F13CR final drive/5th gear question

[paul080803]

I am currently building a 1600 8v engine for the nova and planning on changing out the current F10 4spd to a F13CR 5 speed.

I believe 5 gear on the F13CR will be the same as 4th on the F10?
What is the best way to retain a close ratio 1st to 4th with a long 5th gear for motorway cruising?

Hope that makes sense.

[Novasport]

The CR 5th and WR 4th gear ratio is the same but it is altered by the final drive. The WR will usually have a 3.94 or 4.18:1 final drive and the CR 3.74. The best all round is the Nova SRi box which is a CR cluster with 3.94:1 final drive but they are getting rare.

[Novasport]

I am running a SCCR cluster with a CR 5th gear and a 4.18:1 final drive. 80mph is about 4k rpm

[jimbob-mcgrew]

ive seen some people put the 5th gear in from a wide ratio box, to give them 4 acceleration gears, and a motorway gear.

looking at the ratio of a cr box, its kind of like going from 3 and a half to 5th.

[Stuart]

When Dan had his 1600 it was simply on an f13 cr box with a 3.94 or 4.18 fd and it cruised like a charm at 70-80 with no major hassles.

Imho, having a close 4 then wide 5th is a mega mega pain in the arse for the real world.

[jimbob-mcgrew]

ive done some tests with my previous 2 cars, banning myself from using 5th for several weeks at a time, to compare the difference between regular town driving and motorway runs, between a CR and WR box.

i found it made quite alot of difference. the 500 to 1000 rise in rpm at 70 mph (engine, box, and final drive depending) .. makes the nova's loud tin-can drone that much harsher, and can leave your ears ringing for hours after a 200-300 mile run like that.

the difference in mpg was quite clear too, i was using alot more fuel at the higher rpm, and a 300 mile journey cost me atleast an extra £10.
smaller difference in mpg for town driving, where your top speed is restricted. only slight loss of mpg.

i also tried shifting differently, to see what it might be like, and going from 3rd to 5th on the motorway wasnt much a problem. the revs drop a fair bit obviously, but when you just wanna cruise, thats what you want.
crap for country lanes, but 3 and half-th gear is fine for a spirited 60mph through tight corners.

i guess its different for everyone tho, as we all have different wants, needs, and compramises, so one persons ideal might be another persons nightmare.

i think a daily driver needs to be compramised on myself, as you have to live with it day in, day out, listen to the drone, and pay for the fuel too, where as a track car, or something that rarely gets used, you might aswell go extreme on that, as it doesnt need to be adaptable like a daily.

all i can say is have a play with wide boxes, close boxes, different ratios, and final drives, and set things up to how you want them.

[Novasport]

I had a WR 5th in my CR gearset and it was a pain in the arse to change up. If you did not let the revs drop before selecting or double declutch it would crunch into fifth.

[Iain]

(Mansize engine comment) I had a long fifth in my F20 with 4.2 FD, and it also drove like crap, completely out of the power band in 5th and sounded flat as a pancake.

[mowgli]

My 1600 has a f13wr with a 3.74 diff. acceleration is pretty good, and i've seen 135mph on the clock on 185/55r15 tyres. It used to show 118 on the original f13cr with 3.74 diff.. but I used to drive wagons and got bored of changing gears.

Ps. I checked the gearing to revs and they were pretty close tov the speedo readings..

[paul080803]

So the box I have is a F13CR with 3.74 diff.

From some searching it seems the recommended change is to put a 4.18 diff in to improve acceleration?

And mixed opinion on putting a WR 5th gear in. I don't really mind with having a big rev difference between 4th and 5th if I get a decent motorway cruising gear, however I don't like the sound of crunching between gears.

[jimbob-mcgrew]

personally id keep what you have if i were you.
i would say the 374-cr box, that you have already is the best blend of all 3 worlds :

- it uses the close gearset for generally better acceleration.
- with the longest diff 374 (for best top speed with a cr box)
- and all 5 gears are evenly spaced together

sure you could fit a 418, and a wide ratio 5th, for more acceleration, and better motorway mpg, but itll make the cars abilities very specific to those 2 things, turning it into an acceleration rebel upto 70mph-ish @ 6000rpm, or either that long motorway rato, for the mpg gear.

its what your looking for i think, but it will knock out a chunk of its mid range performance, limiting its overall driving spectrum.

you could even take it the other way, and fit a wide ratio box with an even shorter diff, like a 429, which would probably make the car drive smoother, from top to bottom, but 4th gear is a problem in the wr boxes, and doing it this way, kills your efforts on the acceleration side.

it totally depends how you drive i guess, and what your comfortable with, but like i said before, what you currently already have is a nice medium, that ticks most boxes from low to high.