Using a 4.6 crank and con rods with 4.0L pistons - Page 2 - Defender Source
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  #21  
Old October 17th, 2014, 09:24 AM
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Chris Davis
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My wording was confusing--I ended up using 4.6 Pistons, slightly oversized (and bored block) from Real Steel. I wanted compression under 10:1 so I could use any octane currently available. When you are up in the high 10's to 11's, you typically need premium fuel so you don't pre detonate. For my miles, that is about $400-500 more in fuel per year and you gain a bit more reliability over the long haul... A hot engine, though, is hot-- if I did one today, I might sing a different song
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  #22  
Old October 17th, 2014, 10:00 AM
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Robert F
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They already require premium, so unless you are skimping on that there is no change in operating cost
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  #23  
Old October 17th, 2014, 11:12 AM
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Chris Davis
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Skimping implies that I am being cheap--but there is a difference between "cheap" and not throwing away money.

I don't use premium often. Sometimes, but not always. Not necessary on a 9.35:1 compression--maybe not even for 10.5:1 up at elevation (Im in CO). You just have to know WHY you are running premium. Premium has everything to do with knock and ping and, in some cars sometimes, power which I know some of you will SWEAR they feel a difference. Those that say it adds more power, that is only sometimes. Octane can also be raised with Ethanol which can lower your embodied energy of the fuel--so it doesn't always equate to more power. Some will say that cars run cooler with higher octane--which is true when you suffer from preignition, but I haven't seen any research that the higher octance, slower burning fuel will lower engine temps--I am very open to having my mind changed if you have some research to show me that I will over heat more with lower octane when I am running just fine (no preignition).

BUT, if you are running without knocking or pinging on regular unleaded, and you are running a regular 9.35:1 engine, I would say you are just tossing money away. I have run both premium and regular for 5 tanks of gas each while commuting my 30 miles to work each way when I had to commute in the 90. 60 miles a day. Logged gas mileage, noises and seat of pants power. Know what I found? I found that the premium cost me $35 more dollars and I got only slightly more MPG, and we are talking like .1 or .2.. That is just anecdotal evidence from my own experience. If you have any information that shows why I need to use premium, I would love to see it and I have always been open to changing my mind. I also run my timing pretty advanced--base idle is at 12 BTDC---which if you were even borderline, you couldn't do on regular without ping/knocking. And I tow. uphill. No pinging or knocking. Sometimes I still add premium when I am going to do something special, but I really don't notice much difference compared to the cost.

I dug in and found my original measurements of my engine on build up. Some of you enjoy it as you can compute what the different rod/piston/crank combinations may lead you to compression wise.

I have never felt that I skimp at the expense of quality--I just like to know that the quality is there and I am getting something for my dollars...
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BTW---for those that insist that octane = power, do a little research on fuel. It has nothing---nothing--- to do with the power of your fuel. It is also only really important if you have a knock sensor and then really only important if you experience any knock/ping at the maximum advance that your system is set to...
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  #24  
Old October 19th, 2014, 05:13 PM
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Chris Davis
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Just went camping and while towing our pop up camper on hard acceleration I did have some pinging on low octane-- perfect example of when higher octane is desired.
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  #25  
Old October 19th, 2014, 06:42 PM
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Sam
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I don't know the science behind it but my wife's Prius gets only 35mpg on low octane but 48mpg on the high octane (according to our tests).
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  #26  
Old October 19th, 2014, 10:07 PM
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shayne young
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It would not seem unreasonable to believe that you use less throttle for the same amount of work on a higher octane..??!!??
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  #27  
Old October 19th, 2014, 10:27 PM
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Chris Davis
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Newer cars (unlike mine with a distributer) that have knock sensors adjust timing to be right on the edge of pinging. For those it can make a big deal in performance. Makes sense for a Prius.

Shayne-- curious to know why you think this--- might be true but I don't see why and would find it interesting to know. Please note that higher octane fuel isn't any more powerful (common misconception)
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  #28  
Old October 19th, 2014, 11:30 PM
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shayne young
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Exactly the reasoning you put forth...unfortunately in this new age I am always thinking of the motronic versions and often forget that there are versions that don't have the ability to advance ignition to the utmost ranges..thereby using less throttle for a more powerful power stroke.. Higher octane allows more ignition advance constantly varied for the most out of every ounce of fuel..
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