2.73's in an Automatic car? - TCCoA Forums
 
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post #1 of 13 (permalink) Old 10-07-2003, 01:21 PM Thread Starter
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2.73's in an Automatic car?

I've got this hairbrained Idea....shoot it down for me...will y'all?

I've got a 95 Cougar with 3.08 gears in an open rear end.

I've got a 94 SC with 2.73 gears and a limited slip rear end.

I have been wanting 3.27 gears in my SC, but I think I could live with 3.08.
What would the automatic be like with 2.73 gears. Besides getting better gas mileage on the highway...which is a plus...would there be any negative points to having 2.73 gears in a Cougar with an automatic tranny? I realize that if I wanted to keep the limited slip in the SC, I either have to swap just the gears, or move the limited-slip thimble into the other rear end. Haven't ever done any rear end work, but I'm sure I could manage.

What are the opinions?

Glen "RustyUL" Weldon

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post #2 of 13 (permalink) Old 10-07-2003, 01:51 PM
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It will work fine but the car will be even a little slower out of the hole. As I remember your rpms at 60 will be down around 150ish rpms.

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post #3 of 13 (permalink) Old 10-07-2003, 04:08 PM Thread Starter
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WOW! Should be good for another 2-4 MPG at Highway speeds! Have you done this before, Mark?

Glen "RustyUL" Weldon

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post #4 of 13 (permalink) Old 10-09-2003, 12:35 AM
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How much highway driving do you do?

I am assuming this car will never see the drag strip at all ...

If that is the case, you'll get a little better gas mileage. Acceleration will be slower than the 3.08's for sure.

I think you're the first person I've seen going to higher gears in an auto MN-12 ...

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post #5 of 13 (permalink) Old 10-09-2003, 07:16 AM Thread Starter
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For this particular car...all it sees are highway miles, and no...it will never see the dragstrip. Keep in mind the reason for putting the 2.73 gears into the Cougar will be to swap the 3.08 gears with my SC, which I drive all the time. So I'm not really going to higher gears, I'm swapping to lower gears for my SC!

Glen "RustyUL" Weldon

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post #6 of 13 (permalink) Old 10-09-2003, 03:04 PM
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Dude you will lose your limited slip in the SC. I wouldn't do it. Switching gears or the t-lock carrier is something that you need a shop to do with the right tools or else your rear end will howl. Just leave your cougar alone and find a diff from a 89-93 auto SC. It will have the t-lock and 3.27's.

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post #7 of 13 (permalink) Old 10-09-2003, 04:22 PM
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If you could live without either car for the required amount of time, I'd buy a set of 3.27s for the SC, and throw them in. Then you could take the 2.73s from the SC and have them put in the Cougar and you get what you wanted to begin with.

Or you could just buy a used SC auto pumpkin with T-Lock 3.27s in it, swap pumpkins, throw the 2.73s pumpkin in the Cougar, turn around and sell the 3.08 pumpkin, or rebuild it for when the used 3.27 pumpkin's clutches finally give up the ghost.

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post #8 of 13 (permalink) Old 10-10-2003, 07:56 AM Thread Starter
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Tbird4vr,

Dude, this isn't a flame and I appreciate you taking the time to respond, but....

!
Quote:
Dude you will lose your limited slip in the SC. I wouldn't do it. Switching gears or the t-lock carrier is something that you need a shop to do with the right tools or else your rear end will howl. Just leave your cougar alone and find a diff from a 89-93 auto SC. It will have the t-lock and 3.27's.
You can't make a statement like that and expect to retain any credibility!
You don't have any information about me, my education level, my skill level or my mechanical aptitude, other than what I've mentioned in my previous post!

You mean YOU would use a shop to change your gears/T-lock. That doesn't mean that I should. I don't know how old you are or what experience you've had, but don't assume that others are at your level, or below. Just because I haven't done it doesn't mean that I'm not able to do it properly.

