Go Back  DodgeForum.com > Dodge Trucks > Dodge Dakota > 2nd Gen Dakota Tech
Reload this Page >

Transmissions, Gearing and RPM

2nd Gen Dakota Tech 1997 - 2004 Dodge Dakota Tech - The ultimate forum for technical help on the 2nd Gen Dakota.

Transmissions, Gearing and RPM

  #1  
Old 08-06-2013, 02:58 PM
Blacknights
Blacknights is offline
Veteran
Thread Starter
Join Date: Oct 2012
Location: Georgia
Posts: 297
Default Transmissions, Gearing and RPM (Please read before asking questions)

Hey guys and gals, so in response to a thread I ended up compiling a ton of information about gearing and rpm numbers. I've tried to make it as thorough as possible, everything from transmissions to gearing ratios. If you have some information (or proofreading) that you think could be add to this master sheet, feel free to pm so I can make it even better.

Anyways, on to stuff you wanted facts!

I've divided up everything so things are easy to find and understand, if you donít know what you have, Iíve also taken the time to match your transmission with your engine. Automatic transmissions are first on the list, newest transmission first. With dodge the automatics are often the same or similar construction. Example 45RFE is actually a 545RFE the gearing numbers are the same, what is different is TCM (Transmission Control Module). The 4(2,4,6)RE are differentish, I'll put those in after the 545RFE so scroll farther down for those. For those bastards (I hate you out of jealousy) who have a manual 5 speed tranny NV3500 or upgraded to the NV4500, I've made you scroll past the automatics.

(5)45RFE: This transmission is matted with all 4.7 engines (and the hemi engine in other vehicles). This is actually designed and made by Chrysler itself in the US

1st- 3.00
2nd- 1.67 (With the 545RFE the kick down planetary gearing is 1.50)
3rd- 1.00
4th- 0.75
5th- 0.68 (545RFE's 5th gear, when your TCM allows it)
Reverse- 3.00

42FRE: More information on this tranny in time, it is matted with the 3.7 for our '04 models

4(2,4)RE Torqueflite: The 42RE is matted with the 3.9L, The 44RE is matted with 5.2L engines

1st- 2.74
2nd- 1.54
3rd- 1.00
4th- 0.69
Reverse- 2.21

46RE Torqueflite:
This is matted strictly the 5.9L in our trucks. It is a similar construction to the other Torqueflites but as you can see there is a difference in gearing.

1st- 2.45
2nd- 1.45
3rd- 1.00
4th- 0.69
Reverse- 2.35

Aisin AX-15 Manual:
Is the 5-speed transmission in I-4 model and supposedly early 6 cylinder models as well (someone verify that)

No data found

NV3500 Manual (MD):
New Venture 3500 is the standard/stock manual transmission in our trucks

1st- 4.01
2nd- 2.32
3rd- 1.40
4th- 1.00
5th- 0.73
Reverse- 3.55

NV4500 Manual (L&HD):
New Venture 4500 is a very awesome manual transmission that people may upgrade to truck

1st- 5.61
2nd- 3.04
3rd- 1.67
4th- 1.00
5th- 0.73
Reverse- 5.04

For those of us not great with numbers, I've type a paragraph or two. Traditionally dodge truck/suvs 4 and 5 speed automatic transmissions, have 3 normal gears and 4 & 5th are overdrive gears. The automatics have the lower normal and overdrive gears which is the reason they are more fuel efficient at cruising/highway speeds. The automatic transmissions do just that and are good for cruising around and long distance driving. But for the more truck stuff like towing and off-road they are in my opinion completely inadequate. Chrysler itself actually admits that the older Torqueflite transmissions matted with the 3.9 and 5.2L are not suited for heavy duty work as they were designed for light duty.

Now this is where the NV3500 comes in. The lower 1st gear gives significant advantages when towing, and 5th gear isn't so low that you can still use overdrive while towing in some situations. Plus not to mention every advantage from engine braking, holding gears and intuitive shifting. The standard version is rated with an input of 310 ft. lbs. of torque and has a GVWR is rated at 7,500 lbs. with a CGVWR of 11,000 lbs. As a note for those who are looking around for replacements or are just curious. Our trucks only use the wide gear ratio version of this tranny, not the narrow. No GM tranny version is like a Dodge, don't use them as a replacement, Ram 1500 and Dakota share the same gear ratios.

