Gearing a bit long will changing the final drive mean better acceleration?

Hi

I was going to post this in the transmission section but its track day recommendations I need and then I can ask in that forum.

I have searched and am a little confused. My son and I have a Golf Mk1 with an ABF lump and DFQ 020 box on 15" wheels we use primarily for track days and it is road legal.

It will do a nominal 110mph in 4th and a theoretical 130mph plus in 5th.

EG: 4th at max revs is the end of the long straight on the Bedford Autodrome GT circuit so we don't need 5th even though its a long fast circuit and do most of it in 3rd gear.

2nd gear is perfect and the car absolutely flies, third is good too as is 4th but we find that on track we haven't the grunt to max out on straights using 5th so thought if we geared it differently it would use the gears in a better way.

We cant get the power down out of small sharp bends in 2nd and some bigger ones in 3rd so are looking at fitting an LSD of some sort (Quaife currently comes to mind)

If we commit a not unreasonable amount of money in an LSD would we be better off with a different final drive ratio ie: lower top speed but faster through the gears or does it not work like that.

If we had lower speeds through the gears does this add slightly to acceleration (appreciating you are changing gear more) or are physics not like that?

Are 4th 5th gears interchangeable with different boxes? Is that the way to go?

As a footnote - I have an 02a Formel E type box in good nick with 4 shorts and a very long 5th - would we be better having that rebuilt/strengthened?

Any general pointers as to the recommended route would be appreciated - once understood we'll research in depth which of those routes we'll go down but any info would be appreciated to set us on the right road.

Thanks in advance.

 

Plenty of gearbox ratio guides out there. My preference is a 0.91 fifth and a 4.2 FD. Cheapish and low enough geared. The only gear you can't change (cheaply) in an 020 is the 3.45 first. The gears come in pairs though.
Jon

 

DFQ ratios are:
1st 3.45
2nd 1.94
3rd 1.29
4th 0.97
5th 0.80
Final drive 3.67
go for something as 3,45 / 1,94 / 1,44 / 1,13 / 0,91 with a 4,2 FD
Ideally with a 5 th as short as 1,04 ... you want only a 700 - 1000 rpm ( Max) range to reach topspeed in highest gear
( as close to the rpm were the engine makes max power )
( do the calculations for each gear > Speed @ shift revs and check at what revs it drops in the next gear)

http://www.scirocco.org/gears/
With the smaller steps between ratios and a shorter FD you will pick up speed faster

Tbh i would look first for suspension upgrades before going LSD , after all your tyres need to stay in contact with the tarmac to put power down.

 

Thanks for the responses

Both seem to recommend both gears and FD so I`ll look into those.

Re the suspension upgrades - its difficult to know where to start or what works - we're looking at spring rates and ARB`s also but finances are limited so we need to think about the best compromise.

Its only on very tight bends we have an issue with the inside wheel spinning up and primarily if you nail it with lock on and thought an LSD might help turn in and help reduce under steer a little. If it won't then that's money for other things.

 

Wheelspin in tight corners will not get solved by fitting a Quaiffe diff, even a plated diff has often some wheelspin
Its often faster to turn in and let it roll until somewere halfway the corner, then apply trottle in a progressive way....

IMO its better to sort suspension first....it will bring more in laptime than a LSD,

 

If you thicken the sways with soft springs no matter what you do, you'll lift the inside wheels as the outer spring compresses, the thick sway doesnt flex as much and compresses the inside strut and wheel lifts. See one of my other posts for droop management of arms.

Consider HPR's advice as it's going to take a considerable investment to have all the necessary suspension configurations to suit every corner at every track and there's merit to making compromises to setup to suit the majority of the track and drive accordingly for those corners you can't tune to.

As for getting the car off the bottom, if you have a lightened flywheel, you'll need a lower gear ratio to take advantage of better engine acceleration. If you gear up too much, engine will bog down, hurt your clutch and transmission etc etc. Heavier flywheel makes for more torque and the existing gear might come good and if the car is overweight to spec, reducing weight can help a lot.

