Another big jump in mileage I got was going from 93 octane to 87. There's a ton more BTUs per gallon in 87.
Another big jump in mileage I got was going from 93 octane to 87. There's a ton more BTUs per gallon in 87.
Sorry, but that doesn't make sense to me. The base stock for all grades is the same, with only additives being changed to modify the octane rating, so it's hard to believe the energy content could be materially altered.
That said the burn characteristics could be, with the 87 likely burning faster, which might account for the change ... MPGMike would probably be able to clarify ...
Mike
"The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry
Bad laws are the worst sort of tyranny.
- Edmund Burke
From what I've read there seems to be about a 10% spread in the BTUs per gallon of gasoline depending on what it is. It has been a while since I've looked into that though. A quick search just came up with a ton of results which would seem to confirm that, but I didn't look for a truly credible source either. I do know that I picked up 1-2mpgs when I switched to 87 from 93 octane with no other changes that I can think of.Originally Posted by zin
Interesting... I wonder if you tried going back to 93 but upped the timing a bit if it would have close to the same effect?
If the 87 is burning faster, I doubt you'd be able to get all of it back with timing as more timing means there is more time the burning mixture is fighting the upward travel of the piston, assuming both fuels are tuned to attain peak cylinder pressure in the same "sweet spot" of 15-20* ATDC, but it might get you something... Not that it would be worth it if the engine has no need of the higher octane (assuming the 93 is burning slower), in this case it truly would be wasted money! But, if they both have close to the same burn rate, you should be able to get the same or better MPG, but that would seem to not be the case as you did see a difference with only a fuel change...
Mike
"The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry
Bad laws are the worst sort of tyranny.
- Edmund Burke
I highly doubt that I've optimized the timing in vac though. I'm really happy with the gas mileage the car gets and it's my DD so I don't mess with it anymore.Interesting... I wonder if you tried going back to 93 but upped the timing a bit if it would have close to the same effect?
If the 87 is burning faster, I doubt you'd be able to get all of it back with timing as more timing means there is more time the burning mixture is fighting the upward travel of the piston, assuming both fuels are tuned to attain peak cylinder pressure in the same "sweet spot" of 15-20* ATDC, but it might get you something... Not that it would be worth it if the engine has no need of the higher octane (assuming the 93 is burning slower), in this case it truly would be wasted money! But, if they both have close to the same burn rate, you should be able to get the same or better MPG, but that would seem to not be the case as you did see a difference with only a fuel change...
Mike
I saw you were in the mid to low 50s in vacuum, which seems right, especially if your engine uses EGR... Still working on that magic tool to indicate where peak cylinder pressure is happening... They do exist, but are big $$!
Mike
"The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry
Bad laws are the worst sort of tyranny.
- Edmund Burke
So an update.... On my road trip this weekend, I averaged 32.3mpg. The speed a stay around on the hyway is 105-115 kph or 65-72ish mph. There was the occasional run into the 80mph range, but mostly it was a steady 70. Also my friend went for a quick boot to see how the car felt with 7psi boost.
I see there's still little tweaks to be made as I near the epa rating for that combo (dohc 5 speed)of 35mpg hyway. The sohc 5 speeds were rated at 39mpg hyway I think due to the taller diff gearing.
Here's the fuel table followed by the ignition table. Yes, that's 63 degrees advance.
For reference, what RPM are you turning at that MPH? Tire size?
About 2900 at 70. Tire size is 195/70r14. I just swapped them this weekend and there's a 5% speedometer error and that was factored into the mpg rating I calculated.
That's pretty good gas mileage for those RPMs IMO.
You can see why I'm looking for a 3.55:1 transmission from a single cam gen 1 neon. I could possably run 2500-2600 range.
That's the way to go. We didn't gain much if any mileage when we changed out the transfer gears in our Neon, but we were able to get the same mileage at 10MPH faster speeds due to the reduction in RPM. I'm hoping that the 95' cam will get us a little more torque where we cruise so that we pick up 1-2MPGs.
That's surprising the rpm drop didn't net you any better mpgs. I used to own a 95 5 speed neon and it was undoubtably quicker than all the other year single cam 5 speeds. If I had to guess, I'd suggest the airbox design, the lighter 3 piece clutch, and the cam made the difference of about 5-10 foot pounds of torque.
I just ran through a mixed hyway/ city tank and got 27.2 mpg with no changes to the fuel or timing settings. I also found a 3.55:1 trans and I get it next wednesday, maybe it'll be in next weekend and hopefully the mpg numbers improve.
I think it just doesn't make enough torque to pull the car along without lugging it at lower RPM these days. It doesn't drop gas mileage when you go from 50 to 70mph and I chalk that up to the higher RPM. I've read that the 95' air box is good for 1-2HP so that is something I'll keep an eye out for. I'm just glad I finally found the cam. I really think that will be the difference. I plan on installing it over the Christmas break so we'll see soon enough.
Back with the 3.55:1 transmission.
I found a/f ratios leaner than about 17.2:1 cause a missfire with a steady hyway load applied, so I'm anywhere from 15.3-16.2:1 a/f ratio at cruise without issue. Ignition timing is still in the low 60 degree range indicated on the laptop.
The taller gears return about 400 rpm less hyway rpm at the same 70mph, for a total of about 2550 rpms at 70.
Now the good part. I acheived 32.6 mpg combined city and hyway this week. Traffic has been pretty bad the last couple days, and it's been hovering around the freezing mark in the mornings and that eats into the cold enrichment. I still need some more discipline keeping it out of boost and being easy on it.
I'm sure it's going to improve in the spring but I'm pretty happy about this last tank.
That's pretty darn good. I was thinking about this thread on my way home so I'm glad to be met with an update.
what kind of mileage are you getting with your neon Brian?
i usually only get 28 with mine but its flogged 100% of the time and lots of hills.
on the highway, i get 34mpg. 1997 sohc atx.
as for how lean you can go.... as lean as it will go without knock and missing and stuff like that.
as some have said, it can backfire with going too lean but if you add power with timing and flow efficiency i bet going leaner will amplify the results.
Brian
I'm getting about 36mpgs last I checked in the neon. A small mix of city with mostly highway miles. Dead flat around here. SOHC ATX with .91 transfer gears. I'm hoping the cam swap will help with mileage a bit.
I wonder if 185/75r14 tires would help get more mileage? Probably not much but if tires are needed, might be worth it to try it.
Bryan
86 GLHS #161, 2016 Impala
SDAC National Member, SDAC Buckeye Chapter Member
A man has got to know his limitations.....
I've read that they don't fit very well. I think we have 175/70r14s on there now which is a bit taller than the 185/65s. 185/75 is quite a bit taller than stock.
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