This is where the NV4500 manual transmission comes to the party. This 5 speed stick is perfect and at home in a truck, there can always be better things but this is great. Although the gearing is similar to the 545RFE, the NV4500 was created almost a decade before it. The LD version is designed with GVWR of 14,500 lbs. so in Dakotas and Durangos it is rated to handle 3,000 lbs more then what our GVWR rates us.

Links (I do not vouch for their quality, they are an additional resource):

For rebuilding 42RE transmissions
For rebuilding 44RE transmissions
For rebuilding 46RE transmissions
Video for rebuilding NV3500 transmissions (google search, it keeps embedding the video) - personally I'd vote for just bolting up a NV4500 replacement
For rebuilding NV4500 transmissions - this is an HD version from a cummins but it is well documented

Please note that you should always use a manual when rebuilding transmissions, these links are to give visual examples and further assist you in rebuilding it. To put it simply the post writers and myself are not liable if you mess up.

This link https://dodgeforum.com/forum/1036359-post14.html , is information about how to understand improving your mpg with math and engineering. Not just add more power. For a lot of us, many have tried to find the "magic" efficiency rpm number. One of our members has done quite a bit of math and has brought some engineering to the table. Take a look at this, I found it very interesting to read. A quick facts for those who don't have the time. 4.7L engines cruising (at 70 mph) at less than 2114 rpm and 3.7L/5.7/5.9L at less than 2011 rpm are considered undergeared. I don't quite know how to explain this but undergeared means that the engine is operating before the engine rpm where it can adequately produce power. I hope this helps and that anyone that is trying to understand regearing. Thanks to Magnethead who did probably over an hour worth of math and typing, we have a great first hand example of this.
Originally Posted by magnethead View Post
NOTE: The following data is erroneous. My tires check out at 29.75", but for anybody on 4.10's with 32's, have at it.

I'm going to extend this a touch, just to see if Hank's numbers and my numbers match. Keep in mind I have the weakling 3.9.

Horsepower 175 hp @ 4400 rpm
Torque 230 ft. lbs. @ 3200 rpm
Bore x Stroke 3.91 x 3.31 in.

2175 rpm = 1200/(2x3.31/12)

4th gear with convertor locked up:
= (2175 / 0.69 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 768.82 * 0.0952
= 73 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 530.48 * 0.0952
= 50.5 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 275.578 * 0.0952
= 26.23 MPH


Now lets go run back through that with the 3.55's and 30" tires my truck left the assembly plant with:

4th gear with convertor locked up:
= (2175 / 0.69 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 887.93 * 0.08925
= 79.24 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 612.67 * 0.08925
= 54.68 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 318.27 * 0.08925
= 28.40 MPH

So based on that, Chrysler likely felt it would be better to lug the motor with tall gearing and keep the throttle most of the way open. Basically, the ideal situation would be OD off at 55MPH, or OD on at 75 MPH, and pick whatever you want in between because it's a parabolic curve (actually probably closer to 3rd or 5th degree).

With the regear/bigger, I didn't really make the losses too great for either 55 or 75 MPH. 30 -> 32" = 6% loss and 3.55 -> 4.10 = 15% gain, so I really only gained 9% of torque.

This is why I say I wish they made 4.30's for our trucks. Since most of this section's trucks are on 31.5-32.5" tires, the 4.30 reallocates the entire system.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 733 * 0.0952
= 69.78 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 505.81 * 0.0952
= 48.15 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 262.76 * 0.0952
= 25 MPH


4.30's with a 32" tire moves the economy state to right there at 70 MPH, which is the actually traveled speed of most interstates. The trade off is a pretty steep loss at 55 MPH.

But that's okay. 4.30's don't exist for our axles.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 691.26 * 0.0952
= 65.80 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 476.97 * 0.0952
= 45.41 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 247.78 * 0.0952
= 23.58 MPH

Now we have some pretty big moves. 4th gear isn't so bad, but we just can't get close to a 55 MPH economy number.

