stout

Hey Mark,

I know I asked before, but how many miles do you have in the 981 GT4? Your comments make it sound like you may not be all that familiar with the car.

It's hard for me to categorize the 3.8 in the GT4 as "high-strung," unless maybe I come at it from a V8 point of view. The GT4 gear ratio set is so far from optimal that it's the only one I've found to be sorely lacking in a new production Porsche—and I've regularly spent 1,000-1,500 miles in just about every modern Porsche sports car from the 993 forward. Could some of the other Porsches' ratio sets have been improved or more targeted for the enthusiast? Sure. But they made sense for a production car, were usually a good compromise for performance, generally worked well with the engine, and did not detract from the driving experience. This set is different. It hobbles the GT4 in sub-100 mph acceleration and then adds unnecessary and undesirable fuel consumption, emissions, cabin noise, and engine wear when cruising in sixth.

You've got known drivers stating Matt's shorter third gear for the GT4 creates a "turbo effect" vs the stock third gear. I agree. I also suspect a shorter 1-2 to go with a shorter 3-4-5 would really wake the GT4 up, much in the same way a set of short gears can be magical in a 2.0- or 2.2-liter 911S. On the other side, a taller sixth would give the GT4 longer legs for the drive to and from the track—or anywhere—along with that short stack in 1-5.

I'd call that a win-win. Only questions are: What ratios will get there with the stock R&P? What would the cost be? And, are there enough people out there to justify development?

Alan C.

A close 1 - 5 with a taller 6 would fit my wish list. I'm guessing close to $8000 - $9000 in parts, no labor, for the full 6.

mark kibort

what is more important, the taller 6th? or the closer 2nd to 1st?
sometimes you cant see the trees through the forest, but what about this thought.............$8k in parts to fix a tiny hole, rarely used in 1st to 2nd? wouldnt 8000 bucks buy a TON OF HP mods that you could do to the engine, not to mention driving classes, and suspension upgrades?
just saying.......... im still struggling with the view of the problem, even on the street. most of our cars still can break the tires loose coming out of a turn at 45mph in 2nd, even with non optimal 2nd gears.. why do you think that it is so critical to patch this small void for such a high cost. its a serous question. my car has the exact same gearing....... just went out for a spirited street cruise to the store....shorting up 2nd was not really something that struck me as desired. (same power as a modified GT4 with a little heavier weight).

mark kibort

I dont think my experience in the GT4 (which i have enough to make suggestions here having driven and raced many different cars at the limit at the track) needs to be questioned. my comments come strictly from a performance perspective, with a hint of the cars feel and performance when driving under the performance envelope (street driving) Having raced and street driven a car i ran in world challenge, i can say u clearly understand the trade offs. The trade offs i talk about are strictly physics and address the pure performance of the car.

For example.. if you take video that we all can see of a GT4 at Lime Rock for example, you can clearly see that its optimal for that track as is. in fact, many drivers are not even getting the optimal performance , by short shifting and running in 4th vs 3rd (for example ) on the uphill and downhill sections, forcing them to run at5000- 6000rpm max vs 6000-7700RPM max which sacrifices 50hp for over 7-8 seconds. its this kind of logic that im using in my analysis and comments.

so, when you fully understand that gear box gear ratios are ONLY HP optimizers and cant not truely give you a "turbo feel", you start understanding the trade offs. 0-100mph is not effected notably by changing any gears? why, because what you are all talking about doing is closing up 1st gear to 2nd. ..............say you only do 2nd, at the trade off of bringing all the gears shorter, you end up with a lower top speed and higher RPM during hyway operation. you end up patching a small .25 second period where the stock gears are NOT optimal 1st to 2nd shift, gives a big RPM drop where you are left with a 50hp deficit for 1/5 to 1/4 of a second. then, if you space out 6th, you have a gap from 4th to 5th that will have the same HP drop for a much longer period of time. (robbing peter to pay paul) Now, thats no problem if you like peter better than paul, but you get the idea.

remember what i said about 3rd gear? pretty optimal.. if you lower it, and lower 2nd, that doesnt give the effect you think. maybe you feel because your perception is skewed by the noise of the engine and forces in those particular gears... but based on actual speed ranges, there is no gain. why? because there is a trade off. you lower 2nd and 3rd gears and what happens. you gain a little in each gear (say, 7-8%) but shift in to 3rd, proportionately sooner, into a gear with a LOT less power and force. (30% drop). those losses and gains are proportional to the time spent in them too..... the net net is no gain over a wide vehicle speed range. this is a KEY point based on fact, having nothing to do with driving experience with the car.

your statement of the car being "hobbled" in the sub 100mph range is very inaccurate. its not. there is no change. any time you are in a gear not in the max HP range, you are "hobbling" your car.. this is a driver choice. this has almost everything to do with gear spacing and the GT4 allows for all gears past 1st, to remain in the max HP range... this CANNOT be improved (speed of 55 to 100mph will NOT be effected by any gear changes that are measurable or notable). The other factor, is optimization for the engine speeds vs straights and turns at the track.. this will change track to track, almost infinitely.. (see Lime rock example where a stock GT4 with any kind of 3rd and 4th gear change will hurt its performance.. but might help it at another track)

so, i understand completely the want for a taller 6th.. right now, you have a pretty tall 6th. if you want a taller one, you can change the ring and pinion and not hurt the car too much (or put on a taller rear tire). Ive been fortunate to ahve a car with similar gear ratios as the GT4 both street and track, and I dont see room for much improvement. certainly there isa chance of more harm than good. I also have a street car with the almost identical ratios as the GT4 and actually think the drop from 1st to 2nd is a good idea, especially as the engine power increases. just check out this RSR taking off at rev limiter.. this is the gear spacing that is close to the GT4...........do you see an issue with the 1st to 2nd gear drop of RPM? most all racer and street 911s have this same spacing.

