NOBODY

Cstrab good advice to anyone building there first stroker.

GPM the 850's are marine motors in pairs (2boats).
1 set I freshened at 200 hours, the other set are sill in the boat with roughly 80 hours. I think these guys turn them around 6000 RPM.

Short rod combo's do make more bottom end torque, but I've yet to see a HP difference between the two if we're not talking about extremes.

Panther

How about a 1.48 rod-stroke ratio in a 580 cu. in. blower motor? 6.700" rod with a 4.5" stroke and 4.53 bore.

Normally we would have went with a 6.535 rod but the previous engine builder put in the 6.700 rod so that's what I'm stuck with.

8.5 to 1 compression.

JimV

iTrader: (1)

Somthing else to look at is the piston gets pulled out the bottom of the bore further with a short rod, causing the piston to rock.

cstraub

I think you are much better off with a full skirt piston in the marine enviroment.

Panther

That's why my builder went with Lunati for my pistons, they seemed to be the only one I could find that had a nice full skirt. The JE's that we pulled out were short and you could see all the skuff marks on the skirts from the piston rocking back and forth.

GPM

Nobody, what do the torque curves look like on these short rod motors?

NOBODY

The short rod long rod will never be settled there are to many benefits in both directions, that's why I've tried it both ways. As far as the 632 CI motors it's just to hard to get any longer rod with a 10.200 block. This block is the cheapest way, not the best to build it. You will find that engine builders never agree on a lot of things and it just goes to personal preference usually from good or bad experiences.
The best advise is to put out different views and come up with your own way to interpret it.
All my life I have learned from trial and error (usually error) and come up with my own way to view subjects like this, because even though someone has good advice I still want to know if there is a different way and why. Truly smart engine guys will never take something for granted, they will listen and then try to prove that theory wrong until they know that theory was right.
Smokey was the first person to say get the longest rod you can fit in the motor, but most great engine builders don't take this advice.

GPM these short rod 632's make brutal torque down low.

GPM

Nobody, I'm sure the 632's make the torque down low, I was just curious if it fell off or kept going. I like to experiment with different combos also.

NOBODY

Let's just say you can get away with a bigger cam and not loose as much down low as a longer rod version would, but as for does it fall off up high, I've never seen this.
I'm sure it would depend more on the head and cam selection than anything.
I do know on some small chevy RR motors I've experimented with had unusually long rods and they don't seem to have the grunt the normal rod ratio motors had. Hard to see on the dyno, but at the track you sure could. I think any extreme either way is bad.

hillbilly24

just another opinion here. its been my experience the numerically low rod ratios dont like to wind as high or as fast along with all the other stuff these guys have said, I read in one a smokey yunicks books that for a N/A engine 1.88 is optimal but on a BB chev its pretty unabtainable. You will give up a little low end torque though but its all stuff that needs to be thought out in conjuction with drive ratio and prop pitch.