Dadhawk's FR-S (6AT Firestorm)

[MarkRacerX]

Originally Posted by Dadhawk

Yesterday I had the opportunity to play with cruising speeds a bit. The following photos were taken at the 55, 60 and 70 MPH. The process used was:

Relatively flat road as seen through a GPS elevation (it changed only a few feet over the distance).

Car was at this speed with a stable RPM and MPG reading for at least 30 seconds before the picture was taken.

Cruise control used to hold speed.

The readings were easily reproducible on my 6AT.

Yeah I am closer to 3k range @ 70mph w/ 6spd manual if I remember correctly. Go Auto for Taller gear = better mpg!

[serialk11r]

That's interesting, the 70mph fuel economy is really shitty...in fact, I have a hard time wrapping my head around such a huge drop from 55 to 60. Pekingduck said he was getting 39mpg at 70 in the manual transmission!

48-49 sounds about right for 55 considering the gearing, but 60 and 70 are just completely off. Given the expected load increase and considering the increased efficiency due to increased load, 60 shouldn't be that low. Just punching in 48/(12/11)^3 (aka, zero rolling resistance and constant engine efficiency) gives 37.

Makes me wonder if there's something wrong with your car!

[Dadhawk]

Originally Posted by Spd229

huh.....maybe i'll have to get over my whole "can't drive 55" problem. lol.

I'm second guessing the 55 shot, honestly. I'm wondering if I was in a slight incline or something. One thing I did notice is the MPG can vary widely at the same RPM even tough speed isn't changing if you are going up/down a small incline. I'll try that one again if I get a chance. It did hold there for at least 30 seconds though, and the road was relatively flat.

[russv]

On my Lexus IS 250 which has essentially the same auto, 6th gear usually comes in at 55 mph so I'm not surprised by that mileage.

[Dadhawk]

Originally Posted by serialk11r

That's interesting, the 70mph fuel economy is really shitty...in fact, I have a hard time wrapping my head around such a huge drop from 55 to 60. Pekingduck said he was getting 39mpg at 70 in the manual transmission!

48-49 sounds about right for 55 considering the gearing, but 60 and 70 are just completely off. Given the expected load increase and considering the increased efficiency due to increased load, 60 shouldn't be that low. Just punching in 48/(12/11)^3 (aka, zero rolling resistance and constant engine efficiency) gives 37.

Makes me wonder if there's something wrong with your car!

Could just be the method I used to measure it too. Not exactly scientific and kind of hard to focus on all this to make sure its exactly right.

[serialk11r]

Originally Posted by Dadhawk

Could just be the method I used to measure it too. Not exactly scientific and kind of hard to focus on all this to make sure its exactly right.

Yea, could've been a slight slope or something like that, but those numbers are still really weird. The only one that seems about right is the 55mph reading, on a completely flat road. I feel like 60-65mph shouldn't be causing that big of a drop overall, maybe like low 40s mpg. If Pekingduck's reports are correct, I'd predict ~42 mpg trip average going about 70, locked in 6th gear of course.

[Allch Chcar]

That's actually not too unrealistic, Cereal, but I'd like to hope that something was off at 60 and 70mph. Possibly timing retard under load?

Dadhawk, what's the earliest it shifts into OD? I have a feeling it'll hit 50+MPG if you could get it into 6th at 35mph or even 45mph.

[serialk11r]

Originally Posted by Allch Chcar

That's actually not too unrealistic, Cereal, but I'd like to hope that something was off at 60 and 70mph. Possibly timing retard under load?

Dadhawk, what's the earliest it shifts into OD? I have a feeling it'll hit 50+MPG if you could get it into 6th at 35mph or even 45mph.

Yea I think either he hit a slight incline without noticing or there is something wrong, maybe timing retard (which would be scary, because the load levels are still pretty low). Why did you ask about when it shifts into OD Allch Chcar? rofl, just put it into manual mode, slip it into 6th gear. At 35mph the engine would be turning a little over 1000rpm which is not going to stall, if the transmission doesn't let you do that, the person who did the programming needs to be shot. Although on that note, 1000rpm on the manual transmission's 6th gear is like, 23mph???

Anyhow, it seems a bit unlikely that they would intentionally design the engine to start retarding spark timing this early and then intentionally giving it these tall gears which would cause a significant drop in efficiency...if that's the case though, then maybe this is a good reason to start looking into E85 conversion? The Cobb dyno run showed it running rather rich, maybe the high compression ratio combined with suboptimal fuel is limiting the power...perhaps E85 can allow aggressive spark timing and closer to stoichiometric AFR.

