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Old 02-29-2012, 08:58 PM   #1 (permalink)
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New pistons, higher compression?

I have a Honda B18B1 motor in my Del Sol, which has a stock C/R of 9.2:1. I have a set of pistons laying around that would raise the C/R to 10.8:1.

From what I've read, I would stand a good chance of being able to run 89 octane safely at that compression (though we have 93 available). I'm not likely to do this any time soon, but do you suppose next time I pull my motor apart, it would be worth installing these high compression pistons? Would the potential need for higher octane fuel outweigh the efficiency gains? The cost difference between grades of fuel here isn't very large, often as little as 15 or even 10 cents.


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Last edited by Ecky; 02-29-2012 at 09:28 PM..
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Old 02-29-2012, 11:40 PM   #2 (permalink)
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consider running e15.

you have the basics understood. 9.2 seems pretty conservative, 10.8 kind of high.
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Old 03-01-2012, 07:16 AM   #3 (permalink)
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You'd get a theoretical efficiency improvement of ~5%, with a price hike of only 2-3% and if you already had the parts and enjoyed the labour, it would just about be worth it.
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Old 03-04-2012, 02:36 AM   #4 (permalink)
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i know the price of E85 is different all over the country.

but with its 105 octane and should it be about .50 cents less then 87 octane, it mite be about a wash to run E85. in terms of cost per mile..with the 10.8 to 1 compresson.
but should E85 only be .10 .20 cents less then pump gas its not worth the trouble......

with the lower 9.2 to 1 E85 would need to be more like a $1.00 a gal or so cheaper to be a wash.


any way its just an idea...
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Old 03-04-2012, 12:34 PM   #5 (permalink)
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I've been running on E10 or E15 already, there's only one gas station in town that has ethanol-free gasoline and it's a bit out of the way for me to fill up there regularly.

We don't have E85 in Florida (at least not in my area).


I'm a bit excited, if I tear down my motor (or maybe buy another B18, they're super cheap) there are a number of modifications I could do to improve economy. I have an extra set of cams that I could take to the machine shop, and have them mill down one of the intake cams to improve swirl, and a port and polish of the head couldn't hurt.
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Old 03-04-2012, 12:50 PM   #6 (permalink)
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swirl is vastly overrated. real world says air goes in on the downstroke, and so what if it swirls - it gets squished 10:1 on the compressoin stroke and the swirl all goes away.
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Old 03-04-2012, 06:12 PM   #7 (permalink)
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Er, I think swirl does help in mixing, but swirl tends to get fuel further from the spark plug or something like that...manufacturers are now going for tumble flow I think.
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Old 03-04-2012, 06:33 PM   #8 (permalink)
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...look up the definition of "homogeneous mixture" as applied in HCCI engines. That'll explain *why* swirl and it's "mixing" action are VERY important.
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Old 03-04-2012, 10:05 PM   #9 (permalink)
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you and I are not going to have much positive results playing with swirl unless you have a HUGE budget, unlimited dyno time, and a bunch of employees with not much to do.
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Old 03-05-2012, 12:05 AM   #10 (permalink)
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mabe this map will help?

E85 Stations in Florida

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