High RPMS at 55 MPH

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4spdragtop

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Im wondering why Dads 67 cuda is revving so high...Only going 55 MPH and we are at 4k in 3rd gear... specs are 273 4 bbl, 3:23 gears and above stock torq conv. No idea what the stall is on it but the converter is new. Also havent verified the rear gears, but Dad is 3rd owner and its fairly original so I am assuming orig 3:23 gears

Here is the build/resto thread if that helps
http://www.forabodiesonly.com/mopar/showthread.php?t=178255

Thanks
4spdragtop n pops
 
Assuming is a dangerous thing to do. You should verify the gear set. Also, why would it have an "above stock torq conv" with just 3.23 gears?
 
What rpm are you running in 3rd at 55 MPH.


My 340-s runs 4000 rpm at 70 with a 3.91 gear.
 
What is the size of your rear tires?

Are you sure your tach is correct?

Are you sure your speedo is correct? (can use smart phone)

Do not compare to others unless you know their's and your's tires sizes.
 
Are you sure it's in 3rd gear. Since it's a Formula S it could have 3:91 gears. Unless your converter is crapped out or really cheap, it shouldn't matter much what stall it has at a steady speed.
 
Steve, at 55 with a 26" tire and a 5.56 gear you would be around 4000RPM.

Something isn't right. Speedo off, tach not right and I doubt you have 5.56's.

Could the converter be slipping that bad?

Is the trans shifting firmly into drive?

Do you have the correct toothed gear in the trans to match the rear gear?

What tach, aftermarket?

Does it sound like it's revving high or is this just what you are seeing?
 
Sounds like it is still in 2nd gear to me. Otherwise it would be running close to a 5:1 rear gear by the looks of the tires in the pictures.
 
As others have said do not assume anything

I remember you had troubles with a tach board, was it this car?

1..........First verify the rear gear, and compute what speed should be with the tire size using an online calculator. To do that jack up ONE rear tire, put the trans in neutral, make sure brake is off and see if you can turn the wheel. If you can, Turn the tire TWO revolutions while counting turns on the shaft. Easy. 3.23, with two tire turns, the shaft will turn 3 and about 1/4 turns

3.55, shaft turns 3 and just a shade past 1/2 turn, etc

Then take your gear and tire size and find an online calculator, just google speed, rpm, etc there must be millions

2......Then you must be certain what gear it's in. Auto? should be able to feel it shift twice, and a little playing with the shifter at 35-45 mph should tell you what it's doing.

3.....Use a GPS unit to verify what the speedo reads

4.....Borrow? a tach and see what it's doing. I checked my tach with a sound card lashup and a downloaded signal generator, which produces various musical tones.
 
Speedo n tach factory but recalibrated. tach has upgraded electronic tach board. Torque converter was new and pig deal with the car. its in 3rd for sure.
 
Ok, so pulled Dads cuda outta storage today. Of course it started pouring about 20minutes later....but definitely "seems" to be over revving....approx 3500 @ 50 mph...doesnt seem like as firm a shift into 3rd gear as it is into 2nd.
Tires are 245/60/15
I havent verified the rear end gears, but I will chk that tomorrow as well as the recalibrated factory tach against a new one we bought a while back.
Gears as far as fendertag goes are 3:23.
As for the torque converter, the prev owner had the orig torque converter for the 904 273 commando. But when he put a 400 hp 360 in it, a new torque converter was installed. This new torque converter is the one we went with. If I remember correctly I ground off the weight for it to be used on the 273 that is in it now. We used it as when we put the cam in Dads 273 we put in comp cams 270S. Im going to try and "flash" it tomorrow and gauge what stall it is.
 
CONVERTER IS SLIPPING!....gonna burn up the trans pretty quickly! put in some 4:56 gears or a stock converter back in..
 
The converter is all wrong for your application. What does the comp. chart say to use for a converter with your cam? The converter was built for originally a 400HP 360, not your 273, unless your 273 is putting out the same HP and torque as the 360.
High stalls must be applied to YOUR ENGINE/DIFF/TIRE COMBO not someone elses.
 
CONVERTER IS SLIPPING!....gonna burn up the trans pretty quickly! put in some 4:56 gears or a stock converter back in..

I dont "feel" or "see" it slipping. The rpm's hold steady while driving....
You think a stock converter would be fine?? The reason we went with the one currently in it was because it was to our knowledge new, or very few easy miles on it and we were unsure of how many miles, or how "tired" the factory converter was.
Here is a link to the cam we put in

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=665&sb=2
 
Steve we already posted this.........first thing to do is determine the rear gear, and you can READ the tire size

Jack up one wheel if you don't know if it's limited slip. With car in neutral and parking brake off, can you turn one wheel? Yes? Turn the wheel exactly TWO turns while counting the driveshaft. That is the rear gear, IE 4 turns and "a little" is a 410, etc

If you cannot turn one wheel, IE sure grip, jack up both rear tires. Turn either tire ONE full turn while counting driveshaft turns. Same deal, 4 turns, etc is 4.10 and so on

Trans is 1:1 in 3rd make SURE it is shifting into 3rd. Torqueflites are "easy" there are no hidden OD gears, etc. It's either in 1, 2 or 3rd, and or slipping.

With tire size and rear gear, consult an internet www calculator.

SUSPECT the tach. You have a GPS? Easy Use it for a speedo to compare
 
I dont "feel" or "see" it slipping. The rpm's hold steady while driving....
You think a stock converter would be fine?? The reason we went with the one currently in it was because it was to our knowledge new, or very few easy miles on it and we were unsure of how many miles, or how "tired" the factory converter was.
Here is a link to the cam we put in

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=665&sb=2

Notice that Comp says 'STOCK CONVERTER' on the link you give. Any idea whose converter is in the car now(the one a few of us has presumed is a high stall? Converters usually don't get tired. Common problems: Loaded with contamination from a transmission failure, hub broken or groved, with Chryslers, broken teeth on the ring gear, sprag failure, excessive internal clearance (internal thrust washer worn out). Chrysler converters are well built, and unlike most others, the pump side (hub side) is furnace brazed for added strength.
With out a lot more information, it's hard to say what is the right converter for you. My guess, unless there's a ton more done to the engine, and the HP and torque is way up there, a stock converter should work OK.
 
Ok, finally got a chance to chk things out. Hooked up another tach so I could read it and the factory one in the car at the same time.
Tire size 245/60/15 = 26.5" tire diameter
Rear end gears 3:23= jacked up car turned tire 1 revolution=3.25 approx turns on driveshaft
I "flashed" the stall, and it looks like approx 1800 on new aftermarket tach.
MPH/RPM readings
Idle rpm 1000 factory
500 aftermarket
30 MPH 2300 factory
1600 aftermarket
40 MPH 3100 factory
2000 aftermarket
50 MPH 3700 factory
2500 aftermarket

So to me everything looks good?? Other than dad paying to have the factory tach redone with upgraded electronic board and recalibrated and it looks to be way off.
 
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