One more time.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 645.93 * 0.0952
= 61.50 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 445.70 * 0.0952
= 42.43 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 231.53 * 0.0952
= 22.04 MPH

Now we aren't anywhere close to an efficiency range.


Chrysler engineers win.

Thank you Magnethead for all the work it is appreciated, because of that I can slack a little and give a shorter version of my work. I have a 545RFE tranny with 3.55 gears (you can look up top to get the gears for if you'd like). I have worn tires that stand at 29.25", the A/T3 tires I'm looking at are 30.5". For the purpose of this 30.5" is my tire, this is larger for a 265/70/16 size tire. For the 4.7L with a stroke of 3.40", 1,200 ft/min is 2,118 rpm. With a final gear of 0.68 using the 545RFE tranny and a diff of 4.10. You have your magic number of 69-70 mph. So depending on vehicle set up, your rpms will vary. For those who are closer to stock, 4.10 is better. Still 4.30 would be perfect for those of us who want bigger tires.

For those that are interested in an rpm calculator, I found a very nice one online. Not perfect but quite accurate. http://www.catherineandken.co.uk/sti/tyres.html

I'll edit this post with more information as I remember it, people update it or ask for more. I hope it helps everyone.
 
  #2  
Old 09-09-2013, 08:31 PM
Tom A's Avatar
Tom A
Tom A is offline
Section Moderator
Dodge Forum Moderator
Join Date: May 2012
Location: Concord, CA
Posts: 1,564
Default

Since when was an NV4500 available in a Dakota?
 
  #3  
Old 09-10-2013, 11:40 AM
Blacknights
Blacknights is offline
Veteran
Thread Starter
Join Date: Oct 2012
Location: Georgia
Posts: 297
Default

Originally Posted by Tom A View Post
Since when was an NV4500 available in a Dakota?
Actually you're right, I'll keep that info but I'll add the NV3500 into the list when I have a break from college. I don't know how I got that messed up. Eh, it happens. Thank you Tom A
 
  #4  
Old 09-11-2013, 08:49 AM
Tom A's Avatar
Tom A
Tom A is offline
Section Moderator
Dodge Forum Moderator
Join Date: May 2012
Location: Concord, CA
Posts: 1,564
Default

No problem. I was just double checking. Thanks for going through the trouble to compile all the info.
 
  #5  
Old 01-07-2014, 09:22 PM
Blacknights
Blacknights is offline
Veteran
Thread Starter
Join Date: Oct 2012
Location: Georgia
Posts: 297
Default

Thank you, I appreciate it. I've just updated it again, so I'm highlighting it for anyone who wants to read up on it. New info is on the bottom of the post.
 
  #6  
Old 01-07-2014, 11:30 PM
magnethead
magnethead is offline
Grand Champion
Join Date: Feb 2005
Location: Fort Worth, TX
Posts: 6,654
Default

That last paragraph is why all the rams go to 4.56's and dakotas to 4.10's

Next time I remember, I'll record my dash and pull some 4.10 RPM numbers for this post.
 
  #7  
Old 01-08-2014, 01:12 AM
Blacknights
Blacknights is offline
Veteran
Thread Starter
Join Date: Oct 2012
Location: Georgia
Posts: 297
Default

Originally Posted by magnethead View Post
That last paragraph is why all the rams go to 4.56's and dakotas to 4.10's

Next time I remember, I'll record my dash and pull some 4.10 RPM numbers for this post.
Thank you, I've needed more numbers for this. My Dak may never get new gears the way my money looks but I've been debating between those two for months if I had the money. I'm guessing you're around 2300?

I'm planning on creating a master sheet and article document later in word (once I have Word again). When that happens I'll post it as an attachment so everyone can have this pile of info to go.
 
  #8  
Old 01-12-2014, 12:03 AM
magnethead
magnethead is offline
Grand Champion
Join Date: Feb 2005
Location: Fort Worth, TX
Posts: 6,654
Default

NOTE: The following data is erroneous. My tires check out at 29.75", but for anybody on 4.10's with 32's, have at it.

