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Author Topic: Fuel octane and compression ratio  (Read 5614 times)
baz
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« on: June 17, 2019, 21:39:57 pm »
I've built my motor with 10.5 cr with the plan to run it on super unleaded 98 octane. I've only realised today you can no longer buy this fuel in this country!

Am I going to be OK with 95 octane? Or is there any effective octane booster I could add?
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baz
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« Reply #1 on: June 18, 2019, 08:40:11 am »
I need to pick up some fuel today or tomorrow for this, I have the option of driving 3 hours to Northern Ireland which I believe still sells 98 octane.
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Rocket Ron
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It's old school for a reason
« Reply #2 on: June 18, 2019, 09:40:18 am »
Demon tweets sell this that treats up to 10 gallons

The vp brand is what a lot of racer use for their race fuel

https://www.demon-tweeks.com/uk/vp-racing-madditive-octanium-petrol-octane-booster-vpr2855/
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baz
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« Reply #3 on: June 18, 2019, 12:49:48 pm »
Thanks Ron I'll try get hold of some.
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BeetleBug
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Snabba grabben...
« Reply #4 on: June 18, 2019, 13:07:49 pm »
10.5 CR with 95 octane should be possible but it depends on your camshaft. Which one are you using?

-BB-
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baz
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« Reply #5 on: June 18, 2019, 17:18:42 pm »
It's a raptor 00808 263 duration and 9.64 lift, I'm running 1.4 rockers that are more like 1.45
« Last Edit: June 18, 2019, 17:20:55 pm by baz » Logged
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Joel Mohr
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« Reply #6 on: June 18, 2019, 17:30:27 pm »
If the chambers were Hemi cut, you could run it on 93....I've gone as high as 11.2 on 91 with Hemi cut chambers that Clyde Berg detailed....
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baz
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Posts: 772
« Reply #7 on: June 18, 2019, 18:01:46 pm »
No hemi cuts, the heads are 42x37 with 54cc chambers. I'm running efi if that makes any difference.
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Richierich56
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« Reply #8 on: June 18, 2019, 23:22:02 pm »
My motors 10.2 and runs ok with standard unleaded - if/when I can't get the 99 octane Shell V power or whatever. 
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BeetleBug
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Snabba grabben...
« Reply #9 on: June 19, 2019, 10:39:49 am »
Quote from: baz on June 18, 2019, 17:18:42 pm
It's a raptor 00808 263 duration and 9.64 lift, I'm running 1.4 rockers that are more like 1.45

The lift is not related to your potential issue. I would give Johannes a call or email and listen to his advise. Personally I think you will be fine with 95.

As a reference, the 112hp VW WBX engine has 10.5 CR in combination with a low duration cam that builds cylinder pressure low down on the revs. You can run this engine on 95 octane without any issues. My current car has 11.6 CR and is also running fine on 95 octane but this engine has high duration cams and revs to 8000 rpms.

-BB-
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baz
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« Reply #10 on: June 19, 2019, 18:08:08 pm »
I'll ask johannes for his opinion, save second guessing.

If it needs 98 I'm gonna have to do a trip up north as I'd like to start the engine tomorrow, and nothing I order online to boost the octane will be here before Monday.
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Martin S.
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« Reply #11 on: June 20, 2019, 12:31:28 pm »
Back off the timing until it doesn’t ping.
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baz
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« Reply #12 on: June 24, 2019, 12:24:58 pm »
Johannes says 95 will be fine so long as I go easy on the ignition curve.
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