sorry for the thd jack on 10.99 so i will start this post. From this post https://www.crossfireforum.org/forum...0-10-99et.html most know i am with Rudy's help we are building a 3.46 differential for the crossfire.
I will be building 3 or 4 of them ,,,one i will test in my V8. as a open rear first then ,, it will have a wavetrac in it if you want it with wave trac or open.
will post here any and all updates 12-12-15

https://www.crossfireforum.org/forum...0-10-99et.html

 

Still want something around 2.6-2.8, any luck ? Open diff is fine.

Trying to find a sweet spot for my 6 speed but is a tossup whether faster to start in first (one hop and rev limiter) or second (& take a moment to come up on cam). Is also issue of hard 1-2 shift triggering the TC. Have also exprienced rev limiter/TC in sequence. Not good.

Think something under 3.0 would make first usable and sixth a better Interstate gear.

 

Hoping your 3.46 gearing is a success. Squirrel Crusher

 

I have looked at that for you a few weeks ago and i took apart a 2.87 (I think that is what it was) from the measurements I may be able to make it work,, i have to machine about .o50 off the gears. but don't give up yet. jim

 

thanks ,went to the machine shop yesterday was helping the machinist with the parts, looks good so far will pick up everything Monday afternoon, maybe have one put together by Wednesday .

 

Need a little help with the rpm vs speed as my V8 may be different than a 6 speed,,307,,and 327 so here is what we need

a 6 speed which is a 3.27
255-35/19 stock 26.0 tires
rpm at 60=======2200 rpm 60mph
rpm at 70
rpm at 80
then we need a limited auto
rpm at 60
rpm at 70
rpm at 80
of course we need a srt 6
27.1 tall-35-19 tires 295
rpm at 60 ==== 307 rear 2000 rpm =61mph ----with 3.27 rear =58mph
rpm at 70
rpm at 80=====307 rear 2500 rpm =79mph----with 3.27 rear = 72mph

and we also need another v8 but with a 3.07

and i will post my v8's rpm

 

I'm not sure I understand what you are looking for? Engine doesn't change rpm, and also you need to specify what gear you are looking for.
And with a 6sp, just multiply the 60 speed by 1.33 and that will be rpm at 80, assuming you are in the same gear. With auto, there may be slip if the converter isn't locked, but assuming it is, all straight math, but you need to specify which gear.

 

[QUOTE=pioneer4x4;854558]I'm not sure I understand what you are looking for? Engine doesn't change rpm, and also you need to specify what gear you are looking for.
And with a 6sp, just multiply the 60 speed by 1.33 and that will be rpm at 80, assuming you are in the same gear. With auto, there may be slip if the converter isn't locked, but assuming it is, all straight math, but you need to specify which gear.[/QUOTE
no multiplying I need real numbers. each car's rpm above may or may not be different that is why i ask for real time 60,,70 ,,and 80 mph /rpm and if u are cruising at 60 you should be in high gear for auto that would be 5th gear for the 6 speed that would be 6 gear ,,hope this helps. jim

 

the one i have is a 2.84 i think I could do the machining and it would them fit a crossfire,,it would be a bolt in,,, so you would have your oem one for a spare.
looks like it would cost you 600.00 if we meet in the middle of fl. and i give it to you,, you see i already paid 110 to have it shipped to me. and the machining will cost about 140. let me know . jim

 

I don't have your Speed-RPM numbers requested and wouldn't know how to begain doing the math and wind resistance. But may have something somewhat helpful. I have 295/35/19 Michelin's on back that's 27.1 inches tall. SRT-6 in overdrive with a 307 gear at 2000 RPM's I'm doing 61 MPH. Same RPM with a 327 gear gives me 58 MPH. Then at 2500 RPM's with a 307 gear gives me 79 MPH. Same RPM with 327 gear gives me 72 MPH. Rob has my car so I can't help futher with numbers at this time. Squirrel Crusher

 

I'm going to take a wild guess that 2500 RPM's in a SRT-6 in overdrive would yield 66 MPH with a 346 gear running 27.1 tall tires. Just guessing here!! Squirrel Crusher

 

wow thanks ,,,i for got the tire size.. and that is so important to show the difference.

 

I was out last night on local roads, and could do a 40mph check,
6th gear, 40 MPH, approx. 1450RPM, so 80 would be 2900 (and you could peg the speedometer at 180 at 5800 if downhill...) I have a OBD2 dongle, and a GPS, could get actual numbers tonight, I don't think our tach is very accurate on the low end.
I will test 60 on the gauges today.
Also, I have the factory tires on the rear.

