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post #1 of 35 (permalink) Old 06-16-2008, 11:44 AM Thread Starter
 
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highway speeds with 3.73?

Granted, I have zero experience messing with rear diffs/gearing.

I spoke to someone about swapping in higher gears, 3.73 or higher, and he said to watch out, I'll have more punch off the line, but I'll lose pull on highway speeds, let's say going from 60-90 would be slower. That didn't sound right to me, since I thought the only real difference is the powerband (rpm in reference to mph) is shifted and gas mileage b/c of this.

Any info would be helpful as to whether or not this is true.
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post #2 of 35 (permalink) Old 06-16-2008, 01:24 PM
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He's an idiot. Lower gears will improve pull in EVERY gear and at EVERY speed.

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post #3 of 35 (permalink) Old 06-16-2008, 01:28 PM
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That's BS. Your car will pull more strongly at all speeds.

He may have been referring to the loss of top speed. Your top speed will be reduced to about 85 MPH and you'll need to reprogram the computer to get your top speed back. A driveshaft upgrade is also a highly recommended with taller gears.

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post #4 of 35 (permalink) Old 06-16-2008, 01:28 PM Thread Starter
 
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Originally Posted by Sir William View Post
He's an idiot. Lower gears will improve pull in EVERY gear and at EVERY speed.
sounds good. yeah, he was just some guy that I didn't even know and met at a car meet. didn't think it sounded right, but didn't have any personal experience to go with it.
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post #5 of 35 (permalink) Old 06-16-2008, 01:29 PM Thread Starter
 
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Originally Posted by Trunk Monkey View Post
That's BS. Your car will pull more strongly at all speeds.

He may have been referring to the loss of top speed. Your top speed will be reduced to about 85 MPH and you'll need to reprogram the computer to get your top speed back. A driveshaft upgrade is also a highly recommened with taller gears.
will I be able to reprogram the top speed back with an xcal2? Will I be able to get the same top speed back?
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post #6 of 35 (permalink) Old 06-16-2008, 01:32 PM
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Yes, that's what the xcal2 is all about. You'll actually be able to go faster than the original top speed of about 106 MPH because the xcal can eliminate the top speed governor. But you must upgrade the driveshaft.

Mods? Yea, I got mods ...
Air silencer delete, warp drive, dilithium crystals, flux capacitor, Slingshot Rubber band power adder, Moonshine & Gas, Leaf Blower Supercharger, Hamster Wheel & Hamster, Energizer Bunny generating 1.21 gigawatts, Mr. FusionŽ Home Energy Reactor, hover conversion and a sextant celestial navigation system (The original GPS)
Best 1/4: 1,320 nanoseconds @ 670,616,629.2 miles per hour

"There isn't that much difference anymore between spacecraft, aircraft and modern automobiles..." - Keith Henry, NASA's Langley Research Center
See a list of my real mods and pictures of my car HERE. The true performance of my car was made possible by the Carolinas Crew Chief, RobertP at Rob's Tire & Auto

Last edited by Trunk Monkey; 06-17-2008 at 12:27 AM. Reason: typo correction
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post #7 of 35 (permalink) Old 06-16-2008, 02:07 PM
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....not sure the 3.8L can push the car much over 100 regardless of what the XCal2 does for ya though.

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post #8 of 35 (permalink) Old 06-16-2008, 02:22 PM Thread Starter
 
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....not sure the 3.8L can push the car much over 100 regardless of what the XCal2 does for ya though.
LOL... we'll see... we'll see
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post #9 of 35 (permalink) Old 06-16-2008, 03:06 PM
 
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well... i got my poor ol car up to 103mph. but that was in od, and it was about... 3500rpm - 4000rpm. i probably could of got it to 105-106, but that would of been redlining in od. I dont think i can give it more top speed than that.

How does reprogramming increase your top speed by the way, if my car red lines at 5000rpm, and the gear ratios are the same... i'm confused on how it does that.
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post #10 of 35 (permalink) Old 06-16-2008, 03:14 PM
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I just switched from 3.27s to 3.73s last month. I just broke it in by doing the whole Hot Rod Power Tour (2400 miles) and let me tell you that the highway speeds is where I feel the most improvement. Its like the car wants to keep pulling.

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post #11 of 35 (permalink) Old 06-16-2008, 03:29 PM
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Originally Posted by alasich View Post
well... i got my poor ol car up to 103mph. but that was in OD, and it was about... 3500rpm - 4000rpm. i probably could of got it to 105-106, but that would of been redlining in OD. I don't think i can give it more top speed than that.

How does reprogramming increase your top speed by the way, if my car red lines at 5000rpm, and the gear ratios are the same... I'm confused on how it does that.
There's a top end (speed) limiter built into the EEC program that keeps you from over reving the driveshaft by limiting how fast you can go. The Xcal2 either eliminates or resets the limiter to a higher point and allows your car to go faster. Like you said, the V6 can only go so high but on the V8's it makes a much bigger difference.

Here are some of my video's for comparison these videos are of my car with 3.73 gears installed. The first video is where I hit the rev limiter at 83 to 85 MPH.



