Longer 5th gear for 172 box??

[Andrew Cooke]

if 160hp will get you to 140mph you'll need 240hp to go 160mph.

If you want to go that at the same revs in top you'll need a final drive of 3.56 (PH2 is 4.07, PH1 is 3.89, so neither of those will do).

There are other 5th gears, and swapping them is possible in situ, but they aren't much different, 2-3% maybe? I'd need to check my files to be certain.

 

[Munson]

Reminds me of the "A Clio 1.2 will do 150mph with a 182 gearbox" thread.

 

[warwickstingray]

For a 182 to do it's quoted top speed of 138 (in the renualt literature) it needs every bit of the 176.4bhp (131.5kw iso 182HP DIN) it's supposed to have if you work it out using the cars frontal area, rolling resistance and drag etc. Most of them don't seem to have that. Evo only managed to get 133 round a bowl which even if you add on the 1mph allowance for every 10mph above 100 when your testing at a bowl you still only get 136. You only need the 172's quoted power of 166.3bhp (124kw iso 172hp DIN) to do 136.

The clios gearing seems to only give 133-134 at 6500rpm in 5th using the cars quoted gear ratios and standard tyre size. So i don't know how they got to the quoted figure when the cam timing is backed of at 6500rpm and the power starts to drop off. Who knows but then i'm sure the cup's speed was quoted as being higher in the brochure!? Depsite the drag rating being higher and it not having anymore power. That's Car makers for you. Most owners aren't aware of deliberate speedo error and so think their cars will do more anyway.

Civic type-r's have a higher top speed because they have more power and a lower drag. 0.35/36 for the clio 182 (cup spoiler pack adds more drag despite the 3mm lower stance) and 0.32 (have seen 0.31 quoted) for the type R. It wouldn't suprise me if the shape actually has less frontal area as well but i don't know that for sure.

The clio's drag co-efficient isn't great but it isn't terrible. My XR2 was supposedly 0.42!! which is why you need a well tuned RS turbo lump to hit 140mph in one. As air resistance is your biggest issue at high speed the lower the drag the better. The clio would need more power to reach the same speed as the type-r. My old CRX vtec had a drag rating of 0.30 and was also lowered reducing it a tiny bit further which is why it would do just over 135 on GPS with a bit over 150bhp (UK spec with CAT removed)

The clio's engine though grunty for a 2.0 doesn't really have the oomph for tall gearing and good pull above a hundred. It pulls well to the top of 4th but like most N/A cars once you change into 5th and the gearing is reducing the torque before the final drive the acceleration starts to drop off.

I know a few people running phase 1 cars that do the opposite and have dropped 5th gear a little (i don't know how) for track work because they don't tend to get much more than 120 on most of the straights and get there quicker with a lower ratio. You might be able to get a higher top speed down hill but on the flat it will take you longer to get to the cars current top speed.

There's nothing stopping you doing it but other than lowering 5th to increase fuel consuption a little bit there isn't much gain.

I like the clio as it is. The fifth gear is nicely placed for reasonable pull from 70mph and anything over 2 miles a minute is fine for me.

If you go down lots of very steep long hills not hitting the limiter in 5th might be a bonus.

There is a hell of alot to messing around with cars which is why i'm enjoying driving what renault put out and concentrating on my driving at the track instead of constanly fiddling with it. I did have fun over the last decade fiddling but i've had enough now and it made me very poor!

 

[Jay Payne]

Interesting post, is there much that can be done for the Clio's drag? We race against Civics quite a bit and they just too fast at the end of the straights to make a move on them. We have a lower 5th gear but we never use it as we never get there. Vmax is about 125 on circuits we race on

 

[aucky]

Jay, you only have one wing mirror now so that should help..

I've also seen a few track cars cutting holes in the rear bumper to reduce the parachute effect

 

[Goodj]

blank off the top grille? But that may give cooling issues?

 

[Wick]

Interesting post regarding drag coefficients depending upon shape and height and how that relates to power differences. Sounds like you are very clued up on the situation and it made a very interesting read as it was something I touched upon in sports biomechanics at University.

Like you say it was never intended for top end grunt so I see no reason to chase those few mph. Also had no idea on the bowl correction figure of +1mph/10mph over 100, so that's my "learn something new" for today!

 

[shiftspark]

This gear calculator is good

http://www.gearboxman.co.uk/inforatios.html

 

[radu]

on my 2003 clio 172 i have 5.25 mfactory final drive.i need a longer 5th gear.any advices?

 

[bashracing]

This is the 0.738 from the jc5-107 and 072 the longest available for the jc5 box,
bottom picture is what speed your pull in each gear with a 5.25 cwp

 

[radu]

direct fit?125 at 7200 will be perfect

 

[bashracing]

yep direct fit

 

[radu]

many many thanks