RPMs and Auto Trans
12-28-2008, 10:23 AM
#11
Senior Member
Join Date: 12-20-2008
Location: durham north carolina
Posts: 835
THANKS and ?
https://www.chevyhhr.net/forums/fuel-economy-hypermiling-47/mileage-mods-strange-results-18369/
The thread above has similar discussion about this. Some was changing tire diameter to get better mileage.
I could be wrong but the gear change for your final drive is what you most likely need to change. The TCM or tansmission shift points can be adjusted for their shift point, however driving in "D" or "I" gear will do the same.
When I drove a stock car, we changed engine rpm by changing the size of both rear wheels and tires. This was a while back in the 70's.
The thread above has similar discussion about this. Some was changing tire diameter to get better mileage.
I could be wrong but the gear change for your final drive is what you most likely need to change. The TCM or tansmission shift points can be adjusted for their shift point, however driving in "D" or "I" gear will do the same.
When I drove a stock car, we changed engine rpm by changing the size of both rear wheels and tires. This was a while back in the 70's.
12-28-2008, 11:00 AM
#12
Senior Member
Join Date: 01-13-2006
Location: Superior, WI - Over the Hill Warranty Club member
Posts: 2,999
"D" in the HHR has the drive/overdrive, and the "I" is the lower gear under the Drive.
The "Drive" with the Automatics is mostly for the direct(3rd) and overdrive(4th). I know this has been discussed on the forum. The best known secret with the "Intermediate" drive(2nd) is shifting to "I" and full throttle will get you past the 108 Mph mark. (Disclaimer, Do not attempt this unless you are a professional driver under controlled conditions.)
The "Drive" with the Automatics is mostly for the direct(3rd) and overdrive(4th). I know this has been discussed on the forum. The best known secret with the "Intermediate" drive(2nd) is shifting to "I" and full throttle will get you past the 108 Mph mark. (Disclaimer, Do not attempt this unless you are a professional driver under controlled conditions.)
12-28-2008, 11:51 AM
#14
Senior Member
Join Date: 03-08-2008
Location: United States of Texas
Posts: 505
Just for reference
Just for reference my RPM with the taller tires is 2950 at 75 MPH.
2450 at 65. Do not remember what it was stock, I have it wrote down somewhere.......
I would like to know what the BSFC is for these motors if anyone knows?
Now on to mileage. With the stock car I was getting 31 MPG @ 70. Now I am getting 35 @ 70 and if you add in the 10% speedo error it is 38.5 MPG @ 70.
Mileage improvements appear to be the best in the 70-75 MPH range and have not changed as much faster or slower.
My city mileage has went from 21 to 26 with the exception on the last tank that went stupid?????
Note my mods have helped a little but do not expect full results until all mods are complete. Mainly the tune to calibrate the timing and fuel curves to the mods. Mods I have made so far:
1. Airiad intake filter
2. Lowered car 2 inches all the way around
3. Solstice wheels which are a little taller. 10% speedo error
4. Front air dam
5. 2.4 complete exhaust including down pipe and cat. Then added Cherry Bomb Vortex Muffler. Now it really breathes and sounds good.
6. 2.4 Intake manifold.
Upcoming mods
1. 2.4 Throttle body
2. trifecta Tune
3. Underdrive pulley.
The car breathes better now so the fuel curve is probably a little off as is the timing. Vince at Trifecta is going to help me get the perfect tune for this car and I will post the results. I have talked to him and let him know my goal is more mileage than performance. I fully believe and hope I can get the mileage up to 28 / 40 highway @ 70. And still have a car that looks good and even runs better than stock.
And for full disclosure I do not do mileage tests in strong wind or hills etc. The taller tires may help on level ground with no wind yet may hurt more up hill against the wind. That is a variable we do not know about but I can say the taller tires has helped some in my mileage tests.
Performance- my car is just as fast maybe a little faster than stock even with the taller tires. If I was to put the shorter stock tires on it she would run even harder.
It appears that my mods are working but until everything is complete it is difficult to say for sure and how much. Some have told me that the mods I have made will only hurt the mileage and if so I will be eating crow right here (hope it tastes like chicken!) How well the mods work or how the crow tastes I will post it here. Curly
2450 at 65. Do not remember what it was stock, I have it wrote down somewhere.......
I would like to know what the BSFC is for these motors if anyone knows?
Now on to mileage. With the stock car I was getting 31 MPG @ 70. Now I am getting 35 @ 70 and if you add in the 10% speedo error it is 38.5 MPG @ 70.
Mileage improvements appear to be the best in the 70-75 MPH range and have not changed as much faster or slower.
My city mileage has went from 21 to 26 with the exception on the last tank that went stupid?????
Note my mods have helped a little but do not expect full results until all mods are complete. Mainly the tune to calibrate the timing and fuel curves to the mods. Mods I have made so far:
1. Airiad intake filter
2. Lowered car 2 inches all the way around
3. Solstice wheels which are a little taller. 10% speedo error
4. Front air dam
5. 2.4 complete exhaust including down pipe and cat. Then added Cherry Bomb Vortex Muffler. Now it really breathes and sounds good.
6. 2.4 Intake manifold.
Upcoming mods
1. 2.4 Throttle body
2. trifecta Tune
3. Underdrive pulley.
The car breathes better now so the fuel curve is probably a little off as is the timing. Vince at Trifecta is going to help me get the perfect tune for this car and I will post the results. I have talked to him and let him know my goal is more mileage than performance. I fully believe and hope I can get the mileage up to 28 / 40 highway @ 70. And still have a car that looks good and even runs better than stock.
And for full disclosure I do not do mileage tests in strong wind or hills etc. The taller tires may help on level ground with no wind yet may hurt more up hill against the wind. That is a variable we do not know about but I can say the taller tires has helped some in my mileage tests.
Performance- my car is just as fast maybe a little faster than stock even with the taller tires. If I was to put the shorter stock tires on it she would run even harder.
It appears that my mods are working but until everything is complete it is difficult to say for sure and how much. Some have told me that the mods I have made will only hurt the mileage and if so I will be eating crow right here (hope it tastes like chicken!) How well the mods work or how the crow tastes I will post it here. Curly
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