mark kibort

actually, this is the key point right.. how it feels............ but perception can be misleading. especially with cars with different gearing.. the only way to do this to really know what speeds you are traveling at vs engine RPM . its almost impossible to feel the slight differences in acceleration , but the sounds and visuals (tachomerter) are the most dominating. however, have faith that Newton is not wrong... if you have more power at any vehicle speed, you will accelerate faster. so, there is no logical reason But one that the 997 /CaymanR should ever feel peppier , unless you are driving the GT4 at a less optimal engine RPM for a given speed. and those speeds vs RPM ratios are all over the map with differnt gears, rear ends and redlines.

i dont quite undestand the message here in your post. seems the GT4 has the shorter gear and it should take less time to run through 2nd gear because its happening at a lower speed range, no?

This the key point i was trying to make as well.... ill probably end up doing the comparison if someone doesnt join in first to do that. compare the redline speeds in each gear for your car and compare it to what would theoretical with the different gears.. THEN, we can make an informed decision on what is best for the use of the car (track or street). but eye balling it, or going on feelings, is ok... but not great. I mean , if somene likes the feel of the 997 gearing better... how do you argue with that...........but if that person is educated on what is really happening, and why it might not be optimal for his use (say he is a track junkie) the perception can change.............and this wouldnt be the first time that would happen, espcially on the topic of gears!
Ah..... but there is an override........ it might feel suggish, as we have been talking about , because the engine hp is not being utilized best. when it is.... suddenly the "feel" can change.

And now you are on the right path to gear optimization righteousness.
it would be interesting to see the trade offs VISUALLY. this the ONLY way to reallly have a logical discussion of what is "better" vs all the feelings that have been posted. so far the only logical information , that is based on feelings , is as true as it gets.. on the hyway, running the car at 5% lower RPM is better in top gear for cruising.. i think most of us agree here. there is no performance advantage... just a feeeling based on engine RPM sound and possibly engine efficiency... but thats an entirely different reason for the debate and discussion ehre... after all, matt at GTGears doesnt want to touch 6th because he feels the max theoretical speed is high enough as he said. so, the question becomes what are the gains to be had by going back and forth between the 991S and the GT4?? and by the way, i dont have any axe to grind with Matt and have no dog in the race either... I just like the subject matter. He knows his stuff and is very active in giving relevant information here on gears and costs............ the main thing that the group has to understand though, is " what will be accomplished " by a gear change .. what are teh advantages vs disadvantages, as matt knows, there are ALWAYS trade offs.

mark kibort

makes sense... i wonder why they designed it that way then? However, it begs the question, do you think a 5% change in the rear end is going to make any bit of difference? Plus, you realize that the cup car rear tires are 8% taller too, right? 8%!!!!! so that brings things back to the GT4 pinion speeds , right? in the end, if you want a 5% less rotational speed of the pinion, just put a 5 taller tire (i.e. 26" 305x35 vs a 25" tire as in stock)
i guess the major issue i have with the pinion gear discussion , is that 5% is not going to change the wear factor that much.. in fact, its seeing less torque at the gear face when spinning faster, so it should last longer, but the bearing should wear out faster , right? but if its spining faster and wearing out, due to speed, maybe better lubrication should be looked at or cooling . clearly, if its wearing out, its due to gear spline friction and 5% changes are going to make 5% change correct?

I think i was doing that in my head. because the ratios have not been clearly discussed vs their respective operating speeds, it gets a little confusing. once we get the speeds vs gears for both in question, we can really talk about the true differences and the net effect. Ive been looking at what was posted and maybe some of that was looking at the PDK ratios.
Lets post the top MPH vs gear ratio for what is looked at for a change. that way it all will make much more sense one way or another.

GTgears

Mark,
we aren't talking about a 5% change. The options for cayman are 3.89 and 4.55. I suggest you re-read the thread from the beginning. It is all there. You on going confusion is just distracting from the core discussion.

mark kibort

dont move the goal posts on me, you were talking about the cup car 4:1 ratios having issues on the track also others were talking about 3.89 vs 4.55.. and if you are criticizing that comparison , i agree thats a 17% speed increase of the pinion. does it really matter? is this really a wear concern? there are so many ranges of speeds. cars only it that top speed for very short periods of time.. average speeds on most tracks are 75-80mph. you could find some statistics that show roadamerica racers wear out pinon gears faster than laguna seca racers. i dont think thiis a major factor of wear (my opinion) , considering so many other factors. again, even if it was, all things being equal, the rear end would last 17% longer... but all things are not equal and that would be a stretch to correlate. in other words, of the failures seen on the GT3 cup car pinion, it would be a stretch to say that just reducing its speed, via the final drive ratio, would cure that failure.
i read this thread from beginning to end.. many have different perspectives and the confusion is in that there are so many options, so many goals and so many perceptions. thats why i suggested to just put the stock gears that are being discusses, and their related top speed in each gear and match them up with the "options" available.

