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Discussion Starter #1
I'm looking to upgrade to 4.10's, 4.56's, possibly higher my concerns are what is the top speed in 3rd spinning to 6250rpm? Also aside from a retune what other supporting modifications must be done that I haven't done already?

3.73's look super appealing to me because of the lack of a necessary retune and the fact that the speedo gear on the transmission can be replaced without worry of it breaking off into the transmission, however I plan to remove my IMRC's (4v tbird for those not familiar) and need to skip the lag for lack of better words.

The mark vIII crowd seems to think 3.73's aren't enough, 4.10's are great, and 4.56's are best. The tbird crowd seems to think 3.55's are nice, 3.73's are better, 4.10's are best, and 4.56's and up are for the track car only. This car is driven surface streets 20+ miles a day, I finally have a dedicated highway cruiser. Some of the mark guys don't have the speedo gear problem we do, IIRC they measure speed differently, so I was wondering what needs to be done so the speedo reads correctly and the transmission shifts properly. Will a tune and speedcal allow me to retain the stock transmission speedo gear and still shift right, read mph right? Or is more required?

Thanks,
Chris_Murder
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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What is your tire size?


26" tire
3.73 129.7
4.10 118
4.30 112.5
4.56 106.1

26.5" tire
3.73 132.1
4.10 120.2
4.30 114.6
4.56 108

27" tire
3.73 134.6
4.10 122.4
4.30 116.7
4.56 110.1
 

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We'll I can tell u I prolly wouldant go above 4.10, they are genuine ford gears and last I checked the 4.30s and up were made by someone else, so in my opinion they would be more prone to make nosiy, but this may have changed, let me know what gear u are wanting I can get a heck of a price on ford racing gears
 

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We'll I can tell u I prolly wouldant go above 4.10, they are genuine ford gears and last I checked the 4.30s and up were made by someone else, so in my opinion they would be more prone to make nosiy, but this may have changed, let me know what gear u are wanting I can get a heck of a price on ford racing gears
Well the 4.88s you installed in my differential were "Ford" gears, albeit FRPP. I'm sure someone somewhere makes the <4.10 gears for ford anyways. :zdunno:


Chris, the speedcal and a new tune is all you need. No need to change the speedo gear at all--the speedcal can accommodate huge changes.
 

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Discussion Starter #6
Well the 4.88s you installed in my differential were "Ford" gears, albeit FRPP. I'm sure someone somewhere makes the <4.10 gears for ford anyways. :zdunno:


Chris, the speedcal and a new tune is all you need. No need to change the speedo gear at all--the speedcal can accommodate huge changes.
Thanks GM :thumbsup:


What is your tire size?


26" tire
3.73 129.7
4.10 118
4.30 112.5
4.56 106.1

26.5" tire
3.73 132.1
4.10 120.2
4.30 114.6
4.56 108

27" tire
3.73 134.6
4.10 122.4
4.30 116.7
4.56 110.1
27" Tires. 255/50/17. Maybe 4.30's will do the trick enough head room mph for track use and another gear for highway. What about absolute top speed at 6250 in 4th? Not wot of course, just wondering incase I go somewhere with no speed cap in the future.
 

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They were ford gears boxed but they were built different looked like motives or something
 

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Chris_Murder said:
27" Tires. 255/50/17. Maybe 4.30's will do the trick enough head room mph for track use and another gear for highway. What about absolute top speed at 6250 in 4th?
167Mph!

:eek:




Rayo..
 

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West Virginia Chapter Director /, MA Drag Race Te
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Use the 4:30's and get the Motive gear units. Thats what I have in my car. They are as quiet as any Ford units I have ever used.

They are totally streetable or trackable, will help get the 4V into the power band quick enough to be good on the street and the strip. When you start getting into the 4.56 -4.88's etc you are quickly getting into track only set ups if you do a lot of driving. Just a bit much for the street. 20 miles each way on a day is not bad at all.

Besides, the bird with the 4V is a fair amount lighter than a lincoln and with a decent stall and tune will work quite well especially on your 27's, which is what I also use for the street (255/60/15's).
 

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Dont over rev. your engine.
Shift at the high horsepower point as shown by the dyno.
Thats where you want to cross the finish line at as well.

This summer I was shifting and trapping at 6500 with 4.56 gears and
28" tire.Best [email protected]

Went with 4.10, 6000 shifts and trap rpm.
Et lowered to 12.126 @109.
 

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Dont over rev. your engine.
Shift at the high horsepower point as shown by the dyno.
Thats where you want to cross the finish line at as well.

This summer I was shifting and trapping at 6500 with 4.56 gears and
28" tire.Best [email protected]

Went with 4.10, 6000 shifts and trap rpm.
Et lowered to 12.126 @109.
I'm not talking from experience 'cause I've only raced once, but it would seem to me that every car needs to find it's "sweet spot" for what gears yield lowest times.

Same idea with shift points, right?
 

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Dont over rev. your engine.
Shift at the high horsepower point as shown by the dyno.
Thats where you want to cross the finish line at as well.
Sorry but this is incorrect as this will not produce the greatest overall acceleration. The acceleration rate of a vehicle is still positive well after the HP peak. This doesn't mean that the acceleration is high, but so long as it is a positive number, it means that the vehicle is still picking up speed.

