Welcome To V6Mustang.com!

We are the oldest and largest V6 Mustang forum on the internet. If you have any questions about your V6 Mustang or just want to connect with other V6 Mustang owners around the world, you have found the best place on the internet to do that.

Registering is free and easy! Hope to see you on the forums soon!

High RPMs

Discussion in '1994-2004 V6 Mustang Tech' started by NShinn4, Dec 7, 2017.

  1. NShinn4

    NShinn4 New Member

    Dec 7, 2017
    Likes Received:
    Trophy Points:
    I have a 2001, V6, 3.8L, 5spd Mustang coupe. Nothing too fancy. I just got it last week and right off the bat Ive noticed that 4th and 5th gear are quite interesting. If I shift into 5th any lower than 65mph, my RPMs hit 1500 and it does that loud shaking sound manuals do when there isn’t enough power for that gear. On the flip side though, I have to run 4th gear literally everywhere except the highway. Typically I’m at 50+ MPH so my RPMs are ALWAYS at 2500+. This is obviously a huge gas guzzling issue. This is my first mustang so I was wondering of this is every 5spd mustang or if this is something that is wrong. In all my other manual cars, I could hit 5th gear at about 45 or less and be just fine. Is there anything else I can do to increase my gas mileage (other than the cold air intake already done that one)?
  2. six gun

    six gun Active Member

    Jun 26, 2014
    Likes Received:
    Trophy Points:
    South Dakota
    If those years are like mine, 4th gear is 1:1, and 5th ratio is .68:1, so there is a little RPM jump there. Should be able to cruise at 50+ just fine in 5th - unless 1 you're needing an engine tune-up of sorts, or less likely 2 someone took out your stock 3.27:1 rear end gears for something taller like 3.08 or something. But that would be silly.
  3. Sam36

    Sam36 Active Member

    Aug 23, 2005
    Likes Received:
    Trophy Points:
    San Antonio
    With a stock clutch I can go into 5th at 40mph just fine. I briefly had a ram powergrip clutch and I had to be over 50mph or the car would resonate so bad I thought it was about to come apart! Of course at 40mph in 5th, I am either cruising or very lightly accelerating. I can't really accelerate in 5th until around 55mph or so, really no power under that but the resonance isn't too bad.

    So I'd say something is not right. Use the gps on your phone or something and make sure your speedo is in fact right (or somewhat right). From there I'd try to find out if someone swapped the rear end gearing in it, though it is very strange that they'd go higher instead of lower.

    I think a ghetto way to determine the ratio is to get the rear tires off of the ground and then turn the rear tires one full revolution (both tires need to be turning at the same rate as well) and count how many times the drive shaft makes a full revolution. For a 3.27 rear end, you'd want that driveshaft to make 3 and a quarter revolutions with one revolution of the rear tires (or something like that).

    Other than rear end gears... what size tires are you running? If they are taller than stock that will be the same as running a different rear end. Especially if someone squeeze some 22" rims on there or something....

    I've also heard running a polyurethane transmission mount can be very noisy too, you can check for that. Problem is they were only briefly made for the v6 3.8, they are hard to find. Most all aftermarket mounts are just a copy of stock oem and should be fine. And might also check if the rear control arms are running stock bushings as well and not aftermarket polyurethane.
    Last edited: Dec 8, 2017