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| Compression Ratio https://slantsix.org/forum/viewtopic.php?t=53731 |
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| Author: | 63dartdude [ Thu Oct 31, 2013 10:12 am ] |
| Post subject: | Compression Ratio |
I pulled the engine yesterday. And here are the measurements I got. BORE - looked to be 3.4375 STROKE - looked to be 4.375 GASKET - .039 looks to be a good number for it DECK HEIGHT - looked to be .1875 Now here is where I get lost - the ccs. I had the engine at TDC, with the piston as high as it would go. I greased around the hole, and put plexiglass with a hole on top. It was really easy to see when it filled up. So I am pretty confident on the number. That number came in at 38cc. I then went to the head, and poured into where the valves and spark plugs are. That ended up being at 53cc. So what kind of compression is that, if I got all my measurements okay. And is this the info I needed to get that? And do those numbers seem realistic? Thanks. |
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| Author: | CNC-Dude [ Thu Oct 31, 2013 11:00 am ] |
| Post subject: | |
Well since you already know your deck height and bore size, you really don't need to measure the volume of it, the compression calculator formula does that for you. Also, most all formulas assume a round bore in the head gasket, but any engines are not, so to get more accurate, you can also measure the bore of the gasket and calculate the volume of it as well if your using the long method of calculation. |
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| Author: | DusterIdiot [ Thu Oct 31, 2013 11:42 am ] |
| Post subject: | Lookin like... |
Just using the numbers provided it's at about 8.58:1 SCR (numbers vary by calculator).... stroke is a little long compared to typical 225's (you haven't had the crank modified right...?) if the crank is stock then it lands closer to 8.15:1. -D.Idiot |
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| Author: | Doc [ Thu Oct 31, 2013 11:46 am ] |
| Post subject: | |
The factory SL6 stroke is 4.125 The bore starts at 3.400 so it is likely .040 oversize? (3.440??) Go to: https://www.uempistons.com/index.php?ma ... ba0a36a2f7 That calculator give me 8.1 static compression using a .040 o/s bore & stock stroke. DD |
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| Author: | 63dartdude [ Thu Oct 31, 2013 12:05 pm ] |
| Post subject: | |
You are correct with the .040 over. The head has been milled .093 since I have gotten it. So I thought the compression ratio would be higher, not knowing how much it was milled before I owned the car. I just measured the stroke again. I get 4 inches, and 4/16, which is 1/4. My previous measurement had me at 3/8. I may have just miscounted last time. So that measurement should be 4.250. |
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| Author: | Joshie225 [ Thu Oct 31, 2013 12:57 pm ] |
| Post subject: | |
The stroke is 4.125" unless you've had the crankshaft modified. I had to mill the head of my '67 Valiant .080" just to get 8.5:1, but my deck height was -.167" so that's the big difference here. You will also want to measure the deck height with something accurate like a digital caliper or better yet a depth micrometer. 1/16" is not anywhere close enough. |
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| Author: | 63dartdude [ Thu Oct 31, 2013 1:11 pm ] |
| Post subject: | |
You had me check it again. And still I get 4.250 at both the 1 and 6 cylinders. As far as the crank goes, I bought this car used, and all the guy told me at the time was it was recently rebuilt. He may have modified the crank, but I didn't. Now how did you get a minus number on your deck height. Was your piston over the block top level? Mine was 3/16" deep. |
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| Author: | 63dartdude [ Thu Oct 31, 2013 1:12 pm ] |
| Post subject: | |
Oh yeah, it lands on the 16th mark perfectly. |
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| Author: | DusterIdiot [ Thu Oct 31, 2013 1:51 pm ] |
| Post subject: | Yep... |
Quote: Now how did you get a minus number on your deck height.
Technically true deck height is 0...anything over the top of the deck is positive and if the piston is in the hole it's negative...most online calculators just have you enter it as a positive number since they take into account the possible lack of math skill the user may have...If doing engine work mics and calipers are required as every .001 counts when you start cutting... -D.Idiot |
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| Author: | 63dartdude [ Thu Oct 31, 2013 6:01 pm ] |
| Post subject: | |
http://en.wikipedia.org/wiki/Chrysler_Slant-6_engine says that Stock Compression is 8.1 to 8.5. So that is why I am a little confused when the calculators say 8.1. Is there a way to figure out exactly what has been milled off the head, with 53 cc? A buddy of mine and I are believing .093 has been taken off, based on what the machine shops have told us. Who knows, if they gave us accurate numbers? |
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| Author: | CNC-Dude [ Thu Oct 31, 2013 6:04 pm ] |
| Post subject: | |
Most heads have an average of .006" removal equals 1cc of volume, so you can just work backwards from that and figure up how much .093" removes approx. |
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| Author: | 63dartdude [ Thu Oct 31, 2013 6:16 pm ] |
| Post subject: | |
I think with that info, I need to know what a stock CC amount is. Then subtract the 53 from that number, and divide that by .006. And that would say what has actually been taking off, if my thinking is straight. But I have so much on my plate right now, I don't trust my thinking that much. |
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| Author: | DusterIdiot [ Thu Oct 31, 2013 6:21 pm ] |
| Post subject: | It's... |
Quote: Stock Compression is 8.1 to 8.5. So that is why I am a little confused when the calculators say 8.1. Is there a way to figure out exactly what has been milled off the head, with 53 cc? A buddy of mine and I are believing .093 has been taken off, based on what the machine shops have told us. Who knows, if they gave us accurate numbers?
You have an overbore so that gives back some cylinder volume (hence the reason why you take a bit more off the deck when rebuilding the engine), a .020 overbore isn't too bad, but once you start into the .040/.060 you need to cut the deck to save some meat on the head...FYI the 1963 truck motor I use now as a 12:1 motor calc'd to 7:1 stock...it had a high 60's CC head and the deck height was deep in the hole...I cut .120 off the block and took a .120 cut off a late BL head that started at 54cc to get the SCR I wanted...So if the head was closer to 68cc and he whacked .093 (at .0066 per 1 cc reduction)...that's a 14 cc reduction to 54cc... -D.Idiot |
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| Author: | edd jesiolowski [ Thu Oct 31, 2013 10:27 pm ] |
| Post subject: | compression ratios |
I have milled an early model head .186 , deck the bock .120 was .040 in the hole head cc was 36 cc compression ratio was 13.179..............the new motor is real close to 14:1 with wiesco piston and k-1 rods the old motor had shot pean rods and i polished the beams and 675 grms piston it lasted 1200 pass my only promblem was chewing up oil pump gears so iI went witha daily oil pump and jones crank hub drive onthe new motor witch is real close to mark's except for the cam |
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