I'm going to extend this a touch, just to see if Hank's numbers and my numbers match. Keep in mind I have the weakling 3.9.

Horsepower 175 hp @ 4400 rpm
Torque 230 ft. lbs. @ 3200 rpm
Bore x Stroke 3.91 x 3.31 in.

2175 rpm = 1200/(2x3.31/12)

4th gear with convertor locked up:
= (2175 / 0.69 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 768.82 * 0.0952
= 73 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 530.48 * 0.0952
= 50.5 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 275.578 * 0.0952
= 26.23 MPH


Now lets go run back through that with the 3.55's and 30" tires my truck left the assembly plant with:

4th gear with convertor locked up:
= (2175 / 0.69 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 887.93 * 0.08925
= 79.24 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 612.67 * 0.08925
= 54.68 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 318.27 * 0.08925
= 28.40 MPH

So based on that, Chrysler likely felt it would be better to lug the motor with tall gearing and keep the throttle most of the way open. Basically, the ideal situation would be OD off at 55MPH, or OD on at 75 MPH, and pick whatever you want in between because it's a parabolic curve (actually probably closer to 3rd or 5th degree).

With the regear/bigger, I didn't really make the losses too great for either 55 or 75 MPH. 30 -> 32" = 6% loss and 3.55 -> 4.10 = 15% gain, so I really only gained 9% of torque.

This is why I say I wish they made 4.30's for our trucks. Since most of this section's trucks are on 31.5-32.5" tires, the 4.30 reallocates the entire system.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 733 * 0.0952
= 69.78 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 505.81 * 0.0952
= 48.15 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 262.76 * 0.0952
= 25 MPH


4.30's with a 32" tire moves the economy state to right there at 70 MPH, which is the actually traveled speed of most interstates. The trade off is a pretty steep loss at 55 MPH.

But that's okay. 4.30's don't exist for our axles.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 691.26 * 0.0952
= 65.80 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 476.97 * 0.0952
= 45.41 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 247.78 * 0.0952
= 23.58 MPH

Now we have some pretty big moves. 4th gear isn't so bad, but we just can't get close to a 55 MPH economy number.

One more time.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 645.93 * 0.0952
= 61.50 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 445.70 * 0.0952
= 42.43 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 231.53 * 0.0952
= 22.04 MPH

Now we aren't anywhere close to an efficiency range.


Chrysler engineers win.


Which is more important: having the rpms near this 1200 foot per minute
speed for the pistons, or having the throttle in the 65-75% open range?
Answer: it is more important to be in the 70% throttle range and you should
slow down the rpms to get there. There is not much change in efficiency
when piston speed drops from 1200 down to 800 ft/minute but there is a big
change in efficiency when the throttle goes from 70% open to 40% open.

Why?

Imagine that you have a disassembled engine in front of you. Put a loose
piston in a bore and pull it down against the friction of the rings. It won't
be very hard. Now imagine that same piston in the bore has the top of the
bore sealed off and has a vacuum sucked of 12 inches of Mercury.
12 inches of vacuum is about 6 psi of negative pressure. If the piston is
4.00 inches in diameter it has an area of about 12.5 square inches
(remember pi R squared but most cherry pies are round?)
6 pounds per square inch times 12.5 square inches = 75 pounds would be
required to pull the piston down - you probably couldn't do it with the grip
of just a couple fingers! An engine running with a high vacuum in the intake
manifold has to do just this, and for eight cylinders!
 
  #9  
Old 01-12-2014, 01:15 AM
Blacknights
Blacknights is offline
Veteran
Thread Starter
Join Date: Oct 2012
Location: Georgia
Posts: 297
Default

So much math, it is so perfect to look at but it makes my head hurt.

If you don't mind man I'm going to add to your work in a quote to my main post up top. Great work by the way! And your 3.9 isn't a weakling, just misunderstood.
 
  #10  
Old 01-12-2014, 01:42 AM
magnethead
magnethead is offline
Grand Champion
Join Date: Feb 2005
Location: Fort Worth, TX
Posts: 6,654
Default

NOTE: The following data is erroneous. My tires check out at 29.75", but for anybody on 4.10's with 32's, have at it.

