Hay folks have a 351c 4 barrel t5 tranny. Engine rpms are high to me will verify in am just installed a tac. In my wandering around the forum I have seen guys installing 3.50 gear sets an being happy with that. I am wanting to cruse at 80 mph in the 1800 rpm range. I would like to see miles @ what rpm as a reference.
Thanks. Ralph
I think you are right on the money.
I am running 3.80 rear gear with O/D and at 70 MPH (they don’t like us to run 80 around here) I am tacking 2100.
T5s can have different rations for 5th so without knowing which one you have it is hard to say for certain. In my '70 with a 0.63 5th and 3.50 pumpkin I’m seeing more like 2,100 rpm at 80.
There are online calculators for this. Need to also factor in the rear tire size.
For 1800 rpms at 80 mph, you would probably want to look into a 6 speed with double overdrive.
Well at 80mph turning 3300 rpm at 70 turning 2100 rpm. 3300 is way to high just for crusing. Running 14 in rims with 215 70 r15 tires.
Sure would appreciate one of you numbers fellas figure out what I got an what I want. 2000 rpm at 80!!! Any slower an a blonde in an suv will run all over ya.
With a .67 overdrive, typical for Ford AOD, you will need a 2.80 rear axle with 215/70 14 tires (25.85 inches tall). That will put you at 1952 RPM at 80 mph.
I had this exact setup in a '68 with a Ford 302 crate motor and I hated it. A 3.50 rear gear will put you at about 2500 RPM and be much more fun to drive.
The numbers you posted don’t make any sense. With a 3.0 you would be at 3189 RPM at 80, and 2790 at 70.
80mph turning 3300 rpm at 70 turning 2100 rpm
Well the tac may not be the most accurate. But that’s the numbers I was getting. That 3.50 gear set may do the trick. Thanks for your replys.
Be Safe. Ralph
Hay gentleman. Ok rear tire 1 full rotation have 3 3/4 turns of drive shaft. What’s my gear ratio?? Need some help!!
Thanks. Ralph
3.75. Right?
I was thinking 3.73 so we are both close. Thanks for the reply.
Well I guess we were both close. I figured 3.73. Gonna run a 3.20 gear set an see how that does
Thanks. Ralph
Tremec has a nice calculator on their site where you enter your relevant car details (trans, final drive, tire dimensions) and it calculates engine RPM.
Thanks for the info.
Be Safe. Ralph
Well have the rear chunk installed an took her out for the first Breck in run. 3:40.1 Not impressed 50 mph at200 in third not much diff in 4th and 5th was not close to 80 mph at 2500 rpm. I sure hope the break in process .improves the the rpm to mph. Have ya’ll had the happen to new rear sections. An what is supposed to be above the lower bump stop on rear axle ?
RPM to MPH is entirely controlled by gears, so no, it will not improve with time.
Can you share any more specifics on which gear ratios you have in the T5, which speedo gear you’re using, etc.? I’m not following why you’re not seeing a difference between 3rd, 4th, and 5th.
I doubt this is it but I had a bad clutch in a BMW that slipped in overdrive. Of course that finished it off in a hurry.
Thanks for the replies.
Todd how can I find the gear ratios in my tranny. Can I enter the numbers on the side in a index somewhere?
Thanks. Ralph
I have a '70 Cougar with a 351C that I’m running 245/45/R17 (25.7" dia) tires on the rear and have a Tremec TR3550 5 spd in it. The OD gear is .68 and when I shift from 4th (1:1) to 5th gear at around 50 mph the RPM’s on the tach go from about 2400 to around 1600 or 1700 rpm. The Cat is obviously put away for the winter so I can’t 100% confirm by taking it out for a spin but if my memory serves that’s what I’m getting. I’ve never really taken note of it before but I will in the spring out of curiosity.
My speedo may be off by a mile or two per hour as well. I think I have a 21 tooth driven gear on the output shaft for reference as well. Hope this gives you some extra insight to your calculations.