Post your RPMs at 60mph with your 3.73/4.10/4.30s

E

eduncan911

Registered
Just wanting to know what RPMs you guys are turning, with the converter locked up, with 3.73s, 4.10s, and someone with 4.30s (if there is someone). Trying to guestimate what I'd like in my car.

I love 4.10s in the Cobras, and 4.30s with a 6spd in the Cobras.

It will see a lot of travelling, cruising at (any officers around?) 85 to 90mph most of the time on trips. But, it will see the track as well especially after I get the rear end done, tranny done, and engine swap. The RPM factor will help me decide, as I know how the motor I am building will cruise best at.

Thanks in advance guys!
Eric
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

Check out: www.smokemup.com They have some good auto math calculators that will allow you to change transmission, gears and tire sizes so you can see the differences.
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

Anyone have a good site for 3.73's. also what will I need other than the gears. I know there is an install kit and others. But I know you don't need to buy a new center piece for 3.73's correct?

I believe the company was FRPP or something of that sort.
Any help is appreciated. Also, how many tenths of a second you think 3.73's would knock off ? I heard somewhere from .03-.05.



Jon Ike
95 MKVIII
STRA DOG
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MIDWEST CHAPTER [/font]
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

Check out: www.smokemup.com They have some good auto math calculators that will allow you to change transmission, gears and tire sizes so you can see the differences.
Click to expand...

I don't know the 4th gar final drive ratio in the 4R70W. :p

Eric
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

If you do a lot of cruising at 85 to 90, 4.10's and higher are probably too high. I have seen at least two people sell 4.10's after putting them in their Mark VIII's and realizing they were too much.

I've never seen anybody sell 3.73's thinking they were too much. The owner of the highest mileage Mark VIII just recently put 3.73's in his car.

You could always buy the 3.73 pumkin and change to 4.10's or 4.30's if you think it isn't enough............Johnny did this, but he doesn't do the driving you do.

Ken
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

4th gear is .7 to 1 in the 4r70w (that's what the 70 means).

4.10's here, 80 mph is almost exactly 3k rpm. The car is so much more fun with gears.
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

Excellent replies guys! And thanks for the 4th gear/final drive ratio, that will seal the deal on helping me calculate which gear I need.

If you do a lot of cruising at 85 to 90, 4.10's and higher are probably too high. I have seen at least two people sell 4.10's after putting them in their Mark VIII's and realizing they were too much.

I've never seen anybody sell 3.73's thinking they were too much. The owner of the highest mileage Mark VIII just recently put 3.73's in his car.

You could always buy the 3.73 pumkin and change to 4.10's or 4.30's if you think it isn't enough............Johnny did this, but he doesn't do the driving you do.

Ken
Click to expand...
Ken, I'm more then happy to agree with you; if the motor/electronics was stock. If you click the link in my sig (about my Mark), you'll see I have big plans. 31 splines and LMS upgrades in the rear, built tranny and high stall, and a powerplant of close to 400 to 450rwhp on the pump.

Now I've even ran across a 5th option now for achieving that kind of power, but N/A which is getting me really excited. More on that later if the sponsorship comes through on one of my websites.

I'll be tayloring the cam profiles (I have my own ground for 4.6 4V motors I build) to a pretty high duration and high lift. So a high RPM cruise speed (of 3100/3300rpms) at 90mph is livable when the motor will be turning 7500 to 8000rpms during shift points, and low-end is not all there due to the high duration. ;) I just have to hope I can build the 4R70W, or have the guy who built Geno's, to withstand those high RPMs. Been years since I've been inside of those transmissions. And yes, a scatter-shield will be installed. Not playing around here.


Thanks again guys!
Eric
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

I have 4.30s in mine and at 80mph it is right at 3000rpms. I am not one bit sorry I went that steep, but I will admit to being skittish at first. The first ride changed that though.
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

Where are you going to get 31 spline axles for a Mark? I don't think those are available. The Cobra axles are a different length, aren't they?

I'd say if you're planning on trapping over 110 mph, get 3.73's or 3.90's. If not, i'd stick with 4.10's.
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s


Where are you going to get 31 spline axles for a Mark? I don't think those are available. The Cobra axles are a different length, aren't they?[/quote]

Was thinking of an '03 Cobra parts for the rear (carrier, 1/2 shafts, hubs, two additional braces welded in like the '03s have, etc).

Humm, different lengths? Ok, this might be a problem. Geno? lol I was kind of wondering why no one talked about swappin gin '99/'01 Cobra parts into the IRS (i.e. the posi carrier).

I can get hold of a set and try them out if no one knows.

Once all said and done, I won't rest until I'm trapping 120+ on any motor setup. With a 4,000lbs car and estimated power with moderate traction, I'm guessing 125 to 128mph actually. This is why I was thinking of 4.30s. So to use a good bit of overdrive before crossing the line, instead of just 3 gears.

My Cobra was trapping 138mph, but only via the PowerMeter electronic device. Dynoing 670+rwhp, I can see it trapping that high. Never got a chance to try though on a track.


Eric
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

I've never seen anybody sell 3.73's thinking they were too much. The owner of the highest mileage Mark VIII just recently put 3.73's in his car.
Ken
Click to expand...

yeah but I'd sure trade my 373 pumkin for a 410 pumkin in a hearbeat!

going from 308's to 373's just "wasnt enough" for me.
especially considering the cost.
Granted I LOVE the gears, but I want more More MORE!
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

So to use a good bit of overdrive before crossing the line, instead of just 3 gears.
Click to expand...

Watch out on that. When you shift into 4th gear, two things have to happen, rather than one. If they aren't synched, bad things happen. See ford tranny's 101 under technical articles -> transmission on www.tccoa.com for more details. It's hard to get those two things synched if the engine is changing RPM too fast, esp. at high RPM's. So a tuner who knows a bit about the trans, and who doesn't want to blow it up, generally will set it up to hit 4th at around 5k rpm. If you want to build a motor, with DOHC, you should be planning to spin it to at least 7k, so a 5k shift into 4th will hurt. If you're planning to trap that fast, i think you should go with 3.73's or 3.55's.
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

2050rpm at 60mph in 4th (converter locked) with 3.73's and 27.0" tall tires.
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

2050rpm at 60mph in 4th (converter locked) with 3.73's and 27.0" tall tires.
Click to expand...

Whoa, that's low! lol So far, 4.30s are looking like my option in the future (months from now future).

I've had my Cobra up beyond the 185mph mark (calculated RPM vs 6th vs TireSize) and that was a bit scary, but fun as hell passing that Viper though. ;)

I don't expect speeds beyond 130 to 140 with the Mark. So 4.30s, and the times I think I'll run in the 1/4 come next year (2005), allows me to finalize my decision for now.

Thanks again for everyone's replies!
Eric
 
RE: Post your RPMs at 60mph with your 3.73/4.10/4.30s

Multiply you current rpm at a certain speed by your new ratio and divide by the old ratio to determine what rpm your engine will turn with the new gear.

Roadie
95 Champagne Mark VIII
00 Ford F150 Supercab 4x4
02 Mazda Protege
86 Chevy Monte Carlo SS
81 Honda CB900C
 
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