Maximum Compression for 91 Octane
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Road Warrior
Joined: Apr 2010
Posts: 1,255
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From: Superior, WI
Maximum Compression for 91 Octane
I'm starting to look at perhaps some motorwork beyond Stage 1. One of the self imposed constraints I have identified is that it has to be able to run on 91 Octane pump gas.
What is the highest compression I could build into the engine to safely operate on 91? 10:1?
Thanks.
What is the highest compression I could build into the engine to safely operate on 91? 10:1?
Thanks.
Road Warrior
Joined: Dec 2008
Posts: 1,639
Likes: 2
From: Australia
http://www.daytona-sensors.com/tech_tuning.html
Raising compression by 1 unit (ie from 10:1 to 11:1) increases power by about 3%, assuming you dont have to retard timing to stop knocking.
In reality 10:1 is about right for street, you can go higher (mine is 11:1) but the gain isnt huge and you risk knocking.
Raising compression by 1 unit (ie from 10:1 to 11:1) increases power by about 3%, assuming you dont have to retard timing to stop knocking.
In reality 10:1 is about right for street, you can go higher (mine is 11:1) but the gain isnt huge and you risk knocking.
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Road Captain
Joined: Jul 2008
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Cam overlap will bleed of static compression and bring compression ratios as high as 11:1 to a point where you can run pump gas, but at the same time it moves the power band up the rpm scale and you lose some bottom end power.
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Tourer
Joined: Jun 2007
Posts: 269
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From: Eastern Ohio
Troy is right. The static compression isn't the be all and end all to determining required octane. Cam timing plays a huge role. Also the efficiency of the combustion chamber comes into play as does the rest of the intake system (and the exhaust too if you get picky.)
Doug Coffee at HQ can get 11.5:1 to run on pump gas. As with anything near the edge, there are lots of IFs, ANDs & BUTs attached.
Doug Coffee at HQ can get 11.5:1 to run on pump gas. As with anything near the edge, there are lots of IFs, ANDs & BUTs attached.