Mine is just a hair under 11-1 and I drive it around on 87. I do pop for 91 when I race it though.
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| Compression on 87 Octane??? https://www.slantsix.org/forum/viewtopic.php?t=11177 |
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| Author: | slanter6 [ Mon Dec 13, 2004 4:00 pm ] |
| Post subject: | Compression on 87 Octane??? |
how much compression can a slant take running on average 87 octane. i know some 87 octane is better than others but i was curious how much compression i could run and stay on 87 and not get into any engine probs. |
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| Author: | Dennis Weaver [ Mon Dec 13, 2004 5:11 pm ] |
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I'd say stick with the stock /6 CR to run "regulator" unleaded... D/W |
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| Author: | slantzilla [ Mon Dec 13, 2004 8:06 pm ] |
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Mine is just a hair under 11-1 and I drive it around on 87. I do pop for 91 when I race it though.
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| Author: | sandy in BC [ Mon Dec 13, 2004 9:48 pm ] |
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If you are talking stock cam Mr Weaver is right. With a big Cam Mr Schumers is right. I am trying a 264 cam and 9:1. It is about cylinder pressure/valve overlap. |
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| Author: | Dennis Weaver [ Mon Dec 13, 2004 10:23 pm ] |
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I've got the same (264) cam and 9.14:1 in my Duster. To run the optimal timing and not spark-knock, I have to run "super" unleaded - I probably could get by on "plus" for 'round town driving, but definitely not 87 octane regular. Of course I could probably detune the timing and run whatever crap-gas I wanted, but I don't want to be monkeying with my timing all the "time"  .D/W |
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| Author: | slanter6 [ Tue Dec 14, 2004 9:01 am ] |
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ive heard only good things on here about the 252 and 264. my cam choice will be between these two cams. how much compression could i safely run on these cams and run the cheap stuff? i was thinking of running about 9:1 cr, but would go higher if i could. i know there are casting differences and all that business, but what is a good general rule of thumb about how much to shave the head/block to boost compression to 9:1, 9.5:1 or 10:1? would upgrading from points to electronic ignition and a box like a msd or mallory allow me to run higher compression? |
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| Author: | Dennis Weaver [ Tue Dec 14, 2004 10:27 am ] |
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With those cams, I'd definitely keep it 9:1 or less. D/W |
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| Author: | Pyper6970 [ Sun Jan 02, 2005 6:32 pm ] |
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I have got 9.3:1 CR in my slant, I have done extensive head work and she is great, zero detonation. I too put in 91 on special occasions and still pulls me around 15mpg |
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| Author: | Doctor Dodge [ Sun Jan 02, 2005 10:45 pm ] |
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Good head work with deburred combustion chambers helps a lot. You don't have to polish the chamber, just get-off all the rough stuff and any sharp edges that can super-heat, especially around the exhaust valve. http://www.slantsix.org/parts/list/engi ... ockets.jpg You also need to check the combustion chamber "CC" volume to be sure all the chambers are the same size. Also check the block deck to be sure it is parallel with the crank, I have seen this way off. Doing these things ensures that all the cylinders have the same compression ratio. Other areas of concern: -Cool and even engine temps, especially the cylinder head temp. up at cylinders #1&2 -Even fuel distribution to all cylinders. All it takes is one cylinder to ping and you have reached the limit, even if the other cylinders still have a long way to go before they pre-ignite. Do all the "tricks" and you can run 9 to 9.5 compression with a "short" cam and regular fuel. DD |
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