G Series Diff's

[1JZ.747]

Hi there Boys and Girls

just after information about what ratio's are available for the g series diff.

i currently have a standard 3.9 diff in the cressida but will need to change it in search for higher trap speeds.

so whats ratios are available?

thanks

shane

[Norbie]

Factory ratios go from 3.7:1 down to 5.3:1 from what I've seen. There's lots of aftermarket stuff but that tends to be for lower ratios only; if you want taller than 3.7:1, good luck.

[1JZ.747]

so for the uneducated on diffs, how could i calculate whether the 3.7 will be ood enough for the application.

is there a calculation of some sort

ie tyre size x final drive in box x diff ratio / number of spanners in a chinamans toll box?

and what would i pull a 3.7 out of norbie? or is it a order through toyota type job?

thanks

[Joshstix]

Here's a speed calculator for you to take a look at:

http://www.jekylhyderacing.com/spg.htm

I think you'll only pick up about 5% of speed going from 3.9 to 3.7.

[1JZ.747]

any one know the ratio on third gear in an a340

[Norbie]

Try playing around with this:
http://akb.norbie.net/Public/Gearing.aspx

3.7:1 ratios are found in Aus-spec MA70 Supras with turbo and auto.

[1JZ.747]

wicked

thanks norbie and joshtix.

thats spot on

the 3.7 will be fine eventhe 3.9 should be fine

with a 26 inch tall tire, a340 gb, 3.9 diff ratio and 8000 rpm rev limit i can run 159 mph

with a 26 inch tall tire, a340 gb, 3.7 diff ratio and 8000 rpm rev limit i can run 167 mph

the goal is to run 145 ish mph to get me to a 9.6 ish et, which is all i need.

so if i can get this big bitch on a diet, and if it makes power to a higher rev range which i think it will we may get to 150 mph.

im getting a chub now.

thanks again lads

Shane

[chris davey]

I have been using those speed calculators for a while now and I have found that they are close but not 100%. They don't factor in wind resistance. They were always a little down for me. ie. when I had my 4.87:1 diff it said I would hit 7000rpm at 109mph whereas I actually hit it at 105mph.

Just thought I would let you know.

[1JZ.747]

as long as i can run 145 mph im gong to be happy

[Joshstix]

I have been using those speed calculators for a while now and I have found that they are close but not 100%. They don't factor in wind resistance. They were always a little down for me. ie. when I had my 4.87:1 diff it said I would hit 7000rpm at 109mph whereas I actually hit it at 105mph.

Just thought I would let you know.

Yeah the calculators assume no slip in the driveline. They're accurate for manual transmissions but may be a bit optimistic for an auto unless it has a lockup clutch.

[1JZ.747]

yea i will still be retaining the lock up clutch so all she be good.

[1JZ.747]

well heres an interesting fact for the kiddies

at 8550rpm we crossed the line at 149.9 mph

so im down on MPH even with the lock up activated.

so 3.7 here we come, hopefully we can just break into the 160mph region with a 3.7

[Mr DOHC]

that'd be scary, is there any MORE safety mods u have to do for 160mph

[TA22 1MZ]

Hey Shane
If you need some options on ratio's check this place out;

http://cgi.ebay.com.au/ws/eBayISAPI....6773&rd=1&rd=1

They offfer 3.54, 3.25, 3.35, 3.8, 4.56 & 4.88 crown whhel and pinion sets

Catch ya

Jack

[mrshin]

I've got a set of aftermarket 3.5's, I can't see why you'd have any trouble buying a similiar set.