According to "things to do with any motor" in Oct Hot Rod cutting the rod journals down will decrease friction and lighten the rod big end, improve block clearance for stroker cranks. The article said that 1.88" Acura bearings are being used in SBC motors.

Any opinions on smaller rod journals for slants ?

This can be made to work but it means getting some different "brand-X" con rods. One set-up done recently used BB Chebby con rods on a 225 crank.

One thing that makes this hard is the fact that the SL6 uses a really wide con rod bearing insert so the crank has a wide journal surface. Welding-up the edges and regrinding is the "right" way to do this but it is expensive.

It is possible to simply grind-in a new smaller journal centered right onto the exsisting SL6 2.187 x 1 inche wide crank pin surface. If the stroke is not changed, the appx .300 pin diameter reduction will allow you to create new side walls for con rod side clearance oil control. These "journal on a journal" cranks look really strange but it works. (once the pan is on, no-one knows) Who knows if this will weaken the crank enough to cause a broken crank failure, .150 per side on a crank pin is a pretty deep cut.

As with any of these "hybread" engine combos, you need to collect all your parts and measure everything, then "do the math" and a "mock-up" to be sure things like compression ratio, rod ratio and clearance all work. It is possible to pick-up a good amount of stroke and compression while doing this.

Here is one I have "on paper". Use a 170 block & crank with those special "brand-X" 1.88 journal 6 inch "c to c" con rods & 2.2 pistons. You can get yourself a 3.0 liter high compression short stroke engine with a nice rod ratio, less friction and super strong con rods. (and you are going to need them for the high RPMs this engine will produce)

Too bad there are no interesting 3.0 liter racing classes here in the USA, this would be a good "ringer" engine combo to show-up with.
DD

For those of us who have 170s this sounds like a great idea. I'd like to see someone do this!

anybody got an extra 170 crank for sale?

-james

ludite13@cs.com

If we offset ground a 225 crank for the 1.88" journals are there rods that could work?

I have no idea of the costs, but it would seem that welding a journal to narrow the width, then offset grinding to a smaller journal diameter would cost less than welding to increase the journal size.

Are there rods which might work for a 225 stroked in this manner?

Hi,

I used 7.1" bb-chevy rods and had the rod journal on the crank narrowed to bb-chevy size. I had the crank ground to use 0.030 under chevy bearings (2.170). The problem you'll have with smaller journal sizes is the rods are all very short (compared to our slants) and you wind up with a poor rod/stroke ratio which really hurts the slant due to the poor flowing head.

FWIW, I had about $500 in my crank (std-std) with the welding, straightening, grinding. Its now 0.010 under on mains and 0.017 under on rods (but uses 0.030 under chevy bearings). My stroke is still stock (4.125). This engine is finish machined but not assembled yet. Probably won't get it running in the dragster until next spring.

mark

mldingba@rockwellcollins.com