Anybody go from 3:55 rear gear to 3:08?
 

Yeah. Yeah.
I know. I know.
Typically people want to go lower in their gears but hear me out.....

Mike Forte built 427 stroker
TKO 600 w/.82 5th. gear
3:55 Ford 9" posi. (limited slip or whatever Ford calls it)
315/35/17 tire

Car is primarily street driven. Not a track beast.

Around 80 mph, I`m taching around 3K rpm`s.
(Second Strikes gearing calculator shows 77 mph)
At 75 mph, it`ll tach around 2500-2600

I`d like to drop a couple hundred RPM`s off those numbers.
And a rear gear swap is CONSIDERABLY cheaper than buying a new trans.

Going to a higher gear, I`m not too terribly worried about losing low end torque/power cause that motor has a lot of it under 4K rpm`s.

I don`t spend a lot of time at highway speed either BUT, it`d be nice to not have that engine turning that high for a long period of time.
My pumpkin is leaking anyways and if I have to pull it to re-seal it to the housing, why not swap gears?

My question is, has anybody done this? (Gone higher)
If so, were you happy, or did you swap it back?
Or should I say "F" it and leave it alone? :LOL:

I went from 3:54 to 3:31 and its perfect.
My AC has 2:80 which is too low however its great on the highway.

In SPF1855 I went from 3.73 to 3.27 with the .64OD. SBF 427 530+ HP/TQE.
I liked it a lot. 2,200 at 80mph. 315/35-17

The 3.08s and .82OD should be similar at 80mph but won't have the snap in 1st-4th.

Jim

good friend had 3.08s in his mustang and said fifth gear was useless unless flat on the interstate. He went to 3.55 and says its perfect.

Granted he's heavier and running around 325hp, he says the 3.55 hits all the sweet spots in his setup.

How tall a rear gear you can run is a combination of how much low speed torque you have and how well mannered your engine is below 2000 rpm. If you have the torque and the engine manners, the tall gear will be a nice upgrade for you.

My engine has just under 600 ft/lbs of torque at the hit of the throttle even as low as 1500 rpm and it idles smoothly at 850 rpm. I run the M/T 295x65x15 ET Streets and a 2.73 ring and pinion. Even with that tall ring and pinion, I have to be cautious because a little exuberance in the driver's seat can easily light up the rear tires if the traction control is turned off.

Highway speeds are a whisker below 2000 rpm at 75 mph in fifth gear. I have the TKO600 RR gearset. How your car can / will behave is tightly coupled with the low speed torque you have available in the rpm range below 2000 rpm along with how well mannered your engine is at engine speeds less than 2000 rpm.

The more of a competition car type idle you have, the greater the risk the engine will begin to buck and cough if you pull it down below 2000 rpm in fourth or fifth gear. Be cautious, deliberate and circumspect if you decide to put tall gears in the rear end.

Also worth mentioning, don't overlook the impact tire diameter has on engine rpm. Should you decide on 30" diameter rear tires (295x65x15) you may have more or less massage work needed to fit them, depending on whose replica you have and where in that firm's production history your car falls.

Additionally if you do light up the tires with a tall R&P your driven wheel speed will increase stunningly faster than with a 3.73 R&P. The more rapid increase in wheel / tire speed with the tall R&P makes controlling the car more challenging — a bit of an understatement. If you use a modern engine management system, I would highly recommend implementing and using its traction control. You won't be sorry you did.


Ed

I have a 600 hp, with a 2.88 Posi rear end, with a T5, and 27" diameter wheels, Its great..
2 nd gear is close to 100..

I run a 3.08, same size tires (they're shorter than the 15"s, which increases gearing), TKO 600 w/.64OD and 572hp 585tq. If I could get a 2.90-2.80 rear gear (not available for the 8.8 Ford), I would and switch to the .82 OD. With the 2.87 first gear it tops out around 45mph and NT-01s aren't sticky enough to put it to the pavement. The 2.32 first gear in the Toploader seems better suited for these cars, but lacks an OD. Currently, I'm at 2000 rpm @ 75 mph in fifth. You would be about 2550 at 75 mph and 2730 at 80 mph. According to my calculator, you are 3150 at 80, currently. I know 3.00 is available for the 9", which would get you to 2660 rpm at 80 mph.
ALSO, you can change the OD gear without buying a new transmission. Contact Dederichs Motorsports for parts. He is in Fort Worth. 682 365-5555 .64 OD would get you to 2450 @ 80. Tremec has just released their TKX transmission, it is dimensionally identical to the TKO600, but is gasketed and has better syncros. Dederichs can set you up with that too and you could sell the old TKO. I believe a .73 OD is available with TKO 500 0r 600 gear sets.

Coach had the same problem with his .82 Tremec. We swapped the main shaft and fifth gear. It's been a couple of years ago but I think the parts cost about $350 and we easily sold the .82 shaft for $250. He paid Eddie $200 labor to swap parts.
We pulled and installed the tranny in his Cobra.

I found over the years IMHO 3.55 (3.50 for a nine inch) 26 inch rear tires and .062 5th gear tranny makes a great combination for a Street Cobra, Coupe.

