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PostPosted: Sun Jun 28, 2009 5:45 pm 
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Joined: Sun Sep 28, 2008 9:23 am
Posts: 46
Location: Indiana
Does anybody have a link to tell me why an economy cam grind and advance gets you better fuel economy? Thanks


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PostPosted: Tue Jun 30, 2009 6:41 am 
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Location: Washington, DC
Any engine can be tuned to perform in a variety of different ways. Everything having to do with breathing effects how the engine makes it's power. Generally speaking, smaller intake passages, valves, exhaust pipes, and valve openings keep flow velocity high at low rpm's. This makes more torque down low but the engine is going to run out of steam long before redline. Opening everything up using bigger pipes, bigger valves, and a camshaft that keeps them open longer will increase top end power, or horsepower. Engine will not idle well and probably not start putting out good power until 5K, but is really going to scream up to 9K. There are hundred's of possible changes that can be made, each one having a slight effect in one direction or the other.

Simply put, and economy cam tunes the engine for more low end torque, and torque is what you use on the street. The best use of this is as they did in the Metro XFI. Put in taller gears and then tune the engine to work better at those lower rpm's.

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PostPosted: Tue Jun 30, 2009 9:00 am 
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Shorter duration, and earlier valve timing both result in increased cylinder pressure, and increased low end torque.
Add duration, and the powerband moves up in the RPM range.

viewtopic.php?f=2&t=6212&start=0

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PostPosted: Fri Jul 03, 2009 4:55 am 
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Posts: 471
Location: Auburn Wa
Well I installed the XFI cam in my vert. Gas mileage went up about 3 miles per gallon (freeway). I am running near stock size tires. 175 60R 13's Federal FD1 Formoza. I have a lot more torque now in the low rpm's for taking off on hills. But I think my motor is running too many rpm's on the freeway now with the tires I am running. Since I have a lot of $$'s tied up in the tires and wheels I am considering running a stock metro trans from the 1989 to 1994 vintage.

In hind sight I should have run 155 80R 13's and some MB Seven X wheels which are 13" 4x114.3 or 4x100 rims. They are 5 inches wide with a 30 offset. They are perfect for the smaller width tires. I am confident that should increase my gas mileage on the freeway another 3 MPG.

My vert trans needs a rebuild so I think I will get a regular trans from the wrecking yard and rebuild that.

Link to MB Seven X wheels http://cgi.ebay.com/ebaymotors/4-NEW-13 ... ccessories

Link to the Primax 333 Wheels I am running now 13" 5.5 wide 38 offset. http://cgi.ebay.com/ebaymotors/16-PRIMA ... |72%3A1171

PS I like the fast cleaning of the primax wheels and the lug nuts under the center cap. I also like the tires as they are absolutely top notch in the rain and very good in the dry weather. The tires stick out ever so slightly that they offer a bit of curb rash protection/insurance when parking your car.

For top MPG the 155 80R 13 tires are hard to beat. But when your on a hill taking off from a standstill it felt like you were taking off in second gear. 155 78R 13 are the size of my studded tires and they have a much more desirable freeway rpm. They cruise at 3000 rpm at 60 mph and the 175 60R 13 cruise at 3300 RPM at 60 MPH. Ideally I would like to cruise at 2800 RPM at 60 MPH with the XFI cam installed.

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PostPosted: Fri Sep 11, 2009 9:46 am 
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Joined: Fri Aug 21, 2009 3:07 pm
Posts: 56
Location: Sacramento CA
Just a bit of knowledge and results of my own testing. Here is Sacramento we have hot weather in the 100's recently. I adjusted my timing from 5deg BTDC to 7deg BTDC and very noticeable torque was better on the low end. But in the day when temps were high, I could hear the start of engine pinging during hard accel in second an third gears. I am running the XFi economy cam and they are low end torque monsters. I had to run 91 octane gas to rid of the pinging and advanced timing in hot weather.

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