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Chris
Dodge Dakota
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7/26/2005
18:38:45
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 Subject: cam upgrade
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hello,
When upgrading the cams to either the krc 200's or 206's is it necessary to run premium fuel (91+ octance)
Thanks
Chris
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Gaston
Dodge Dakota
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7/27/2005
00:29:31
| RE: cam upgrade
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Why would it?
Changing the cams does not change your engine's compression ratio, ignition timing or air/fuel ratio.
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gen1dak
Dodge Dakota
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7/27/2005
01:49:56
| RE: cam upgrade
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Actually, changing a cam can (an usually will) change the effective (note the term...effective, not static CR) compression ratio of an engine. It involves cylinder filling, and is also affected by overlap. Typical hi-torque units, for example, boost cylinder pressure (thanks to improved cylinder filling) in midrange rpms. The effective CR increases in this range. However, usually, the biggest issue involves the ignition timing. If the engine is already running close to detonation tolerance with a given setup, then receives a cam upgrade, it could potentially have detonation where it did not before. The main solutions are increased fuel octane, cooler thermostat (but not less than 180 degrees), and reduced ignition timing.
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FLDak
Dodge Dakota
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7/27/2005
14:43:29
| RE: cam upgrade
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I have had the HO cams and now have the KRC 206 cams, still running 87 octane.
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Gaston
Dodge Dakota
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7/27/2005
20:05:30
| RE: cam upgrade
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Oops.
You're right, gen1dak.
I answered in haste, and at the time thought a difference in cylinder filling insignificant. I had not considered the ignition timing aspect of it, though.
Well put.
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2003 4.7
Dodge Dakota
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7/27/2005
22:22:06
| RE: cam upgrade
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To add, after I swapped to the HO cams I did some real world tests and found that fuel milage was better with 89 oct. Wasn't much, 1/2-1 mpg more. But it was consistent.
May be that it is burning more effiecently at the cams effective engine rpm's?
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gen1dak
Dodge Dakota
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7/28/2005
20:43:33
| RE: cam upgrade
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2003 4.7. Typically, when you see something like that (better mileage with a higher octane vs lower octane, all else being equal) you are experiencing a very mild detonation on the lower octane. You may not be able to hear it, but it's happening, and this is stealing some power, and costing mileage.
Gaston, thanks.
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2003 4.7
Dodge Dakota
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7/28/2005
23:36:25
| RE: cam upgrade
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Message:
True, I do live in Florida and it's pretty damn hot. Mild detonation worries were what made me start running 89 anyway.
Strang though , I told one of my friends about it and he showed no improvement in a Jeep GC.
non H.O.
Shows how different every engine is huh?
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gen1dak
Dodge Dakota
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7/29/2005
00:01:29
| RE: cam upgrade
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Yep. Even two that came off the same production line, same day can show very different personalities.
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