And Dadhawk, thanks again for providing the community with some info

[Dadhawk]

Originally Posted by serialk11r

Yea, could've been a slight slope or something like that, but those numbers are still really weird. The only one that seems about right is the 55mph reading, on a completely flat road. I feel like 60-65mph shouldn't be causing that big of a drop overall, maybe like low 40s mpg. If Pekingduck's reports are correct, I'd predict ~42 mpg trip average going about 70, locked in 6th gear of course.

I'm going to try and duplicate this again this weekend on a different road just for verification.

[MTeator]

Originally Posted by Dadhawk

I'm second guessing the 55 shot, honestly. I'm wondering if I was in a slight incline or something. One thing I did notice is the MPG can vary widely at the same RPM even tough speed isn't changing if you are going up/down a small incline. I'll try that one again if I get a chance. It did hold there for at least 30 seconds though, and the road was relatively flat.

don't forget wind... a 5mph headwind at 55mph means you've got the 60mph wind resistance.

I do wish 5th and 6th were taller in the MT. At 70mph I'm doing 3,000 rpm. Still, even if the computer is off a bit I'm averaging 27mpg since pickup yesterday.

[Allch Chcar]

Originally Posted by serialk11r

Yea I think either he hit a slight incline without noticing or there is something wrong, maybe timing retard (which would be scary, because the load levels are still pretty low). Why did you ask about when it shifts into OD Allch Chcar? rofl, just put it into manual mode, slip it into 6th gear. At 35mph the engine would be turning a little over 1000rpm which is not going to stall, if the transmission doesn't let you do that, the person who did the programming needs to be shot. Although on that note, 1000rpm on the manual transmission's 6th gear is like, 23mph???

Anyhow, it seems a bit unlikely that they would intentionally design the engine to start retarding spark timing this early and then intentionally giving it these tall gears which would cause a significant drop in efficiency...if that's the case though, then maybe this is a good reason to start looking into E85 conversion? The Cobb dyno run showed it running rather rich, maybe the high compression ratio combined with suboptimal fuel is limiting the power...perhaps E85 can allow aggressive spark timing and closer to stoichiometric AFR.

And Dadhawk, thanks again for providing the community with some info

I didn't ask that because I'm not driving it and I can't just ask him to drive 35mph and put it into 6th and set the cruise control. I don't know how it will act and I do not want to make Dadhawk uncomfortable. Plus it would make me responsible.

I wouldn't assume it's retarding timing without actually looking at the ECU readouts, it's just a thought since the MPG doesn't seem to correlate with the increased load. It could be entering enchrichment too, though I doubt it. Then again, I don't program ECUs. I do know that ATs operate at higher loads than MTs.

And yes, Cereal. I am still thinking about E85 conversions but I'm trying to keep it low key while I'm just doing research. There is another E85 guy here that I am kind of competing with. I don't want to lose.

[Dadhawk]

Originally Posted by MTeator

don't forget wind... a 5mph headwind at 55mph means you've got the 60mph wind resistance.

I do wish 5th and 6th were taller in the MT. At 70mph I'm doing 3,000 rpm. Still, even if the computer is off a bit I'm averaging 27mpg since pickup yesterday.

Its possible although they were all on the same stretch of road within a few minutes of each other, heading due West the entire time.

[Dadhawk]

Originally Posted by Allch Chcar

That's actually not too unrealistic, Cereal, but I'd like to hope that something was off at 60 and 70mph. Possibly timing retard under load?

Dadhawk, what's the earliest it shifts into OD? I have a feeling it'll hit 50+MPG if you could get it into 6th at 35mph or even 45mph.

Honestly, I don't know. When you're in "D" and standard shift mode, the shifting is so smooth in the higher gears I don't even notice it. Obviously, I could do it manually or just need to pay closer attention. I'll do that if I rerun the test this weekend. I'd also be interested in what others are seeing so we can get a baseline. I suspect each car will be slightly different.

[Allch Chcar]

Originally Posted by Dadhawk

Honestly, I don't know. When you're in "D" and standard shift mode, the shifting is so smooth in the higher gears I don't even notice it. Obviously, I could do it manually or just need to pay closer attention. I'll do that if I rerun the test this weekend. I'd also be interested in what others are seeing so we can get a baseline. I suspect each car will be slightly different.

Heh, I understand. Thanks for sharing with us!