shorter piston from ACL. This allows the 250 to have a better rod/stroke ratio and rev higher. Unfortunately, the manufacturer quit making the pistons, except for the forged units ($1700+/set).
Hope this helps.
The Aussies use the 200 rods with a special shorter piston from ACL. This allows the 250 to have a better rod/stroke ratio and rev higher. Unfortunately, the manufacturer quit making the pistons, except for the forged units ($1700+/set).
Hope this helps.
Bayrunner:
All the above posts hit the mark about the [domestic] 250 rod being usable in the 200 block. The 200 and 250 rods share the same big end dimension of 2.1236" and I presume (but don't know for a fact) that the small ends match as well. So the questions is whether, with a custom piston package, you could use the 250 [long] rod in the 200 block to improve the rod ratio and reduce the cylinder side loading. Unfortunately, there just doesn't seem to be enough room to make this work.
If you are assuming a zero deck, then you can compute the required custom piston pin height as follows:
Pin.height = 200.block.height - (200.crank.stroke / 2) - 250.rod.cc.length
Pin.height = 7.808" - (3.126" / 2) - 5.880"
0.365" = 7.808" - 1.563" - 5.880"
If I've done the math properly, the custom piston package would require a pin height of just over 1/3 of an inch (at 0.365") and that just isn't doable. The shortest pin height I've seen used was somewhere in the 1.120" range and that's short enough that the pin hole intersects with the 3rd (oil) ring land, requiring a "support".
Russ
All the above posts hit the mark about the [domestic] 250 rod being usable in the 200 block. The 200 and 250 rods share the same big end dimension of 2.1236" and I presume (but don't know for a fact) that the small ends match as well. So the questions is whether, with a custom piston package, you could use the 250 [long] rod in the 200 block to improve the rod ratio and reduce the cylinder side loading. Unfortunately, there just doesn't seem to be enough room to make this work.
If you are assuming a zero deck, then you can compute the required custom piston pin height as follows:
Pin.height = 200.block.height - (200.crank.stroke / 2) - 250.rod.cc.length
Pin.height = 7.808" - (3.126" / 2) - 5.880"
0.365" = 7.808" - 1.563" - 5.880"
If I've done the math properly, the custom piston package would require a pin height of just over 1/3 of an inch (at 0.365") and that just isn't doable. The shortest pin height I've seen used was somewhere in the 1.120" range and that's short enough that the pin hole intersects with the 3rd (oil) ring land, requiring a "support".
Russ
PS:
The rod-to-stroke ratios for the Ford "small six" are as follows:
* For the stock 200 ci engine: 1.51 : 1
* For the stock 250 ci engine: 1.50 : 1
* For the 200 block with the 250 rod (if it were possible): 1.88 : 1
As you can see, the rod ratio using the 250 rod in the 200 block would be a significant improvement if it could be done. The question is then: would the improvement be worth the effort and cost. On a street application, I can't imagine it would make any difference at all. On a maximum effort race engine, it might. But there are a number of guys on this forum that are much smarter than me on this subject that have differing perspectives on using "long rods". But it's an interesting topic to be sure.
Russ
The rod-to-stroke ratios for the Ford "small six" are as follows:
* For the stock 200 ci engine: 1.51 : 1
* For the stock 250 ci engine: 1.50 : 1
* For the 200 block with the 250 rod (if it were possible): 1.88 : 1
As you can see, the rod ratio using the 250 rod in the 200 block would be a significant improvement if it could be done. The question is then: would the improvement be worth the effort and cost. On a street application, I can't imagine it would make any difference at all. On a maximum effort race engine, it might. But there are a number of guys on this forum that are much smarter than me on this subject that have differing perspectives on using "long rods". But it's an interesting topic to be sure.
Russ