compression ratio, octane, ignition lead

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dan miller

compression ratio, octane, ignition lead

Post by dan miller » Sat Apr 30, 2011 8:05 pm

This year, EMC provides Q16 fuel, and the compression ratio is unrestricted.

Several in our group (including me) wanted approximately 16:1. Several in our group (including Gene Adams) wanted approximately 12.5:1, but were "OK" with a little more. Turns out that it's a moot point, as we're limited to high 13's:1 due to our piston of choice (Ross "392" forging).

Detonation shouldn't be an issue, as early hemi's on both methanol and gasoline seem to run best at between 26-30 degrees lead.

As the compression ratio goes up, so does the dome, which might be detrimental. Also, I suspect that as the compression ratio goes up, there are diminishing returns.

Can anyone 'splain all this to me? What might be the range of the optimal compression ratio? How much, if anything, are we "leaving on the table"?

It should be noted that Q16 has a considerable methanol content, or so I've been told. It's not the same fuel (nor legal) as run in NHRA gas classes like pro stock, that utilize compression very high compression ratios.

It's a mystery. lol

Thanks, Danny

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Re: compression ratio, octane, ignition lead

Post by bigjoe1 » Sat Apr 30, 2011 8:39 pm

I* have seen a 30 HP increase using the Q -16 race gas with 15 to one compression. With 13.5 to one , the gains were somewhat less. It seems you need high compression to reap a large increase from the fuel. I was surprised and impressed too


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Re: compression ratio, octane, ignition lead

Post by 900HP » Sat Apr 30, 2011 9:05 pm

Joe, I have heard that people who run Q-16 have seen the cylinder walls get very hard to the point where they are difficult to hone. I have heard this is because of some of the chemicals in the fuel. Have you seen this?
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Re: compression ratio, octane, ignition lead

Post by bigjoe1 » Sat Apr 30, 2011 9:38 pm

I have not seen anything like that so far. Again, I am impressed with the increase in performance, just from the gas itself. I have not seen any ill effects.


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Re: compression ratio, octane, ignition lead

Post by Adger Smith » Sun May 01, 2011 1:46 am

557 jet boat engine. 14.2 compression, properly jetted , worth 40 hp over c-14... HP peak developed below 7,200.
Use it quite a lot in Boat racer engines. Nothing negative about it except corrosion. Not sure what the oxidizer compound is. I don't think it's methanol.
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Re: compression ratio, octane, ignition lead

Post by RCJ » Sun May 01, 2011 8:05 am

Never used q-16 ,but I have lost power when going to 116 octane.I was guessing I didn't have enough c/r to support that octane

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Re: compression ratio, octane, ignition lead

Post by Adger Smith » Sun May 01, 2011 8:49 am

116 is designed for NOS. I've always lost power on NA engines with it. Not a N/A fuel. Burn rate is slower & designed to burn in a Nitrogen rich environment, is my assumption.
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Re: compression ratio, octane, ignition lead

Post by dan miller » Sun May 01, 2011 9:25 am

Thank you, everyone. Good info. Danny

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Re: compression ratio, octane, ignition lead

Post by rfoll » Sun May 01, 2011 11:42 am

In regards to the diminishing returns for increasing cr, I was told that eventually at higher levels the chemistry involved produces new molecules that absorb heat energy and send it out the exhaust. I imagine the fuel used will be the determining factor.
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