3:55 rear end dragstrip improvement?

[sparkrn]

Does anyone have real numbers on what 3:55 gears have done for your viper. Looking for some before and after results.

[sparkrn]

I'm so disappointed, so many talk up the 3:55's, yet not one response. Come on viper world, let's here it!

[Joel]

Not been on a dragstrip but I can tell you seat of the pants feels faster. That's probably not what you want to hear. From my drag racing days in old muscle cars, I can tell you that a change from a 2.92 or 3.23 to a 3.55 or a 3.91 made 2 or 3 tenths difference but in a Viper it is all about how many shifts you have to do and most of my drag strip days were in automatics. If you're just looking for faster quarter mile times, you're missing the point of the gear change. As many others have said, the change in drive-ability is amazing. It makes the car more fun and 6th gear useable. To me that was worth the money. I'd say a change from 3.01 gears to a 3.55 will make you change to one more gear in the quarter mile. Instead of third you may have to shift to fourth so you may not see a difference in quarter mile times.

[sparkrn]

Thanks Joel, that all seems to make good sense.

[kirkinsb]

I had my 3.55s put in 3 weeks ago...so I can vividly remember how my Gen 3 viper was with the stock gearing. I don't quarter mile either..but just driving around town is so much more fun and seat of the pants feel is night and day. My Viper just seems happier with the 3.55s.

I have not had warm weather yet nor am I past the break-in period on my gears...but I can already tell it is going to be a blast! Here is a nice write up...and the same place I bought my gears.

http://www.viperpartsrack.com/gears-...al-dana-quaife

[Luisv]

I'd be curious to see what is said... I can however tell you that it may not make a difference in the 1/4 mile.

Believe it or not, it may make no difference. A number of factors come into play. It depends on the overall combination and where you change gears. That is why people talk about "drivability" changing. In the 1/4 mile a 3.73 will give you more acceleration but will give you a slower speed at a given RPM. For example, you might hit redline faster than somebody with a 3.06 gear, but they will be in each gear longer, or in the power band longer, and will be moving at a faster speed. That means that the gain you have at the line and at 60' may be lost when the 3.06 car catches you because they are moving faster at the top of first gear.

Will a 3.73 feel "faster".... Yes because you are rowing through gears faster.... But are you losing the hole shot at the top of first.... Most likely.

I've been on the fence about the gearing. You will see dozens of folks telling you to do it. The most common message is the "drivability is better" and "now 6th gear is useful". My view... 6th gear, for me, is quite useful. At 75 or 80 mph I get 20+ mpg. I'm turning 1500 RPM at those speeds on the highway. I live in Florida... it's flat and straight. That's useful. Am I using 6th when driving in the mountains of Tennessee or at the track? Nope. Drivability? I'd have to see about that... sure it'll be more fun to row through gears faster, but in the end all that is changing is where I change gears. One thing though.... you are putting down more torque.... this is a BIG plus. Let's face it... the cool part of our 10 cyl is the crazy torque just about anywhere in the band. Making that increase will just make it more visceral. There's a lot to be said about that. Hence my first comment... I am on the fence... I will likely do it eventually but I may do other things first.

Bottom line... spending $1200 to have gears put in may be better spent (in terms of better ET's) if you go to better headers and high flow cats...

I think a buddy of mine gave me a few runs on an engine/race simulator that ran 3.73's vs. the 3.06... I'll have to find it, but he gives me 1/4 mile passes with the options. He did it to show me what some mild mods would do with the Viper. He was curious and was surprised how much is in our stock engines that even just a set 1.7 rockers can make. If I find it, I can give you the theoretical differences.

[02ACR]

Back in the day I changed the gear in my 6 speed Camaro from 3.42 to 4.10 and it dropped my quarter mile time by about 4 tenths and added about 3 mph. Viper results may differ, but both cars have T56 transmissions with the same gear ratios. Remember that the 3.55 will probably need a stickier tire to take advantage of the acceleration.

[James430]

I tried the 3:55 gears in mine and should have taken the advice not to use it if your running high HP......I'm sure with a stock motor it would be great.....But impossible to hook up without slicks if your running higher HP...Is your car stock?....went back to stock rear after 3 weeks

[tagoo]

I don't have any back to back experience with only the gear change (I did heads/cam) at the same time. But, depending on you and your mods, 3.55 gears could help or hurt you quarter times.

