632 cid rod length 6.7 or 6.8

Need some input on this one,
Callies 4.75 p/n99S-H29-MG crank
have a new set of Grp 6.8 aluminum rods but not sure if they are optimal for this.
going with TFS a460 p/nTFS-5451T804-C03
Eliminator ultra block 4.6 bore


just want to know what the best would be

I don't think you'll have room for a 6.800 rod with that stroke just because the piston is getting pretty darn short. Maybe if you used a C460 style cylinder head with no side can't you could possibly reduce the compression height enough to make it work and still have some room for the ring pack.

.

was thinking the 6.8 rod would not work with that stroke, going flat top on this deal, thinking will have plenty of compression with that bore and 85 cc head.

ran 6.800 venoila s in mine

Run the longest rod you can. Keep the piston in the bore at the bottom!!

With that short of a C.D./C.H. be sure your piston guy knows the thickness of the rod above the pin. It's a lot more than a steel rod.

DaveMcLain wrote:I don't think you'll have room for a 6.800 rod with that stroke just because the piston is getting pretty darn short.  Maybe if you used a C460 style cylinder head with no side can't you could possibly reduce the compression height enough to make it work and still have some room for the ring pack.

I have built 632 Chevies for over 20 years with a 6.750" rod and 4.750" stroke ... their deck height is only 10.200".
With a 6.800" rod length using a 4.750" stroke and a 10.300" deck, the piston has MORE compression distance; which is also more than a common 347 Ford stroker.

Generally speaking, I might have recommended 6.75” aluminum since it has long been an industry-wide standard length (ie, cheap and plentiful) but that’s a moot point these days as aluminum rods are all priced pretty much the same regardless of C-to-C.  And 6.75” does lower the pin and facilitate overall piston design and other necessary features.  (Incidentally there are steel H-beam Chrysler 440 rods (6.76”) available with BBC ends on them if that length is desired but steel is preferred over aluminum.)

If your current 6.800” rods can be used in the parts combo then that’s just fine, and maybe even preferred.

Lem Evans wrote:With that short of a C.D./C.H. be sure your piston guy knows the thickness of the rod above the pin. It's a lot more than a steel rod.  

On that subject:  I did talk with Bill Miller at BME about pin end wall thickness and he told me he has gone as little as 0.200” wall on the pin end.  Of course aluminum pin end wall thicknesses are usually much greater and acceptable thickness depends on the build and application—a rod set with 0.200” wall probably wouldn’t find its way into one of Frank’s engines, for example.  

Lem Evans wrote:With that short of a C.D./C.H. be sure your piston guy knows the thickness of the rod above the pin. It's a lot more than a steel rod.  

Well you will be the "piston guy"... and also "cam guy"..... so what measurement will you want/need to do pistons for it?
or i can make it real simple and send you one of the rods i guess

69bluehotrod wrote:

Lem Evans wrote:With that short of a C.D./C.H. be sure your piston guy knows the thickness of the rod above the pin. It's a lot more than a steel rod.  

Well you will be the "piston guy"... and also "cam guy".....  so what measurement will you want/need to do pistons for it?
or i can make it real simple and send you one of the rods i guess

Deck ht. of block, ring package preference [if any], etc. I short conversation would be in order.