E85 Results
Posting Guru
Joined: Mar 2006
Posts: 1,526
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From: fargo, nd
good reading 
fits that it would have to be jetted 30% bigger because the energy content is about 30% less for e-85... but i thought it would have to have a bigger carb to flow more air for the increased fuel output to be fully burnt
fits that it would have to be jetted 30% bigger because the energy content is about 30% less for e-85... but i thought it would have to have a bigger carb to flow more air for the increased fuel output to be fully burnt
Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
There's more than just jetting it different, you'd have to recalibrate the whole carb. You'd probably want a larger accelerator pump (or change the nozzles), mess with the air bleeds, recalibrate the choke, etc. And then if you have a 4160, you'd need a larger secondary metering plate, or convert it to a metering block so you can richen the secondaries.
Although, I dont think it's 30%. I've heard anywhere between 10% to 30%.
Although, I dont think it's 30%. I've heard anywhere between 10% to 30%.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
From: http://en.wikipedia.org/wiki/E85
For non-fuel-injected engines, this may be accomplished through increasing the diameter of the carburetor running jets to a size that is slightly larger in diameter. The theoretical change is not to increase the hole diameter by 25% to 30%, but rather to increase the area and hence the fuel flow rate by 25%-30%. Hence, the diameter of the jets must be increased by 11.8% to 14%, while keeping the general shapes at the opening of the jets as close to nearly the same as possible. (The idling jet must also be increased in diameter in addition to the running jet, primarily to accomplish successful starting in colder weather.) An excellent starting point, if one doesn't want to experiment with multiple test trials over the 25% to 30% range, is simply to increase the fuel flow by 27%, which just requires increasing the diameter of the jets by 13%.
For non-fuel-injected engines, this may be accomplished through increasing the diameter of the carburetor running jets to a size that is slightly larger in diameter. The theoretical change is not to increase the hole diameter by 25% to 30%, but rather to increase the area and hence the fuel flow rate by 25%-30%. Hence, the diameter of the jets must be increased by 11.8% to 14%, while keeping the general shapes at the opening of the jets as close to nearly the same as possible. (The idling jet must also be increased in diameter in addition to the running jet, primarily to accomplish successful starting in colder weather.) An excellent starting point, if one doesn't want to experiment with multiple test trials over the 25% to 30% range, is simply to increase the fuel flow by 27%, which just requires increasing the diameter of the jets by 13%.
Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
Wikipedia? I wonder if the guy that wrote that ever tuned a carburetor.
Here is a quote from "Super Tuning and Modifying Holley Carburetors," by Dave Emmanuel, page 46:
While the Wiki article does say something about the opening shape, the results are still unpredictable. Better just to get the appropriate size jet and forget the drilling.
Now if you read the rest of this book, it becomes painfully apparent that to do it right you need to do a lot more than drill the jets. If you can get away with it just changing jets, then great, but expect to have to do more tuning.
Here is a quote from "Super Tuning and Modifying Holley Carburetors," by Dave Emmanuel, page 46:
It is entirely possible that a jet redrilled to a larger diameter will in fact lean the mixture rather than provide the desired enrichment. If the front and / or rear side of the jet is chamfered, enlarging the orifice will remove all or a portion of the chamfers, thereby increasing the length of the restriction and reducing flow capacity. Additionally, removing the entry chamfer exposes a sharp edge which creates turbulence as the fuel attempts to flow into the metering orifice. The jet chamfer performs the same function as a velocity stack, that of smoothing the entry area to reduce turbulence and increase flow. Removing it significantly alters flow characteristics.
Now if you read the rest of this book, it becomes painfully apparent that to do it right you need to do a lot more than drill the jets. If you can get away with it just changing jets, then great, but expect to have to do more tuning.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
That is why I never drill jets but buy new ones... They are somewhat difficult to obtain for OEM type carbs tho. My cousin keeps several boxes of them and treats them like gold. Changing the entry and exit "chamfer" can alter flow radically and often unpredictably. Notice the author never really says to drill them, but does mention shape.
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