stephenw22 Posted July 20, 2006 Share Posted July 20, 2006 This was the first step in my quest for supreme fuel eceonomy out of my soob. I took the roof rack off my car last week, and I've only had 1 tank of gas through the car right now. That said, my results are VERY preliminary. My fuel economy with the roof rack on was around 22-23mpg(ish). With the roof rack off, my first tank of gas gave me 26-27mpg. Is this possible? Almost 100% of my mileage is done on the highway, so I guessed that reducing drag would have a pretty big impact. This is insane though! 20% fuel economy improvement from taking off the rack? I'm going to have to run a few more tanks through the car before I say this is the actual increase in mileage, but WOW, this was big! Next on the list will be to tune my car for highway driving, and for ethanol-blended fuel. Quote Link to comment Share on other sites More sharing options...
calebz Posted July 20, 2006 Share Posted July 20, 2006 Not surprising. I read an article a while back. It was a little experinment with a minivan and a thule aerobox (or whatever they call them). 7mpg difference over the course of a few tanks. Quote Link to comment Share on other sites More sharing options...
tizzle Posted July 20, 2006 Share Posted July 20, 2006 Same thing with my RX. And that annoying noise from the window suddenly dissapeared, and the car seemed to handle better. Quote Link to comment Share on other sites More sharing options...
sparkster58 Posted July 20, 2006 Share Posted July 20, 2006 Steve.. was that the roof basket that was on the Hornet .... if so thats a TWB basket made by Tony in Medford,or...... spark Quote Link to comment Share on other sites More sharing options...
Indrid cold Posted July 20, 2006 Share Posted July 20, 2006 whew... luckly I didn't check too see what my millage was before I put up the rack... won't know the difference :-p Quote Link to comment Share on other sites More sharing options...
Andyjo Posted July 20, 2006 Share Posted July 20, 2006 i took the factory rack, and thule racks off, and i gained 2 mpg (27, from 25).. although an odd thing.. when i had the factory racks on, and the box, i would get 29 on the highway Quote Link to comment Share on other sites More sharing options...
DaBrizat Posted July 20, 2006 Share Posted July 20, 2006 That matches my experience with a '96 Civic Coupe with a Yakima bike rack (with Fairing [sp?]). With that gear on top I was getting about 25mpg and without closer to 30 (with an automatic). So your experience is believable to me. Probably especially if the miles are hwy miles, I'd guess. Quote Link to comment Share on other sites More sharing options...
stephenw22 Posted July 20, 2006 Author Share Posted July 20, 2006 Steve..was that the roof basket that was on the Hornet .... if so thats a TWB basket made by Tony in Medford,or...... spark Yup, that's the one. I was sad to take it off - it looked so good. But, this one little change will save me about $300/year in gas. I've stashed the spare in the back for now, since I want to keep the space up front for 'future projects'.... If I ever move back into town from the farm, I'll put it back on, since most of my travel would be in town. For now though, the rack will have to stay off.. Oh well, it's the price I have to pay for... SUPREME FUEL ECONOMY P.S. - Spark, I'm still trying to get some pics uploaded of the Hornet. Maybe I'll toss the rack back on to take some photos of that, too. Quote Link to comment Share on other sites More sharing options...
sparkster58 Posted July 20, 2006 Share Posted July 20, 2006 Yup, that's the one. I was sad to take it off - it looked so good. But, this one little change will save me about $300/year in gas. I've stashed the spare in the back for now, since I want to keep the space up front for 'future projects'.... If I ever move back into town from the farm, I'll put it back on, since most of my travel would be in town. For now though, the rack will have to stay off.. Oh well, it's the price I have to pay for... SUPREME FUEL ECONOMY P.S. - Spark, I'm still trying to get some pics uploaded of the Hornet. Maybe I'll toss the rack back on to take some photos of that, too. Sounds good Steve.............spark Quote Link to comment Share on other sites More sharing options...
Tom63050 Posted July 20, 2006 Share Posted July 20, 2006 Next on the list will be to tune my car for highway driving, and for ethanol-blended fuel. How do you tune for highway & ethanol? Quote Link to comment Share on other sites More sharing options...
