I have 2.2 turbo pistons with 198 rods. No decking on the block, head was cut around .010" for straightness.
Cutting .125" off the block and .100 off the head will get you around 11-1 with stock pistons/rods I believe.
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| hey slantzilla- compression question https://slantsix.org/forum/viewtopic.php?t=14185 |
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| Author: | sick6 [ Sun Aug 28, 2005 3:49 pm ] |
| Post subject: | hey slantzilla- compression question |
I know you are running an 11 to 1 compression mill, and this is around the compression I was shooting for. did you just put in higher compression pistons, or did you get it up there by milling a ton? yes, I realize chamber volume has everything to do with this, but I was wondering how high just milling will take the ratio. what cubic inch block did you start with? I probably need to get special length pushrods anyway, so I was wondering how far you can take it with just millwork. |
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| Author: | slantzilla [ Sun Aug 28, 2005 6:02 pm ] |
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I have 2.2 turbo pistons with 198 rods. No decking on the block, head was cut around .010" for straightness. Cutting .125" off the block and .100 off the head will get you around 11-1 with stock pistons/rods I believe.
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| Author: | argentina-slantsixer [ Sun Aug 28, 2005 6:29 pm ] |
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hey slantzilla. do the 2.2 pistons have the wrist pin offset like the OEM stuff? wich grade do you use? 92, 95, 98 octane? advance curve? thanks Also: head gasket? composite? steel? |
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| Author: | sick6 [ Mon Aug 29, 2005 12:05 pm ] |
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I was also wondering about the head gasket too, (how much distance, and compression) are you losing using the newer aftermarket gasket? |
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| Author: | slantzilla [ Mon Aug 29, 2005 6:44 pm ] |
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I use a Fel-Pro gasket. How much compression am I losing? I never really worried about it. I do have a handful of steel shim head gaskets, but I would only use them on a freshly machined deck and head, not the old junk I run. I am not really sure about the offset either. Mike tells me which way the piston points and that's how they go in the hole. 
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| Author: | sick6 [ Tue Aug 30, 2005 2:03 pm ] |
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Quote: Cutting .125" off the block and .100 off the head will get you around 11-1 with stock pistons/rods I believe.
anybody else want to confirm this too? I am sending mine off to the machine shop soon......
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| Author: | 1969ron [ Wed Aug 31, 2005 6:18 am ] |
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bump. hi, i'm also looking for a resonse from doc. ron |
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| Author: | sick6 [ Thu Sep 01, 2005 1:59 pm ] |
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anybody? |
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| Author: | Ron Parker [ Thu Sep 01, 2005 6:08 pm ] |
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Gary told me he milled my head 125 thousand and 100 off the deck and were shooting for 11.5 but the forged Venola pistons had such big valve cuts in the top we were around 11 to 1. Thanks Ron Parker  Hey Has That Thing Got A Bagel Bamboozler In It |
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| Author: | Rob Simmons [ Fri Sep 02, 2005 12:29 am ] |
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sick6, I am no engine pro and have only built one performance 225, but through several conversations with Doug Dutra and my own experience... The only sure way to know what you are building is measure everything with precision tools that machine shops have. The factory tolerances for maching millions of engines varied enough that you could be off several thousandths from one block to the next. Reading what other people's experiences are certainly gets you into the ball park, but to be precise you really have to measure closely. I had to buy new pistons because 2 of the 6 I had were a little bigger around than the others. I already had the block and head milled, so when I got the replacement pistons and discovered that they were a little shorter than my first set I just sucked it up and settled for 9.6:1 compression ratio than my goal of 10:1. I could have had the head milled more, but I was in a time crunch and the head was already complete and ready to install. You're heard the expression "measure twice, cut once" in carpentry. It is true for machine work too! |
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| Author: | slantzilla [ Fri Sep 02, 2005 4:50 am ] |
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Rob, that is why I never do any machne work until all the parts are here. Been burned once too.
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| Author: | sick6 [ Fri Sep 02, 2005 6:19 am ] |
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I have been a machinist for tweleve years now, so I do understand it. I run CNC mills all day. I just wanted to know what would get me close. the consensus seem to be a total of .225 for millwork gets me around there (11 to 1). I already had .090 taken off my head, so that leaves .135 off the block to go. okey dokey. thanks guys- |
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| Author: | Doctor Dodge [ Fri Sep 02, 2005 6:29 am ] |
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Quote: sick6,
The only real way to know your final compression is to measure everything and calculate it. As Rob stated, the factory tolerances and piston heights are "all over the map".The only sure way to know what you are building is measure everything with precision tools that machine shops have. The factory tolerances for maching millions of engines varied enough that you could be off several thousandths from one block to the next... You're heard the expression "measure twice, cut once" in carpentry. It is true for machine work too! If you are building a race engine and don't care abnout having to run race fuel and you don't have the time, parts or equipment to do the mesurments / calculations.... then yes, go ahead and cut .100 to .125 off the head. For a real fast engine, you need to look at your camshaft "numbers" and even 'mock-up' the engine so you can test for cylinder pressure. Camshaft and valve lash has a big influance on low RPM cylinder pressure / low to mid speed power. Target 150 to 160 psi for a street performance and 175 to 185 psi for race. DD |
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| Author: | sick6 [ Fri Sep 02, 2005 2:33 pm ] |
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can you give me the mathmatical equation so I can do that? I would really like to..... head flow:  camshaft:  
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| Author: | Rob Simmons [ Fri Sep 02, 2005 2:56 pm ] |
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Hey 'Zilla, I had the .040 pistons in a box for several years and took them to the machine shop with the block. The assumption was, "Yep, cut it .040 for these pistons." Unfortunately, we found out a couple of them were out of round after the block was bored and milled. So the calculations we did for those pistons didn't quite work out the same when the new pistons were a couple thousandths shorter.  It was another one of many learning experiences building my first Slant 6 race car. hopefully it won't be the last. (Lesson, or race car  )
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