Two identical EF's, both do different rpm at 100, any ideas?

Deanodriver · 07-03-2006, 06:12 PM

I've just bought an EF, and driving it home from Vicroads today, I was noticing it was doing about 2000rpm at 100km/h. However, my old man's got a virtually identical car (series 1 Futura, mine's an August 1994, his is a March 1995, I think, both autos), and his does about 1700rpm at the same speed.

I wonder what could be causing it, could I have an aftermarket diff in mine? Did they offer a shorter diff as an option in Futuras?

svo347 · 07-03-2006, 06:15 PM

was your power/economy switch on or off , same as the other vehicle

Deanodriver · 07-03-2006, 06:15 PM

Quote:

Originally Posted by svo347

was your power/economy switch on or off , same as the other vehicle

Both were set to economy, and both speeds were with the cruise control on exactly 100.

MickyB · 07-03-2006, 06:23 PM

Same size wheels? Although that shouldn't make much of a difference.

MAD · 07-03-2006, 06:30 PM

Maybe one is not locking the torque converter, either that or one has a different diff in it to what is expected.

2000rpm is about what our EL monty ghia does at 100kmh from memory. thats with the 3.45 diff.

maybe you got a nice score.

DentEd XR8 · 07-03-2006, 07:04 PM

Different diff ratios most likely, or the speedo/tacho is out on one of them but that's highly unlikely for that much of a difference tho

Stevo · 07-03-2006, 07:20 PM

Quote:

Originally Posted by svo347

was your power/economy switch on or off , same as the other vehicle

My power/economy switch makes no difference to cruising rpm.

Deano, try testing the diff rations, id say 1 has a 3.45

ilsautomotive · 07-03-2006, 07:21 PM

The diff should have a tag on it. There is a small chance that one vehicle has the wrong speedo sender gear but that's a pretty substantial difference between the 2.

cArSiK · 07-03-2006, 07:25 PM

tyre size most probably.

eb91xr6 · 07-03-2006, 07:31 PM

maby u have more tyre presure in your dads and thiner tyres or it could be the diff

efgiar · 07-03-2006, 08:40 PM

power/econ switch doesnt effect it in 4th gear, has to be diff, stall, or wheels

mr_efxr · 07-03-2006, 08:43 PM

Tyre size, type of tyres/rims and tyre pressure.

niko · 07-03-2006, 08:48 PM

prolly got different diffs.

ie series 1 and series 2

whats take off like?

Deanodriver · 07-03-2006, 09:06 PM

Quote:

Originally Posted by MickyB

Same size wheels? Although that shouldn't make much of a difference.

The wheels are different (he has stock steelies, mine has 15x7 EB XR alloys, but both have 205/65 tyres on them), it should be about the same at that.

I'm keeping up with the flow of traffic when it's on 100, so I don't know if the speedo is out.

I'll have a look at the diff, it could be different. I think the 3.45 is the most likely, to be honest. I just got the auto serviced (while getting the roadworthy), so I don't know if it's that.

Thanks for that

MAD · 07-03-2006, 10:22 PM

If your speedo is accurate, then it is definately your diff. If it was the wheels/tyres/pressure it would affect the accuracy of the speedo at the same time.
Also if the tyres were the difference, the tacho would still match up with the speedo reading, even though the speed reading was wrong.

Jet-Star · 07-03-2006, 10:33 PM

Maybe ones not running right? When my dad got his 95 ghia we noticed that his idled at about 650RPM where as my 95 Futura Idles at about 800RPM....Quick Spray into that little motor/sensor thing ontop of the throttle body and problem solved...Perhaps its a machanical problem your having?

Southy · 07-03-2006, 10:44 PM

different diffs

outback_ute · 07-03-2006, 11:30 PM

I'd go the different diffs theory too, especially since it is the early EF that is revving higher. They started off with 3.23's across the board but later change back to 3.08 in GLi's (can't remember if in Futura as well) for better economy.

BABOSS · 07-03-2006, 11:56 PM

Maybe if we posted our RPM@100km/h EF stock diff ranges you will have something else to compare it to.

Mine is the same 2000rpm@100km/h EF NOV '94 Stock diff

efgiar · 08-03-2006, 02:18 AM

mine 2000@100km/h with a 3.45 96 ef ghia series 2

Racecraft · 08-03-2006, 02:28 AM

My EL 3.08 s/s (without the A/C on) is 1700.. with the A/C on its 1850'ish

EAman · 08-03-2006, 02:59 AM

id say tyre profile or 3.45 diff ratio

cArSiK · 08-03-2006, 08:04 AM

Have you ever had a drag with your dad? If one was faster off the line than the other then they will have the higher revving car at 100.

Mr_4.0 · 08-03-2006, 10:13 AM

mine is november 94 ef and does 1850 at 100km/h. pretty sure mines a 3.23

however, mine is an LSD and i didnt think ford had an LSD in this ratio.

Fairlane · 08-03-2006, 11:07 AM

3.23's came in LSD, on Fairmonts and as an option on GLi's/Futura's. From memory my EL did about 1850/1900 rpm at 100km/h on a 3.23 LSD.

Deanodriver · 08-03-2006, 06:42 PM

Well, I've checked the diff, and it's a 3.08:1, so that idea is out the window. My dad's taken it for a drive, and he doesn't know why either. He does reckon his accelerates quicker (but it's kind of an unfair comparison, since he's comparing a car with one person in it running on premium to a car with two in it running regular).

Mine does have a rear wing on it (small one), but it wouldn't cause that much drag, would it?

I figured maybe everyone else was speeding, but my speedo was saying I wasn't.

Who knows?

LUXO_8 · 08-03-2006, 06:50 PM

just an idea - one may have torque converter issues. (not locking up)

RavenLS1 · 08-03-2006, 06:55 PM

i would say diff.

Racecraft · 08-03-2006, 06:57 PM

are you sure that you are both doing 100? sit side by side with one car @ 100 and see what the other reads.. Just to be sure , a slight difference there, tyre pressures, dragging idler pulleys, A/C compressor bearing etc etc all labour the engine to a certain point

jonbays · 08-03-2006, 07:08 PM

tacho and speedo error is the most likely reason you know. The tacho isn't exactly instrument quality