With 3.55 gears, you will notice that it is much easier to lose traction at the line or in second gear if you don't have a well prepared track or if you don't have good drag radials or slicks. Spinning tires = slow times. Also, the shifts will come much quicker. That took me awhile to get used to. Until you get used to the quicker shifts, your times may actually get worse.


If there are no traction or shifting issues, depending on your mods, 3.55 gears can help your quarter times. When my car was stock, I had two choices at the drag strip. I could 1) leave the car in third gear and cross the finish line at, or near, redline, or 2) I could shift into 4th about 100 feet before the finish line. Neither of these felt really good. It always felt like my car accelerated most in the 3-5K rpm range. If I crossed the line in third gear at redline, it felt like my power was starting to drop off for the last 100 feet or so. If I crossed the line in fourth gear, I felt like I still hadn't started pulling hard in that gear yet (although I consistently had better traps and ETs crossing in 4th gear).

After switching to 3.55 gears, I am still in 4th gear when I cross the line - so i have the same number of shifts - but I am at a much higher rpm. I feel like I am able to take advantage of the "sweet" rpm range of 3-5K in fourth gear. I believe that being able to use that range of the rpm band provides a significant improvement in ETs and maybe even trap speed. However, if you do enough modifications that you need to shift into 5th gear before crossing the line, you would probably be better off sticking with stock gears than adding yet another shift.

[Camfab]

I don't have any back to back experience with only the gear change (I did heads/cam) at the same time. But, depending on you and your mods, 3.55 gears could help or hurt you quarter times.

With 3.55 gears, you will notice that it is much easier to lose traction at the line or in second gear if you don't have a well prepared track or if you don't have good drag radials or slicks. Spinning tires = slow times. Also, the shifts will come much quicker. That took me awhile to get used to. Until you get used to the quicker shifts, your times may actually get worse.


If there are no traction or shifting issues, depending on your mods, 3.55 gears can help your quarter times. When my car was stock, I had two choices at the drag strip. I could 1) leave the car in third gear and cross the finish line at, or near, redline, or 2) I could shift into 4th about 100 feet before the finish line. Neither of these felt really good. It always felt like my car accelerated most in the 3-5K rpm range. If I crossed the line in third gear at redline, it felt like my power was starting to drop off for the last 100 feet or so. If I crossed the line in fourth gear, I felt like I still hadn't started pulling hard in that gear yet (although I consistently had better traps and ETs crossing in 4th gear).

After switching to 3.55 gears, I am still in 4th gear when I cross the line - so i have the same number of shifts - but I am at a much higher rpm. I feel like I am able to take advantage of the "sweet" rpm range of 3-5K in fourth gear. I believe that being able to use that range of the rpm band provides a significant improvement in ETs and maybe even trap speed. However, if you do enough modifications that you need to shift into 5th gear before crossing the line, you would probably be better off sticking with stock gears than adding yet another shift.

I agree with your comments. I just upped my tire size 345/35-18. Larger OD tempers the gear so I'm just below redline going through the traps. The larger OD also puts more rubber on the ground.

[Vprbite]

I loved 355s in my 02. I will do them in my 06. But I just did full exhaust and am enjoying that at the moment. Can I say something about this "useable 6th gear" thing though please. I can't understand how anyone can find 6th gear "unusable." I think this is a matter of perception from two things. 1, people used to driving automatics most of the time, as their DD, for years, are used to being able to stomp on it while doing 65 and feel the car pull hard because the automatic downshifted for them. They will not get this feeling in a 6 spd manual running a little above idle. This factors into my 2nd point. Around town we are used to our cars being absolute torque monsters. Because they are, and also because around town we tend to run around in a sweet spot gear. We don't run at redline or bog down in 5th at 35 mph. We probably run around town in 2nd or 3rd where we can step on the gas and leave almost anyone in the dust and the exhaust sounds good. When we are on the freeway, we could stay in 4th but if you are doing a long cruise, aside from getting bad mileage, it becomes bit too intense on the senses after 20 minutes or so. Of course you will have monsterous acceleration, but it won't feel good for cruisin. This all adds up to people cruising in 6th, getting 21mph and enjoying the low RPMs but they step on it and wonder where the acceleration went because their perception tells them they should be pinning themselves in the seat right now. The truth is you probably accelerate as fast as the average passenger car but you are thinking "my Viper runs like a rocket" and usually when on the freeway the RPMs go up quickly when I press the pedal.

