2007 Spec B Final Drive and Ratios

[edkwon]

I have a 6 MT and have driven several 5 MTs, i dont have information about the gear ratios and final drive, but from a driving standpoint, the first few gears feel spaced closer together, but not as much as the 6MT in the Sti. It's true you have more room to do longer pulls in a tuned 5MT, but either one feels fine with me.

 

Ed

[SubLo]

2007 LGT 6-speed w/3.90 Rear

1st - 3.636 14.1804 effective revs in first gear

2nd - 2.235

3rd - 1.521

4th - 1.137

5th - 0.971

6th - 0.756

 

2005 - 2006 LGT 5MT w/4.11 Rear

1st: 3.166 13.01226 effective revs in first gear

2nd: 1.882

3rd: 1.296

4th: .972

5th: .738

 

Then, figure in 17" vs 18" (LGT vs. Spec.B) if necessary.

 

One more comment: The 5Mt vs. 6MT debate... one is not necessarilly faster than the other in the 1/4 mile per say. Neglecting driver differences, weather, hookup, etc. and speaking just fundamentally, a lot of it really depends on where the power band and efficiencies are at various times down the track in certain gears.

 

My 2 cents...

[Richard B.]

Here you go:

 

05 Leg GT

 

5th Gear:

 

65mph: 2700 rpm

70mph: 2860 rpm

75mph: 3070 rpm

80mph: 3300 rpm

 

I run about 3400 at 80 mph (typical cruse speed in Michigan...) if I remember, I will double check EDIT: After checking 3300 is more accurate, it may be a hair over that rpm, but it is not quite 3400.

 

07 Leg Spec B

 

6th gear:

 

 

65mph: 2040 rpm

70mph: 2240 rpm

75mph: 2380 rpm

80mph: 2520 rpm

 

BIG difference, I am scheduled to test drive a spec b when one is at my dealer, and I will report how accurate these numbers are...

 

EDIT, so people don't read this and have a cow, these are the correct estimates, with 3.9 final drive, keep reading for more information:

 

65mph ~ 2300 rpm

70mph ~ 2480 rpm

75mph ~ 2600 rpm

80mph ~ 2900 rpm

85mph ~ 3050 rpm

 

 

crazy.

 

my 5eat is exactly at 3500rpms at exactly 100mph.

 

80 is right at 2800.

[Richard B.]

 

One more comment: The 5Mt vs. 6MT debate... one is not necessarilly faster than the other in the 1/4 mile per say. Neglecting driver differences, weather, hookup, etc. and speaking just fundamentally, a lot of it really depends on where the power band and efficiencies are at various times down the track in certain gears.

 

My 2 cents...

 

i believe christian from cobb says the 07 holds more boost at redline. about 2psi worth. iirc it's in the cobb ap update thread.

[sickdrift]

 

Then, figure in 17" vs 18" (LGT vs. Spec.B) if necessary.

 

 

I dont know if you know, but I'll ask anyway. Does the spec B have the same final drive as the LGT with the bigger tire.

 

I was suprised to find that the B's have a whole inch bigger tire. I figured they changed the axle ratio's to accomodate this. But as I cant make sense of gearing ratio's to begin with, I cant tell the difference.

 

Has anyone gone to a 245/35R18 (a similar diameter to the LGT tire) and noticed much difference in a B? Is there a big difference in milage?

 

 

Laurence

[Guest]

2007 GT and SpecB have same final drive ratio (3.90) despite difference in wheel diameter.

 

Actually 2005-2006 GT and SpecB have 4.11 final drive ratio despite smaller diameter wheels.

 

In other words, Subaru is not worried about 1" inch difference in wheel diameter.

 

OTOH, OBXT has 4.44 final drive ratio which with bigger stock wheels behaves like 4.11 on LGT.

[Vimy101]

^ The OEM Spec.B tire is about close to 5% larger circumfirence than the LGT. I've not done a head to head comparison but it seems that that extra 5% does translate to lower cruising rpm and higher gas mileage. 3k rpm puts me at 75 mph indicated.

 

Edit: thats with the 06 5mt.

[sickdrift]

that that extra 5% does translate to lower cruising rpm and higher gas mileage. 3k rpm puts me at 75 mph indicated.

 

Edit: thats with the 06 5mt.

 

I don't think it benefits greater gas milage due to the larger diameter as It takes more fuel consumption to get up to speed. I think the two facts cancel eachother out.

[sickdrift]

2007 GT and SpecB have same final drive ratio (3.90) despite difference in wheel diameter.

 

So that I understand correctly, you are saying that the final drive at the axle of the Gt's and the specB is the same? So did SOA compensate for this difference at the computer to keep the sB accurate in regards to MPH? If these two statements are true I guess my next question would be does the AP give you the ability to recalibrate the computer to adjust for different tire size?