Uberoo Posted July 20, 2006 Share Posted July 20, 2006 so then how much mpg does a lightbar and four rectangular off-road lights on the roof eat up?Does a 102" whip subtract any? Quote Link to comment Share on other sites More sharing options...
stephenw22 Posted July 20, 2006 Author Share Posted July 20, 2006 How do you tune for highway & ethanol? Ethanol has fewer BTUs/lb than gasoline, but it has a much higher octane rating. Ethanol is also an oxygenate (it contributes some O2 to combustion when it combusts). First (ideally), I would rejet the carb slightly bigger. The stoich AFR for a 10% ethanol blend is something like 13.2:1 (gas is 14.7:1, ethanol is around 7:1, i think). In reality, I will probably just fiddle with the mixture screw a little bit. I'm planning on swapping an spfi exhaust onto the car, and use the 02 sensor to tell me what the mixture is like when I'm cruising. Second, I can advance the timing a few degrees above the stock values. 90% of my driving is at 3300-3500 rpm, so I can try to optimize my ignition for operation at that speed. Also, for the next 6 months or so, the regular gas in town will have an octane of around 90, versus a pre-ethanol 87. I can adjust timing and mixture to try and find the best combination for fuel economy. If I do it right, I'll be able to have fuel economy that is as good as running 100% gasoline. Of course, if I just switched over my carb to an SPFI system, it would do a lot of the trial and error for me. Plus, the higher compression of the SPFI block will give more power per unit of fuel I put into the engine. Quote Link to comment Share on other sites More sharing options...
stephenw22 Posted July 20, 2006 Author Share Posted July 20, 2006 so then how much mpg does a lightbar and four rectangular off-road lights on the roof eat up?Does a 102" whip subtract any? Those actually ADD horsepower, so you should be getting around 80mpg. Quote Link to comment Share on other sites More sharing options...
NorthWet Posted July 20, 2006 Share Posted July 20, 2006 Ethanol has fewer BTUs/lb than gasoline, but it has a much higher octane rating...I can adjust timing and mixture to try and find the best combination for fuel economy. If I do it right, I'll be able to have fuel economy that is as good as running 100% gasoline... Less energy-dense fuel, marginal increase in knock resistance index (your "90 octane" may be equivalent to about 87-88 USA); I don't think that you can achieve that 100%. I would be glad to be wrong. ...In reality, I will probably just fiddle with the mixture screw a little bit. I'm planning on swapping an spfi exhaust onto the car, and use the 02 sensor to tell me what the mixture is like when I'm cruising... Mixture screw should only effect idle mixture. Did you Northern Neighbors not get our feedback-carbs/EGO-sensors/ECUs by 1987? Those should/would have (mostly) taken care of mixture issues. SPFI even moreso. Good luck. The ethanol blends that they have us using down here are good for a 5% or so drop in fuel economy. We get it sometimes with the reasoning that "oxygenated fuels cut emissions by 5%"... but then we use 5% more fuel to do the same task, and we are back to square one. Quote Link to comment Share on other sites More sharing options...
stephenw22 Posted July 21, 2006 Author Share Posted July 21, 2006 Less energy-dense fuel, marginal increase in knock resistance index (your "90 octane" may be equivalent to about 87-88 USA); I don't think that you can achieve that 100%. I would be glad to be wrong. Mixture screw should only effect idle mixture. Did you Northern Neighbors not get our feedback-carbs/EGO-sensors/ECUs by 1987? Those should/would have (mostly) taken care of mixture issues. SPFI even moreso. Good luck. The ethanol blends that they have us using down here are good for a 5% or so drop in fuel economy. We get it sometimes with the reasoning that "oxygenated fuels cut emissions by 5%"... but then we use 5% more fuel to do the same task, and we are back to square one. I realize that 100% isn't going to happen, but I hope to get close. Our octane calculation is (MON+RON)/2. I think it's the same in the US, isn't it? The reason for the extra octane is that the fuel terminals aren't set up for both ethanol-blended fuel (for local sale) and non-ethanol fuel (for export). Basically, they take the 87 octane gasoline (normal for regular gas) and add 10% ethanol. Eventually, once they build more storage facilities, they will drop the local gasoline blend to 84/85 octane and bring it up to 87 with ethanol. If the mixture screw is only for idle, then a re-jet might be on order. No feedback carbs up here (on subes). Maybe I'll just hold off on carb mods and focus on a future SPFI swap. Quote Link to comment Share on other sites More sharing options...