Yah, you will accelerate quicker in 6th with 3:55s, but I don't believe that 6th is barely usable. I believe this to be a matter of perception, as I hope to have explained clearly. That doesn't mean it isn't a worthwhile mod or fun as all get out around town. I just don't think 6th is "useless" as people seem to say.

[dmerkle]

I'm so disappointed, so many posts on this thread since last week, yet not one response from op since day one! Come on sparkrn, let's here it!
: )

I'll attempt to summarize things...
1) With the stock 3.06, the cops will clock you at 80. With the 3.55, they'll get you for 85.
Either way, that's an infraction over 30 mph in a 35 zone, so you'll be wearing "bracelets" as Mike would say

2) Once you start autocrossing this year, 3.55s will have you doing donuts in the middle of Rockford speedway while the rest of us are eating donuts in the grandstands applauding
3) The extra shifting with the 3.55s will build your arm strength, which will come in handy as your burying another Viper grave

I'll see you at Women's Day

[Camfab]

I'll attempt to summarize things...
1) With the stock 3.06, the cops will clock you at 80. With the 3.55, they'll get you for 85.

I think you got this part reversed..........

[Matt Dillon]

JonB is the EXPERT on this, can't Believe he hasn't Responded! Just go to his Partsrack website & look it up, He Explains EVERYTHING that you'd want to know! But, as far as anything else i Don't believe it makes it Faster! Quicker on the low end, but you Lose MPH on the Top End! Guess, it Depends on What you Wanting! I STILL Very Rarely use 6th gear though, i could have probably went to the 3.73's as far as Shifting it's NOT that much difference as you would think, mostly 1st & 2nd! GL!

[Camfab]

I can assure you my car is quicker in the qtr with 3:55's

[Tom, F&L GoR]

Years ago someone on the PacWest chapter posted an article about the math of this. The key data can be gleaned from this:
thrust2.jpg

You will have more thrust (forward push) in first gear, but after that it depends on shifting. For every gear choice and engine speed above 40 MPH each rear axle ratio is about the same. So for drag racing, the improvement depends on traction at the line. For any other type of event that requires shifting, not so much different.

[Steve M]

Back in the day I changed the gear in my 6 speed Camaro from 3.42 to 4.10 and it dropped my quarter mile time by about 4 tenths and added about 3 mph. Viper results may differ, but both cars have T56 transmissions with the same gear ratios. Remember that the 3.55 will probably need a stickier tire to take advantage of the acceleration.

For reference, I came out of a 2002 Camaro...that car stock with 3.42s put you in a bad spot for 1/4 mile racing. 3rd gear wasn't long enough to make it through the traps, so you were shifting right before the traps, and that's never good. 4.10s allowed you to get into 4th gear well before the traps, and it also let you get out of the hole a little easier (provided you had traction)...those two things make a world of difference when it comes to the 1/4 mile.

You really need to look at the overall picture of how you will use the car...if you are doing 1/2 or full mile events, gears will likely hurt more than help. 1/4 mile will depend on your projected trap speed/power level...what works for stock power levels might not work if you start doing some heavy modding. Road courses will depend on the course you frequent the most...in general, more shifting doesn't = faster lap times. If you aren't into racing, the 3.55s will likely make it more fun around town, but not so much fun on the highway since you'll be turning more RPMs (more potential for exhaust drone, and less MPGs).

This isn't a no-brainer by any stretch of the imagination...you have to be very honest about what you intend to do with the car, and not just listen to the "I did 3.55s and they were AWESOME" crowd that lingers on here. Mechanical torque multiplication often sounds good on paper, but there's the additional heat and more wear and tear that comes along with it that people fail to mention or even take into account. There are also folks on here that will quickly point to the fact that the Gen 5 Vipers come with 3.55s now, but fail to mention that the transmission ratios were completely changed in addition to the 3.55s to make everything work together. There are also lots of people that live in areas like Texas with long stretches of open roads that don't care for the 3.55s and shorter 6th gear in the Gen 5 due to the 2,000+ RPMs you turn while cruising @ 80+ MPH, and want the taller 6th gear back.

There's no such thing as a free lunch.

[stuntman]

Years ago someone on the PacWest chapter posted an article about the math of this. The key data can be gleaned from this:
thrust2.jpg

You will have more thrust (forward push) in first gear, but after that it depends on shifting. For every gear choice and engine speed above 40 MPH each rear axle ratio is about the same. So for drag racing, the improvement depends on traction at the line. For any other type of event that requires shifting, not so much different.

