Stillen 3.90 Gear Info
- Thread starter dbk
- Start date
californiacuda
GT Owner
- Oct 21, 2005
- 919
With the 3.90 gear change, more tractive force is generated at the rear wheels, but with whipple, the tires can already be blown off in 1, 2, 3rd gear.
More shifts may be needed to obtain a certain speed(0-60) and take maybe .25 seconds. During shifts, acceleration does not occur.
I don't see how time to a certain speed can be decreased with the 3.90 gear change. But I'm open to other ideas.
More shifts may be needed to obtain a certain speed(0-60) and take maybe .25 seconds. During shifts, acceleration does not occur.
I don't see how time to a certain speed can be decreased with the 3.90 gear change. But I'm open to other ideas.
cobrar1339
GT Owner
This is not a change for everyone. Those that have the whipple or turbo cars may be better off with the 3.30's.
Those with fairly stock cars or those with pulley and conservative tune may want to consider this option.
Provided you could get traction and say the race was to 50 mph, the 3.90 geared car should be quicker. Gears will make you feel like you have better throttle response, easier to stay in the sweet spot, less RPM drop between shifts.
Get on your ten speed bike, put it in 10th gear. You have to stand up and use all your weight and energy to make it go. Now down shift to fourth and it is a lot easier. The 5th gear bike will get to a certain point quicker, but after the 10th gear bike builds momentum, the race is over. It will come from behind to win. The 5th gear bike will max speed by how fast you can pump the pedals. But who will win the 50 yard dash from a roll?. The 5th gear bike will. All depends how long the dash is.
The geared car will be quicker in more typical driving situations than the 3.30 car.
Just my experience with gear changes over the years. You can go too far as well. Is the 3.90 perfect?, maybe 3.70 is the number. But I think the guys at Stillen have a good handle on this from the rally run. Steve and crew know a few things about selecting gears I am guessing. If you have never played with this ,you will be skeptical until you drive one or ride in one that has been changed. I was, but that was 30 years ago.
Those with fairly stock cars or those with pulley and conservative tune may want to consider this option.
Provided you could get traction and say the race was to 50 mph, the 3.90 geared car should be quicker. Gears will make you feel like you have better throttle response, easier to stay in the sweet spot, less RPM drop between shifts.
Get on your ten speed bike, put it in 10th gear. You have to stand up and use all your weight and energy to make it go. Now down shift to fourth and it is a lot easier. The 5th gear bike will get to a certain point quicker, but after the 10th gear bike builds momentum, the race is over. It will come from behind to win. The 5th gear bike will max speed by how fast you can pump the pedals. But who will win the 50 yard dash from a roll?. The 5th gear bike will. All depends how long the dash is.
The geared car will be quicker in more typical driving situations than the 3.30 car.
Just my experience with gear changes over the years. You can go too far as well. Is the 3.90 perfect?, maybe 3.70 is the number. But I think the guys at Stillen have a good handle on this from the rally run. Steve and crew know a few things about selecting gears I am guessing. If you have never played with this ,you will be skeptical until you drive one or ride in one that has been changed. I was, but that was 30 years ago.
AGREED !!!!!!!!!!!
Excellant Post Kendall !!!!!!!!!!!!!!!!!!!
:thumbsup :thumbsup :thumbsup
AZGT
GT Owner
Here's an old link I started about ratios.
Shows some of the figuring to get "ideal", etc.
What I saw said 3:83 would be perfect, so 3:90 is great.
http://www.fordgtforum.com/forums/showthread.php?t=765
Shows some of the figuring to get "ideal", etc.
What I saw said 3:83 would be perfect, so 3:90 is great.
http://www.fordgtforum.com/forums/showthread.php?t=765
As much as I am in favor of shorter gearing :biggrin all this talk about the "drop in revs" changing as you shift, with just a rear gear swap is ... wrong.
The change in revs as you shift from first to second, for example, is set by the ratio of first gear to second gear. It's not impacted by the rear gear.
In more detail :
Stock gearing, run first gear out to redline. Vehicle speed will be 62mph, at the engine speed we'll just call "redline". When you shift to second, you'll still be going 62mph. We know that vehicle speed at redline in second gear is 95mph with stock gearing, so engine speed just after the shift to second will be (62/95)*redline, or 65% of redline after the shift to second.
Proposed gearing, run first out to redline. Vehicle speed will be 53mph, at the engine speed we'll just call "redline". When you shift to second, you'll still be going 53mph. We know that vehicle speed at redline in second gear is 81mph with the proposed gearing, so engine speed just after the shift to second will be (53/81)*redline, or 65% of redline after the shift to second.
Bottom line : the drop in revs as you shift, at any engine speed, is NOT a function of the rear gear. It's only impacted by the different ratio of each gear. Stillen should know better.
I still want the product, but obviously not for this reason.
The change in revs as you shift from first to second, for example, is set by the ratio of first gear to second gear. It's not impacted by the rear gear.
