I have been working on a super light weight rotating assembly for a long rod 225 SL6 and had a chance to put an early (1960) crank next to a late cast crank. It is amazing that Mopar was able to take 26 lbs out of the SL6 crank over the years.
DD

Is there reprocutions (sp?) to cleaning up the crank like you would your exahust port? Essentially it will shave a few grams and might help with the windage? Just got this idea from looking at your pictures. Is there any other points you look at on the crank other than the little pigtails that sitck up and cut you when you try to take it out?

DOC, what is the size of the journals for that crank ? Width and cross section measurments. on mains and rods. Will the cast crank fit in the older block ?


26lbs is a lot of weight to be taking out of the rotating assy.


Back in a day we ran the 440 cast cranks at over 650hp, but we keep the rpm down to 6500. Never seen the first problem out of the cast cranks, heck the blocks would get into trouble before the cranks would.


On the SL6 though I got to wander about the four mains and such a long crank. What power level will the cast crank hold ? I guess that has yet to be seen. I believe it was the build in the mag where they made 300hp, they used the light cast crank in that build-up, but I wander if its ever been hit with a shot of NOS ?

I have a cast crank engine setting here... I have been wandering about what to do with it.

Jess

I alway take off the "hanging burrs" and razor sharp edges the factory left behind, even on cranks that do not get rebalanced. (I don't like getting cut-up during engine reassembly)

The next step is lightening and windage work. There are a lot of nasty parting lines and sharp edges that can be removed and doing so helps prevent cracks from forming.

Next step, look at the direction of crank rotation (clockwise, viewed from the front) and round / smooth-out any leading edges. You want that crank to cut thru the oil mist.

For all-out weight reduction, look for the factory's balancing "drill bosses" they are spaced 120 degrees apart, 3 drilling "lumps" in front, between rod pins 1 & 2, and 3 in back between pins 5 & 6. You can take even amounts of material off all 6 and not up-set the balance to much.

Once you start taking-off more material then basic deburring, have the crank rebalanced.
DD

The bearing diameters are the same for the forged and the cast cranks but the widths are narrower on the cast crank, this is why those have their own special blocks, con rods and bearings.

Getting a cast crank into a forged crank block can be done, but it takes some special machining work to do it.
DD

so my friend's '78 van motor should go into my shed?

I have a friend that just had a bunch of weight removed from a Hemi crank to run in a 440. Going with aluminum rods etc.

_________________
'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

I just got ahold of a truck motor 225, 7/6/84 casting date (thanks Paul Moran). Broke it down last night.

Block weight - 153 lbs
Crank weight - 60.4 lbs

By my previous measurements, this block is about 12-15 lbs lighter than a late 60s/early 70s forged crank block (165-168lbs). Crank is 16 lbs lighter than a forged crank out of a similar engine (76 lbs).

I'm going to build one...

Lou

_________________
Home of Slant6-powered fun machines since 1988

30 lbs is a bunch. If I were still road racing I'd build one too!

_________________
Joshua

Total engine "package" weight reduction is good but these late cast crank engines give you the opportunity to also reduce rotating / reciprocating weight.

With the engine I am doing, we have already reduced the crank's weight to 56 lbs, it is now in the shop getting rebalanced.
Our attention is now focused on the 198 con rods, we just gave a set of those "long rods" a pretty good "hair cut" and now we are taking a bunch of material off the big end.

It looks like we are well on the way to getting 25 lbs of rotating weight out of this combination.
DD

So, are you going to narrow the 198 rods, or broaden out the rod journals on your cast crank?

I bet we can find an aftermarket set of BB V8 7" rods that would just about go right on the cast crank journals. Or, maybe our K1 guy Tom can just finish machine the ones he has to fit the cast crank. I need to have a talk with Mike J and see what all he has done.

Lou

_________________
Home of Slant6-powered fun machines since 1988

We are going to narrow the con rods...
See This Link for the details.
DD