Very helpful. I have this thrust graph for a different car and it is a great visualization tool. Do you have a picture of the thrusts above 100mph? I would still say the 3.73s are averaging slightly more thrust on average up to 100mph. Do you have another on for 3.55 gears? (That may be the sweet spot).

[sparkrn]

The last three post seem quite helpful, for what I do and don't do, I think the stock gears will stay put.

[Alley]

3.55s? How cute. I run 3.73s w/ Hoosiers. I pretty much outlaunch anything with comparable hp including awd cars. 4th gear will end at redline at approx 126mph so keep that in mind if your planning on trapping higher then that. Fun factor is off the charts.

[Bugman Jeff]

I've often wondered why we keep our gear ratios what they are. In T-56 F-bodies and Mustangs, 3.73s and 4.10s are very common swaps, but 3.73s are fairly rare, and 4.10s almost unheard of in the Viper. I've heard things like "you have to do too much shifting" and "it cuts down your top speed." Those guys don't seem to have any trouble with extra shifting, why should we? And sure it will knock your top speed down, but how many of us actually use the high speed our cars are capable of?

[Tom, F&L GoR]

I saved the PacWest article; following is a cut-n-paste.


So you've heard that changing the rear differential gear ratios is one of the best "bang for the bucks" you can get, and now you're stumped on which ratio to choose. The stock gear ratio is 3.07:1. Most folks seems to be recommending the 3.54:1 ratio, while others are saying that you should go with the 3.30:1 gears. One person is even happy with their 3.73:1 gears.

So to lend you a hand in the decision making process, I'll discuss two issues that may help you figure this all out. The first thing to talk about is why numerically higher gear ratios give you quicker acceleration. The second is real world issues, namely matching gears to your engine and car useage, traction limits, and effects on top speed.



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Okay, so why might you accelerate faster with 3.54 gears? It all boils down to torque (actually torque mulitplication) which I go one step further and think of simply as thrust. After all, divide the rear wheel torque (in ft-lbf) by the radius of your rear tire (in feet) and you have pounds of thrust.

I'll take a step back and explain motor torque and gearing. You can't just hook up the motor directly to the rear wheels with a 1:1 ratio shaft. Sure, the Viper has about 500 ft-lbf of peak torque, but this is still not enough to get you moving swiftly from a green light. Plus, you'd have to slip the clutch tremendously to start moving smoothly. In sixth gear, your Viper is putting out over 600 ft-lbf of torque at the rear wheels, so you get the idea of how little oomph that is. This is why your Viper need gears.

The six-speed combined with the rear differential multiplies the engine's torque. Since you're stuck with the six ratios built in to the transmission, you can only alter the torque multiplication by choosing a different rear end gear. From the factory, here's how much the motor torque gets mulitplied:

Gear Transmission Ratio Rear Differential Ratio Combined Multiplication Factor Redline Limited Speed
1st 2.66 3.07 7.98 56 MPH
2nd 1.78 3.07 4.35 84 MPH
3rd 1.33 3.07 4.08 113 MPH
4th 1.00 3.07 3.07 150 MPH
5th 0.74 3.07 2.27 204 MPH *
6th 0.50 3.07 1.54 302 MPH **
* Requires 590 hp
** Requires 2400 hp

So in first gear, the motor torque is mulitplied by 8 before it goes to the tires! That's close to 4000 ft-lbf !

And like I said, I prefer to look at all this in terms of Thrust, so if we plug in the stuff from the table above, here's what the numbers from a stock Viper GTS look like:
Gear Peak Thrust (in pounds)
1st 3200
2nd 2180
3rd 1610
4th 1200
5th 890
6th 600



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If your curious about the calculations, here's how it works: Thrust = Peak Motor Torque x Gear Multiplication Factor x 0.86* / 1.08**
* This is the typical Viper drivetrain efficiency, which means 14% of the motor torque is lost by the time it gets to the rear tires
(see Dyno Tech for more on drivetrain efficiency)
** This is the rear 335/35/17 tire radius, in feet



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So now you have a better idea of how gearing ties into how much oomph your Viper has. And you've probably figured out why increasing the multiplication factor causes greater acceleration in each gear than you previously had. There's more thrust !



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Now you have to shift sooner, because you run up to the redline at a slower speed than before. First gear with a 3.54:1 gear is now only good until 48 MPH. keep in mind that, although there is now additional torque available due to more aggressive gearing, you don't have any more horsepower than you originally had. So what you're essentially doing by changing rear gears is affecting the speed range that your Viper operates most powerfully in. Stay with me here, I'll try to explain.