Now, I cannot comment on your particular situation because I do not have your datalogs to analyze, but a few people who have heeded my advice have indeed bettered their ETs by following my advice. Just the fact that the "RPM drops" after each upshift are different for each gear change mean that shift RPMs have to be different for each upshift to achieve maximum acceleration rate. In your case, it could simply be a situation of a torque converter lock-up schedule that was not optimum for your tire/gear combo, but perhaps was optimum for your new tire/gear combo. No one will truly know without datalogs and seeing your tune file, but just the fact that all your gear changes are occuring at the same RPM (whether it be 6500 or 6000) means that the shift schedule is likely not optimized at all.

Where is your HP peak occuring (RPM)? Post up your dyno sheet please.
 

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50 years of Mercury Cougar 1967/2017
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gm, where do you get your information?
Your first paragraph is flawed.

Most people over reve their engines.
This takes away from the most rapid accleration.
I have a transmission controller that allows the converter to lock up and unlock
during each shift.

Whenever you get your engine running you'll find out about over reving.

In its present form, peak hp is 5900, peak torque, 4900.
Thats a guess eyeballing with ruler.
 

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gm, where do you get your information?
Your first paragraph is flawed.

Most people over reve their engines.
This takes away from the most rapid accleration.
I have a transmission controller that allows the converter to lock up and unlock
during each shift.

Whenever you get your engine running you'll find out about over reving.

In its present form, peak hp is 5900, peak torque, 4900.
Thats a guess eyeballing with ruler.
I get it from actual datalogged performance on a datalog that I did myself--all real-world no guessing here. I have posted acceleration vs RPM graphs multiple times.

You're confusing peak acceleration rate (which occurs at the torque peak), with cumulative acceleration which is over the course of several gear changes. With a HP peak of 5900, you're losing out on extra acceleration that can be had by accelerating over the peak HP RPM. There is absolutely no way I am flawed----I can guarantee you with 100% certainty that acceleration is still quantitatively positive and thus a car still picks up speed past the HP peak---don't let my words convince you, my datalogs do all the talking, so long you can interpret a standard datalog plot. If you refuse to believe correctly done datalogs on an actual vehicle run, then there is nothing anyone can do to show you the truth.

You can do a search in the EEC tuning forum if you want to see where I explain this with an actual datalogged screenshot from an actual run. My new engine is not necessary for this----this can be seen with any engine that uses mutiple speed transmissions IF a person is willing to datalog the vehicle's acceleration rate. Whenever you're ready to datalog this with your car, let me know and we can go from there if you wish. It's my knowledge on this type of stuff that is the reason that the person who built your engine comes to me for tuning advice ;)
 

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His information is correct. JL among many others was a huge proponent of datalogging the acceleration rate to achieve the optimum shift points in the tune.

The idea is to keep the area under the acceleration curve as great as possible during each gear. You have to know the curves to do the fine tuning. Trial and error will get you close eventually, but doing the datalogging is a much more precise and effective method to get it right.
 

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The idea has merit.
The real world of racing makes it just theory.
The only time when its good to over rev. and engine in that manner is for a national record. (nhra-ihra)
The only time to over rev. is in direct drive.
Otherwise the fastest accleration is wasted on the lower power high rpm.

Data logging is good for those automobiles that are not sorted out.

Sorry for my explanation, but that is as well as I can explain it.
I have run 5:13 gears, 4:56 gears, 4:10 gears, in my crap box, with the
present combination.

Next is the 3:73's. To put it in the 12.00's.

I don't want to start a *i#= measuring contest.
Just adding experience to the equasion.

Nothing against math teachers.
 

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The idea has merit.
The real world of racing makes it just theory.
The only time when its good to over rev. and engine in that manner is for a national record. (nhra-ihra)
The only time to over rev. is in direct drive.
Otherwise the fastest accleration is wasted on the lower power high rpm.

Data logging is good for those automobiles that are not sorted out.

Sorry for my explanation, but that is as well as I can explain it.
I have run 5:13 gears, 4:56 gears, 4:10 gears, in my crap box, with the
present combination.

Next is the 3:73's. To put it in the 12.00's.

I don't want to start a *i#= measuring contest.
Just adding experience to the equasion.

Nothing against math teachers.
I don't have a ton of drag racing experience by any means, but I will tell y'all this from the little when I had a Mustang GT 5.0L I used to take to the track.

I drove and my friend Dale drove; he NEVER got close to the times I pulled - he was always 0.5 second slower or so. My car was a 5 speed and the difference was I would shift around 6k or so (depending on what shift) since I could 'feel' the acceleration drastically dropping off; Dale would shift closer to 7k. I said he's just revving and not pulling, he'd say, "Jon's Camaro we shift at 7k and turn great times!" (the Camaro had a much bigger cam than my GT)

I always told him it was because my GT wasn't built for those kind of revs and he was TOO far off the peak and simply revving. Stay in the power band, under the curve.

Logic would suggest that if you data log and figure out the total area under the hp & tq curves that where you have the greatest area would be optimal, but I can't swear by it. I simply went by "the seat of my pants". :zdunno:

Rear gears? Who knows - trial and error?
 
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