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 Diff Ratio

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seany-boy
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Number of posts : 158
Age : 56
Your location : Australia
Registration date : 2008-07-28

PostSubject: Diff Ratio   Tue 3 Mar - 5:49

Hi Guys,

Firstly the car is ON THE ROAD and legal downunder so a big smile on the dial!
Now i am a bit confused, I am running a mildly warm 351C 4V currently with C6 and a plan to put her back to a 4Spd Wide ratio. I have 4.11 rear and it ain't good to drive on open roads, revving hard at anything like 50 mph (80-kmh). I am looking at whether to drop to 3.5, 3.25 or even 3.0 rear so I can drive her reasonably on the highway at about 65mph/110kmh.

Can you tell me who is running what setup and how you find it off th m ark and about these speeds for open road?
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1970twisterspecial
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Number of posts : 105
Age : 45
Your location : Netherlands
Registration date : 2007-12-24

PostSubject: Re: Diff Ratio   Tue 3 Mar - 14:50

What is the ratio of the highest gear in the gearbox ?

I'm runnin' my 351C=4V [stroker] FMX [highest gear 1:1] with a 3.50 rear axle
3000 rpm = 120 km/h [75 m/h]
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seany-boy
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Number of posts : 158
Age : 56
Your location : Australia
Registration date : 2008-07-28

PostSubject: Re: Diff Ratio   Tue 3 Mar - 18:42

Thanks Ronald,

Yep both the C6 and TopLoader have 1:1 ratio in top gear. I guess I am leaning a little towards a 3.25 rear but just don't want to be sluggish off the mark. The 4 spd has a 2.78 1st so I am thinking a 3.25 may be fine?
Interested in any opinions though Bad)
Sean
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seany-boy
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Number of posts : 158
Age : 56
Your location : Australia
Registration date : 2008-07-28

PostSubject: Re: Diff Ratio   Tue 3 Mar - 18:43

Thanks Ronald,

Yep both the C6 and TopLoader have 1:1 ratio in top gear. I guess I am leaning a little towards a 3.25 rear but just don't want to be sluggish off the mark. The 4 spd has a 2.78 1st so I am thinking a 3.25 may be fine?
Interested in any opinions though Bad)
Sean
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Raytags
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Number of posts : 289
Age : 51
Your location : Boucherville, Québec, Canada.
Registration date : 2004-09-20

PostSubject: Re: Diff Ratio   Wed 4 Mar - 1:59

Hello!

Your auto trans is probably the FMX not a C6 ? the C6 is for a big block.

my car is a 351 4V with FMX and 3:00 rear end and is drive very confortable.

Ray

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seany-boy
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Number of posts : 158
Age : 56
Your location : Australia
Registration date : 2008-07-28

PostSubject: Re: Diff Ratio   Wed 4 Mar - 2:10

thanks Ray, yep seems to be a C6 that was put in. Thanks for your details.

sean
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1970twisterspecial
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Number of posts : 105
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Registration date : 2007-12-24

PostSubject: Re: Diff Ratio   Thu 5 Mar - 13:41

Raytags wrote:
Hello!

Your auto trans is probably the FMX not a C6 ? the C6 is for a big block.

my car is a 351 4V with FMX and 3:00 rear end and is drive very confortable.

Ray

The Smallblock C6 does exist:

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Mustangs Alley
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Number of posts : 30
Your location : Garnet Valley, PA
Registration date : 2009-03-10

PostSubject: Re: Diff Ratio   Tue 10 Mar - 10:47

Hi Sean,

My Mach's diff was switched out, prior to my ownership, from the stock 3.0 to a 4.11. (I also have the FMX Trans)

It certainly gets out of the gate fast, but if you want to cruise at highway speeds, the 4.11 is a bit much. You will be reving high and gulping gas faster than you can imagine.

I do have a new top end that gives me all the power I need (400+hp), so I really don't need the 4.11 rear. At this point, it won't make much difference for me. With the beefed up hp, I can still smoke the rubber completely off when I want to. I'm agressively considering putting the 3.0 back in (or something similar) to take advantage of longer cruising and road rally's.

Hope this helps.
Kirk
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seany-boy
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Number of posts : 158
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Your location : Australia
Registration date : 2008-07-28

PostSubject: Re: Diff Ratio   Tue 10 Mar - 17:03

Thanks Kirk,

Yep, I think I have come to pretty much the same point as you. Just looking now to move back to maybe 3.25 although I am considering lower as well. Will let you know how I get on.

Cheers

Sean
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Mustangs Alley
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Number of posts : 30
Your location : Garnet Valley, PA
Registration date : 2009-03-10

PostSubject: Re: Diff Ratio   Wed 11 Mar - 12:36

You're welcome,

As Ron noted, he has a 3.5, which is what folks are telling me to lean towards, rather than back to the original 3.0. With the higher performance top end, the 3.0 may not be the most viable option.

Thoughts from the group ?? You'd be helping both Sean and I on this one.

PS: My 351w's top end was traded out for a Edelbrock 400+hp with large cam. The 4.11 rear is just to much!

Thanks for all of the great knowledge you share...its priceless !!

Kirk bounce
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seany-boy
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Number of posts : 158
Age : 56
Your location : Australia
Registration date : 2008-07-28

PostSubject: Re: Diff Ratio   Sun 5 Apr - 7:09

Well I finally decided on the original 3.00 ratio as the one I had in was a 3.9 not 4.11. Dropped the revs down a fair bit although still revs a bit hard at 50-60 mph compared to my newer cars. The bottom end seem fine still with more than enough 'get up and go' and lights up no problem.A mildly worked cleveland and lots of gas available probably help Very Happy
Rides a bit better not the LSD has been rebuilt to.
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