258 connecting rod vs. 4.0

[dwg86]

I took some pictures of a 258 and a 4.0 rod & piston in a 4.0 block with a 258 crank. I was trying to show how far the piston comes out of the bottom of the bore.

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[dwg86]

more pics

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[dwg86]

rod squirt hole sprays directly on cam

[John]

Great photos, the last ones also nicely shows our cam lobe lubrication, the galley feeds the slinger and gets in the area of our cam.
John

[oletshot]

Cool pics, unfortunately they may fool you a little, as that piston and 4.0 rod would hit the head on the top side (assuming those aren't custom or KB stroker pistons). If we could see, lets say, a silvolite 2229 on a 4.2 rod next to a KB stroker piston on the 4.0 rod and compare how they differ, then you would be comparing a working combo to a working combo. Not knocking your pics, just wanted to point out that different pistons have different skirts and the picture may change some with the the other combo.

For those who didn't know the 4.2/258 rod will pull the piston out of the bore at bottom dead center than the 4.0 rod will, the caption under the first pic is backward and should read 258 left, 4.0 right. Still not flaming, just clearing it up for a beginner.

[oletshot]

I failed to notice the picture is showing the wristpin location, which is more important than how much of the skirt is sticking out of the bore. Since the pistons ARE THE SAME, you can see that there is a 1/4" more of the piston showing on the 4.2 rod which means the pin is a 1/4" lower in the bore, allowing the piston to rock more. Sorry, I got hung up on what I thought I saw and failed to look at the whole picture.

If you still have it together, does the piston on the 4.2 rod rock alot more than the one on the 4.0 rod?

[amcinstaller]

can we see the same comparison from the top side??

nice pictures!

[dwg86]

I used the stock 4.0 piston. Thats all I have to use for a comparison. Yes, I can get any pics that you guys want...using what I have. Unless someone has any old or damaged pistons that you can send me.

I am in Vegas right now. My wife brought me here for my birthday. Just shoot me some PM's of what you want to see, and I'll try to get the pics that you need when I get back home. I will also post some pics of the stock cam compared to the Engle cam that I have(compared to each other and in the block).

[Mgardiner1]

I am in Vegas right now. My wife brought me here for my birthday.

Happy Birthday Dave!

[dwg86]

Thanks Mike...I am getting old... 41!!!! Although its better than not making 41.

[dwg86]

Cool pics, unfortunately they may fool you a little, as that piston and 4.0 rod would hit the head on the top side (assuming those aren't custom or KB stroker pistons). If we could see, lets say, a silvolite 2229 on a 4.2 rod next to a KB stroker piston on the 4.0 rod and compare how they differ, then you would be comparing a working combo to a working combo. Not knocking your pics, just wanted to point out that different pistons have different skirts and the picture may change some with the the other combo.

For those who didn't know the 4.2/258 rod will pull the piston out of the bore at bottom dead center than the 4.0 rod will, the caption under the first pic is backward and should read 258 left, 4.0 right. Still not flaming, just clearing it up for a beginner.

Yes you are right, the piston/rod combo on the left is the 258. Good catch.

You are also right on the 4.0 piston/rod combo coming out of the top of the block with the 258 crank. I just threw this together to try to figure what piston/rod combo I am going to use. I wanted to compare the location of the piston pins in the bore at BDC. So I put just the rods on the crank first. Then I put the stock pistons on both rods to try to compare piston rock. Wouldn't the taller compression distance help offset the piston rock caused by the shorter 258 rod? Yes I would need a KB or custom piston for a accurate comparison. I know the longer rod is better for less piston side loading, and the longer rod is a better way to go...no argument there. But the difference in rod ratio is so small(1.51vs1.57) I wanted to see how they compare. I don't need a high dollar forged piston for an every day driver, but I also want to build an engine that last.

One more thing...I am no engineer, but I have seen more side loading on most V8's that I have built as compared to the Jeep inline 6.

[amcinstaller]

yea, i wasnt thinking that that would cause much issue either (pistons being "so far down"). but then again, i dont build engines. i have seen, however, on a honda engine that was bored out the guy got this thing he called a piston saver. it was to kind of counteract the piston being too far out of the bottom of the bore. wonder if one could be made for this engine? it looked like a set of rings (all one piece) that mounted to the bottom of the bore, effectively lengthening them.

[oletshot]

Yes you are right, the piston/rod combo on the left is the 258. Good catch.

You are also right on the 4.0 piston/rod combo coming out of the top of the block with the 258 crank. I just threw this together to try to figure what piston/rod combo I am going to use. I wanted to compare the location of the piston pins in the bore at BDC. So I put just the rods on the crank first. Then I put the stock pistons on both rods to try to compare piston rock. Wouldn't the taller compression distance help offset the piston rock caused by the shorter 258 rod? Yes I would need a KB or custom piston for a accurate comparison. I know the longer rod is better for less piston side loading, and the longer rod is a better way to go...no argument there. But the difference in rod ratio is so small(1.51vs1.57) I wanted to see how they compare. I don't need a high dollar forged piston for an every day driver, but I also want to build an engine that last.

One more thing...I am no engineer, but I have seen more side loading on most V8's that I have built as compared to the Jeep inline 6.

I agree, longer rod is better, and if cost isn't a factor, it's the way to go. Seems to be way more stroker failures caused by valvetrain than using the 4.2 rod. That's good news for me because I'm using the 4.2 rods. Like I said in my second post, I got caught up in what I didn't see in the pictures and failed to see what was really there. Thanks for the pictures.

Oh yeah, you're right 41 beats the alternative, happy belated birthday from another 41 year old Dave.