Hey guys a few questions...

Atm Ive got a 351 with a C4 and a Diff with around 3.8 diff gears, 225/50/16 wheels and it cruises at 100kph on 3500rpm

ok first question... Can anyone tell me the ratios of the C4? (is there only 1 type)

2nd question
What would I have to change my diff gears to get it down to around 2500rpm at 100kph or at least 3000rpm... or maybe with a combination of larger wheels as well? And it would have a very noticable difference in accelerations wouldnt it?

3rd Q
This is all just curiosity cos i like how it pulls up to 100kph but would like a accurate speedo (100kph is 130kph on the speedo) is there a speedo gear drive that will suit my combination?

4th
Whats the 4th gear ratio of the 4-speed auto? and what rpm would it be at 100kph with 3.8 diff gears

Umm thats enough questions for now i think hehe

You can get different speedo drive gears that go into the gearbox.This is rated according to your diff ratio.You would probly get the 3.7 cog as I don't think they make a 3.8 one.Superoo Falcon spares is where I got mine.The speedo is still affected by the size of your tyres.Mine still varies depending which rims and tyres I have on but it is a lot closer than it used to be.

c4 is 3 speed auto should be 1/1 in D

2/profile tyre change may change 100-200rpm but woulnt be noticable

3/ like foz stated change speedo gears looks like this



superoo has years of experance should set you straight with correct gear. then can up tire ratio or lower to get exact if your picky.

the c4 c10 fmx possably bw have same gear toploader and single rail are different.

4/ could find youself a usa AOD auto if yor c4 ever blows up to get a overdrive gear then keep rpm down.

your still going to have shocking fuel acconomy though with a ford v8

if its acconomy factor keeping revs down could look at carby vacume secondary better acconomy than double pumpers holleys or get it jetted.

Mmm partly ecconomy and partly I jus dont like sittin on 3500-4000rpm, and cos it tops out at 150kph. anything over 100k's jus feels like its kaneing the motor

But yea I dont think the 850 double pumper with 1/2" lines is helping with economy either lol...

should check with a gps found mine to be at least 4 km out on the au ute.
but good having a police speedo cluster can give of take -10 OR +10 without getting my hands dirty or leaving drivers seat.

Yea that is how I found the speeds I was goin, as well as cruising next to a friend whol was sittin on 100kph in a new car