In more detail :
Stock gearing, run first gear out to redline. Vehicle speed will be 62mph, at the engine speed we'll just call "redline". When you shift to second, you'll still be going 62mph. We know that vehicle speed at redline in second gear is 95mph with stock gearing, so engine speed just after the shift to second will be (62/95)*redline, or 65% of redline after the shift to second.
Proposed gearing, run first out to redline. Vehicle speed will be 53mph, at the engine speed we'll just call "redline". When you shift to second, you'll still be going 53mph. We know that vehicle speed at redline in second gear is 81mph with the proposed gearing, so engine speed just after the shift to second will be (53/81)*redline, or 65% of redline after the shift to second.
Bottom line : the drop in revs as you shift, at any engine speed, is NOT a function of the rear gear. It's only impacted by the different ratio of each gear. Stillen should know better.
I still want the product, but obviously not for this reason.
Red Rocket
GT Owner
Right. But unlike what Cuda thinks, a car with a lower-geared rear end will be quicker than one with a taller rear end, all things being equal. The trade-off is the top speed in each gear. It is interesting to note that the way top fuel dragsters get "away with'' using lower gearing on their cars is because their rear tires grow taller as the dragster accelerates, thus raising the gearing as the car goes thru the 1/4 mile. They calculate the amount of tire growth into their choice of gearing.
agreed :thumbsup
Again, i'm all in favor of a lower rear-gear ... above, i linked my old thread on this topic :biggrin The "60mph in first" is purely marketing-driven ... that's old news. But there's some bad info in this thread (including the original post by the potential supplier of the new gear :frown ) about the rear-gear swap having an impact on the rpm change between gears ... just ain't so.
Red Rocket
GT Owner
Absolutely right. If it is going to be a big problem for Whipple cars to keep traction, are there any new stickier tire options available? If so, please distinguish between track and street options.
By the way ... i absolutely recognize that with the proposed lower gear, when you shift into second at 50 mph you'll immediately have more "accelerative force" available to you ... compared to shifting into second at 60 mph with stock gearing :biggrin But that's not because the engine speed is any different :wink that's my point ... and i'll let it drop now.
Yes, stickier tires are always a plus! And remember ... those huge diameter rear tires are not your friend for acceleration ... they conspire to make the stock gearing even "taller". So for anyone comparing a 3.90 rear-gear to, say, a vette or viper with similar gears, it's still not a valid comparison. The ratio needs to be "adjusted" by tire diameter as well. Might just find that 3.90 is not short enough! :biggrin
As i said almost two years ago ... i'd just like to use more than 2 or 3 gears (out of SIX, for crying out loud!) for street duty. And yes ... the more gears i can stand on and smoke the tires, the bigger my grin will be :biggrin
Yes, stickier tires are always a plus! And remember ... those huge diameter rear tires are not your friend for acceleration ... they conspire to make the stock gearing even "taller". So for anyone comparing a 3.90 rear-gear to, say, a vette or viper with similar gears, it's still not a valid comparison. The ratio needs to be "adjusted" by tire diameter as well. Might just find that 3.90 is not short enough! :biggrin
As i said almost two years ago ... i'd just like to use more than 2 or 3 gears (out of SIX, for crying out loud!) for street duty. And yes ... the more gears i can stand on and smoke the tires, the bigger my grin will be :biggrin
STORMCAT
GT
I agree with this last paragraph. That a 3.90 maybe too short for a modded car. 3.70 or 3.73 maybe the best of both worlds if you plan to add more power..
The point isn't comparing a 3.90 gear in a GT to a 3.90 gear in a Vette, the point is going from a taller to a shorter gearing in any car, as long as the change is reasonable.
fjpikul
GT Owner
Kirby Vieira
GT Owner/B.o.D
IMO, the optimum rear ratio is likely the single best performance modification that can be made to a fast car. If Stillen has found the 3.90 to be optimum, I would expect a stock GT with the 3.90 to be at least as fast from zero to its top speed as a GT with the basic pulley upgrade and the stock 3.30. The GT with a pulley upgrade and the 3.90 may perform very similar to a Whippled GT with 3.30. The 3.90 in a Whippled GT would likely render 1st gear useless, but with the proper tires, from 2nd gear on it would probably be Veyron-like. Lastly, Piko Joe would probably be undefeated if he had a 3.90.
Don't worry, I didn't think you were. I was just making sure you didn't think I thought a 3.90 in the GT was equivalent to a 3.90 in the Vette. Just that it's a change to the more aggressive gearing. Or at least that's what I thought. I think....
AZGT
GT Owner
Should be OK since it is a six speed with final overdrive.
In the past I ran a Chevy with 4:88 and wide ratio transmission. Would start in 3rd and shift to 4th for normal driving. BUT, when the foot was in it for 1st, OMG.
Even a 4:11 with a 4 speed isn't bad, but that was about the limit for NORMAL street driving. That, with a 6 speed, would have been no problem.
Geez, even had one friend that ran 6:17. Can we say stump puller?