My background is in machining of Aerospace and Automotive parts, Tool design for manufacturing, and Tool making for manufacturing. My title now is Manufacturing Engineer, but in the past it has been Machinist, Toolmaker, Tool Designer, CNC programmer/operator, and Manufacturing Technologist. I can measure and machine parts to .0001 inch accuracy with the proper tools. I have access to a machine shop with several milling machines, lathes and surface grinders. I personally own a set of 0-6" micrometers, a surface plate and height guage and 3 different dial indicators. I work with pneumatics, hydraulics, gears, belts, cutting tools, steel structures and logic controls almost every day.

Trust me....I can handle the job. I wouldn't have even mentioned it unless I thought I had the ability. That doesn't mean I know everything about it and don't have to ask questions to those who have more knowledge/experience than I do. It also doesn't mean that just because I can do the job, that I want to do it, or even that it is wise to do! That's the type of information that I'm looking for here....practical experience and advice from those who have done it or have information about doing it. Thank you to those who have answered what I have asked.

Glen "RustyUL" Weldon

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post #9 of 13 (permalink) Old 10-11-2003, 11:03 PM
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From what I hear, 2.73's will give you worse gas mileage. The motor strains too hard at normal driving speed. You want your rpm's to be around 2500 at cruise. If you drive 90 most of the time, the 2.73's would be the way to go. Otherwise, you may actually want to go shorter. That is... if economy is a concern.

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post #10 of 13 (permalink) Old 10-12-2003, 12:29 AM
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There's no way I'd touch 2.73's for my car. Way to hard getting up and going, it's like taking off in 2nd gear ALL the time. I have a magazine where they tested a '91 5.0L XR-7 with 2.73's and it threw down a whopping 17+ e.t. I wouldn't be at all suprised if the right gear for improving mileage is a 3.55. With 3.27's I don't hit 2,500 at 70. Also remember you can get NEW Ford Racing gears for $140.

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post #11 of 13 (permalink) Old 10-13-2003, 08:15 AM Thread Starter
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The 3.08's in the Cougar right now turn 2200 at 77 MPH. Car gets about 23 MPG on the highway. The 3.8 Cougar I had turned 2600+ RPM at 77MPH and only got about 19-20 MPG.

Does it really make sense that 3.55 gears would get better mileage than 3.08 gears in this application? I highly doubt it. As to being too low and causing too much strain on the engine, this is what I'm thinking and it is the reason that I asked the question in the first place....but how would you really know?

BTW, my 4R70W (which would see the 2.73's) starts out just fine is second gear.

Glen "RustyUL" Weldon

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post #12 of 13 (permalink) Old 10-13-2003, 11:46 AM
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Glen,

That's pretty high gear (numerically lower) for a 26-27 inch tire on an automatic. I'd be willing to assume that at the least, it would be hard on the transmission. City driving would be all slip just about until it shifts into second. The heat and clutch wear alone would become a potential problem.

At highway speeds (legal highway speeds) I'm not sure that the engine would be in it's prime RPM band for cruising. This could result in worse gas mileage.

Certainly you can work around these things, and install a large transmission cooler, a higher stall speed torque converter, a computer chip (to take care of the EEV aspects) and advance the timing of the camshafts about 4 degrees (if possible) to try to move the powerband into lower RPMs.

Aside from that, I don't think I would necessarily try to do this. You got a definite plus on wanting lower gears (numerically higher) in the SC. I think I would just do that and leave the 2.73:1 gears out of the equation for either car.

Just my opinion, I'm sure others will disagree.

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post #13 of 13 (permalink) Old 10-13-2003, 01:43 PM Thread Starter
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Ok, it seems like you are in the majority. Although I do have a Mark VII converter and a 26000GVW B&M Supercooler on the tranny, it seems like the negatives are stacking up against the swap....I just thought it would be more convients since I have a car that will interchange. Guess not.

Thank you to all of those who have posted.

Glen "RustyUL" Weldon

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1 of 722 1994 SC 5-speeds made.
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