GT4 = speed in each gear at redline
GT4 CS = speed in each gear at redline
CarerraS = speed in each gear at redline
GT3cup car= speed in each gear at redlne
cayman = speed in ead gear at redine.

then, we cna discuss advantages and disadvantages.

for example.. early in the discussion , there is a perception that the big spread of 1st to 2nd is a problem. this is done on purpose... the Aston martin and maseratti do this with their granzano gear boxes. why? (and it makes perfect sense) because you use 1st just to get out of the parkinglot out of the paddock,etc... you dont really use 1st on the street or track that much. the AMvantage 1st gear i think is 12:1..... i think its perfect. you can chug along in traffic witih minimal clutch wear and full clutch release at slow speeds. (redline is 7700rpm) then, there is a big drop to 2nd and the rest of the gears to 6th are very close. why?? to keep the car in the powerband. making a shorter 2nd gear that has redline speeds of 40mph or 45mph is not optimal.. why, because its tough to downshift into such a low gear on the track, AND many of the turns,( when driving at good -lap --time- clips) are around 45mph, so 2nd gear is the gear of choice anyway.... you are traction limited in 2nd initially, so its ok that it starts out at a little less hp range, but on the exit, you are full tilt and in the max HP range. 5500rpm to 7700rpm. this is the goal usually.
75 to 80mph 2nd gears are quite normal.... 100 to 120mph 3rd gears work well and 4ths from 130 to 155 work well too. most only have 3 gears to play with at the track , but if you can get 4 or 5 gears used to stay in the HP range , then thats all the better at the cost of rowing the gear box more.

so, if you really want to see what will work best, we need to see the 3 to 4 options of max MPH in each gear on a matrix . the trade offs willl be obvious.

also , keep in mind. this alll changes with the Hp available, and the track are street use your using the car for too. in other words, as the car gets more HP by design or improvements, the top speeds on any give straight will change, this requires the gear set changes to keep optimal. sometimes individual gears need to change... other times, rear end ratio needs to change. its a moving tartget!

GTgears

Mark,
I'm not moving the goal posts. I gave an example, with math, about why a shorter ratio wears out more quickly. That's all it was. You are the one who has latched on to the particular ratios and started making arguments for or against. Hell, you started with saying that I was defending the 3.44 as better, which was so far off in the weeds.

Since you haven't read the original final drive thread, which was bumped, and aren't paying close attention in this thread I'll spoon feed you. There are two options for a Cayman R/P, 3.89 (stock) and 4.55 (German aftermarket). Pete has the opinion, which I agree with, that the 4.55 F/D isn't a good solution, for a number of reasons, one of which is accelerated wear. And now you are caught up since you can't seem to be bothered with the hard details, like which final drives and which gear ratios are actually in these cars. You keep going on about how there is no universal best and that you need to know this and that. We know this and that. You are the one in the conversation who doesn't seem to get it.

The parameters for where Pete, and others here, are seeking "best" performance, and to improve upon the stock gearing are pretty clearly defined. Get with the program.


On second thuought, nevermind. I'm hiding your posts again. It was a mistake to give you another chance. I'm done wasting my time on you.

mark kibort

Matt, sorry i got lost in the conversation then.... i tried to follow it best i could, but from the start there were several options and options for the gearing situation. thanks for laying it out clearer. i was mainly addressing that the gear ratios and their shifts come with trade offs that are not usually apparent at first glance. so, yes, it seems that the 4:5:1 gear box would definitely give more wear and probably require new gears as well, because that would a substantial change to overall ratios. (thatk's where you come in with new gears i would think).

anyway, gearing is always a lengthy discussion and what makes it more involved is the varied use cases.... track, which track, hyway, change of power, economy for the hyway, and of course "driveability", which comes into all street conversations.

anyway, ill let you and the others take it from here.

Mark

ExMB

Dam nit GTgears

Even so I can't see his posts (but see he is posting) its obvious that this thread has now been "kiborted".

okie981

I believe you are right. I'm thinking about 4 years down the road when most of the warranties on GT4s are expiring, there may be more numbers of enthusiasts wanting a custom gearbox in their cars.

Bill Lehman

Way back in the day, when I was seriously racing an MGB in SCCA, I had 6 different ring and pinion sets. These were 3.90 (stock), 4.11, 4.30, 4.55, 4.88, and 5.12. I bought the 5.12 when I was into hill-climbing but found it useful at tracks with short straights such as Marlboro (really dating myself) and Waterford Hills. I switched them out depending on the track I was racing hoping to red line 4th gear just before the end of the longest straight. At the SCCA Run Offs at Road Atlanta I changed for the "Wet" qualy. Guess which destroyed itself first? The 5.12 which for sure had the least miles on it.

GTgears

Sorry mate, I've moved on now. I will answer your pm in the morning when I'm back at my desk.

To Bill's point the main reason Porsche Motorsports dropped the 5.00 Cup cwp was because they only lasted 15-20 hours. People were trying to race certain 24 hour races and dnf-ing because of gearbox failures. Not good press for a company with such an endurance pedigree.

cmosman

Wow! What a discussion. But I am totally confused now. Everyone has been complaining that 2nd is too tall. .. 80+mph at redline! .. not peppy enough in 2nd .. don't get to use the gears .. and so on.
And now that there seems a pretty straightforward way of reducing max. speed in 2nd into the same range where most other P-cars are (996 GT3 was 75mph IIRC), the argument moves to -- all wrong - the gears are just fine ??

