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 Post subject: 4T60 Final Drive Ratio?
PostPosted: Tue Mar 21, 2006 7:13 pm 
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I was browsing ebay...looking at transmissions since the one in my delta although it functioned okay, was welded up and pretty much on its last leg...but anywas...I saw this.

So my stock ratio is 2.73, and I could get 3.06. Would it be a noticeable difference? Seems a little pricey...the drive gears are "reconditioned" so they are obviously pulls...anyone know what cars?



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PostPosted: Tue Mar 21, 2006 8:46 pm 
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weird... how tough is that to install? I would think the only way its going to go on is during a rebuild. That would wake your delta up a little!



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PostPosted: Tue Mar 21, 2006 9:06 pm 
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yes...of course....I thought I posted...but I'm rebuilding the engine and trans in the delta.

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PostPosted: Tue Mar 21, 2006 9:35 pm 
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i know that the small quad4's got the steeper final drive as well as the Tq converters are installed in 3100's etc for a higher stall converter (the trans behind the 3100 in the front of the 442 has the factory 3100 FDR but we had them put in the Tq converter from the 2.3L HO ~400 rpm more flash stall than the stock 3100 one...

good luck with the project...the 3.06 would get you acrost the intersection faster...how much highway ya gonna be driving?



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PostPosted: Wed Mar 22, 2006 11:26 pm 
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Hi Brando, hello everyone,

Quote:
........ Would it be a noticeable difference? ........

Definitely.

Quote:
........ Seems a little pricey ........

$200 to go from a 2.7 to a 3? That's cheap.

Process of ratio selection for a particular app is fairly easy. Hardest part is defining your intended use, and in your case, estimating the possible loss in fuel mileage and the higher interior noise levels.

Regards, Norm



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PostPosted: Thu Mar 23, 2006 9:48 am 
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at 120km/h (70mph) my engine sits at a happy 1300rpm. This engine and trans (I assume you've got the same deal, brando) is geared for the highway. I am sure with the proper math, you would be able to estimate final RPM at a certain speed also...

If I am correct, after specified gear swap, your 70mph rpm will be 1457, instead of 1300... Is this right?



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PostPosted: Fri Mar 24, 2006 3:04 pm 
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That year 3.8 is such a low revver that you don't want to overdue the gearing. It has been determined that the LN3, (the 88-91 3800) actually accelerates faster with the 2.84 gearing vs. the 3.33 gearing by a fairly large margin. Most say that 2.97 or 3.06 would fit that engine very well. Since the 87' engine makes is powe even lower, i'd say 2.97 would be perfect.



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PostPosted: Fri Mar 24, 2006 9:50 pm 
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Hi All,

accelerate88 wrote:
........ That year 3.8 is such a low revver that you don't want to overdue the gearing .......

Any facts and/or figures that might help explain what you just said?

accelerate88 wrote:
........ It has been determined that the LN3, (the 88-91 3800) actually accelerates faster with the 2.84 gearing vs. the 3.33 ........

Who determined it? How were the figures obtained, and under what circumstances?

accelerate88 wrote:
........ by a fairly large margin ........

Is that measured in time, distance, or percentage?

accelerate88 wrote:
........ Most say that 2.97 or 3.06 would fit that engine very well. Since the 87' engine makes is power even lower ........

Most say ........ ? Please be more specific.

accelerate88 wrote:
........ i'd say 2.97 would be perfect.

Did Brando post his intended use and what comforts he might be willing to trade for more acceleration? If so, I missed it.

If not, please explain how you found that ratio to be "perfect" without knowing what his use will be.

Regards, Norm



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PostPosted: Sat Mar 25, 2006 12:33 am 
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The 3.8L H.O. from 87' and the LN3 from 88-91' both reach max torque at 2000rpm. The 87' 3.8 has 150hp at around 4200 rpm, hence it makes its power down low.

As to where I get this info is from the bonneville club. Lots of LN3 powered Bonnevilles with these different gear ratios exist there. It was determined that 3.33 gearing keeps the revs too high and out of the power band. 0-60mph was ~ 9.5sec for the 2.84 gearing, and ~11 sec for the 3.33. Heck, even vids where posted and the 2.84 is clearly quicker. I still think 2.97 would offer the best acceleration.

I just don't want him to gear it to high and see no gains and loose gas mileage in the process. I will admit throttle responce will be much better but doesn't nessesarly mean the car will accelerate quicker.



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PostPosted: Sat Mar 25, 2006 2:56 am 
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accelerate88 wrote:
The 3.8L H.O. from 87' and the LN3 from 88-91' both reach max torque at 2000rpm. The 87' 3.8 has 150hp at around 4200 rpm, hence it makes its power down low ........

