At my job I have been learning how to build large displacement turbo diesel engines. The first 2 we did were

Caterpillar 346 a v8 with a r/s of 1.75 to, 1 it is under sqaure
Komatsu 172 a I6 with r/s of 1.88 to 1, it is sqaure

Both of these engines rev well below 3k and show little cylinder wall wear. I expected in the 1.40 to 1.60 range considering ther low rev high tq. nature.

These engines also need bearings long before rings. Also the upper rod bearing needs replacement long before the lower, because it is the load bearing. Some times the rod bearings are even flipped.

If you don't know about diesels, they are compresion ignited. they have c/r of around 20-1 and boost over 1 bar all of the time.

I compare everything to hondas and thought I would share this info. What do you think?


[Modified by TREVER, 1:01 AM 2/8/2003]

 

you are presenting something that is in a larger scale
number of cylinders are not the same as ours, and..
Diesel
imo, its not a good comparison to our low displacment fours.
but its a good thing you brought that up though...

I remember one of my old posts..
A Caterpillar Dump Truck with C-12 engine
weighs somewhere between 30,000-40,000 lbs.

Horsepower is needed to pull the weight??
Nope..
The engine only produces 430 hp But... 1650 lb-ft of torque

Lesson: If you have more weight you need torque.

 

so whats the relationship between rod stroke ratio and torque?

 

i think the better relationship is displacement vs torque.

while i don't understand engine geometry that well (ie rod/stroke ratio's..etc) i always felt like it was less important to have the r/s ratio closer to 1.75 with a motor that isn't revving that high...

as was posted above, in the motors he's talking about they show little cylinder wear because the rod/stroke ratio combined with a motor that revs no higher than 3k. and it seems like the bearings would need replacement sooner because they are facing the majority of the power thats being created to produce the 1000+ torque that these engines surely put out.

i wish i understood this better, and what i'm saying may or may not be true...so feel free to correct me if i'm wrong.

 

The subject has been beaten to death, but I can pretty much sum it up..
For the average street enthusiast, rod stroke ratio won't mean anything.
Honda has manufactured motors with r/s ratios ranging between 1.75:1 & 1.49:1,
all have different output curves but are well suited for most street driving. -Quick 200k


[Modified by Quick 200k Mile Motor, 7:08 PM 2/8/2003]

 

I always thought the higher r/s would promote high revs and a higher tq curve. Maybe if honda had as much room for taller decks there r/s would be a lot higher?

 

That's sorta true, but it takes many other engine design points to support high RPM operation. R/s ratio is not one of your primary concerns IMO, but it's always nice to have a high one.

 

so high revving say 8k-9k won't matter on a 1.52:1 r/s engine?

 

I have seen ls stroked motors peak over 9k many times. Airflow and balancing are key.

 

all of the diesel engines i have seen have really long piston skirts.
this probably promotes the nice cylinder wear more than r/s ratio.

and FYI, 1.52 isnt that bad. it can go to 10000 with no problems.