Main Menu
|
Nevada Classics
|
Advertise at CC
|
S |
M |
T |
W |
T |
F |
S |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
21 |
22 |
23 |
24 |
25 |
26 |
27 |
28 |
29 |
30 |
31 |
|
|
|
|
|
CC Advertisers
|
|
11-29-2012, 09:27 AM
|
CC Member
|
|
|
Join Date: Jun 2007
Location: Georgetown,Ontario,
ont
Cobra Make, Engine: D&D Cobra,302 stock for now,IRS
Posts: 329
|
|
Not Ranked
Rear end gear question
Hi guys, I have 3.08 gears in my IRS 8.8 diff. and I would like to go with lower gears for more low end torque but wonder what's the better gear I could put,should I go 3.55 or 3.73.
Right now with the 3.08 when I'm cruising on the highway if i'm on 5th (because i have a t-5 and my engine is a stock 302) the RPM is really low and it's boring so I'd like the engine to rev a little higher and also a little more torque on take off would be fun too,what do you think.
What's the RPM difference between 3.55 and 3.73. Thanks guys !
|
11-29-2012, 09:42 AM
|
CC Member
|
|
|
Join Date: Jul 2002
Location: The Woodlands,
TX
Cobra Make, Engine: FFR Roadster
Posts: 42
|
|
Not Ranked
If you're running a stock 302, then I would definitely go with 3:73's.
Rob
__________________
GOD IS MY COBRAPILOT!!!
|
11-29-2012, 09:48 AM
|
|
CC Member
|
|
|
Join Date: Sep 2010
Location: Northfield,
MN
Cobra Make, Engine: B&B, FR302
Posts: 218
|
|
Not Ranked
I Agree with rokfor. I have a 3:55 in my car with a FR306 and a T5. It almost seems to lug in 5th gear at 60. I've considered going to a 3:73.
Roger
__________________
There are two kinds of people - those smart enough to know they don’t know, and those dumb enough to insist they do
|
11-29-2012, 09:51 AM
|
|
CC Member
|
|
|
Join Date: Dec 2011
Location: West Chester,
PA
Cobra Make, Engine: ERA #795 427 S/C completed Jan. '14 - '68 FE 427 side oiler
Posts: 1,051
|
|
Not Ranked
Hi Michel,
Here's a simple to use calculator that you can play around with to see what the RPM's will be at various speeds with various rear gears. My kit from ERA is in the final stages, and I have no experience driving different configurations. I went with their recommendation - 3:54 rear with .64 5th gear in a TKO-600. This is thought to be the "best of both worlds", providing fairly low gearing with reasonable RPM's on the highway. Gearing is a topic where you'll get lots of different opinions.
Gear Calculator
Regards,
Kevin
__________________
"Anyone who drives faster than you is a maniac and anyone who drives slower than you is an idiot" - George Carlin
|
11-29-2012, 10:09 AM
|
|
CC Member
|
|
|
Join Date: Dec 2011
Location: West Chester,
PA
Cobra Make, Engine: ERA #795 427 S/C completed Jan. '14 - '68 FE 427 side oiler
Posts: 1,051
|
|
Not Ranked
Hi again Michel,
I should have added that my car will be an FE 428, so the best configuration for you will be different. That calculator, along with comments from others with sb's should tell you what you need to know.
Regards,
Kevin
__________________
"Anyone who drives faster than you is a maniac and anyone who drives slower than you is an idiot" - George Carlin
|
11-29-2012, 10:17 AM
|
|
CC Member
|
|
|
Join Date: Feb 2010
Location: Hermosa Beach,
ca
Cobra Make, Engine: ERA#520, Roush 427SR
Posts: 203
|
|
Not Ranked
I have a TKO600 with .83 5TH and 3.54 Differential. Pulls strong 50mph and up. About 2600 RPM at 70MPH. Cruising on Ca freeways a down shift to 4TH is not required often. For my driving style the .64 required more time in 4TH..........Thats my 2 cents........Note that the engine is a Roush 427SR.........Good luck
|
11-29-2012, 10:39 AM
|
|
Half-Ass Member
|
|
|
Join Date: Jun 2005
Cobra Make, Engine: ERA #732, 428FE (447 CID), TKO600, Solid Flat Tappet Cam, Tons of Aluminum
Posts: 22,004
|
|
Not Ranked
Quote:
Originally Posted by csx4017
I have a TKO600 with .83 5TH and 3.54 Differential. Pulls strong 50mph and up. About 2600 RPM at 70MPH. Cruising on Ca freeways a down shift to 4TH is not required often. For my driving style the .64 required more time in 4TH..........Thats my 2 cents........Note that the engine is a Roush 427SR.........Good luck
|
Yep, it all depends on your state highway speeds (the real speeds, not the posted speeds). If you regulary road race over 130mph or so, then you don't want the .64 coupled with the 3.54 and 15" wheels. If you keep it under that, you never use fifth anyway. On the highway, if you like to cruise your Cobra in the 70s, then a 3.54/.64 combo is perfect. Your RPMs will be just over two grand, it's relatively quiet, and peaceful -- I love it. If your state insists you keep it around 60MPH, then opt for the .83 gear.