Let's take a hypothetical trip from zero to 100 MPH. Let's say "Jon" has a 3.73 rear gear in his GTS, while "Paul" has the stock 3.07. Who's going to get there first? Due to the different torque mulitplication effects of their gearing, Jon has 21% more rear wheel torque in each gear, which also means he has 21% more thrust in each gear. Sounds like fun, and now we're thinking Paul is going to be seeing Jon's taillights for the next nine seconds.

We'll return to Jon and Paul in just a minute, but let's look at the mechanics of what's going on here. Each car is blasting full throttle to the century mark. One person is going to be doing some more shifting, becuase thrid gear won't get you to 100 MPH with 3.73s. Both cars are operating in the same RPM ranges as they row through the gears (the transmission is still the same, so the RPM you drop down to after each upshift remains unchanged).

The trick to numerically larger gear ratios is that, from a stop, it allows you to put all of that power to the pavement SOONER. And if you are a drag racer with really, really sticky tires, chances are you'll be spanking the stock-geared competition.

Now I need to show some graphs to help illustrate what's going on here. Here is the thrust produced as they make the trip to 100 MPH. It's pretty obvious where the gear shifts occur:

thrust2.jpg


First Gear shows a BIG difference in available thrust. This is where you'll get the best benefit from a gear change, as you have the potential to put all the motor's power to the ground sooner.

A really good way to look at this graph and compare the two Thrust curves above is to calculate the area under each curve. Interestingly, the area under each curve turns out to be the Total Horsepower Applied to the Pavement. (For you engineer-nerds, Thrust x Speed will give you units of power).


power2.jpg

So by the time Jon gets to 30 MPH, his Viper has planted 300 hp to the ground, while Paul's ride has pushed out only 250 ponies.
After Jon has banged through the gears and hits 100 MPH, 750 horspower has made it's way from crankshaft to pavement, whereas Paul has planted only about 680.
But wait, before you jump up from your computer down to the speed shop and spend your hard-earned dinero on a gear swap, ask yourself if you are purely a drag racer or not. And realistically, do you run hot sticky R1s or BFG Drag Radials every day? The reason I ask is because, for other types of usages, you may end up slowing your car down. If you spend a lot of track time doing 80 to 100 MPH pulling through curves, you don't have a gear shift to contend with in that speed range like you would if you ran a 3.73 gear. And is there really that much more thrust available at that speed anyway due to a gear swap? Actually there is not! Check out the first graph again, the real benefit is at slower speeds, say, less than 65 MPH.

Also consider that getting traction with the 3.07 gear off the line is a challenge, now add 21% MORE TORQUE and try it. So there are a few more things to consider. Oh, and for those concerned about top-speed bragging rights, say goodbye to 192 MPH, because a 3.54 gear will drop that down to 180 MPH, which is the new fifth-gear redline. Granted, your quarter mile times will drop about four tenths of a second, and getting to 60 MPH in less than four seconds sounds like fun (with those R1s, of course), but autocrossing and track racing may have you shifting into and out of the powerband more than you (and your lap times) may be comfortable with.

The best source of information is talking to Viper owners with similar mods who use their cars similar to how you do and ask them what their experience has been. It turns out the the 3.54 gear does work pretty well with a variety of applications. (for those interested in more graphs, e-mail me and I'll send you whatever you want) Also, the degree of modifications you've done to your motor also have a big effect. A stock Viper's torque starts to drop off after 5500 RPM, but a Viper with good exhaust mods has pretty healthy torque just about up to the redline, so maybe it's acceptable to operate at the top range of the RPM band.

[Resident Alien]

^ Excellent explanation!

I've wondered if the 3.55 gear combined with a numerically higher 5th and 6th gear transmission ratio revision (ala 2010 SRT-10 transmissions) would not make the best overall combination for a Gen 1/2/3/4 for all types of driving (except possibly certain autocross and road race events)? I recall Dan Craigin had a solution for numerically higher 5th and 6th gears even for the T-56s.

[stuntman]

6th gear is WAY overdriven and is useless for anything other than highway fuel mileage. I'd still like to see the torque curves through fifth gear, I may plug the Vipers numbers into my graphs for another car. Sounds like 3.30 or 3.55 may be better all around...

[Matt Dillon]

Tom, Awesome Write-Up! Now, can you do one for the RT/10! Lol! jk of Course!