Part 2: Because we don't drive bleeping Priuses!

[Footnote: This data is pretty limited to my build only, but the data can be processed similarly for any other setup]

I do have this video from 2011. I'm not sure if it's before or after the re-gear, so lets find out.


40 MPH @ 5,000 RPM in first gear = 8 MPH per 1,000 RPM

40 MPH = (5000 / 2.74 * 0.8 / X ) * (32" * 3.141591 / 12 * 60 / 5280)
40 MPH = 1459.85 / X * 0.0952
40 MPH = 138.98 / X
138.98 / 40 = X
3.4745 = X

So it was with the stock 3.55 gears. But since 3.4745 is unequal to 3.55, the convertor efficiency is off. Let's figure it out.

40 MPH = (5000 / 2.74 * Y / 3.55 ) * (32" * 3.141591 / 12 * 60 / 5280)
40 MPH = 514.03 * Y * 0.0952
40 MPH = 48.93 * Y
40 / 48.93 = Y
0.8174 = X


Now for second gear.

I'm going to call it being 3150 at the fallback @ 45 MPH, for 14.28 MPH per 1,000 RPM.

45 MPH = (3150 / 1.54 * Y / 3.55 ) * (32" * 3.141591 / 12 * 60 / 5280)
45 MPH = 576.18 * Y * 0.0952
45 MPH = 54.85 * Y
45 / 54.85 = Y
0.820 = X

And for the top of second gear:
4,000 RPM @ 60 MPH, for 15 MPH per 1,000 RPM.

60 MPH = (4000 / 1.54 * Y / 3.55 ) * (32" * 3.141591 / 12 * 60 / 5280)
60 MPH = 731.66 * Y * 0.0952
60 MPH = 69.65 * Y
60 / 69.65 = Y
0.861 = X

[footnote 2: The rest of this is pending newer footage]

Since that video, I've added Methanol Injection, a high-stall convertor, 4.10 gears, 1.7 roller rockers, E-fan mod/clutch fan delete, and SCT 94 octane tune.

If you are into math and almost-calculus, I refer you here: https://dodgeforum.com/forum/racing-...the-track.html

otherwise, continue with abbreviated version below:

On the night of that video, I 60'd in the 2.70 even range.

60 feet divided by 2.7 seconds = average speed of 22.22 feet per second.

That divided by 2.7 seconds again is an average acceleration of 8.230 feet per second squared. (verify: 60 divided by 2.7^2 = 60/7.29 = 8.230)

60 feet divided by 2.3 seconds squared = an average acceleration of 11.342 feet per second squared.
Now let's jump ahead to the reverse engineering part.

32,096.162 poundals divided by 3400 pounds = 9.44 feet per second squared (an improvement of 1.21 feet per second squared)

60 feet divided by 9.44 feet per second squared = 6.35 seconds squared.

square root of 6.35 is 2.52 seconds

So the gears alone will put me from a 2.7 to a 2.52 second 60 foot time.
Thanks to my form of archiving (and keeping every time slip for the truck) -> https://dodgeforum.com/forum/2nd-gen...-the-dako.html

[Footnote: the atmosphere was significantly different for the following run data, so it's hard to compare them]

Stock,
2.678 | 7.676 @ 46.00 | 11.798 @ 58.94

with only the SCT and 180 stat, best pass was
2.684 | 7.565 @ 47.10 | 11.574 @ 60.30

with 180 stat, SCT, clutch fan delete, 1.7 roller rockers, 4.10 gears, best pass was
2.610 | 7.282 @ 48.95 | 11.132 @ 62.90

After adding the high stall convertor and methanol,
2.460 | 7.7073 @ 48.86 | 10.920 @ 62.37

Let's focus on the 60 foot. The quicker the sixty, the quicker the run.

2.678
2.684
2.610
2.460

That's quite the bit of a difference. But the math above said I would go from a 2.70 to a 2.52 with the gear change. I only got to the low 60's, about half that change. Why? Because I was losing torque multiplication through the torque convertor. By going to a deeper gear, I removed load from the convertor, tightening it up, lowering it's stall/hydraulic lock-up RPM. So even though I was getting more torque multiplication through the rear gears, I was losing it through the torque convertor.