|
11-29-2012, 12:37 PM
|
CC Member
|
|
|
Join Date: Apr 2012
Location: Bay Area (Peninsula),
CA
Cobra Make, Engine: ERA 427, 427/487 side-oiler
Posts: 1,248
|
|
Not Ranked
I recently made this choice for my build and went with a TKO-600 with a 0.82 final drive, and a 3.54 rear. The engine will be a 427/482 built to about 600 HP. I found that this exercise was sort of a multivariate equation (excuse my engineering geekiness) between (1) highway noise/exhaust choice/cruising RPM, (2) how the engine is built (cam choice among other things), and (3) driveability (e.g., drop off between gears, tractability, etc). Brent will be building my engine and he was helpful here. In the end we decided that if I want a higher HP build that necessitates a hotter cam, cruising at highway speeds with the 0.64/3.54 combo would be challenging. With that gear combo, a milder engine that is happier at low RPMs is better. The other factor is that, with a 0.64 trans, the drop off between 4th (1.0) and 5th (0.64) is big and would require more 4th gear driving, as pointed out by CSX4017 above.
|
11-29-2012, 02:05 PM
|
|
CC Member
|
|
|
Join Date: Aug 2009
Location: Adelaide,
SA
Cobra Make, Engine: AP 289FIA 'English' spec.
Posts: 13,150
|
|
Not Ranked
Michel - kevins2's suggestion of using a gear calculator is a good idea.
Here is another that I've found useful...
Second Strike Gearing Calculator
As well as working out rpm at highway speeds, don't forget to look at first gear rpm and speeds. It's not that helpful if your rear gears are too low (ie higher number) and your first gear is only good for pulling stumps.
Cheers,
Glen
|
11-29-2012, 03:07 PM
|
CC Member
|
|
|
Join Date: Mar 2011
Cobra Make, Engine: #6101 streetbeast Ingelese stack EFI 351w/t-5 9" 4link 3.55
Posts: 277
|
|
Not Ranked
I agree with rokfor. Stock 302. Def. 3.73.
|
11-29-2012, 04:19 PM
|
CC Member
|
|
|
Join Date: Jun 2007
Location: Georgetown,Ontario,
ont
Cobra Make, Engine: D&D Cobra,302 stock for now,IRS
Posts: 329
|
|
Not Ranked
Thanks guys,that is some very helpful info, It will help me decide, I appreciate
Michel
|
11-29-2012, 05:04 PM
|
|
CC Member
|
|
|
Join Date: May 2009
Location: American Fork,
Ut
Cobra Make, Engine: 66 Cobra
Posts: 930
|
|
Not Ranked
I went through the issue, did the calculators and all that. As said earlier cam selection has a lot to do with it. If you have a milder cam the 3.54s work good but for a radical cam the 3.73 works better. Consider with the 3.73s first gear just about becomes useless because of the first gear on the T-5. For the FEs it's is whole 'nother story. I finally went with the 3.50s in my nine in. after calling FF and talking with their tech boss. Their experience was the 3.54 just seemed to work better. They only offered the 3.73 in their complete kit for awhile becasue they couldn't get the 3.54 from the factory.
It's really good to hear some discussion about gearing. It is critical and deserves just as much discussion as cam selection. You create a dog by putting the wrong cam in with the wrong gears.
__________________
Wayne
"Everything is alive. If you get angry at a vehicle or the trans, it won't fix until you apologize and say you are sorry." "The vehicle always knows what it is doing and what the cause of it's bad feeling is. If you ask it humbly what the problem is, it will tell you. Then you and it will both be happy."
