bmwe21.net forums

Jeroen wrote: Thu Feb 13, 2020 9:55 pm If it ain't broken, don't fix it!

Indeed, I admit having a tendency to scratch where there is no itching...

uwbuurman wrote: Thu Feb 13, 2020 11:18 am Well, I have mine rebuild. It gives 13.2volts, but when the engine is warm, it drops to 11.2volts. Don't know why...

Asked my electrician: He said that your problem might be due to one of the following

1) a "cold soldering of the coils" (meaning if I understood correctly that the soldering material was not warmed properly)
2) bad earth

Oké, thanks, will check. Thank you for asking!!

I would really like to have your opinions here, although I know this is rather a matter of personal taste:
It seems that decision between 3.45 and 3.64 is more difficult than I thought.
If we suppose that the engine power is between 155 and 165 hp at about 6500 rpm (well I haven't dyno'd but I assume it is somewhere in between, no less no more) which ratio would you go for? Gearbox is the dog leg C/R Getrag with the direct 1:1 5th gear, so this is why I am a bit reluctant to take the final decision towards the 3.64, even though the current 3.45 seems to be a bit longer than desired. Tyres dimensions are 205/50-15 on 7"x15" wheels rear and 195/50-15 on 6"x15" wheels front. Road use, no track days, but I like to be ready for some spirited driving (combining motorway and mountain roads)

Your opinions will be really appreciated ladies and gentlemen, yes I am seriously asking!

And please do not bother directing me to all the gear ratio calculators existing in the web, as I have gone through all those a thousand times, I know the results by heart.

Many thanks in advance!

With a regular 'eco' 5-speed I feel that the gears are too far apart if combined with a 3.45 diff, and a 3.64 made a subtle change but it made things match. With a close ratio gearbox that is a different situation (it's in the name already) and I probably would choose the 3.45.

3.64 with CR box is to short. I would also keep the 3.45

Thank you guys. This is why I am asking for opinions.
You see, what happens is that, I also passed from the 3.64 myself with the first custom built engine.
(And current engine is of course better than the other) :

For the 1st 3.5-4k km with the other engine (when let's say it was still working ok) and the 3.64 ratio, I felt the car was rather short as well, but also: Engine was producing way more db than the current one. Also, that diff was whining a lot. So I guess the above facts influenced my judgement as well. I changed the ratio to 3.45 which is my current ratio.
Some km later, I was unfortunately obliged to build a new engine as well due to already known problems.
The new engine is more powerful and torquey than the other one.
However, now this diff sometimes feels a bit longer than I expected. A little.
And at high speeds, especially near the top, I have a feeling that the car would be a bit faster with the higher ratio (although the lower ratio is the one that gives higher theoretical speed). This happens because I feel that when around 175-180 km, the (worst ever maybe?) aerodynamics, make things very difficult with the current torque/power. And I believe that with the higher ratio (3.64) finally car would more easily increase rpm at already high motorway speeds.

Concerning in between gears changes, yes it is the gearbox and not the diff at all there: fall of RPM between changes has only to do with gearbox and not with diff ratio (of course diff ratio has to do with torque at rear wheels, and this is also a big difference - 5.3 % I think between 3.45 and 3.64)

Also, in mountain roads (and when spirited driving is the point), some extra torque can always be used.

Finally these 45mm webers do give some extra torque, but maybe not enough to combine the lower ratio to 2.0? I am wondering

I am pretty sure that my last post, with all these thoughts of mine, was confusing for most people, most I guess did not even bother or make it reading it all.
However, I found this

https://www.badasscars.com/index.cfm/pa ... prd446.htm

I did the maths and it seems to me that an "ideal" final ratio for my case is a 3.59ish, thus closer to 3.64 than 3.45
Difference between the two ratios (3.64 and 3.45) in cruising speeds is 172 rpm at 100 kph and 206 rpm at 120 kph
And difference at 6500 rpm (where, if I guess right highest hp is produced, thus the peak of the hp curve should normally be) is 3.9 mph (6.3 kph) so both around +/-200 kph which means, I guess that I could easily switch to the "shorter" one (higher ratio-3.64) as the car could gain from this extra 5% torque

Oh, also, as I see that the "cargister" gear ratio calculator doesn't open anymore, I found another, a bit simpler, but still interesting:

https://www.tremec.com/calculadora.php

Have a question:
What does a steering damper do?
Do E21 racks have steering dampers? I think they at least have a place to fit one, is it a useful add on (if it may be found and fitted) ?

It does exactly what it says. However it is not an option, it is a part of the design of certain manual racks.

Which means that our factory racks do have a damper already fitted from factory?

certain manual racks do indeed but not all

And to the ones that did not have it, could it be retro fitted?

And how about our sport (quick) racks from Kiley-Clinton?

let's start with me completely not understanding you. What is the problem you want to fix? Why do you want to change the design of an absolute steering specialist like ZF?