Better MPG's w/ Main Cat vs. MP/Hi-Perf Cat Conv. combo
#26
Super Snuggles
![](/images/misc/20_year_icon.png)
Originally Posted by Kento
The problem there is that there is no "size standard" among the tire manufacturers. One maker's "P235/ZR40-17" may be slightly different in diameter than another (yes, it's small, but that can make a big difference in rpm per miles traveled). Just because they have the same size designation doesn't mean that they're exactly the same size.
#27
Originally Posted by areXseven
Stock ECU. Disconnected Air Pump. Also, I never let the AWS rev the engine at cold start-up. I bump it and let the engine idle into operating temp before the car is driven.
#28
il Cosa Nostra e vivo!!
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Thread Starter
iTrader: (1)
Join Date: May 2003
Location: Dove le cose sono fatte il vecchio moda il senso
Posts: 2,097
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by jimlab
Try filling the tank until the pump kicks out by itself (do not top off), zero your odometer, drive for awhile, and then fill up until the pump kicks out by itself again. Divide the number of miles shown on your odometer by the number of gallons shown on the pump and you've got your average (assuming your tires are approximately stock diameter).
The gas gauge and sensor are not incredibly accurate. It's far more accurate to let the gas pump do the calculating of how much fuel has been consumed.
The gas gauge and sensor are not incredibly accurate. It's far more accurate to let the gas pump do the calculating of how much fuel has been consumed.
Thanks.
#29
il Cosa Nostra e vivo!!
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Thread Starter
iTrader: (1)
Join Date: May 2003
Location: Dove le cose sono fatte il vecchio moda il senso
Posts: 2,097
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by patriick
Interesting. How do you judge operating temp, middle of the stock temp gauge? (~58C)
![Smilie](https://www.rx7club.com/images/smilies/smile.gif)
#30
il Cosa Nostra e vivo!!
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Thread Starter
iTrader: (1)
Join Date: May 2003
Location: Dove le cose sono fatte il vecchio moda il senso
Posts: 2,097
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Kento
The problem there is that there is no "size standard" among the tire manufacturers. One maker's "P235/ZR40-17" may be slightly different in diameter than another (yes, it's small, but that can make a big difference in rpm per miles traveled). Just because they have the same size designation doesn't mean that they're exactly the same size.
I'm still cruising 80mph at 3K just as before when I had the Yokos.
#32
il Cosa Nostra e vivo!!
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Thread Starter
iTrader: (1)
Join Date: May 2003
Location: Dove le cose sono fatte il vecchio moda il senso
Posts: 2,097
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by rx7fdfc
Try testing with a GPS unit. Buy and return one after using it.
#34
Originally Posted by jimlab
Try filling the tank until the pump kicks out by itself (do not top off), zero your odometer, drive for awhile, and then fill up until the pump kicks out by itself again. Divide the number of miles shown on your odometer by the number of gallons shown on the pump and you've got your average (assuming your tires are approximately stock diameter).
The gas gauge and sensor are not incredibly accurate. It's far more accurate to let the gas pump do the calculating of how much fuel has been consumed.
The gas gauge and sensor are not incredibly accurate. It's far more accurate to let the gas pump do the calculating of how much fuel has been consumed.
-Max
#35
2/4 wheel cornering fiend
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Originally Posted by areXseven
I think that in order for the new Dunlops to have a positive enhancement in fuel consumption (additional 5.4 mpgs), they would have to be much taller than the Yokos that were replaced. Taller tires will effect final gear ratios by lowering rpm per mph ratios. Thus the engine doesn't work as hard to accomplish the same mph. Assuming driving habits remain unchanged.
I'm still cruising 80mph at 3K just as before when I had the Yokos.
I'm still cruising 80mph at 3K just as before when I had the Yokos.
#37
il Cosa Nostra e vivo!!