 

If you have an 02a casing. I have my entire 4.2 Gearset with lower 5th gear that I will be selling. I took them out of my 02a and fitted the entire innards from a 3.9. You`d need to fit the 4.2 ring gear to either a standard diff (will be supplied) or LSD.

Sorry to thread hijack


I used to run an 020 with fairly tall gears, switching to a lower ratio did help, it`s certainly noticeable on acceleration. However, as alreadysaid, suspension would help.

 

Its stripped out - half caged - say 930 ish kg with a driver

Sorry to persist - I have searched

It doesn't appear straightforward to swap out a diff if you look at Broke VW`s site - it needs special tools etc so is it straightforward with basic tools to strip down and swap/refurb an 020? I`ve done loads of cars and engines in the past but never a gearbox and if I have to spend 300 on tools I might as well get it rebuilt by a specialist.

Will a diff be straight swap from other 020 boxes as I see lists of boxes with varying diffs close to 4.2 - which boxes are a straight diff swap?

I also have a Hotgolf lightened flywheel I want to fit. Can I assume the lower 4.2 ratio on its own will help even if the gears remain the same?

Nige's offer is a good one but I don't have the ring gear so I`d need to get another box anyway. Also - I always thought the 02a boxes were weaker - which is why I fitted an 020 ??

 

My gearset includes the ring gear.

 

The 020 is the weaker of the 2, but 02a internals don't fit in an 020.
I woldn't worry about loss of torque, it's proven you don't lose that much if any

 

020 has a nicer gearchange though IMHO
Jon

 

Agreed.

 

Why not go for an 02j with a 4.2 FD as standard? Ratios work well at Bedford. Then you can add the better shift system too. Add LSD to that. Would add more cost but a worthwhile mod.

 

020 is the most direct gear change you can get.
Add some of Hotgolf linkages and nothing comes close for shift quality.
Also a tad bit shorter with the 4.25 FDR vs a 02A/J with a 4.23FDR. So a bit more snappy.
This is what I run in JENVEE the track car with a Quaife diff and 16v ratios for 1-4th and an 8v 5th.
With over 160lbft available from the engine, in that application, it feels like "every gear is a 3rd gear" lol

 

Great information all - many thanks - keep it coming :-)

 

02A /02J boxes dont like fast shifting above 6000 rpm, the synchro`s need a tad longer... must have to do with inertia

 

I see the 02J box is hydraulic and cable but my Mk1 has the rod shift and I fabricated a shortshift bracket and its absolutely fine so dont really want to (need to) go down the route of changing to a cable shift and hydraulic clutch.

Good advice - I think I`ll probably go for a 16v 020 and see how it goes from there and I can swap the 5th gear from my current box. Economics play a part too lol

I assume I`ll need to swap the flanges for 90mm?

 

To be honest I wouldn't go for the 16v box, its no better or stronger than the 8v, despite what you may think or people assume, and there is far more availability for the 8v box and better ratios. 020 boxes are light and stronger than people would have you believe, make sure they are built properly and have the correct amount of oil. Early 1600 gti FM/FD boxes have the best ratios. Personally I'd use the later MK2 020 cases as it allows a wider range of fitments and you can add 100mm flanges at a later date if you want - 90mm CV's are strong enough for most uses, again use decent quality components GKN etc. the Early MK1 cases have a bolt missing on the back that makes it trickier to fit to a MK2 and won't take 100mm flanges. Use decent gear oil and make sure you understand the oil levels required and how to check - this is important, there are differences between the cases etc. Even some manuals get it wrong!

 

Having done a bit of research I understand that the mk2 16V box has the 24mm shaft same as the 8v Mk 3 but has closer ratios? Its the ratios I'm interested in and would then need a lower FD but I`ll have to find out if it has bolt in or circlip flanges as my MK 1 has 90mm flanges that used to connect to an 02a.

Nige`s offer is an interesting one but I`m not sure I have the skills or tools to rebuild the 02a.

 

The Mk3 2.0 8v gearbox has larger gear spacing to suit the low down engine torque of the 8v motor.