I needed a looser torque convertor that would multiply torque for a longer period of time. So I got one and put it in. Not only did I hit that target 2.52, I passed it and hit 2.46 (but I will also attribute some of that to the methanol and Hemifever's tune to suit it).

I passed it so hard, I've run into traction problems. Being an open diff, the right rear tire is no longer staying attached to the track. I have no doubt that I can get into the low 2.40's once I get hooked up. The goal is to get into the 2.10's-2.20's-2.30's to break into the 9's.

I'm going to do it by manipulating the effective ratio.

By going from a 32" AT to a 26.5" DOT slick, I'm reducing the diameter and therefore circumference by 17%. I'm taking the effective ratio from 32" @ 4.10:1 to 26" @ 4.95:1.

In an ideal world, that's 17% increased torque = 17% thrust. In an ideal world, 17% gain in thrust = 17% gain in 60ft. 17% gain takes a 2.46 sixty to a 2.04 sixty. But we don't live in an ideal world.

The trade-off in changing the effective ratio, is now I have other things to consider. Instead of making big torque at little RPM like a V8, I'm taking advantage of the V6 making mediocre torque at high RPM. The smaller tire doesnt go as far per rotation, so RPM goes up. Higher driveline RPM + high torque RPM = I'm closer to the torque number.

= (3200 / 2.74 * 0.8 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 227.88 * 0.0952
= 21.69 MPH

= (3200 / 2.74 * 0.8 / 4.95 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 188.75 * 0.0952
= 17.96 MPH

= (3200 / 2.74 * 0.8 / 4.10 ) * (26.5" * 3.141591 / 12 * 60 / 5280)
= 227.88 * 0.0788
= 17.96 MPH

(For an apples to apples comparison, I'm going to neglect convertor torque multiplication)

230 ft-lb * 2.74 * 3.55 = 2,237 ft-lb / (1.25 ft) = 1,789 pound-force thrust
230 ft-lb * 2.74 * 4.10 = 2,584 ft-lb / (1.25 ft) = 2,067 pound-force thrust
230 ft-lb * 2.74 * 4.10 = 2,584 ft-lb / (1.10 ft) = 2,349 pound-force thrust
230 ft-lb * 2.74 * 4.95 = 3,119 ft-lb / (1.25 ft) = 2,495 pound-force thrust

That's just due to round-off error.

The problem I now face, is that I have now once again removed load from the torque convertor, so it will tighten up again. But that's okay, for for this reason: since the engine RPM will be higher, I will want it to hydraulically lock up to maximize the amount of torque passed through at the torque peak.

The idea of a looser torque convertor is that the engine can be closer to the powerband (an arbitrary point between the torque RPM peak and the HP RPM peak) with the driveline locked, so that the engine is already nearly making peak power the instant that the brakes are released. Then you want it to hydraulically lock as quick as possible to transfer the power peak into the driveline. Between those two points, torque multiplication occurs inside the torque convertor, as much as 2.5:1 at the asymptote to the not-locked stall point.

Another issue that must be dealt with is gear choice vs rev limiter. With the 26" tire (Excel helped me greatly here), I'll be around 34 MPH at the rev limiter in first gear, 61 MPH at the top of second gear, and 94 MPH at the top of third gear.

Why is that important? Because I'm already going through the 1/8" traps against the high side in 2nd gear with the 32" tires. No question I'll be using third gear on the 26.5" tire. Also, 94 MPH high side in third gear is up to an 9.00 @ 76 MPH 1/8 mile pass or 14.00 @ 94 MPH 1/4 mile pass. I have to consider the ability to do 1/4 mile because it may crop up now and then. I don't think I will ever get that fast with this motor, but you never know. 76 MPH will be around 4,000 RPM in third.

So there you have it. How gearing, tire size, and torque convertors all play together on top of what Hank said in that other thread.

And I still need to get video of the current setup on the street for actual RPM/speed equivalencies.
 

Thread Tools
Search this Thread
Quick Reply: Transmissions, Gearing and RPM


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: