The gear set defines the rpm delta between changes and the FD the overall axle torque factor that controls and defines the speed in gears for a given tyre size. The gear calculators allow a quick glance of this infomation.
The 16v set is the closest regarding 1st through to 5th. (Some mk1 stuff is also the same/similar) Using the 8v long 2nd (which means using 8v input shaft as 1st & 2nd are part of the shaft) effectively makes 3rd shorter as you will change into it at a higher speed from 2nd thus higher 3rd rpm. This would only be good for mid/high speed circuits. When using the 4.25 FD (8v) you must use an 8v diff as the diameter is different to 16v. Also, you must use a 4th gear from an 8v too again because of fitment to the output shaft. I know a few of the other local guys are interested in having a go at boxes too so I was thinking of doing a gearbox day one weekend just to show the breakdown process and things to lookout for. Sound interesting/useful for you? Gurds
It does sound interesting, I hold your thoughts on this in high regard as you live with and drive yours all the time; you should have an excellent subject knowledge of the 4.25 2Y Would you change any of the ratios? I think for me fifth would need to be a bit longer so that im not revving so hard on the motorway. I have an 8v diff and a spare 8v box to plunder for 4th gear and others if needed
If I had to change any it would actually be 1st & 2nd. I would want them to be longer ideally. I tried to get close to VWMS 8v spec but it wasn't possible with standard stuff. Really could do with a 6th gear too for which I would use a longer 5th from another box. As it is now, you get used to buzzing along the motorway at high RPM and it hasn't really been too much of an issue. Always on cam for instant overtakes . Gurds
It's all a compromise if you're not building a box just for track use. My current plan is AUG ratios with a 3.9 diff. It gets you more or less the same effect as the 4.2 in the CHE ratios, without the effect of rendering 1st gear completely redundant except for hill starts. I don't know if Gurds still uses 1st, but with his torque curve, there's probably no need (subject to mapping out any pinking).
If the car starts detonating 1st, it will have a very big problem in 2nd let alone the rest of gears!!
Having done a quick test, to try and figure out the functionality, here's a quick comparison, presented in the easily read, if slightly anally retentive table format. Code || Diff || 1st || = || 2nd || = || 3rd || = || 4th || = || 5th || = | AUG || 3.67 || 3.45 || 12.66 || 1.94 || 7.12 || 1.44 || 5.28 || 1.13 || 4.15 || .89 || 3.27| AUG w. 3.9 || 3.89 || 3.45 || 13.42 || 1.94 || 7.55 || 1.44 || 5.60 || 1.13 || 4.40 || .89 || 3.46| CHE w. 4.25 || 4.25 || 3.45 || 14.66 || 1.94 || 8.24 || 1.29 || 5.48 || .97 || 4.12 || .80 || 3.40| the "=" numbers are the gearing multiplied by the final drive - the number of revolutions of the engine for 1 revolution of the wheels. It's impossible to make pronouncements about what's the best compromise here - it depends on what you want, what car it's going in, the engine, where you're going to drive it, etc.... For me, the CHE on the 4.25 is no better than the AUG on 3.9 FD. I'm definitely a fan of the taller 2nd gear, specifically for the back section at Curby, to avoid changing up to 3rd and back to 2nd (twice) in there, but also in general, as I feel like I've got more than enough poke in 2nd. It's the 8v 'talks' y'know For me, the CHE setup is a bit tall in 4th and 5th... On faster tracks, this will be more relevant to real performance than the 2nd to 3rd change. For example, on my car (currently on an ACD with a 3.67 FD) I want lower 4th and 5th to help going up the big hill on the Nurburgring, where the car runs out of puff a bit in 4th and 5th, but it would also help on other fast circuits, and should still leave me with about 135 top speed, at 7k RPM in 5th - it won't quite pull to the red line in top with the 3.67 FD, but I think it might with the 3.89... and I could always raise the rev limit a bit
@smudge, I need to know the flywheel weight ( for inertia calculation) before and after and the engine speed you generally clutch in before setting off. Cheers.
I never weighed it but say 3kg - 3.2kg after it was lightend. I useally pull away at around 1500-1800rpm. Sounds like you are busy working through some serious math with this one I await the results with baited breath.
With regard to the revs at motorway speed mine is louder at 38--rpm than it is at anything in the 4000rpm... but im just thinking that holding high revs for long periods (hours) will not be great for the engine? Also at Curby i was changing up on the back straight at 7000/7200rpm into third (well before the timming line - with standard ratios) and hitting indicated 80mph before braking - that would definatly mean 3rd gear (do not remember any revs) would need to be used even with the ratio's and FD your thinking of Mike. Or did I read your post incorrectly?
I think you're talking about the long straight - I'm pulling hard in 3rd on the main straight, indicating about 80mph too - up to 85 on the lap where I don't have to brake for the hairpin (just in case Alonzo is reading in ) The point I'm making about gear changes is around the back of the circuit, where I'm hitting the rev limiter in 2nd, but it's not worth changing up into 3rd. If I was running a 3.9 diff with the 2.12 2nd, I'd definitely need to change up to 3rd, back down to 2nd for the chicane, up to 3rd again, and back down to 2nd for the long 180 at the top of the circuit - so having a taller 2nd saves 4 gearchanges in a lap, in that specific case. I think with a 1.94 2nd and a 4.25 diff you'll be either in 3rd round the back of the circuit, or pulling about 8k rpm in 2nd.
Second that ... (~ 19mph / 1,000rpm in 5th) smudge ... To experience it maybe blag a ride with ianb at Combe ... that is if you don`t mind the kjet
See I was reading it wrong Yep im hitting 7000+rpm coming into the mole hill so can hang onto second ATM but a different FD and that will mean changing gears. It was 2nd all the way around the back of the curcuit and then up to 3rd for the start/finsih straight. The hairpin i was having to short shift as when accelerating out on lock I would end up spinning wheels hehehe. Nice little curcuit Curby - if a little to small. As for Combe, I may be there and if I am ill try and blag that lift with CFJ - Ill repay the favour if im out of track
I'm into 4th and accellerating down the main straight at curby and 1st is pretty hard to use but I do use it when doing a standing start. Much throttle control required! Mike, I have another table at home which shows how much speed is genrated in each gear & at what rpm and what the speed & rpm are when shifting into the next gear. This can then be cross referenced with the dyno plot to see what is going on with the torque for all these values. Gurds
No worries. Nope. Any issues with audible det would at high rpm where in that tin can buzz box any thing sounds like det. Det cans and dyno time helped to validate that issue.
