What the hell Gearbox issues.

[nova_saloon]

Ive always had an F16 gearbox on the car and as far as i remeber doing motorway journeys in it would be a doddle as the RPM to road speed seemed quite healthy, But i decided to up it for a F20 at the beginning of the summer. Now it seemed to be doing insane revs and having a lower top speed. I cant remeber what its doing mph wise at what rpm. but being impatient with it because i prefer mpg to sheer stupid acceleration i bought another f20 and stuck that one in. Now it appears this one is just as usless. it does 80mph at 4,000rpm is this correct? as it doesnt feel it, really still pulls at that speed more then it should. and i thought my old f16 did 80mph at roughly 3,500rpm. can please someone help me out with this, with what is going on? what rpm i should be experience at what speed, and i do believe the f20 in it now has not been tampered with.

[craig green]

Ratio's & most likely the final drive is different to that of the F16. All the GM boxes (16/20 etc) come in different types depending on the car they came from.


Seeing as a Calibra/cav had much bigger diameter wheel/tyre combos than a Nova does, this whats throwing out your speed/revs. If you had 205/55 tyres on 15"s you'd likely get your cruising revs back down.

[comptoncj]

My xe nova has a f16 box in it and it cruises at 70mph under 3000 rpm 60 is 2500.

[Nova_Tek]

There are literally 4 varying types of F20 mate (final drive/last gear ratio) whereas the F16 is either CR which does about 70mph @ ~3000rpm and a WR which theoretically tops out at 160MPH IIRC

You probably have the very CR version of the F20. I can understand what you are saying as I wanna stick an F20 on the LET and really don't wanna be hitting the limiter at 80mph. Just can't seem to find any number stampings on the casing to see what it is.

[nova_saloon]

see i think thats what was with my f16 is that it was longer, and it was WIN!!! cause petrol consumtion i thought was brilliant, might just rebuild it or something and whack it back in, looks like im may have to f20 for sale now then! but how do you tell if you have the WR apparently says it somewhere. but any ideas where, this helps alot guys thanks a bunch :)

[swedge]

It will be stamped on the end plate of the gearbox, when you look through from the wheel area to the left of the shaft as your looking at it

It's only very lightly stamped as when I was checking my f16 I had to wire brush it a fair bit

I'm sure it has 3 sets of numbers

The lower set on mine says c355 which means mines is a close ratio

Give it a good wire brush and look for a w or c followed by 3 numbers

Ill take a pic of mine today to show you

[Will F]

All F20s are 'CR' but as said there are slightly different FDs etc.
If you want 'economy' - go with a later cav Sri c20xe. You will also see a date stamped on teh end plate - the later ones (1993)were obvioulsy in Cavs and Calibras and are more likely to be the ratio you want.

[mowgli]

is there any gain from fitting an f18 box?

[Paul]

As said nothing to do with f16/f18/
f20 all to do with fd ratio etc.

[Mazz]

F18W is what you want, just swop out the 5th gear set from that to the F20

[nova_saloon]

Just getting hold of the right gearbox, I take it the f18 has the longest 5th? Might just rebuild the f16 n swap it

[Paul]

Nope, totally irrelevant. 5th on a 18WR and 20CR are the same iirc. 0.79 both underdriven, its the FD the important bit.

[Stuart]

http://slindborg.hostei.com/gears/n15wef.jpg

F18CR and F20 are nearly the same

I'd be taking the F16WR 5th gear pair for uber cruise lol