MarcD147

ahhhh one hash into the red. never realized that...
that together with the 1% variation makes sense

also I am running 19" RE71R but with virtual identical diameter

sounds like your numbers are on the money

GrantG

Yeah, it's a little confusing because Porsche is not consistent about that. With the GT4, you can drive one hash into the red (as you can with most non-GT Porsches).

But most GT Porsches, it lets you drive to exactly the beginning of the red (like 9k redline on GT3), and some GT cars let you drive to different revs, depending on what gear you're in (like current RS), and some cars don't even let you get to the redline (911R hits a rev limiter at 8,500 rpm, even though the tach shows the red starting at 8,600 rpm).

neanicu

GT4Tony

This. Common in race and off road communities to change FD ratio higher for more TQ.

Warwick Morris

I thought this would be the way to go too. My 996.1 GT3 has a higher FD from the original cup car and it is brilliant. GTgears however says it's a more expensive way to go than just changing gears and he should know. However, if you end up changing the stock LSD out (they wear out quickly) for a Guards or race unit, it might be worthwhile as you to have dissemble the lot anyway and re-set the lash in the crown and pinion anyway. I don't want to be pioneer here, so will wait to see how others go with the gear ratio swap vs FD in a year or so. 2017 will be my first comp year in the GT4 so I'll see how the competition works out and respond as required in a thoughtful fashion.

Bardman

So in the latest EVO review of the 718 cayman s they Rev it out to 81 mph in second. Why do they keep making the gears so long????

GrantG

If true, that would indicate gearing even taller than the GT4's, since the redline is lower. With fast cars, lowish redlines, and only 6 gears, there is no way to have low gears without truncating top speed (or unnatural gaps between gears).

stout

I wouldn't be interested in a final drive change. While it would address 1-5, it would exacerbate what I view as a too-low 6th gear from comfortable freeway cruising.

With no autobahn—or 150-mph plus race tracks—handy, I'd be a lot more interested in an idealized 1-5 stack for street use built around an idealized 2nd gear, plus a taller 6th (similar to the effective ratio of 991-1 in 7th). Add in the cost and reliability advantages of the stock final drive and I find it hard to argue for a different final drive. Spoke with some friends in Germany, who have no problem with the GT4 gearbox as is. That makes sense to me, given their proximity to the autobahn and desire to see the car hit a maximum speed determined by its engine and aero rather than its gearbox...which means starting with 6th and moving down the gears from there.

Accel Junky

I would not be surprised if it was the same trans. Also the 718 has boat loads of low end torque so the taller gear is not as much of a detriment. Still less rowing on the street.

GrantG

Could be same trans since 718 has even bigger rear tire diameter than GT4 but 300 rpm lower redline.

mark kibort

very common and HIGHLY misunderstood.

one of the things ive gone out of my way to mention, is that with a broad HP curve, you stay in the HP range more and this is the MOST acceleration forces available. if you are at 6500rpm to 7500rpm, there is nothing you can do at those speeds to accelerate more. thats why knowing the HP curve is so important. (and understanding the laws of physics).

again.. gearing doesnt make HP, it only optiizes the use of the HP available. shifting up or down the rear end rarely can optimize anything, as each track has a different range of speeds.... the good news, the GT4 has a flat HP curve and as long as you are in it, you are maximizing acceleration .. PERIOD

As i detailed... lowering all the gears will cause more problems than you would solve. at many tracks it would cause awkward shift points. watch the Laguna seca video, sears point video and NJMP videos.... there are plenty of spots where a lower 3rd would cause problems and create NO gain what so ever.

in a straight line, whats the speed range? again, changing a rear end only optimizes all the gears for a unique and specific speed range . what porshe did was near perfect with the design for many reasons.

name a speed range and ill give you actual values to show this to be true.

its not even needed. keep in mind again, from 3rd to 6th, you can operate in the max HP range. this means there are no gains to be made. there is a slightly wide gap from1st to 2nd, but due to operation of that shift range in real life situations, its not an issue due to you more than likely being in a turn, or exiting a turn and its only for a very brief period. (key point)

mark kibort

I know this kid... oy boy!! wrong wrong wrong... let me explain.. he is a little lost as to the effects of rear end gearing. sure, each gear is shifted up or down 8% in his first step of change, example. what he keeps on saying is that the torque is increased in each gear.. this is true... top speed is sacrificed.. this is also true. BUT.. and this is a HUGE but (and he mentions this) hp of the engine is not change. torque of the engine is not changed, so what really happens???

1. the new lower gearing shifts the shift points up or down. no power is created. sure, the new 1st gear will redline at a lower speed, but you need to shift earlier, which loses 30% torque.. so you gain 8%, but lose 30% for. in the end. no gain. next gear, same thing.. more torque, but at a lower speed, then an earlier shift to a 30% lower torque gear... net gain 0
2. you only mess with gear ratios to match your max HP range and operational range to the speed range you will be in. Example: turn 5 at a track near you... if the lower gears force you to shift in a taller gear before braking, the net gain will be less! however, if you dont redline, and are at the max HP range during the final gear, you are at the maximum acceleration potential of the car
this kid comes off like he knows what he is talking about , and he has the correct facts but draws the absolute wrong conclusions.

Jimmy-D

Interesting stuff

GT4Tony

Match gearing to the characteristics of the engine to the characteristics of the track to optimize. I have no issue with the FD as is for my uses. Just know it's not optimized for all situations / applications.

mark kibort

This is the point of rear end changes......you may be optimized for the utilization of the HP of the engine for most all speeds, but the main point is that shift points might not be optimal..... example, you dont want a redline to happen 100m from your braking zone..... or you might want to take a certain high g load turn at a lower RPM even though you are at max HP to avoid oiling issues and you dont need the power there.
But, for pure performance, a wide HP band, as the GT4 has, it is optimal for most all uses and all tracks . this is because the wide HP band assures you are always at the max acceleration force potential at any speed IN that HP range.

It's common misconception that a lower gear down a certain straight, would improve acceleration performance, if you didnt get to redline in that gear by the end... say you were 500RPM-1000RPM off redline before braking, but still in max HP range.
If you shorten the rear end ratio, you would hit that straight before braking at redline now, but have you gained anything? sure, you have shortened the ratio, increased the mechanical advantage but there is no gain. Why? because the HP is the same ..... This means the engine torque had to of gone down... flat HP means torque goes down proportional to engine RPM. So, there is no net gain. All the gears before it, all had trade offs. (more initial torque in those gears, but much less torque at an proportionally earlier shift point) the net net is no gain. In fact if there is a slight gain, there are just as many situations where that gain could be a slight loss.. Again, gears are just HP optimizes. its all about maximizing time in the max HP range. in the case of the GT4, its 6000 to 7500rpm. Run in this range, and there are few gains to be made by changing gearing.

All the above is for the GT4 and others with flat HP curves up top (or gears that are close enough to keep RPM in the max HP range) ... an older GT3 cup car with a peak HP at redline, can benefit more by optimizing shift points on the track. however, in a straight line, redline shifts and average RPM operation near redline, assure max acceleration overall