FWIW, I am in Dallas and the straights on the local track require 4th, but not close to max. speed. F1 tracks may be different, but from my vantage point, less tall-ness would result in more power-delivery on average.

stout

Holy thread gone off the tracks. I think this thing got drive-by'd.

The good news is I think it covered a lot of good ground and had a lot of good inputs and perspectives. The only thing missing from my standpoint is to figure the right set of ratios to mimic gears 1-5 and 7 from the 991-1S in light of the GT4's stock R&P. That would also leave people with 2-3 sixth-gear ratios to choose from between the stock 6th and GT's offerings.

The result is an evergreen thread with info waiting for a time when 20 (?) GT4 owners are willing to step up to fully re-gear their GT4s...which may be a matter of warranty window above all else.

mark kibort

As long as you stay above 5500rpm, you are near the sweet spot of power. this means 55mph to 80mph is the sweet spot. (this means no gains in this region will be beneficial... in fact, will be a net loss) . for most tracks, that seems to be the most common speed range. think of the trade off....... you get a shorter 2nd, gain an advantage from 45 to 55mph vs original...... but then you have a substantial loss when shifting to 3rd from the new shift point 75mph to 80.. thats a spot where i wouldnt personally want to give up HP because you are in that speed range for a longer period of time too.,

There was SO much talk on another GT4 racing discussion where 2nd was never used because they (some said) were scared to downshift into 2nd due to too much torque. NJMP turn 5 for example. it seemed obvious to me, and others that a downshift was needed there. Also, this was seeen around the "uphill /downhill" area of LimeRock. Folks were not downshfting and just bogging out of a turn in 4th where 3rd could have been easily selectred after big bend , and through uphill and downhill for an average HP gain of near 50hp for 5-7 seconds!....... the point is, if its street driveability goals, or auto x where you would be in the 30-70mph range for a lot of the time, sure, that calls for a change. I just dont see the need and would be interested in the top speed in each gear that is desired with the mix of 991 and GT4 ratios.

with the wide HP spread mated to the close gears, each gear keeps the RPM in the max HP range, so there is nothing to optimize after 3rd gear by changing a ratio. (racing perspective). the old GT3 had a very peaky HP curve..... closer gears were much more valuable, especially down at the lower speeds.. you could give up close to 100hp with a GT3 if you had GT4 gear spacing 1-2nd gear.

I dont mean to argue any points here. just tossing some info out there because its an interesting topic to me and ive played around, extensively with gear ratio changes and seen how those changes effect lap time and racing strategy optimization.

GTgears

Not how I remember the conversation at all. I'll let readers draw their own conclusions on it. The Kibortion starts on page 4...
https://rennlist.com/forums/racing-a...n-the-gt4.html

mark kibort

Matt, can the name calling/insults stop right here? im only trying to add a little color here that might help with the discussions of changing something that is farily optimal from porsche already.

You talked about a change of gearing by Porsche with the GT4 as it might hurt performance and create some model differentiation. You do realize that if you operate in the max HP range, there is no change of gearing that will increase rear wheel forces,, correct? In other words, if you go to the shorter 2nd gear, do you increase 2nd gear forces at the wheels? Most people think you do because you are getting more mechanical forces out of a shorter gear, BUT if you are already at max Hp levels, 55mph to 80mph, the rear wheel forces stay the same..... no gain! (seems couner intuitive, but it is true) And certainly every gear after that (3rd through 6th), if you are in the 6000 to 7700rpmm range, there is no gain possible by making any gear shorter. the closeness of the gears keep the RPM in the max HP range (6000rpm to 7800rpm) and that max HP range creates max torque at the wheels. this is a commonly forgotten principle of gearing and optimizing rear wheel forces.

what im saying above is my only point. there is a void, as the thread started out pointing out, from 1st to 2nd......it's at the top of a very short 1st gear and at the beginning of second.. around 45mph.... but after 55 and to 190mph, (if you can get there) there is no areas where the stock gearing doesnt fully utilize the max HP range of the car.

as far as lime rock or NJMP, there was debate on whether to use 2nd going into turn 5. it seems clear to me that in a GT4 it is a perfect gear for an extra 50-75hp punch out of that turn, with the wheels near straight. clearly at lime rock, going into "uphill" and through "downhill" could use 3rd as well, as the goal here is to keep the car over 6000rpm at all times. the gear box looks pretty optimal for these tracks and many others. (from strictly a track perspective, not the hyway perspective)

edit: Matt. I went to that link.. yes, that was an "interesting discussion thread" but its the message is typfied by one of my strongest critics in this post. the point is.... the GT4 is geared pretty welll for the track......and the changes discussed here might hurt overall performance, sans a change of 2nd, for reasons made very clear in that discussion . https://rennlist.com/forums/racing-a...l#post13620799