Flat Changing In A Manual

[God666]

With a synchro box, the gears are helical cut. Now, unless recent gearbox design has changed, a flat change is almost technically impossible unless you whack a piece of pipe on the gear lever to extend it. With the gearbox under heavy load, the end load on the gears due to the helical cut keeps them engaged.

My understaning of the Hollinger gox as used in the V8 Supercars is that they are a straight cut gear therefore, don't have any end load on them under acceleration. This allows a flat change. You will note that even when the drivers are cruising around behind the pacecar, they still do a very rapid gearchange as the gears don't have synchro rings. If they were to try a slow change, they would grind like a bas*ard unless you matched the engine revs to the next gearchange revs as describe by Turbo6man. The idea is to slam them from one gear to the other and avoid the crunch.

Now, do that (if you can in a T) and you will find that 'clean teeth are healthy teeth, unless of course they are lying in the bottom of your gearbox'.

[Wazza2]

Anyone here ever driven a truck before

[ms700]

You will see in the in car shots of V8 Supercars where you are looking at their feet, in the sprint races they will do flat changes wheras at Sandown/Bathurst etc they will generally just dip the clutch a touch to relieve the pressure off the gears, right floot still buried.(which is what youre saying I think)

If you get a chance, watch Greg Murphy, the only time he uses the clutch is starting off the line! He left foot brakes, and blips the throttle (as you have to) when he downchanges and holds it 100% flat on upchanges. Love your work!

[Trumpy]

Anyone here ever driven a truck before

yup.

[WBT56]

With a synchro box, the gears are helical cut. Now, unless recent gearbox design has changed, a flat change is almost technically impossible unless you whack a piece of pipe on the gear lever to extend it. With the gearbox under heavy load, the end load on the gears due to the helical cut keeps them engaged.

My understaning of the Hollinger gox as used in the V8 Supercars is that they are a straight cut gear therefore, don't have any end load on them under acceleration. This allows a flat change.

The helical cut on the gears has got nothing to do with changing. Helical cut promotes quieter, smoother operation and extended gear life.

Synchro boxes have small drive dogs, synchro rings(duh), and very small hub dog to gear dog clearances. This is what gives you minimum power on/ power off backlash. As the dogs and clearances are small, time is taken to line them up during engagement.

A non synchro box has very large drive dogs, and large gaps between them. The upside of this is that you can manourvre the dogs into this large gap very quickly. The downside is that you have a huge amount of relative rotation (20degrees in a Hollinger) across any hub/ gear unit when in that gear. This translates to massive power on/ power off backlash, which is not a problem in a racecar, but clearly no good for the street.

Straight cut gears are used as they are cheap to manufacture, and when designed correctly allow more ratio variants to be used from less gears. (By having more or less teeth in a group of gears that will run on the same drive gear.)

[edo]

edo> a flat change is a gearchange with the throttle flat to the floor. You will be hard-pressed to do it in a street car without using the clutch - the syncros simply won't work and you'll be sitting in the middle of the road with a whole lot of mashed up gears and lots of time to watch the traffic going past. The V8 supercars use a Holinger non-syncro close-ratio gearbox and are designed to withstand the clutchless up-changes that you see the drivers doing.

I wasnt suggesting it was a good idea!

You most certainly can flat change a syncro mesh gearbox though, I have had several race cars where this was a regular practice. Its brutal & harsh but its fast. Its particuarly not a good idea where the gearbox might be considered the cars weakspot...like in the T.

Ive had non syncro dog boxes in race cars too & you absolutely have to be rough & forcefull with them.

[Turbo6man]

Anyone here ever driven a truck before

Before what? breakfast? yeah, I've driven a truck before breakfast, what of it???

I've even drank a beer before lunch - but not while I was driving the truck :lol:

Now does wazza wanna also know what I've done before dinner???

[NT TURBO]

Now does wazza wanna also know what I've done before dinner???

I'm sure we all do. :hiwelcome:

[Turbo6man]

Well I'm not tellin' - a gentleman doesn't tell ... :lol:

[mickq]

Nah, that's just a bad change!

The idea with a flat change is to save time. You usually wouldnt lift off either, just slam that lever through...eeekkk! If you time it correctly you will change just as the ignition cuts with the rev limiter (relieving that pressure)...its still harsh though.

You will see in the in car shots of V8 Supercars where you are looking at their feet, in the sprint races they will do flat changes wheras at Sandown/Bathurst etc they will generally just dip the clutch a touch to relieve the pressure off the gears, right floot still buried.(which is what youre saying I think)

Nope, as others have also said, that's wrong.

A flat change is simply keeping it floored. The concept is related to ensuring the car is still high in the rev range when the new gear is engaged. It can pay dividends with cars that need to have some revs up before producing much power, and also on turbos which will come to full boost faster when exhaust volume is kept high. As soon as the gear is engaged (assuming the car has a vaguely smart ECU) load will increase and this combined with high exhuast output will ensure fast boost response.

It works on most if not all cars, and whilst I havent bothered to try it on my T (too much low down torque to generally bother), Im sure it would work unless you hit redline between gears (silly) or I guess its possible their ECU has smarts built in to detect the car in neutral/between gears and the throttle still beign at 100%. (Quite possible - its not a dumb car by any means).

Flat changes are about fast gear changes (something the T5 isnt well known for!) and maintaining momentum within the engine and with the flywheel (and exhuast output in turbos). You can do them with or without the clutch, and you can do them in cars with helical or straight cut gears or with or without synchro. It all comes down to how hard you want to work your 'box.

(Ive never yet found a car I couldnt force into ANY gear at ANY speed under ANY conditions, and that includes reverse at 100kmh. Dont ever say Volvos arent indestructible!).

They are not necessarily a bad change. Under the right circumstances they can be a damn good change - unbeatable.

Edited 12/02/04 01:19 PM by mickq