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VH rpm at 100kmh

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I have a GU6 diff in my VH wagon which is a 3.36 Small Salisbury
at 100kmh i'm at 3150rpm and at 110kmh im at 3500rpm
M21 4 speed, 253 V8
from a diff calc looks as though its 3.9 ratio, I though small salisbury diff went 3.36, 3.55, 4.44
must be a faulty tacho i think
 

SL/ENUT

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Going though my commodore records stuff, GU6 was never fitted to a Commodore, never a Holden option.
My understanding is the following
GU4 3.08:1 on both ten bolt and 8 bolt Sals diffs
GV4 3.36:1 on both same diffs
GU7 2.78:1 on 8 bolt diffs
GU8 3.90:1 on 8 bolt diffs(common on the Starfire 4 powered ones)
GV7 3.55:1 only ten bolt diff
G70 2.60:1 only a ten bolt diff

4.44:1 is a ten bolt only diff, used only in the one tonner cab chassis-HQ-WB
 
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i meant GU4, maybe its got a starfire diff, i'll have to jack it up and check the rotation
 
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sorry GV4 i just looked at the vin plate
 

Guzzoline addict

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The speedo or tacho might be out,have you got a Automotive Multimeter and some sort of gps to check?. Also what code for the engine is on the vin?, if it was a 6 check if the tacho has been switched.
 
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the car was a 2.85l 6 with a vacuum gauge, the dash was out of a VH V8 but that was already fitted when i bought it. I do have a multi meter with tach and gps on my phone so i can double check next time.
 
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i don't have access to the car yet pick it up friday however i did some googling and the speedo drive gear is a light blue 24 or 25 tooth which is meant for a 3.9 ratio, the speedo reads true so i'm thinking it has a 3.9 ratio fitted, i will double check though. i will end up with a VL 3.45 BW later after i can find one local, already found a VS diff with disks but will fit these to the VL diff once i find one.
 

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Those revs sound right for a 3.36 diff and 14 inch wheels. My old HT Kingswood used to sit on 3500RPM at 70MPH with a 3.36 diff.
 
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picked the car up today, got it to 110km on the gps (dash is spot on) and its was revving at 4100rpm and at 100kmh it was about 3700rpm... i can drive everywhere in 4th gear its almost as bad as the old 2.6 diffs that could do 120kmh in 1st gear.
i'm pretty sure its a 3.9 ratio but i will remove the cap and change the oil and check soon
 
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