Lowering octane

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RCJ
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Lowering octane

Post by RCJ »

Dyno a motor on 91 then 87. Made more power on 87(8.5 cr).How can you lower the octane even more? Kerosene?
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Re: Lowering octane

Post by travis »

You can get 85 octane in Denver/Colorado Springs area...I would assume it would be available at other high elevation city’s
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Re: Lowering octane

Post by mt-engines »

RCJ wrote: Sun Oct 25, 2020 8:33 pm Dyno a motor on 91 then 87. Made more power on 87(8.5 cr).How can you lower the octane even more? Kerosene?
oil. that seams to do a great job at lowering octane
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Re: Lowering octane

Post by BOOT »

This a carb?
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Re: Lowering octane

Post by digger »

I’d be more interested in finding out the other differences in the ingredients. The octane just went along for the ride
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Re: Lowering octane

Post by RDY4WAR »

digger wrote: Mon Oct 26, 2020 2:18 am I’d be more interested in finding out the other differences in the ingredients. The octane just went along for the ride
Exactly. Was the 87 E10 and 91 was E-free?

Octane by itself doesn't make power. What was the timing curve with both fuels?
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Re: Lowering octane

Post by rebelrouser »

I would want to check the alcohol content of both fuels and do a specific gravity test. Then if the dyno had O2 sensors on it, look at the air fuel ratio. I have seen higher octane fuel make less power on several occasions, usually this is due to burn time differences, which could be made up for in ignition timing. If the fuels have difference specific gravities, maybe a slight jet change will be needed.
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Re: Lowering octane

Post by RCJ »

We’ve tried multiple timing curves,jets ,and pump gases. Non E 87 has always shown best. An over the counter fuel oxgenator Will add some power but hits the point of demising returns with only a few ounces . Trying think out side the box . What is the brand of the stations in Denver that have 85 and is it non ethanol?
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Re: Lowering octane

Post by RDY4WAR »

RCJ wrote: Mon Oct 26, 2020 7:40 pm We’ve tried multiple timing curves,jets ,and pump gases. Non E 87 has always shown best. An over the counter fuel oxgenator Will add some power but hits the point of demising returns with only a few ounces . Trying think out side the box . What is the brand of the stations in Denver that have 85 and is it non ethanol?
It's been the opposite for me. Testing it with 2 different engines, I found E10 93 made slightly (~1%) more power than E-free 93. The high heat absorption and low boiling point of ethanol means a cooler, denser intake charge entering the cylinders (with a carbureted engine at least).
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Re: Lowering octane

Post by Ks Fats »

"We’ve tried multiple timing curves,jets ,and pump gases. Non E 87 has always shown best." If all of this has been done then you have reached your sweet spot at non e 87; further reducing octane number will probably not render any improvement. Read David Redszus reply to the " 90 Octane Ethanol Free" post in the similar posts at the bottom of the page. There is more to consider than octane number; mix in the seasonal changes in blends (happens in non e also) and pump octane numbers don't really tell you much.
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Re: Lowering octane

Post by canuc »

I have only tuned with a butt dyno but have found that more octane than needed was not only a waste of money in a dd but could also be down on power . Had a yamaha dirt bike back in the seventies , thought I'd treat it to some premium , ran ok but actually felt it lost throttle response and overall zip . Next tank back to reg , and all was good . Have found the same with low compression vehicles . Need some science guys to help me here (or correct me) but believe the lower octane can have more btu ? heptane ...
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Re: Lowering octane

Post by travis »

RCJ wrote: Mon Oct 26, 2020 7:40 pm What is the brand of the stations in Denver that have 85 and is it non ethanol?
I don’t remember offhand...haven’t been there in a few years...but I remember it was everywhere. We probably have a few members in that neck of the woods...Vortecpro for one I think
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Re: Lowering octane

Post by RDY4WAR »

Octane has no effect on the fuel's burn rate and flame propagation. Going down to an 85 AKI probably won't show a difference either if both fuels have a MON of 82.
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Re: Lowering octane

Post by strokersix »

Add some diesel fuel... Can't speak from personal experience but I would try this first to lower octane rating of gasoline.

Whether this is the right approach for what you want to do is a different question as above posts are saying.
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Re: Lowering octane

Post by David Redszus »

digger wrote: Mon Oct 26, 2020 2:18 am I’d be more interested in finding out the other differences in the ingredients. The octane just went along for the ride
Exactly correct. Fuel octane does not have an affect on power. It does allow a more aggressive tuning while
avoiding engine destruction.

There is never a reason to lower fuel octane values.

The are several reasons to alter fuel composition and distillation curves.
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