Oh yea '66 Fairlane

You have enough gears for the street light and can cruise at 2,000 rpms.

Of course your cam plays a big part. Your motor small or big needs enough torque at 2,000 rpms to push your car.

To put it in perspective, with the 2.87 Tremic first gear a 3.08 rear gives you the equivalent first gear of a 4.00 rear end in the old close ratio 4 speed days. I think it is a good move for you, in my opinion first gear is way too short in these light cars with lots of power.

My 2.73 gear is an OEM Ford gear for their 8.8 like used in T-Birds and Mk VIII's. They also have 2.92 and 3.08 available and if you go to the aftermarket I believe there are 3.00 and 2.90 ratios available. The 3.00and 2.90 are not hunting gear sets. If you select a new gear set you should look for a ratio that is a hunting ratio. It will run quieter.


Ed

Good info.
I did buy my trans from Dederich also.

I doubt I want to pull my trans due to a leaky rear that needs re-sealing anyways. BUT...the other info was great none the less.
Thanks!!!

Sounds like you're confident that your engine can handle the taller rear end well enough. You have a five speed gearbox and a big torquey V8, so no big deal if you feel the need to change down a gear or two to power past other vehicles on the open road.


Cheers!
Glen

The 315/35/17s are shorter than the original tires and increases gear ratio as well.

I have an 8.8 solid axle. Do you know of gears below 3.08 for it? I couldn't find any. I have a FFR and am considering swapping to IRS. I may have a choice between T-Bird and Mk VIII or '15 and newer Mustang. Any thoughts on the two? 3.08 and bigger is all I've found for the current platform.
Thanks,
Mark

My preference, Mark, is the earlier 8.8 housing out of a 2007 to 2010 Ford Explorer. It is a HD version
of the T-Bird, MK VIII or SVT Cobra housing. It also has massive dual front mounts that dwarf the Cobra
generation housing. Here are the two side by side;

http://www.clubcobra.com/photopost/data/500/Expl_2.jpg

The Explorer version is a bit heavier and Ford added some "Vitamin C" in some of the tender areas to
offset warranty issues in the much heavier Explorer chassis. There are a number of nice covers for the
back. Do not use a stock cover they are paper thin and break like this SVT Cobra piece,

http://www.billetflow.com/IRSFailure_Case3_Pic002.jpg

Ford offers a reasonably priced HD cast cover for the housing that looks like this;

https://turn5.scene7.com/is/image/Tu...prodpg640x480$

There are all manner of differentials available for the Ford 8.8 rear end,Tru-Trac, Quaiffe etc, but I liked
(and bought) the Wavetrac Torque Biasing unit, click here => Wavetrac for a nice visual of how
the interior geared mechanism works (there are no clutch packs). An extra added benefit to the
Wavetrac is it comes with a lifetime warranty.

The nice thing about the remaining IRS rear spindle hardware is you can purchase it all from Ford because
they make the pieces available just for kit cars. You have a choice of either the newer 2015 -2020 rear
knuckle kit or the earlier 2003/2004 Cobra style knuckles depending on which you like better. You can also
buy the parts from a salvage yard and save significant $$. Ford offers a full kit car version of their OEM rear
brake package or if you like, you can use stuff like Wilwood.

Although they (Ford) do not offer them I would opt for the Mark Williams billet steel caps, They cost right at $100 brand new on eBay.

The mounting cage for the IRS is really simple to craft;

https://www.roninspeedworks.net/imag...sG-900x600.JPG

The "tall" gears are an over the counter item at your local Ford Dealer. If you go to Tasca's online FRPP site
you can get a little break on the pricing.

Here is an OEM Ford 2.73 ring and pinion (ring only in the picture)

https://i.ebayimg.com/images/g/ZYMAA...Xc/s-l1600.jpg

You can buy these brand new right over the counter at Ford parts counter pricing or you can buy excellent
used parts off eBay below $100. This particular one was going for $80 or so — because no one wants them!
Not only that they usually come out of granny's daily driver and are in near new condition!!

Use your mouse, your keyboard, Google and a little initiative and you can probably do even better. These were
the first items that came up in my Google search. A focussed search will probably do better.


Ed

Thank You.

Mike, i'm thinking about the same thing. I have 427w 600hp/600tq .. TKO600 w/.82 OD. Ford 9" w/3.50:1. 15" Goodyear billboards. I get about 3k rpm at 80mph. was looking at going to 3.27 but a complete differential LSD center section from Hurricane (via John's i think) was over $1k if I recall.

Actually I would have liked to have gone with T56 6-speed. best of both worlds. but was afraid of the longer trans, shorter driveshaft with a solid live axle. But Hurricane's latest demo car has the T56 and live axle, no problems so far. so maybe .....

In my FFR, I switched from 3.55 to 3.27 as a test. The car had a well built 427W with a very flat torque curve.

I didn't like it at all. I was surprised that such a small change would make a big difference. I was going to change the gears to a 3.73 next, but other things got in the way.