by the way, any car that has a redline of near 7700rpm or higher most would say is highstrung. (bottom of the "high strung range")



great article about shortening 3rd 4th and 5th.. (by Guard) . you can see all th things im talking about are feelings, most are not reality when it comes to really improving the performance...
http://www.sharkwerks.com/products.php?pid=464

a snip from the article says that a closer 3rd to 2nd helps with getting the engine into the power band.. this is a little misleading, because the gear closeness with 2nd and 3rd already do this quite nicely stock. there is no advantage for all uses to do such a gear change and it is quite expensive too. the article also says, by shorting the gears, you make them closer.. NO, the gears are no closer by shortening, (unless you make them closer) And, even if you did, it wouldnt matter because porsche already matched the closeness of gears to match the HP range very well. this means, very little gains in acceleration by modifying it depending on the speed ranges you drive in. (and they are varied, especially in street use)

We have tested re-gearing on our own project GT4 and have settled on a solution that changes 3rd, 4th, and 5th gears to shorter, closer ratios (approx difference is 14% in 3rd, 18% in 4th, and 16% in 5th). This allows shifting to 3rd gear sooner when needed, or staying in 2nd til the normal shift point and jumping to a better position in the powerband in 3rd, and staying in 3rd gear in more situations (ie mid-low speed corners) with improved acceleration. By shortening 3rd, 4th, and 5th gears, you have closer ratios and stay in the powerband longer through typical top speeds, and will be able to retain the original freeway overdrive gear, since 6th gear is unchanged.

stout

I do.

It's a fair question to understand your experience level with this car since we are discussing this car. Charts and theory and general knowledge, while useful, are never the whole story.

So...how many miles or minutes of seat time do you have in a 981 GT4?

I've driven that very car, and shared my observations here on RL. That new 3rd gear wakes the GT4 up on back roads, making more of the GT4's power more accessible at the speeds more likely to be driven on those roads. The shorter 4th is more useful, too. That's not only a feeling—point for point, I have little doubt the SW GT4 is quicker over the road than my car on gearing alone. You no longer run out of 2nd gear and need to shift up to 3rd. You just leave it in 3rd, and rarely lose time on downshifts from the too-tall stock 3rd to the stock 2nd. But "sector times" don't matter on the street. Fun does. That gets back to real-world observation rather than theory. The downside is the mod essentially leaves you with two 3rd gears—because the split between the stock 2nd and the new 3rd is tiny...something like 9 mph iirc. These aren't feelings, these are hard data points.

Manifold

When a theoretical conclusion clearly conflicts with empirical experience based on extensive observations, the theoretical model is too inaccurate. Period. The theoretical model needs to be revised to better fit reality or junked, not defended.

Beantown Kman

Amen!

Alan C.

Mark, I can see where you are coming from. On a shorter track or even longer tracks with a couple of slower turns the shorter gears would help. On some tight back roads they would add a bit more fun.

Power mods would no doubt mask the longer 2nd gear. To that end I have added the Dundon headers which I am very happy with. On the suspension side I installed the TPC DSC control box. With a track alignment.

As to track time and classes I started tracking cars in 1990. Since then I've participated in HSR and PCA club racing. A lot of tracks and time some with a coach.

Is it worth $8k to modify the box? It's up to the individual. I've had a few boxes built by Brian Copan. One in a 993 which turned that car into a whole new car. Worth every penny to me.

Mech33

The trouble is what "feels best" or is "most enjoyable" is subjective and hard to model.

Modeling what gearing puts down the most power at any given speed is easy and there is nothing to refute there.

Automotive tuning market is littered with mods that don't actually do much, and are fed by placebo. "Lightweight crank pullies" where folks can "feel the powa!" are a great example.

Most of the gearing change ask here seems to be related to fun factor on the street, not optimizing lap times.

ajw45

I would like a shorter/closer 1-5 (esp 1-3) and a longer 6. I don't care if it is slower on any or all race tracks, I'm not a professional race car driver, I just want to have fun. I welcome all flaming from the pro drivers on this forum that want to tell me how to gear a street car for maximum performance on public roads.

Alan C.

stout

Yep, 993 is one Porsche that can really benefit. 2.0- and 2.2-liter 911s and 914-6s are "two" more that become new cars with short gears. I believe the GT4 is poised to make at least as big a leap, with a big bonus in terms of livability/comfort/efficiency with a taller 6th.

Sort the engine breathing, and I suspect the GT4 would be pretty insane.

stout

Precisely. There's a reason cars don't go straight from CAD to the production line.

Many, many cars look great on paper—from engine to transmission to damper valving to grip—but don't shine in the real world. Conversely, there are a lot of cars that are not impressive on paper but nevertheless shine on the road.

The same goes for components and systems.

GTgears

And when it is repeated in a thread ad naseum hoping that saying it more times more loudly will somehow make it more true, that's what we call a Kibortion folks...

mgerber

"Most of the gearing change ask here seems to be related to fun factor on the street, not optimizing lap times."

Yes. The street is where I will spend most of my time in this car. And at the risk of speaking for others, likely where most folks will do as well. For me it is all about how the car feels and works as an integrated machine. The more I drive it the less I like the box and ratios. Sign me up for a better set of gears. I spent the $ on my 993 and it transformed the way the car feels, and as a result how much I enjoy driving it.