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UGH! 48 MPG - What is holding Sippy back?
Topic Started: Sep 27 2009, 09:04 AM (1,821 Views)
rmcelwee
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OK, I've been busy as hell so I haven't had time to play much with the car but I see some free time coming up. Right now I am stuck at around 48 MPG. My test course is the drive to and from work. 32 mile course (round trip) that could be considered HWY driving with the exception of 1 stop light and two stop signs. I drive around 45 - 50 MPH. Not much coasting or hypermiling, just easy on the gas and get into 5th as soon as possible.

The car:
93 vert with a freshly (1000 miles) rebuilt engine
5 speed from an XFI
low weight motor oil
13" tires inflated to 50 PSI ("44 max" printed on the sides)
10+ 3tech cam
about 18+ degrees of crank timing
stock exhaust and no aero improvements
some (80 pounds?) lightening
car has AC but the compressor has been removed
MPGuino

The MPGuino shows a max of around 58-60 MPG "instant" on flat surfaces and I believe it is calibrated fairly well. I need to get this cruising MPG up if I am to get my overall MPG up to where I want it.

Failed experiments:
cat delete - I pulled it and didn't see any change in my "instant" MPGs. My MPGuino acts up from time to time so I may have possibly been getting 1 MPG better but a plugged cat or muffler wasn't the source of my "poor" mileage.
XFI tranny swap - I expected much better results (looks like a 3-4 MPG increase) when I went to the different gear ratios

So, what should I do next? I would like to do some aero (especially radiator block since it would be so easy to do) for a quick test but I do not want to permanently change the outer appearance of the car (no screw holes). I am a shade tree Mig welder so I can fab up a larger free flowing exhaust without much problem. I really wish I had something other than a vert to play with but it is what I am stuck with for right now. I know that I should be seeing better mileage than I am (the gear ratios are so out of wack that most "normal" people would not drive a car like this) and I don't know what is holding me back.

Edited by rmcelwee, Sep 27 2009, 09:06 AM.
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Woodie
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I think Sippy's doing pretty good. 1000 miles isn't broken in yet, wouldn't be surprised if your mileage continues to increase until you've got 10,000 on it. XFI tranny with 13" wheels makes for an extreme highway car, 45 - 50 probably isn't fast enough to get full benefit. A 32 mile round trip isn't helping you any either, 15 miles is what I consider warm up time. :lol Bit of an exaggeration, but you get the idea. Highway driving is when you drive the entire 550 miles worth out of the tank.

My XFI got 52 mpg in normal driving and that's with better aerodynamics than a vert, I think you're doing well. Doubt if exhaust mods would do anything good for your mileage.

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Johnny Mullet
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Fear the Mullet

:gp

Fred's "weekend Rebuild" took over 1500 miles before it actually broke in.
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rmcelwee
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Johnny Mullet
Sep 27 2009, 09:51 AM
Fred's "weekend Rebuild" took over 1500 miles before it actually broke in.
Are you saying that 1500+ miles started getting better compression, better mileage, etc?

I haven't looked at my compression for a while but have been meaning to. I'll take a peak at it this week.

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Coche Blanco
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Troll Certified

I would post, but everything I wanted to say has been said. :)
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91 ragtop
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Have you taken in consideration how much your speedo and odometer has changed with the taller gear ratio? By going from a 4.39 to a 3.89 tranny with 13'' tires the difference should be 10% or so.
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Bad Bent
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Facetious Educated Donkey

I see 91 ragtop's point. ;)
If his math is correct and it could be 10% then your Odometer is off and that would mean your MPG is actually closer to 52... which was my combined mpg for my vacation. :hmm
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rmcelwee
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I had 4 separate posts about this so I will condense them all into one post with correct info.

All Metro trannys are the same (can be swapped). Some metros had 12" tires and some had 13" tires. To make up for this difference they put a different plastic gear in the speedometer. You can swap trannys from a 12" car to a 13" car and your speedometer will never change. If you put 12" tires on a vert or 13" tires on an XFI then you will have to change the speedo gear to make up for the difference. You can read more about it here (kind of):

http://metroxfi.com/2008/04/metro-transmission-and-speedometer-gear-ratio-information/

FWIW, IIRC my speedo is off by about 2-3% (meaning I am actually getting 2-3% better mileage). It was off before the swap as well as after.
Edited by rmcelwee, Sep 27 2009, 12:12 PM.
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Will
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Victory is mine!!!!

Even if your speedo was thrown off, would that effect the MPGuino? Hmmm... At any rate I agree that you should give the break in a little longer. I would run it for about 5,000 mi just doing what you are now, and then switch to something like Royal Purple. That might help push it over the big 50.
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nerys
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Grr

Just curious but what does rim size have to do with the accuracy of the speedometer? if the rolling circumference of your tires does not change then your speedo odo won't change.

Am I missing something?
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rmcelwee
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nerys
Sep 27 2009, 12:32 PM
Just curious but what does rim size have to do with the accuracy of the speedometer? if the rolling circumference of your tires does not change then your speedo odo won't change.

Am I missing something?
Most people would assume that 12" and 13" tires would have a difference circumference but yes, you are correct. In this case, the 12" to 13" OEMs swap has been done many times by people wanting to get a larger circumference tire to allow for lower cruising RPMs. I'd like to put low profile 14's on mine to change the ratio just a little bit more but I am having a hard time figuring out how to do it for $50.
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mwebb
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FOG

...."about 18+ degrees of crank timing"......


that is probably advanced to far ,
what type of fuel are You using ?
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starscream5000
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Got 70 MPG?

With stock cam and cam gear, I'm only able to get +14 degrees on 93 octane (non E-10).

Hope this gives SOME point of reference :)
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rmcelwee
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mwebb
Sep 29 2009, 12:35 PM
...."about 18+ degrees of crank timing"......


that is probably advanced to far ,
what type of fuel are You using ?
87 Octane. Everyone said to advance it until I heard ping. I haven't heard it yet but I didn't go any further than that.
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Murf 59
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One thing to remember also. The parts are not liking them selves yet. As it wears in, it will get better. One of the problems for me with the last of the break in for the Rocket is not punching it. I am enjoying not having a worn out engine. I know this will wear off. After a while it will start to go the other way. To sloppy, but that is a long ways down the road. It will get better.
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