 

After I eventually wear out the tires of the sB I get this month I will most likely like to drop down to GT tire diameter.

 

Thanks guys for the responses!

 

 

Laurence

[Guest]

ECU, or rather BIU has a 17"/18" wheel setting for speedo. It can be changed by dealer via SSM.

[SubLo]

I don't think it benefits greater gas milage due to the larger diameter as It takes more fuel consumption to get up to speed. I think the two facts cancel eachother out.

 

Hate to point this out, but you're not necessarily right. It depends on the efficiencies along the engine curve combined with transmission, final drive ratios, and tire diameter (neglection proper inflation, weather, resistance, weight and driver habits). Aside from a controlled lab environment for a real world test, you'd need some crazy calculations to know for sure. Regardless, a 1 inch difference will not make a substantial difference that most people would notice.

[Vimy101]

I don't think it benefits greater gas milage due to the larger diameter as It takes more fuel consumption to get up to speed. I think the two facts cancel eachother out.

 

There is no effective difference between having larger diameter tires or having a taller top gear. It may take more fuel to get to speed but once there the the rpms are lower.

[Vimy101]

Hate to point this out, but you're not necessarily right. It depends on the efficiencies along the engine curve combined with transmission, final drive ratios, and tire diameter (neglection proper inflation, weather, resistance, weight and driver habits). Aside from a controlled lab environment for a real world test, you'd need some crazy calculations to know for sure. Regardless, a 1 inch difference will not make a substantial difference that most people would notice.

 

5% is 5%. (I think the difference is actually ~4.7%.)

[SubLo]

There is no effective difference between having larger diameter tires or having a taller top gear. It may take more fuel to get to speed but once there the the rpms are lower.

 

What??? :eek:

 

This may be negligible in our scenario (LGT 17" vs. Spec.B 18") since the difference is so slight but there is absolutely a difference as diameter and/or axle ratio increase between mileage (increasing) and acceleration (decreasing). There are however diminishing returns that would look something like a bell curve if you plotted them.

[Vimy101]

^ At 3000rpm in 5th gear the 06 Spec. cruises at 75mph indicated. The LGT truns about 3200rpm at the same speed. I'll get 27.3-27.6mpg in long distance steady state cruising. The 6mt Spec.s are breaking into the 28s.

 

5% is 5%.

[sickdrift]

Hate to point this out, but you're not necessarily right. It depends on the efficiencies along the engine curve combined with transmission, final drive ratios, and tire diameter (neglection proper inflation, weather, resistance, weight and driver habits).

 

I appreciate the input. I do agree with you that in theory there would be little to no difference if the cars mechanicals and electronics were calibrated to compensate for the difference, but from what other have said it "appears" the only difference is a small calibration difference in the computer to correct the speedo. As you said, there would have to be a change of final gearing at the axle as well, which doesnt appear to be there, to make up for the diameter change.

 

Do you know if there been comparisons of the sB fuel maps and the GT's? I have heard people complain the the sB wasnt properly tuned for it's 6 speed. It would seem that peroperly tuned for it, the car with the 6 speed should almost always outperform a 5sp GT. For those negative nellies out there, I am not saying the sB is blessed with super powers, just that the close-ratio 6sp is a strength if properly utilized.

 

Aside from a controlled lab environment for a real world test, you'd need some crazy calculations to know for sure. Regardless, a 1 inch difference will not make a substantial difference that most people would notice.

Again, I agree. I believe that and the gas mileage difference at cruising speeds are a wash. That said, I would rather have the 25" dia. as opposed to the 26" dia.

 

**Edit**

BTW, Sublo, I've been wanting to ask, is your avatar image of you or a friend? Thats a funny damned picture.

 

 

Laurence

[SubLo]

[quote=sickdrift;1556276

BTW, Sublo, I've been wanting to ask, is your avatar image of you or a friend? Thats a funny damned picture.

 

 

Laurence

 

http://www.ebaumsworld.com

 

[Richard B.]

^ At 3000rpm in 5th gear the 06 Spec. cruises at 75mph indicated. The LGT truns about 3200rpm at the same speed. I'll get 27.3-27.6mpg in long distance steady state cruising. The 6mt Spec.s are breaking into the 28s.

 

5% is 5%.

 

not to be nit picky...but a m/t gt runs that (so you say. dunno myself) but the 5 eat at 80mph is 2800rpms and 100mph is 3500rpms.

 

 

that's a HUGE difference imo. also that is why the 5eat is "slower" than the m/t.