This video is with a program that gave me my top end back.


Mods? Yea, I got mods ...
Air silencer delete, warp drive, dilithium crystals, flux capacitor, Slingshot Rubber band power adder, Moonshine & Gas, Leaf Blower Supercharger, Hamster Wheel & Hamster, Energizer Bunny generating 1.21 gigawatts, Mr. FusionŽ Home Energy Reactor, hover conversion and a sextant celestial navigation system (The original GPS)
Best 1/4: 1,320 nanoseconds @ 670,616,629.2 miles per hour

"There isn't that much difference anymore between spacecraft, aircraft and modern automobiles..." - Keith Henry, NASA's Langley Research Center
See a list of my real mods and pictures of my car HERE. The true performance of my car was made possible by the Carolinas Crew Chief, RobertP at Rob's Tire & Auto

Last edited by Trunk Monkey; 06-16-2008 at 03:39 PM. Reason: Added Videos
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post #12 of 35 (permalink) Old 06-16-2008, 03:32 PM
 
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sweet, so it pretty much wont do anything for a v6.
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post #13 of 35 (permalink) Old 06-16-2008, 03:35 PM
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Without a program you'll be limited to 85 MPH. A program will get you back to 100 or so and 3.73 gears will get you there a lot faster.

Mods? Yea, I got mods ...
Air silencer delete, warp drive, dilithium crystals, flux capacitor, Slingshot Rubber band power adder, Moonshine & Gas, Leaf Blower Supercharger, Hamster Wheel & Hamster, Energizer Bunny generating 1.21 gigawatts, Mr. FusionŽ Home Energy Reactor, hover conversion and a sextant celestial navigation system (The original GPS)
Best 1/4: 1,320 nanoseconds @ 670,616,629.2 miles per hour

"There isn't that much difference anymore between spacecraft, aircraft and modern automobiles..." - Keith Henry, NASA's Langley Research Center
See a list of my real mods and pictures of my car HERE. The true performance of my car was made possible by the Carolinas Crew Chief, RobertP at Rob's Tire & Auto
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post #14 of 35 (permalink) Old 06-16-2008, 03:38 PM Thread Starter
 
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Without a program you'll be limited to 85 MPH. A program will get you back to 100 or so and 3.73 gears will get you there a lot faster.
hmmm, so what kind of top speed will I be able to get in the end, or is 100ish it?
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post #15 of 35 (permalink) Old 06-16-2008, 03:48 PM
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Yea, unless you do some other mod to the car. You'll have the same top end you had before. The reason the rev limiter is there is to keep you from spinning your driveshaft off of the car. So, in order to go faster you need to get a program and you need to upgrade your driveshaft. And you need tires rated for higher speed. Going fast is a complicated process. Neglect one part of the system and it will bite you.

Mods? Yea, I got mods ...
Air silencer delete, warp drive, dilithium crystals, flux capacitor, Slingshot Rubber band power adder, Moonshine & Gas, Leaf Blower Supercharger, Hamster Wheel & Hamster, Energizer Bunny generating 1.21 gigawatts, Mr. FusionŽ Home Energy Reactor, hover conversion and a sextant celestial navigation system (The original GPS)
Best 1/4: 1,320 nanoseconds @ 670,616,629.2 miles per hour

"There isn't that much difference anymore between spacecraft, aircraft and modern automobiles..." - Keith Henry, NASA's Langley Research Center
See a list of my real mods and pictures of my car HERE. The true performance of my car was made possible by the Carolinas Crew Chief, RobertP at Rob's Tire & Auto
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post #16 of 35 (permalink) Old 06-16-2008, 03:54 PM
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Have you read through the Gears section of the technical articles yet?

If not, Here's a link to them.

http://www.tccoa.com/articles/gears/index.html

Mods? Yea, I got mods ...
Air silencer delete, warp drive, dilithium crystals, flux capacitor, Slingshot Rubber band power adder, Moonshine & Gas, Leaf Blower Supercharger, Hamster Wheel & Hamster, Energizer Bunny generating 1.21 gigawatts, Mr. FusionŽ Home Energy Reactor, hover conversion and a sextant celestial navigation system (The original GPS)
Best 1/4: 1,320 nanoseconds @ 670,616,629.2 miles per hour

"There isn't that much difference anymore between spacecraft, aircraft and modern automobiles..." - Keith Henry, NASA's Langley Research Center
See a list of my real mods and pictures of my car HERE. The true performance of my car was made possible by the Carolinas Crew Chief, RobertP at Rob's Tire & Auto
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post #17 of 35 (permalink) Old 06-16-2008, 04:28 PM Thread Starter
 
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Have you read through the Gears section of the technical articles yet?

If not, Here's a link to them.

http://www.tccoa.com/articles/gears/index.html
thanks for the link, just read through everything. Still doesn't give me much hope on a higher top speed though... the only thing I can think is a larger overall tire/wheel diameter, but not sure how effective that would be plus I'm not a huge fan of super large wheels/tires.
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post #18 of 35 (permalink) Old 06-16-2008, 06:16 PM
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Just for the record, I had a 91 3.8 tbird with the speed sensor wire going to the computer cut, and was able to hit 127mph in it. That was with stock 3.08 gears, and I don't remember what the rpms were, but for people saying the 3.8 won't go over 100, you are very wrong. With 3.73s on a 3.8, and a tune, you would probably be able to go slightly faster than that since you would be at a higher rpm and making slightly more power than with the stock gears. You would definitely be able to hit 120+ though, even with a 3.8.

