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By 59flatbedford - 15 Years Ago
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ok so from what i have found standard 292 rod journal sizes are 2.188 with a 3.3 stoke. now if you offset grind to 2.000 journal sizes it is roughly 3.48 stroke. If this is correct that means that by taking .188 off the journal size you pick up .18 increase in stoke. Close to a one to one correlation. Now is this really the case? im wondering as im thinking about trying to stroke my 2.9l v-6 in my ranger by offset grinding the crank from 2.125 rod journals to either 2.000 or 1.8999 journal sizes. im trying to figure out roughly how much stroke that would gain me first to see if it would even be worth it and if i could find parts that are made close enough that i could modify them to work. If i can figure out what stoke i would be looking at i could see if i could find a rod that would work and a piston that would work. thanks and i hope you don't mind the off topic motor but i figure you guys have more experience with offset grinding than anyone else and this general information could be useful to y-blocks as well. Thanks guys.
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By charliemccraney - 15 Years Ago
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It will move the centerline of that rod journal .094" from the centerline of the main journals. So the old radius (1.65") plus .094" = the new radius (1.744"), diameter is twice the radius so the new stroke is 3.488"
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By John Mummert - 15 Years Ago
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The math is correct but the easiest way to increase the displacement of a 2.9 is to go buy a 4.0. Same basic block. A friend put a 4.0L in his 86 Bronco II.
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By 59flatbedford - 15 Years Ago
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yea i relize it would be much easier and cheaper to swap a 4.0 in but i already have an extra 2.9l i can experiment with and i like experimenting with what i have. now this brings me to my next question. I have a rough estimate on stroke now how do i figure out what length of rod and piston compression height i need. I know the deck height from center line of the crank, and now i know an estimate of the stroke. Im assuming i would take half the stoke plus the length of rod plus the compression height of the piston and that would equal the deck height. Is this right or do i need to factor in some other things.
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By pegleg - 15 Years Ago
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By the time you find the correct length rod's or pistons,(and pay for them) the 4.0 will be a WHOLE lot cheaper and easier.
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By mctim64 - 15 Years Ago
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The 4.0 would be cheeper but when I had a 2.9 in my Ranger I always wanted to experiment with different bore/stroke combos so I can see what you are getting at. Have fun, but when you get frustrated buy the 4.0  .
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By 59flatbedford - 15 Years Ago
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So i have another question now. Would it generally be safe to take a aftermarket rod with .927 wrist pin hole and ream it to take a .945 wrist pin. That would be a total of .018 which isn't really a whole lot only .009 all the way around. Do most aftermarket rods like scat and eagle have enough meat in the pin end to do this. Keeping in mind this is NOT a 700 horse race motor more like 200 or a little over. If so i might just be able to make this work if im adding all this up right.
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By mctim64 - 15 Years Ago
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59flatbedford (6/23/2010)
So i have another question now. Would it generally be safe to take a aftermarket rod with .927 wrist pin hole and ream it to take a .945 wrist pin. That would be a total of .018 which isn't really a whole lot only .009 all the way around. Do most aftermarket rods like scat and eagle have enough meat in the pin end to do this. Keeping in mind this is NOT a 700 horse race motor more like 200 or a little over. If so i might just be able to make this work if im adding all this up right.I don't think that would be a problem.
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By Ted - 15 Years Ago
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59flatbedford (6/22/2010)
.....now this brings me to my next question. I have a rough estimate on stroke now how do i figure out what length of rod and piston compression height i need. I know the deck height from center line of the crank, and now i know an estimate of the stroke. Im assuming i would take half the stoke plus the length of rod plus the compression height of the piston and that would equal the deck height. Is this right or do i need to factor in some other things.Here’s a link to a past thread covering the deck height calculations. http://www.y-blocksforever.com/forums/Topic8010-3-1.aspx
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By 59flatbedford - 15 Years Ago
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ok thanks for that link that helps me out a bunch turns out i was adding everything up. Also thanks for the reassurance on the rods. So far i think with a little bit of tweaking i might be able to pull this off i just have to calculate my compression ratio as im a little worried its gunna be really high. The way my math is working i can use a 2.9l piston and a 5.850 rod with 2.000 journals and if i ream the rods and take about .013 of the top of the pistons and .008 off the deck just to clean it up ill end up with right at zero deck. The pistons are dished so that might help with the compression. Now i need to see if im calculating the dish correctly. The silvolite website lists them as having a 2.42X.300 recess. Now pi*r^2*.3 to give me the volume gives me 1.37988 cubic inches. Now converting to cc give me 1.37988*16.387 which would give me 22.6cc dish. Now i don't think this could be right. that seems like a huge dish and it would drop my compression to below standard 2.9l levels. What am i doing wrong here.
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By Ted - 15 Years Ago
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59flatbedford (6/24/2010)
.....The silvolite website lists them as having a 2.42X.300 recess. Now pi*r^2*.3 to give me the volume gives me 1.37988 cubic inches. Now converting to cc give me 1.37988*16.387 which would give me 22.6cc dish. Now i don't think this could be right. that seems like a huge dish and it would drop my compression to below standard 2.9l levels. What am i doing wrong here.Your math for the dish looks correct as I get the same 22.6 cc’s.
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By 59flatbedford - 15 Years Ago
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yea i did it several times but there must be a misprint or something and its suppose to be .030. surely the dish is not over a quarter of an inch deep. heck my heads only have a 43cc chamber the piston cant have half that big of a dish. That and if i plug that into the compression it gives me like 7.somthing to 1 compression at zero deck so that cant be right. not sure might just have to call them and check.
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By John Mummert - 15 Years Ago
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Maybe a 2.8L piston will work. Same bore, same wrist pin but it is a flat-top. Pin ht. is 1.511 instead of 1.527". Rings are a little funky at 2.0 2.5 4.0mm. 2.9L rings are 1.6 1.75 3.5mm
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By 59flatbedford - 15 Years Ago
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yea i was looking at the 2.8 pistons too. i need to redo some calculations as the deck height i was using was wrong so that changes things considerably. The only worry i have with running flattops is keeping the compression to usable levels. zero decked with only 43cc combustion chambers might run it up a little high with flattops. im still in the research phase but im having fun, and this is going to help me when i go to build by 292. Im also waiting to get a big end width measurement so i can keep that in mind too.
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