Gil Younger
|
11-30-2012, 04:49 PM
|
CC Member
|
|
|
Join Date: Jun 2007
Location: Georgetown,Ontario,
ont
Cobra Make, Engine: D&D Cobra,302 stock for now,IRS
Posts: 329
|
|
Not Ranked
I bought a e303 cam and looking at a set of E7 heads that were professionally ported,polished to meet GT40 specs with 1.7 roller rockers and stiffer springs to go with it,
my bottom end will be stock so should I go with 3.73 or 3.55,thanks guys !
|
11-30-2012, 06:20 PM
|
|
CC Member
|
|
|
Join Date: May 2009
Location: American Fork,
Ut
Cobra Make, Engine: 66 Cobra
Posts: 930
|
|
Not Ranked
This is like a what color is the best question. Are you driving around town more or on the freeway. The E-303 cam has 220-220 dur. at .050. It's power band is a little higher, but it's not a high RPM cam by any means. You could go either way. These are the numbers.
Trans ratios for most T-5s
1st 3.35 after market 2.95
2nd 1.99
3rd 1.33
4th 1.0
5th .68
5th gear RPMs @ 65 mph with 295s with a diameter of 25.65"
3.08 1775
3.54 2035
3.73 2175
4th gear RPMs @ 65 mph with 295s with a diameter of 25.65"
3.08 2635
3.54 3000
3.73 3200
You choose.
__________________
Wayne
"Everything is alive. If you get angry at a vehicle or the trans, it won't fix until you apologize and say you are sorry." "The vehicle always knows what it is doing and what the cause of it's bad feeling is. If you ask it humbly what the problem is, it will tell you. Then you and it will both be happy."
Gil Younger
|
11-30-2012, 11:33 PM
|
|
CC Member
|
|
|
Join Date: May 2006
Location: Denia / SPAIN,
ESP
Cobra Make, Engine: NAF 289 Blue/White strips
Posts: 188
|
|
Not Ranked
Another gear calculater: Put in your dates and press CALCULATE
Tire Size and Gear Calculator
Rico
__________________
Rico, NAF 289
Last edited by cobra 53; 11-30-2012 at 11:52 PM..
|
12-02-2012, 04:42 AM
|
|
CC Member
|
|
|
Join Date: Nov 2001
Location: Windham,,
Me
Cobra Make, Engine:
Posts: 1,590
|
|
Not Ranked
Originally started with 460, top loader and 3:55's did not like turnpike driving.Went to Tremec TKO and 3:73 turned out to be the perfect combination.Car now has gut wrenching off line torque and excellent turnpike cruise speed rpm's in 5th.Good Luck
|
12-02-2012, 04:51 AM
|
|
CC Member
|
|
|
Join Date: Apr 2006
Location: Charlottesville,
va
Cobra Make, Engine: Coombe, Shelby Block 496
Posts: 1,187
|
|
Not Ranked
mdross1
What 5th gear is your tko?
|
12-02-2012, 11:57 AM
|
CC Member
|
|
|
Join Date: Mar 2009
Cobra Make, Engine: FFR
Posts: 388
|
|
Not Ranked
Michel, you report that 5th gear is boring, lol. It's overdrive, it's supposed to be boring and will stay so even with a gear change. Heck, I make triple your hp and overdrive is still boring. If you add heads and mild cam the 3.55 gears will still allow 1st gear to be useful and fun. If you want fun on the hwy you'll have to downshift to 3rd to get it. Cheers.
|
12-02-2012, 02:19 PM
|
|
CC Member
|
|
|
Join Date: Aug 2009
Location: Adelaide,
SA
Cobra Make, Engine: AP 289FIA 'English' spec.
Posts: 13,150
|
|
Not Ranked
Quote:
Originally Posted by cobra 53
|
That's a good gearing calculator. I like it.
Cheers,
Glen
|
12-04-2012, 03:49 AM
|
|
CC Member
|
|
|
Join Date: Nov 2001
Location: Windham,,
Me
Cobra Make, Engine:
Posts: 1,590
|
|
Not Ranked
Quote:
Originally Posted by cobrakiwi
mdross1
What 5th gear is your tko?
|
Cobrakiwi,there were 2 choices and it was more than 10 yrs ago but can tell you when clicking into 5th rpm's drop near 1k. Thought about the other option 500rpm drop, but with the 460 knew it had the torque to pull it.It has more than enough even in 5th this car is a blast passing others and cruising is ecstasy.
Have fun
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -7. The time now is 09:52 AM.
Links monetized by VigLink
|