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Old 07-11-2006, 09:25 PM   #1
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Default Decreased mpg with higher ratio rockers

I've noticed some claims stating that with higher ratio rocker arms, there is no penalty to your fuel economy. This sounds like a myth to me. Does anyone actually have data to back this up?

Higher ratio rockers mean higher lift of the valves and longer duration which allows more air/fuel mixture to enter the combustion chamber. The more flow in and out of the engine means more fuel is needed to mix with the air to avoid a lean condition and hence, less economy.
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Old 07-11-2006, 09:54 PM   #2
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The engine can breathe easier with the higher ratio rockers. Realistically all you are adding is lift. You aren't really adding any duration, just increasing the rate at which the valves open and close and peak lift, not WHEN they open and close. Obviously, while at WOT, this will allow more air into the engine, thus requiring more fuel, and making more power. But thats what you want at WOT, thats the point. At partial throttle during crusing the engine can only take in as much air as you let it. Thats what the throttle plate is for. If the throttle plate is only 10% open it won't be that easy for the engine to suck in more air. You are however increasing the amount of power the engine can make at X rpm because it can bring in more air due to the higher lift, because of this you are actually increasing the efficiency of the engine. Doing this under partial throttle typically IMPROVES gas mileage.

FWIW, in every car I've put 1.9 rockers in (which is quite a few), the car has noticed a gain of AT LEAST 1mpg on the freeway, usually more like 2-3mpg though.

Now once you start playing with duration and overlap this changes a bit and you will likely lose mileage due to unburnt fuel going out the exhaust due to increased overlap and things like that. Of course this is all simplified to make it easier to read/understand and there is more to it than this. But in a nutshell, not losing gas mileage with rockers isn't a myth.
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Old 07-11-2006, 11:15 PM   #3
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When your power to weight ratio goes up, so does your mpg at cruise (for the most part).
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Old 07-12-2006, 03:44 PM   #4
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Thanks both for the details. I was thinking about adding higher ratio rockers, but do not want to change valve springs or strain the stock system. I was thinking of going with 1.7 or 1.75'* (if they exist) Any thoughts or recommendations? The car will be primarly stock with the exception of maybe a stage one intense kit, but will definitely stick with either the 3.5 or 3.6 pulley to avoid any KR.

Thanks.
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Old 07-12-2006, 03:50 PM   #5
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Quote:
Originally Posted by 67Goat
Thanks both for the details. I was thinking about adding higher ratio rockers, but do not want to change valve springs or strain the stock system. I was thinking of going with 1.7 or 1.75'* (if they exist) Any thoughts or recommendations? The car will be primarly stock with the exception of maybe a stage one intense kit, but will definitely stick with either the 3.5 or 3.6 pulley to avoid any KR.

Thanks.
1.8s would get you about 20hp and not require stronger springs (for most cars anyways)
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Old 07-12-2006, 06:31 PM   #6
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Quote:
Originally Posted by 67Goat
Thanks both for the details. I was thinking about adding higher ratio rockers, but do not want to change valve springs or strain the stock system. I was thinking of going with 1.7 or 1.75'* (if they exist) Any thoughts or recommendations? The car will be primarly stock with the exception of maybe a stage one intense kit, but will definitely stick with either the 3.5 or 3.6 pulley to avoid any KR.

Thanks.
ZZP Aluminum 1.84 Roller Rockers are the highest ratio you can use on stock springs.
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Old 07-12-2006, 06:47 PM   #7
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Quote:
Originally Posted by llBlazin_llLo
Quote:
Originally Posted by 67Goat
Thanks both for the details. I was thinking about adding higher ratio rockers, but do not want to change valve springs or strain the stock system. I was thinking of going with 1.7 or 1.75'* (if they exist) Any thoughts or recommendations? The car will be primarly stock with the exception of maybe a stage one intense kit, but will definitely stick with either the 3.5 or 3.6 pulley to avoid any KR.

Thanks.
ZZP Aluminum 1.84 Roller Rockers are the highest ratio you can use on stock springs.
I don't think that is a correct statement as others have professed time and time again they run 1.9'* on stock springs with no issue however, I personally would never run a higher ratio than 1.80 without stronger springs.
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Old 07-14-2006, 02:55 AM   #8
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Thanks for the feedback.
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Old 07-14-2006, 01:09 PM   #9
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Old 07-14-2006, 06:42 PM   #10
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If you can add the 1.8 or higher (1.84) to the stock springs, what are the risks? Do the springs float earlier, just not before the usual shift point? Please clearify for me. I have a 2003 SSEi with just a tick over 80,000. I assume the springs are good for this mod but what are the limitations. Thanks for your help. Mark l
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