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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain.


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Old 12-28-2015, 08:28 AM   #71
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Originally Posted by bfrank1972 View Post
Hi, Just read that other thread where I did that spreadsheet - look at the calcs and it will show you. What you're talking about is torque multiplication. Power is not increased at the wheels, torque is multiplied, and at the same time, RPM of the wheel is divided. It's why we even bother to rate things in both HP and TQ. HP is RPM dependent.

Regarding the other post regarding AT with wider gear spacing being faster than narrower gearing on a MT equivalent, that's entirely believable if the car has a broad torque curve. You see the same thing with Camaros, Corvettes, etc. You need close gearing to optimize a narrower power band, 370z's and GTI's likely don't have that issue. Not sure about the Nissan, but pretty sure the VW is dual clutch too which avoids the losses associated with "slush boxes" (I think I'm dating myself with that comment!) in these cases your shift times are often better than your typical MT driver, and you probably have some sort of launch control. Yay computers!


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Our torque band is flat once you past the torque dip in which the shorter FD keeps the revs higher from 2nd gear all the way up. Also a Header and tune would essentially make our torque band become just as flat as a 370Z.
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Old 12-28-2015, 09:19 AM   #72
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Our torque band is flat once you past the torque dip in which the shorter FD keeps the revs higher from 2nd gear all the way up. Also a Header and tune would essentially make our torque band become just as flat as a 370Z.

Not sure if I'm interpreting you correctly, but a shorter FD will not keep the revs higher. Gear spacing is the same - regardless of your FD, shift from 2-3 at redline will drop your revs to the same point in the rev band. FD will help you get through the torque dip a bit quicker though when starting from low RPMs.

Our torque band is slightly stronger above the dip, but you're right it's pretty flat aside from the 'dip'. But you still have to get it above the torque dip and keep it there (5k and up). Are we talking about modded cars or stock? Yup a decently designed header will help greatly or eliminate the torque dip, effectively giving the car a much more useable torque curve - probably would benefit AT cars even more than MT cars.


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Old 12-28-2015, 11:02 AM   #73
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Not sure if I'm interpreting you correctly, but a shorter FD will not keep the revs higher. Gear spacing is the same - regardless of your FD, shift from 2-3 at redline will drop your revs to the same point in the rev band. FD will help you get through the torque dip a bit quicker though when starting from low RPMs.

Our torque band is slightly stronger above the dip, but you're right it's pretty flat aside from the 'dip'. But you still have to get it above the torque dip and keep it there (5k and up). Are we talking about modded cars or stock? Yup a decently designed header will help greatly or eliminate the torque dip, effectively giving the car a much more useable torque curve - probably would benefit AT cars even more than MT cars.


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In the auto with a 4.1 fd after you redline 1st gear you will drop to 4500rpms for 2nd. But in the video I posted earlier the 4.88 fd equiped automatic drops the rpms to 5200 rpms instead for 2nd gear. With the 4.88 you miss the torque dip for 2nd gear and above. I'm thinking a 5.29 would make the shift sit 10% higher after every shift over the 4.88 and. 29% over a 4.1 which will keep the car in the power area more often.
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Old 12-28-2015, 11:29 AM   #74
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Hmmm that's really odd - your gear ratios determine the rpm spacing, not your FD. Maybe it's something weird with the 'play' in an automatic transmission. See attached image of spreadsheet calc to illustrate
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Old 12-28-2015, 11:38 AM   #75
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OK, I think we can agree that a FD won't increase the horsepower of the engine. It will increase the power to the tire however. Allow me to prove it to you. Two cars one an FRS, and one a BRZ both with stock engines. The FRS has stock manual gearing and a 4.10 FD. The BRZ has stock manual gearing and a 4.88 FD. At 60MPH the FRS engine is spinning at 2575 rpms, while at 60MPH the BRZ engine is spinning at 3065 rpms. Both engines have the same horsepower, but the power to the wheels is different. The FRS has 7295.83/PI*R2 horsepower per minute, but the BRZ has 8684.17/PI*R2 horsepower per minute.
Its not a horsepower increase, its a mechanical advantage increase. Horsepower at the wheels is not increased. The power band is just moved. Both cars still made the same power at X PM regardless of speed.

You're trying to use a gearing difference between two cars as a horsepower calculation. This is a gearing and mechanical advantage calculation, not horsepower.
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Old 12-28-2015, 12:07 PM   #76
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New FD is as old school mod as it gets, hot rodders do it all the time.

Want more acceleration, higher numerical ratio. Want more top end, lower numerical ratio.

Its not that complicated.
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Old 12-28-2015, 12:20 PM   #77
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Not sure if I'm interpreting you correctly, but a shorter FD will not keep the revs higher. Gear spacing is the same - regardless of your FD, shift from 2-3 at redline will drop your revs to the same point in the rev band. FD will help you get through the torque dip a bit quicker though when starting from low RPMs.

It is difficult to convince them. Many people will never get it, because they focus on the feeling. It is easier to feel acceleration, than to feel speed. They see that all gears accelerate stronger, so they believe that their car is overall faster.
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Old 12-28-2015, 12:26 PM   #78
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Hmmm that's really odd - your gear ratios determine the rpm spacing, not your FD. Maybe it's something weird with the 'play' in an automatic transmission. See attached image of spreadsheet calc to illustrate

You know what you're right it doesn't change. After 1st you sit at 5k rpms even with the 4.1.
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Old 12-28-2015, 12:29 PM   #79
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It is difficult to convince them. Many people will never get it, because they focus on the feeling. It is easier to feel acceleration, than to feel speed. They see that all gears accelerate stronger, so they believe that their car is overall faster.
Yah and I totally get it - it's one of those more counter-intuitive things. Not trying to bash anyone over the head about it - in the end it doesn't really matter, as long as everybody's happy with the mods. As I mentioned before, I'm thinking upping my FD ratio too
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Old 12-28-2015, 12:37 PM   #80
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It is difficult to convince them. Many people will never get it, because they focus on the feeling. It is easier to feel acceleration, than to feel speed. They see that all gears accelerate stronger, so they believe that their car is overall faster.
I understand him and you. My point is there is more left on the table for the auto. I'm not arguing for the manual. The auto was intentionally screwed over because Toyota focused on MPG and the manual. If a manual FRS had a 3.3 FD it wouldn't be able to get to 60 in 6.3 seconds and 100 in 16.4, so therefore it would be much slower with a higher theoretical top speed. In the ND Miata the auto is .5 seconds slower because it's geared more economy.
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Old 12-28-2015, 01:20 PM   #81
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With a Gtech SS meter
http://www.gtechpro.com/ss_fanatic.html

8 and 7 seconds.
Was this achieved before you added bolt on mods? I'm assuming yes as 8 seconds sounds stock to me.
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Old 12-28-2015, 06:39 PM   #82
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Was this achieved before you added bolt on mods? I'm assuming yes as 8 seconds sounds stock to me.
Yes.
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