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· FFCobra Owner
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854 Posts
Discussion Starter · #1 ·
Not the same as a prior thread..
I am considering moving from a 3:73 to a :3:35 or 3:27
I will have my guy do it but as we don't really have a clear pic as to estimated cost, does anyone have a rough idea?
My guy is great, but we haven't done this one before

Thanks
Fred zoo
 

· Blue Oval Scribe
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9,175 Posts
It's very easy to over gear these light cars and the short wheel base doesn't help matters. Many donor builders find a 3.55 or 3.73 gear in their 8.8 and find it can be a bit much for the lighter Roadster. When I built ours I used 3.27 gears (new build, non donor) and find it the perfect gear for cruising and still plenty of torque from the 427W to move the car.

Depending upon shop labor costs and what they reuse (sometimes bearings are in perfect shape due to low mileage) you're looking at a range of $500-$750 for the typical gear swap. You might be able to offset some of it by selling your current gears too.

HTH...
Mark
 

· DRIVING!!!
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307 Posts
I had my IRS built by a local racer with all new parts. All parts were new off Ebay and labor was $300. HTH

p.s. local FORD dealer wanted .........wait for it...... $900 for the install... no kidding
 

· Senior Charter Member
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Doug, what prompted you to go from 3.27 to 3.73? Do you like the change? I have 3.73 and have mulled the idea of going to 3.27/3.35.

I took my car to Summit Point (road course) and was limited to a top speed of about 122mph on the straight in 4th (my 5th gear is too high to continue accelerating). 3.27 will give a top speed of around 140.
 

· Master Student
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1,499 Posts
Doug, what prompted you to go from 3.27 to 3.73? Do you like the change? I have 3.73 and have mulled the idea of going to 3.27/3.35.

I took my car to Summit Point (road course) and was limited to a top speed of about 122mph on the straight in 4th (my 5th gear is too high to continue accelerating). 3.27 will give a top speed of around 140.
I have a 5.0l (302) and 3.27s made 5th unusable. I was turning about 2000 rpm at 80 mph+-. By going to the lower gear it made the car funner to drive all the way around. It only made a 12% difference but what a difference. I don't need to go any faster than 122. It was one of the best changes I made to the car. :001_smile:
 

· FFCobra Fanatic
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2,600 Posts

· Junior Charter Member
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1,146 Posts
It's dependant on tire diameter, too. The Coupes were known to use 29" tires on some courses, which might account for the reported 175+ speeds.

With 28" tires, 3:55 gears give you about 3,000 rpm at 70. If trips on the interstate and a semblance of gas mileage are part of the plan, something down around 3:00 delivers - which is exactly what we see stock on a lot of sedans.

I was all about the deeper ratios until I factored long trip mileage and top end into it. If quarter mile, sure, but not at the Mojave Mile.
 

· Cobra Nutcase
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1,629 Posts
I bought my 3:55s from Fortes for $150. If I recall, the crush sleeve came with some white stuff to see where the gears touched. Then I just guessed on the backlash because we didn't have the tool either. 8 years now, and no problems.

Rob
 

· Registered
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Interesting thread. I was thinking 3.27 when I do my build, but this has me wondering if 3.55 or 3.73 is a better way to go. A lot depends on the engine and trans gearing combo as well, no? I'm going to do a 427/351w + Tremec and looking around the 475 hp level. I want to try autocross and woul like to run it on a road course, but will also see a lot of street duty.

Is 3.27 the way to go or should I go lower?
 

· Junior Charter Member
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1,146 Posts
I think it's significant much of the conversation has left out what transmission and gear ratios are involved. It's all part of a total package, and that's what delivers the end results. Choosing a rear end ratio is a lot more about understanding what final numbers you get in each gear at the engine, the rpm drop, and whether that is in the torque curve for that motor. That's where the high performance is, not what number is cool to install.

Goes to building the car with a specific goal in mind, something it will do 85% of the time. Then it's a lot more optimized for that. Cross dressing it to give it more versatility means it doesn't do anything very well, and that's a lot more disappointing to discover.

Don't set yourself up for a really bad blind date.
 

· Registered
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567 Posts
I agree with tirod, the OP didn't mention tranny ratios or intended purpose and we all started making ratio suggestions. We kinda hijacked his thread. Find me guilty for the following...

Some of the others sound like they have the .63 5th. Doug, not sure why yours is so different. I have a near stock 5.0 efi and stock T5 ratios with 3.27 final. I am at 70 with 25.5" tires (275/40/17) at 2k rpms. I can still accelerate in 5th. Pushing close to 2400 at 80. Been on several 200+ mile drives and couldn't imagine having to bare the sound of 3k for any significant amount of time. Your mind-set is far different with fatiguing sounds while cruising vs on the track.

GTA, If you go with a .80 5th, I think you'll have plenty of power to run 3.27s and still pull strong in top gear.

I'm waiting for my Levy SA T5 to arrive. I went with the tall OD 5th as I mostly cruise and will do some autox.
 

· FFCobra Craftsman
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25,999 Posts
GTA, I think you will like the 327 gear. I have a 351 400 hp and am happy w/ my 308 but I am going to do 327 over the winter for better grunt in 2nd in autocrosses. The problem w/ your power level and 355s or more is that 1st gear goes real quick even in normal slightly spirited driving. It's time to shift real soon. Also, w/ that power you will be easing on the gas in first (probably never full throttle unless you run drag radials) and spinning up tires way easily even in second. So basically more gear doesn't do you any good.
 

· Registered
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CraigS, thanks for the input. Very helpful. I think 3.27 is the way to go. Now I need to decide on the OD ratio. I actually like the OD ratio on the TKO500 better, but I don't think it's going to be able to handle the 427 torque output. Likely I'll go with the .64, but there are things about the .82 that would be nice for racing...

Btw, Fred Z, apologies for the thread hijack!
 

· Charter Member
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6,164 Posts
mg2, use an inch pound torque wrench for that. Watch the crush sleeve when you torque. Once it starts going, it goes quickly.

I had 3.27s for a long time. I think it is the happy medium.

I recently switched to 3.08s for a 160 top speed in 5th (1:1 ratio). Definitely feel a little less grunt when I am down near 60mph accelerating.
 

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GTA, if it is going to spend more time cruising on the fwy than on a big track, I would stick with the .64.

.82 would be very nice for racing, but if you think about it, you would only need to be shifting to 5th on a long straight at 120+, and that's only if you want to keep accelerating. If you're not going to be reaching 130, you can stay in 4th.
 
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