There are 2 generations of 2.5 piston. One is all it's own, and one is the same as a 2.2 piston. IIRC, the 2.5 that is all it's own will sit .220" or so lower in the hole.
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| 2.5L Piston question https://www.slantsix.org/forum/viewtopic.php?t=25199 |
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| Author: | Crazy Dart [ Thu Oct 04, 2007 11:20 am ] |
| Post subject: | 2.5L Piston question |
I have read and been told that the 2.2L piston will work in the slant 6 with the 198 rod. I have seen that some are using the 2.5L piston? What is the difference between the 2.2L and 2.5L piston? Is there an advantage/ disadvantage to using one or the other? |
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| Author: | Joshie225 [ Thu Oct 04, 2007 11:32 am ] |
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Is it safe to assume you read Doug's article on stroking the slant? http://slantsix.org/articles/stroking/stroking.htm For the later common block engine the 2.5 piston is shorter. I would swing by www.kb-silvolite.com and look at the various 2.2/2.5 pistons to see the differences. You can search by engine or diameter (3.445" for both 2.2 and 2.5). I came across some early 2.5 pistons which are very similar in configuration to the '86 and later turbo 2.2 piston which is 1.573" compression distance with a dish and valve reliefs. They were cheap so I bought 8 for my next engine build. |
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| Author: | blasphemous [ Thu May 15, 2008 2:57 am ] |
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I've been searching for information on using these pistons. This is the closest I've gotten so far. What's the difference in the compression heights? 1.573" as opposed to what? What is the expected compression ratio for either piston? |
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| Author: | slantzilla [ Thu May 15, 2008 9:44 am ] |
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There are 2 generations of 2.5 piston. One is all it's own, and one is the same as a 2.2 piston. IIRC, the 2.5 that is all it's own will sit .220" or so lower in the hole.
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| Author: | DionR [ Thu May 15, 2008 10:22 am ] |
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Quote: There are 2 generations of 2.5 piston. One is all it's own, and one is the same as a 2.2 piston. IIRC, the 2.5 that is all it's own will sit .220" or so lower in the hole.
That doesn't make any sense to me. The 2.2/2.5 share the same block and rods, but the 2.5 has a longer stroke. The piston should be shorter, and probably have a bigger dish.Don't know, could be wrong. Just doesn't seem logical. |
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| Author: | Doc [ Thu May 15, 2008 10:42 am ] |
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Here a link to the spec sheet on the 2.5 piston, 1986 - 88 http://kb-silvolite.com/spistons.php?ac ... ls&S_id=33 Here is the later 1989 -95 version, it is a much shorter piston. (.221 shorter) http://kb-silvolite.com/spistons.php?ac ... s&S_id=524 And another 2.5 piston that is even shorter and has a bigger dish. http://kb-silvolite.com/spistons.php?ac ... ls&S_id=35 And for a final "cross-check", the specs on the KB version of the 2.2 piston. http://kb-silvolite.com/performance.php ... s&P_id=133 You will need to know your block's deck height and cylinder head combustion chamber size to calculate appx compression ratios. DD |
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| Author: | DionR [ Thu May 15, 2008 2:29 pm ] |
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That answers my question. The pre-89 2.5 and 2.2 pistons are almost the same. In '89 when they went to the common block, the 2.5 piston got significantly shorter. So, Dennis is right, if you pick the correct year of 2.5. Just as an FYI, from everything I've seen on the TurboDodge side of things, avoid the later cast 2.5 pistons if at all possible. If you plan on using '89 and up 2.5 pistons in a high hp motor, step up to forged. The piston is short and the ring lands are too fragile to stand up to much detonation. Might work in an non-boosted application, but I wouldn't waste the money if the setup could see any pinging. Just a thought. |
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| Author: | DionR [ Thu May 15, 2008 2:32 pm ] |
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 Public appology; Dang Dennis, I guess I didn't read your post very well. What you said is correct the second time I read it. Guess I should read twice before I speak. I apologize. I thought you were wrong, and for that I get to eat crow. 
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| Author: | slantzilla [ Thu May 15, 2008 5:13 pm ] |
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Quote: Public appology; Dang Dennis, I guess I didn't read your post very well. What you said is correct the second time I read it. Guess I should read twice before I speak. I apologize. I thought you were wrong, and for that I get to eat crow. The only reason I know there is a difference is because I built a 2.5 for a buddy last year and the machine shop gave me the wrong generation pistons the first time. I had a positive deck height of almost .220". The pistons also used the same ring set as the 2.2, so I did end up with 4 extra ring sets for my junk.  The 2.5 pistons use their own ring package.
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