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Thread Starter
iTrader: (1)
Join Date: May 2003
Location: Dove le cose sono fatte il vecchio moda il senso
Posts: 2,097
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Kento
Unfortunately, you're overlooking one important aspect: your speedometer reads off the transmission, so it's always going to read 80 mph at 3000 rpm no matter what size tires you have. The speed you're actually traveling will be different, however.
![Smilie](https://www.rx7club.com/images/smilies/smile.gif)
#38
Racecar - Formula 2000
![](/images/misc/20_year_icon.png)
Two points:
1) Different tire types and brands can have significantly different rolling resistances, even at the same pressure. Obviously, lower rolling resistance means better mileage.
2) Different tires will have different effective radii, giving a different number of rotations per mile. A tire with more rev/mi will give better fuel economy on two counts - lower actual speed at a given speedo reading, and less actual miles traveled compared to the odometer reading.
I would suspect these tire factors have much more effect on your mileage than the type of cat, especially since the cat is really restrictive only at high flow rates, when you are producing more HP (say above 100), and you only need 75 or so to accomplish most non-spirited driving.
1) Different tire types and brands can have significantly different rolling resistances, even at the same pressure. Obviously, lower rolling resistance means better mileage.
2) Different tires will have different effective radii, giving a different number of rotations per mile. A tire with more rev/mi will give better fuel economy on two counts - lower actual speed at a given speedo reading, and less actual miles traveled compared to the odometer reading.
I would suspect these tire factors have much more effect on your mileage than the type of cat, especially since the cat is really restrictive only at high flow rates, when you are producing more HP (say above 100), and you only need 75 or so to accomplish most non-spirited driving.
#39
il Cosa Nostra e vivo!!
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Thread Starter
iTrader: (1)
Join Date: May 2003
Location: Dove le cose sono fatte il vecchio moda il senso
Posts: 2,097
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Kento
......one important aspect: your speedometer reads off the transmission, so it's always going to read 80 mph at 3000 rpm no matter what size tires you have. The speed you're actually traveling will be different, however.
#40
il Cosa Nostra e vivo!!
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Thread Starter
iTrader: (1)
Join Date: May 2003
Location: Dove le cose sono fatte il vecchio moda il senso
Posts: 2,097
Likes: 0
Received 0 Likes
on
0 Posts
Weather was a little foggy this a.m. so I decided to scratch the San Antonio trip. I did take her out for 107.2 mile round trip cruise. Temp was 52 degrees.
I fuel'd up as Jimlab recommended and zeroed out the trip odometer at the gas station. Got on the highway and maintained a speed of 72 mph (2600 rpm). Had a few passes at 90 and 115mph. Turned around and headed back to Corpus.
Stopped at the gas station and refueled in same manner before the trip was initiated. When the pump handle automatically stopped the pump read 4.425 gallons.
That comes out to 24.2 MPGs. A little dissapointed I didn't cross the 25mpg mark. It may be time to change the plugs and the fuel filter
I fuel'd up as Jimlab recommended and zeroed out the trip odometer at the gas station. Got on the highway and maintained a speed of 72 mph (2600 rpm). Had a few passes at 90 and 115mph. Turned around and headed back to Corpus.
Stopped at the gas station and refueled in same manner before the trip was initiated. When the pump handle automatically stopped the pump read 4.425 gallons.
That comes out to 24.2 MPGs. A little dissapointed I didn't cross the 25mpg mark. It may be time to change the plugs and the fuel filter
![Smilie](https://www.rx7club.com/images/smilies/smile.gif)
#41
2/4 wheel cornering fiend
![](https://www.rx7club.com/images/misc/10_year_icon.png)
Originally Posted by areXseven
According to your explanation, [MPH to RPM] readings will not change even if rear-end gears are swapped to a lower/higher ratio?? EXAMPLE: If my car is equipped with 4.55 ring and pinion, it would still mark 3K at 80 mph??
Originally Posted by DaveW
1) Different tire types and brands can have significantly different rolling resistances, even at the same pressure. Obviously, lower rolling resistance means better mileage.
Thread
Thread Starter
Forum
Replies
Last Post