Miles Per Gallon of a 20B
Miles Per Gallon of a 20B
09-15-05, 01:29 AM
#4
As with any rotary, porting the engine to the point it's adding overlap will kill the fuel economy. I think it could get really good mileage with the right combination of tuning and gearing.
Example: Look at the v8's in the Camaro's and Vetts. Those cars get 28-29 mpg on the highway. Why? The engines have soo much low end torque GM can engineer the 6th gear to be very tall keeping the rpm's low at highway speeds. I think at 70mph the rpm's are like at 2k? At that low an rpm, the engine is barely sipping any fuel(even though 8 injectors are pulsing). In hindsight, think about how much worse these same v8's fuel economy would be if the highway cruising rpms was at 3k? The mileage would drop like a rock.
In my fd, if I cruise at 75mph my rpm's are at 3k. I get about 26mpg in this range. Imagine if I had a 20b in place of my 13b and still had the same gearing? The mileage wouldn't be nearly as good even with a great tune. Since the 20b has more low end torque, you could use a taller final gear to take advantage of it and put the rpm's lower just like what GM does for it's v8's. This is the number one reason I want a tall 6th gear for my 20b conversion.
Bottom line, there is no reason a 20b can't get good mileage (especially on the highway).
Example: Look at the v8's in the Camaro's and Vetts. Those cars get 28-29 mpg on the highway. Why? The engines have soo much low end torque GM can engineer the 6th gear to be very tall keeping the rpm's low at highway speeds. I think at 70mph the rpm's are like at 2k? At that low an rpm, the engine is barely sipping any fuel(even though 8 injectors are pulsing). In hindsight, think about how much worse these same v8's fuel economy would be if the highway cruising rpms was at 3k? The mileage would drop like a rock.
In my fd, if I cruise at 75mph my rpm's are at 3k. I get about 26mpg in this range. Imagine if I had a 20b in place of my 13b and still had the same gearing? The mileage wouldn't be nearly as good even with a great tune. Since the 20b has more low end torque, you could use a taller final gear to take advantage of it and put the rpm's lower just like what GM does for it's v8's. This is the number one reason I want a tall 6th gear for my 20b conversion.
Bottom line, there is no reason a 20b can't get good mileage (especially on the highway).
Last edited by t-von; 09-15-05 at 01:36 AM.
09-15-05, 01:42 AM
#5
Damn what the hell! Might as well add one more example.
In the Rx8 crusing at 75mph the rpm's are at 3,750. All because of gearing. And they wonder why they have such crappy fuel economy.
That same rpm is also the staging point for the secondary injectors. The 6th gear in the 8 is pointless IMO.
In the Rx8 crusing at 75mph the rpm's are at 3,750. All because of gearing. And they wonder why they have such crappy fuel economy.
That same rpm is also the staging point for the secondary injectors. The 6th gear in the 8 is pointless IMO.
Last edited by t-von; 09-15-05 at 01:47 AM.
Trending Topics
09-24-05, 01:23 PM
#16
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,835
Received 2,604 Likes
on
1,847 Posts
my 20b fc got 19.9 highway, tuned to 14.5ish afrs, stock engine/turbos
in mixed driving it was more like 14-16, put your foot down and you could almost watch the gas guage move
in mixed driving it was more like 14-16, put your foot down and you could almost watch the gas guage move
Thread
Thread Starter
Forum
Replies
Last Post
RPOdesign
New Member RX-7 Technical
5
08-27-15 11:42 PM
stickmantijuana
20B Forum
8
08-18-15 02:46 PM