starkiller Posted August 6, 2006 Share Posted August 6, 2006 back on track for a second here...decided to take off the cross bars on my 86 wagon which i put 65 miles on a day with basicly all i-5 driving...average increase over 4 tanks is 5.2 mpg increase!! that is incredible..i now average around 30 mpg on my carbed 86..put the cross bars in the car in case i need them..increase in mileage drops a bit down to 3 mpg when i leave some windows down(no a/c) but i will certainly take the 3 mpg! thought i would share this news since gas in certainly not getting cheaper and come october my commute will go to around 85 miles a day and i will need every mpg i can get Quote Link to comment Share on other sites More sharing options...
NorthWet Posted August 6, 2006 Share Posted August 6, 2006 I realize that 100% isn't going to happen, but I hope to get close. Our octane calculation is (MON+RON)/2. I think it's the same in the US, isn't it?... Yes. We down here seem to think that The World copies us, so I try not to assume. Out blends are typically 87octane, at least on the Pacific Coast. Quote Link to comment Share on other sites More sharing options...
Indrid cold Posted August 6, 2006 Share Posted August 6, 2006 Last year there was a local car show, a section was dedicated to the newer extreme gas economy cars and they, like this post always challenge each other on how to get the best mpg. Can't remember any exact numbers but they were calculating difference do too wind drag off side view mirrors and removing them and any other off loadable weight (x-tra seats etc..) If you took the roof rack, how about antenna, & both side mirrors (if allowed by law). Or design and build a new set that would induce less drag..... Quote Link to comment Share on other sites More sharing options...
WheaT_BeeR_MaN Posted August 6, 2006 Share Posted August 6, 2006 wait a second u guys are saying the 2 stock bars on top of my 83 gl10 cause about a 3mpg difference!? i think i need some more beer. mirrors!? im getting my screw driver and going to go take care of this! Quote Link to comment Share on other sites More sharing options...
WheaT_BeeR_MaN Posted August 6, 2006 Share Posted August 6, 2006 uhh just thinkin again "i do it alot" but my grill came off awhile ago jumpin and thats gotta be a huge wall for the air stream to get by. or what about the whole front of the car! its got sqaure flat lights! im gonna have to think about this some more Quote Link to comment Share on other sites More sharing options...
Elroy Jetson Posted August 7, 2006 Share Posted August 7, 2006 What about all the intense aero testing Sube did on the XT to achieve .29 Cd and then they put a moonroof on and optioned the rear luggage rack/spoiler. At least the 4WD is on demand. 24mpg with 89 octane agrees with the EPA sticker. Wonder how much that spoiler is costing me per year Quote Link to comment Share on other sites More sharing options...
starkiller Posted August 7, 2006 Share Posted August 7, 2006 yeah, i wouldnt think the bars would make that much of a difference either, that's why i did it over a bunch of tanks of gas instead of just a couple..and again, this is based on alot of highway driving...probably isnt as drastic if its alot of city miles.... Quote Link to comment Share on other sites More sharing options...
baccaruda Posted August 7, 2006 Share Posted August 7, 2006 washing your car more than once a year (guilty!) and keeping it waxed will reduce friction over the entire surface... also keep the tire pressure properly monitored. Quote Link to comment Share on other sites More sharing options...
WheaT_BeeR_MaN Posted August 7, 2006 Share Posted August 7, 2006 oh i have good psi in tires at about 45psi and i wash it every month. i go 30miles every day to work. i get about 220 to 250 right now on a tank but man its running like sh*t. Quote Link to comment Share on other sites More sharing options...
RONAN Posted August 7, 2006 Share Posted August 7, 2006 I`ve noticed the same on both of my vehicles (Justy & Loyale wgn) with cargo baskets. It`s about a 3mpg loss... Quote Link to comment Share on other sites More sharing options...
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