Not enough numbers to make any sense. Take the two cars you wish to compare, and list all specs for each.

accelerate88 wrote:
........ from the bonneville club ........

Lots of good information there. Where are the parts that relate to this thread.

accelerate88 wrote:
........ 3.33 gearing keeps the revs too high and out of the power band ........

What precludes a driver from upshifting at peak power? You know, the normal shift point. Or maybe I don't understand the term "powerband".

accelerate88 wrote:
........ It was determined that 3.33 gearing keeps the revs too high and out of the power band. 0-60mph was ~ 9.5sec for the 2.84 gearing, and ~11 sec for the 3.33. Heck, even vids where posted and the 2.84 is clearly quicker ........
88 Coupe wrote:
Who determined it? How were the figures obtained, and under what circumstances?

Is the question too hard?

accelerate88 wrote:
........ I still think 2.97 would offer the best acceleration ........
88 Coupe wrote:
If not, please explain how you found that ratio to be "perfect" without knowing what his use will be.

Another question that's too tough?

accelerate88 wrote:
........ I just don't want him to gear it to high and see no gains and loose gas mileage in the process .......

I don't believe Brando would make a change without knowing exactly what he was doing. I also don't believe he'd change to a higher gear, because his query concerned a change to a lower gear.

accelerate88 wrote:
........ I will admit throttle responce will be much better ........

Throttle response has nothing to do with gear ratios.

accelerate88 wrote:
........ but doesn't nessesarly mean the car will accelerate quicker.

In any apples to apples comparison you would be proven wrong.

Norm



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PostPosted: Thu Sep 28, 2006 11:35 pm 
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Well,
I emailed Jeff through eBay. He can put together a kit that would change my final drive ratio from stock 2.73 to 3.42.

Jeff wrote:
The valve body is set up to provide shifts based on rate of acceleration. You might end up with short-shifts. This can be fixed by using an adjustable vacuum modulator and increasing modulated line pressure (tightening the screw up to, but no more than, two full turns).

The "3.42" is a perfect combination of performance and mileage. Your overall ratio with the 4th gear overdrive ratio of .70:1 will still be a very low 2.39:1 (you currently have an abyssmal 1.91:1!!!!


My other option is 3.06 FDR. I'm not sure what accelerate88 was referring to before...perhaps he didn't know that the 440t4 has overdrive. Really...it's not going to change highway driving much, thanks to overdrive.

Any opinions? 3.42, 3.06,...or you're stupid and don't change a damn thing. :lol:

They also happen to have a Limited Slip Differential...

http://www.engineered.net/eplsd.htm

:cool:

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PostPosted: Fri Sep 29, 2006 2:00 pm 
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Jeff wrote:
........ You might end up with short-shifts ........

This is an indication, that, he knows little about your combo. If so, how would he know what final drive ratio is best for your application?

Jeff wrote:
........ This can be fixed by using an adjustable vacuum modulator ........

I wonder what the actual range of adjustment is, in this case.

Jeff wrote:
........ The "3.42" is a perfect combination of performance and mileage ........

Aside from it being a sales pitch, is there anything wrong with the statement?

3.4 is a big jump from 2.7. Did he know your intended use?

Jeff wrote:
........ Your overall ratio with the 4th gear overdrive ratio of .70:1 will still be a very low 2.39:1 (you currently have an abyssmal 1.91:1!!!!

1.9 and 2.4 are high gears, not low. Other than that, it sounds like, he knows what he is talking about.

Brando wrote:
........ My other option is 3.06 ........

Pros and cons will vary, depending on your tire diameter, intended use, and at what RPM your engine is happiest.

Brando wrote:
........ I'm not sure what accelerate88 was referring to ........

I assumed, his statements were based on a high performance combo with a first gear that's too low. There's no way that could apply to you. He refused to respond to my requests for clarification, so we will never know what he meant.

I put him in the same class, as anyone else who makes recommendations without knowing any of the factors involved. Isn't that a diplomatic way of saying, he doesn't have a clue?

Brando wrote:
........ it's not going to change highway driving much, thanks to overdrive ........

The 3.1 could improve your MPG.

Brando wrote:
........ Any opinions? ........

88 Coupe wrote:
Process of ratio selection for a particular app is fairly easy. Hardest part is defining your intended use, and in your case, estimating the possible loss in fuel mileage and the higher interior noise levels.

Of course you can flip a coin. 50% chance you'd pick the right one. Upside is, you might never know if the other was the better choice.

If the 3.4 proved to be too low, you could compensate by using a taller tire. Works for a rear drive.

Brando wrote:
........ They also happen to have a Limited Slip Differential.

Other than driving during your Michigan winters, do you plan on having a traction problem?

Norm



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