The discussion about gear changes is correct. The drop / increase in RPMs is related to the spacing between transmission / transaxle gears (hence wide and close ratios).
I would imagine what does change is the torque (I think - so now I am fair game for attack) which gets in to the power band quicker because of the lower ratio - therefore less potential bogging between gears.
If the price is right, a 3:90 is a no brainer performance upgrade - and a wonderful driving experience upgrade.
Last edited:
- Aug 25, 2006
- 4,436
This is an interesting thread surrounding a product/service that IMO (this after considering it long and hard for the last several days) would be better placed within a gal lacking in torque.
The GT even in OEM trim is not lacking in torque and this is typically a primary reason why an alternate gear would be installed into any gal. Changing the ring gear will not change the gear shift spread but rather move them (in this case) down. Then add to this that a large percentage of folks have elected to install smaller pulleys further increasing the gals torque not to mention those that have pulled the proverbial trigger on the Whipple or the TT conversion for which this would make absolutely no sense.
I have said many times that I both enjoy and tweak on my gals all the time however unless the idea of a ring gear swap is tied to a specific action such as racing where one finds based on a specific course layout that with a little more or little less gear they could maintain their gal in peak power without another shift then sadly (please do not take my opinion the wrong way because it is just that; my opinion) I feel that this is an exercise in futility because on the street all will become accustomed to the gearing and gear spread afforded them and I suspect that even after such a swap it will remain as little more than a lapel pin.
These gals are not lacking in grunt
Takes care
Shadowman
The GT even in OEM trim is not lacking in torque and this is typically a primary reason why an alternate gear would be installed into any gal. Changing the ring gear will not change the gear shift spread but rather move them (in this case) down. Then add to this that a large percentage of folks have elected to install smaller pulleys further increasing the gals torque not to mention those that have pulled the proverbial trigger on the Whipple or the TT conversion for which this would make absolutely no sense.
I have said many times that I both enjoy and tweak on my gals all the time however unless the idea of a ring gear swap is tied to a specific action such as racing where one finds based on a specific course layout that with a little more or little less gear they could maintain their gal in peak power without another shift then sadly (please do not take my opinion the wrong way because it is just that; my opinion) I feel that this is an exercise in futility because on the street all will become accustomed to the gearing and gear spread afforded them and I suspect that even after such a swap it will remain as little more than a lapel pin.
These gals are not lacking in grunt
Takes care
Shadowman
i hear you, man of shadow ... our motors are torquey, no doubt. But that torque translates to "accelerative force" through some pretty tall gear ratios and large rear tires. So, the counterpoint question is : what's the downside of being traction limited through, say, the first 4 gears? I'm not talking about planting your foot and getting a squeak :wink Heck you've still got two more gears left after that. Don't forget ... you can always modulate the torque down with your foot too.
My vote is simple : tire-melting torque on tap in all first 4 gears :biggrin With appropriate throttle control, you'll know you're getting maximum possible acceleration in all those 4 gears. And, you might actually use more than 2 or 3 out of the 6 gears on the street.
What's wrong with that?
My vote is simple : tire-melting torque on tap in all first 4 gears :biggrin With appropriate throttle control, you'll know you're getting maximum possible acceleration in all those 4 gears. And, you might actually use more than 2 or 3 out of the 6 gears on the street.
What's wrong with that?
BlackICE
GT Owner
You guys that want the 3.90 bought the wrong car. You should have gotten a F430 or a motorcycle. The GT stock has monster torque. Even stock with the extremely high 1st gear acceleration is outstanding. Would it be better with a lower diff ratio, yes! But depending on the cost of the gear change you might be able to get a Whipple for the same cost. Now what is going to go faster, a stock car with 3.90 or a car with a Whipple and a 3.3? The rear end ratio chosen should depend on what you what to achieve. There are valid reason to change it to optimize 1/4 mile times, top end speed, or to optimize it for a particular track. Note that most race cars change not only rear end ratios, but also gear spacing to optimize the cars power band for a given track.
My choice would be to gear it lower such that the car could pull 6th all the way to peak HP, around 6500-7200 depending on the engines tunes. Now is that useful for me, no, because I don't ever see myself driving at 200+ mph, but it makes me feel better knowing the car can. Right now 6th is useless for anything other than keeping the noise down and the gas mileage up. Only a TT GT can theoretically use 6th with a 3.30. A Whippled GT would need something between 3.3 and 3.9. A 3.9 on a Whippled car would make 5th too low and 6th too high!
My choice would be to gear it lower such that the car could pull 6th all the way to peak HP, around 6500-7200 depending on the engines tunes. Now is that useful for me, no, because I don't ever see myself driving at 200+ mph, but it makes me feel better knowing the car can. Right now 6th is useless for anything other than keeping the noise down and the gas mileage up. Only a TT GT can theoretically use 6th with a 3.30. A Whippled GT would need something between 3.3 and 3.9. A 3.9 on a Whippled car would make 5th too low and 6th too high!