 

I assume you have stock 3.27 gears and stock 26" tall tires

 

A 2.87 would be close though a 2.73 would be better, without a body mod can only increase the rear tire diameter about an inch.

The problem is that this is not a real 6 speed (5th is 1:1) but a five speed with a granny low. The jump from fist to second is almost 2:1 and while flywheel inertia limits the speed the engine can accellerate, it works against you on a hard 1-2 shift (back in the day we used to lighten flywheels A Lot to compensate).

On the other end, while a 7.6 cDA isn't bad (not great, my Fieros were 6.75) but OK, the 3.2 has plenty of torque for a 1900 rpm/70 mph cruise. Engine would be more efficient there anyway.

Keep in mind that the purpose of an OD is not top end but a relaxed cruise and for our engine geometry (3.3" stroke is near ideal for gasoline) a sub-2000 rpm cruise at 70 mph would work very well.

Math isn't simple, tied up the GMI computers for quite a while in the early '70s calculating ideal engines/trans for different conditions. Since was going to school in Michigan and home was in Florida, many hours at cruise was important to me. Had a 67 Camaro 327 with a late Rochester FI, four speed, & free flowing exhaust that turned in some amazing numbers but had real Sunoco 260 then.

ps I also use OBD-II for RPM and GPS for speed. Is close enough for government work.

 

Yep, I assume it is all stock. There are times where I think a lower number ratio for the rear would be ideal, then times where I think it is perfect. I think a 3ish ratio would allow 60 in 2nd, and give better numbers on paper for 0-60 times, but not necessarily better overall drivability. I think it comes down to where and how you live. In SW PA, there is no such think as a flat road, and you do a lot of uphill starts so the lower 1st is nice, and on down hill starts, 2nd is nice. 6th gear cruising is fine at all speeds, with 60 being just a hair under 2200, I guess if you are out west and can do long stretches over 70-80 then a lower number rear would be nice.

 

sounds ok just let me know if and when you want it ,,,i would then take it to my machine shop, and get it ready for you. jim

 

"I guess if you are out west and can do long stretches over 70-80 then a lower number rear would be nice."

Way down souf also. Is hard for some from the "slow corner" to believe but I make the Orlando to Boynton Beach run several times a year. 180+ miles without any need to stop (unless you hit the one traffic light between the pike and I-95 wrong).

Over 100 miles from St. Cloud to Ft. Pierce with one exit (Yeehaw Junction), two rest areas, and a 70 limit all the way. Occasional gradual curves. Miles and miles of set the cruise and let the tunes roll.

Same when I go to the Autogeek "Cars and Coffee" in Stuart (met Wayne Carini last time) except only 140 miles.

Gas is also 20c-30c/gal more expensive in South Florida so I like to make the round trip plus some putzing around on one tank.

So to me, a 2600 rpm cruise is 600 rpm high for this car/engine combo and that is like an itch. Would also be nice if first was good for more than halfway across an intersection.

Do understand why a 4,000 lb Jeep Wrangler needs a first that can climb a wall slowly (same trans). A Crossfire doesn't.

 

I understand your pain,,it's like the automatic has a switch to allow us to start out in 2 gear. you could do the same i think. going from a 3.27 to a 2.87 is like going from a 3.07 to a 3.46 wow it could change your cruising speed/rpm to around 60/1900. I bought the rear to go to the mile run to try to brake 190mph ,, but now am only going to go for the 1/2 mile run when i can. and then use a 3.27 because of the pick up off the line and the top rpm of the engine. so if you want this one I will eat the shipping i already paid and meet you between melbourne and orlando,,500. and it is yours. the best of two worlds is that you do not need a tcu for this rear to work,, if anyone with a srt wants it theu would pay 1000 for tcu and diff. jim

 

Here is something i failed to answer got this from another member here! Jim still following your rear end build and just curious you originally said that it could be any gear ratio you wanted but now your talking 3.46 specifically. Just wondering if it got too difficult and you gave up on doing multiple ratios and are only doing 3.46 now? Thanks in advance

the multiple ratios was with the Ford 9" diff,, and i already put in and lost 4800 and now they want to modifly our sub frame ,,so it would no longer be a bolt in so i said drop it,, they are working on giving me back 2800 because everything they did could fit in the new mustang if they sell it i get money back.