I think the only regret somebody would have, if they bought a stroker from a certain re-manufacturer, is if their Jeep is their DD and now have to run higher octane fuel. (Read the fine print on a lot of websites.... says their stroker engines have to run on 92 octane because of the higher compression ratios.) So yeah you're getting a lot more power (and fun), but now not only are you getting worse gas mileage, but you have to fill it up with more expensive fuel!
Originally Posted by wendell
JP mag says they haven't seen a stroker get over 20,000 miles on them.
Sometimes stroker's aren't as durable. Now, that's not to say, "Oh my God! A stroker will wear down after 10,000 miles." Let me explain. (Hmmmm, let me do some Googling here.)
Its mostly about rod ratio (rod to stroke ratio). Rod Ratio = (rod length / stroke) This little calculation tells you the motor's rod angularity. A LOW rod ratio means a HIGH rod angle. A high rod angle creates a greater potential for accelerated wear to cylinder walls, pistons, and piston rings (picture an extremely low rod ratio that is driving the piston into the side of the cylinder wall). For example, a motor with a 5.400" rod length and a 3.000" stroke yields a rod ratio of 1.8:1. If we maintain the same stroke and shorten the rod length to 5.000" we get a 1.7:1 rod ratio. The rod angle has increased.
The picture on the left is Low Rod Angle (or High Rod Ratio) and the picture on the right is High Rod Angle (or Low Rod Ratio). The bottom picture is just there as an extra visual aid.
By lengthening the rod (as stroke is increased) you can offset the increased rod angle. But this requires further shortening of the piston. The further the piston is shortened the more likely the piston pin will intersect the oil ring groove, creating a potential for increased oil consumption.
Basically, there comes a point when you cannot shorten the piston any further before dependability is compromised.
The consensus, from what I've read, among engine manufacturers is that a ratio of 1.50" is the lowest acceptable rod ratio for a street motor. Realistically, rod ratios between 1.65 - 1.80 are ideal. (Maybe this has a lot to do why the 4.0L engines are so long lasting. Their rod ratio is 1.794)
When I was originally researching this topic, it was for my 68 Mustang ----> Insert lame bragging picture here: (Don't mind the skinny-ness. I was 16 at the time.)
I was considering stroking a 302 out to a 347. A stock 302 has a rod ratio of 1.696:1 ------- A 347 would put the block at a 1.588:1 ratio. So I actually decided against stroking out the engine because I was more concerned with durability than power. (Actually I went with a 289, but thats a different story. Long story short, I was "persuaded" by my parents to save money for college. And by "persuaded" I mean "Listen to me or else.")
A stock 4.0L (241.5 cubic inches; 3.875" bore) has a 6.123" rod and a stroke of 3.413" so its rod ratio is 1.794
A stock 4.2L (258 cubic inches, right?) has a 5.875" rod and a 3.895" stroke so its rod ratio is 1.508.
As you already know, most guys who build their own "poor man's" stroker out of the 4.0L get the 3.895" stroke crankshaft from the 4.2L engine. On a 4.0L engine with the stock 6.123" rods and 3.875" bore, the stroker crank increases displacement to 276ci (4.5L). This gives a rod ratio of (6.123 / 3.895) = 1.572.
There are many ways to get around a "bad" rod ratio, but with them comes increased cost. Here's some real good stroker information. Definitely Google around and read up:
Jeep Stroker Motor Information
Jeep Strokers • Dynamic\Static Compression Ratio Calculator
From Junker to Stroker