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post #19 of 35 (permalink) Old 06-16-2008, 08:00 PM Thread Starter
 
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Just for the record, I had a 91 3.8 tbird with the speed sensor wire going to the computer cut, and was able to hit 127mph in it. That was with stock 3.08 gears, and I don't remember what the rpms were, but for people saying the 3.8 won't go over 100, you are very wrong. With 3.73s on a 3.8, and a tune, you would probably be able to go slightly faster than that since you would be at a higher rpm and making slightly more power than with the stock gears. You would definitely be able to hit 120+ though, even with a 3.8.
yeah, i just confirmed over at SSM that the 3.8 will definitely go higher than the claimed 106, closer to 120 stock
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post #20 of 35 (permalink) Old 06-16-2008, 09:24 PM
 
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really, this is very interesting. I didnt think that the 3.8 could reach 120. i was out of rpms, although that could have something to do with my torque converter. Like i said, only had mine up to 165kmh. (digital tops out at 99)
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post #21 of 35 (permalink) Old 06-16-2008, 09:47 PM
 
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(digital tops out at 99)
theres a mod for that lol
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post #22 of 35 (permalink) Old 06-17-2008, 03:21 AM
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theres a mod for that lol
There is? I thought only the 93 clusters went higher than 99.

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post #23 of 35 (permalink) Old 06-17-2008, 08:12 AM
 
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There is? I thought only the 93 clusters went higher than 99.
yes there is, but i figured why bother, my car can barely see 99mph, and i never get going that fast anyway
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post #24 of 35 (permalink) Old 06-17-2008, 02:01 PM
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What is the mod? I would definitely be interested in knowing how to make the older clusters read up to 199.

-91 Cougar LS, coming soon, complete overhaul with a 427" Windsor.
-90 XR7 5-speed black on black w/sunroof, MP2, coated rotors, double intercooler, 15%OD, ported heads, comp stage 1 cam, 85mm TB, 90MM LMAF, 80# injectors, and ported big valve heads
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post #25 of 35 (permalink) Old 06-18-2008, 09:46 AM
 
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http://www.coolcats.net/tech/advanced/199speedo.html

doesnt work with our cougars though
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post #26 of 35 (permalink) Old 08-30-2008, 02:17 AM
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kick this thread up again... I can't see a MN12 with a N/A 3.8 going that fast... But yeah if you do 3.73's upgrade the driveshaft. I have done well over 140 in my tbird. I think I've got 145 left in my GPS. I don't know how Accurate my Tach is but the fastest I've ever had my bird (before GPS) was pegged out on the 145 speedo and the RPM's on the tach were 5300. But that took a very long time to get there. I'm pretty sure I was approaching a top speed.

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post #27 of 35 (permalink) Old 08-30-2008, 02:54 AM
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kick this thread up again... I can't see a MN12 with a N/A 3.8 going that fast... But yeah if you do 3.73's upgrade the driveshaft. I have done well over 140 in my tbird. I think I've got 145 left in my GPS. I don't know how Accurate my Tach is but the fastest I've ever had my bird (before GPS) was pegged out on the 145 speedo and the RPM's on the tach were 5300. But that took a very long time to get there. I'm pretty sure I was approaching a top speed.

i beg to differ, 94 lx 3.8, it was in overdrive, od button was on the fritz.

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post #28 of 35 (permalink) Old 08-30-2008, 01:52 PM
 
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OMG!!!!! when mines at 165km/h the car is about 4000rpm. could i really get that much faster with the remaining rpm... dont forget i dont have a locking torque converter. but have 2.73 rear gears
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post #29 of 35 (permalink) Old 08-30-2008, 02:10 PM
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lol, i think it had the 3.27's as soon as it would hit the limiter the tach would do a little dance between 3,000 and 4,000 when i snapped the pic it was on the low side. (this of course was done on a private road. do not attempt this at home. )

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post #30 of 35 (permalink) Old 08-30-2008, 04:01 PM
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if you wanna calculate out your speed I like to use Denny's Potential Speed calculator. But I think for it to work you need a locking conerter so you can get a guestimate of your RPM range. Without a locking converter and 2.73's I don't know if you'll have the power to make it that high. 3.73's are a good compromise for Hwy and speed. As of right now without a decent tune that locks the TC up when it should and no EGR the car gets anywhere from 24-26MPG on the interstate. Which really isn't bad at all in my opinion. We'll see how she does after I get all the vacuum lines hooked back up and EGR turned back on and all the work done to the car.

I'm also going to try and find a private road back around my home town. I use one that all the race guys use to test their cars on in Washington. Doubt I'll find one in NC though.

Here's the speed calculator http://www.dennysdriveshaft.com/pote...alculator.html

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