SoCal Jet Boats

Tech Talk => Engine Mechanical / Electrical => Topic started by: Tikotiko on June 29, 2020, 05:38:50 PM

Title: Octane choice
Post by: Tikotiko on June 29, 2020, 05:38:50 PM: Quick question. I got into a discussion today at work. This dude was telling me he has to run 91 octane on his stock 460 for his boat. I told him i run 87 because the previous owner told me thats what he ran and it doesnt matter if I put in it, its gonna eat it up regardless.
I have a 460 with a rv cam. What should i be running but most importantly Why?
I dont know anything about my compression thanks guys

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Title: Re: Octane choice
Post by: angermgmt on June 29, 2020, 05:41:51 PM: Compression?

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Title: Re: Octane choice
Post by: Tikotiko on June 29, 2020, 06:03:27 PM: Quote from: angermgmt on June 29, 2020, 05:41:51 PM
Compression?

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I wish i knew

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Title: Re: Octane choice
Post by: angermgmt on June 29, 2020, 06:22:04 PM: Be safe go 91

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Title: Re: Octane choice
Post by: Tikotiko on June 29, 2020, 06:52:17 PM: Quote from: angermgmt on June 29, 2020, 06:22:04 PM
Be safe go 91

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Ok will do thank you

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Title: Re: Octane choice
Post by: Tikotiko on June 29, 2020, 07:02:48 PM: Quote from: angermgmt on June 29, 2020, 06:22:04 PM
Be safe go 91

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Found some info on the cam. 8.4.1 compression ratio.

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Title: Re: Octane choice
Post by: FordLover on June 30, 2020, 11:17:02 AM: Quote from: angermgmt on June 29, 2020, 06:22:04 PM
Be safe go 91

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Yep. 91 in a boat for sure.

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Title: Re: Octane choice
Post by: 96Laveycraft21Xt on June 30, 2020, 12:10:26 PM: my factory marine power 454 has " 8:0 " compression. more likely 7.8. i always run 87 no problems there.

The ONLY way to know what you need, is to know your compression.

you can also do a compression check to get a feeling for cylinder pressure and work backwards with the cam from there.

and for all those that say "always 91 in a boat" just remember that if you dont have enough compression, the motor will actually perform WORSE with the higher octane.

Second - altitude makes a big difference too as the air, and therefore compressed air is less dense. Thats why places with high elevations offer 85 octane fuel at the pumps.

where are you boating?
Title: Re: Octane choice
Post by: Tikotiko on June 30, 2020, 01:17:59 PM: Quote from: 96Laveycraft21Xt on June 30, 2020, 12:10:26 PM
my factory marine power 454 has " 8:0 " compression. more likely 7.8. i always run 87 no problems there.

The ONLY way to know what you need, is to know your compression.

you can also do a compression check to get a feeling for cylinder pressure and work backwards with the cam from there.

and for all those that say "always 91 in a boat" just remember that if you dont have enough compression, the motor will actually perform WORSE with the higher octane.

Second - altitude makes a big difference too as the air, and therefore compressed air is less dense. Thats why places with high elevations offer 85 octane fuel at the pumps.

where are you boating?
Lake perris and hopefully the river soon

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Title: Re: Octane choice
Post by: 96Laveycraft21Xt on July 01, 2020, 04:59:41 PM: Nice! maybe ill see you at Perris soon, if they dont close it back down

for reference, at the same temp - say 100*f , my boat will pull about 100 - 150 rpm less at Perris then at Parker. Pulls 250 rpm less at Powell then Parker.