Peugeot 205 Si

PeterT

1000+ Posts
They are usually custom. I take the sample to B&R Brakes and hand over about $160 for the pair. Make sure they add the rubber bush for the strut mount. They need to be road legal.
 

natumbri

New member
@PeterT I've be been thinking about what you said about gear and FD ratios, and (apart from the ridiculously short 1st, which probably doesn't really matter too much), your suggestion of a 4.43 cwp plus 3-4 and 5 out of a GTi/late XSi/GTi6 looks just about perfect for getting the most out of an Si!

Obviously, you knew that already, but the difference really becomes pretty stark when you put it in a picture: https//205.si/gearbox

I assume that, when building a gearbox for a racing car:
  • first, work out the implied top speed is, based on the power of the engine and the shape of the car (no point having ratios that suggest 250km/h top speed if physics says "No")
  • next, pick a top gear and final drive combination that implies top speed at redline (don't need to be sitting at 1500 rpm on the freeway)
  • next, find a longish first gear, to get from 0 to some kind of speed (and reducing the range to be covered by 2-4)
  • next, find an evenly spaced combination of 2-3-4 to fill out the gap between 1 and 5
And I assume it is similar for a rally car, but maybe with a bit less emphasis on top speed (so everything a bit shorter)?
 

PeterT

1000+ Posts
  • first, work out the implied top speed is, based on the power of the engine and the shape of the car (no point having ratios that suggest 250km/h top speed if physics says "No")
  • next, pick a top gear and final drive combination that implies top speed at redline (don't need to be sitting at 1500 rpm on the freeway)
  • next, find a longish first gear, to get from 0 to some kind of speed (and reducing the range to be covered by 2-4)
  • next, find an evenly spaced combination of 2-3-4 to fill out the gap between 1 and 5
Basically, that's it! Thus for circuit racing, you need to just hit the rev limiter in 5th at the end of the main straight. The problem with BE1/BE3, is that all 2nd gears are the same. The next problem is that 3-4 are joined as a pair. So there's really only a few combinations of 3-4 that you can use and the GTi6 combo is excellent, as it's nice and close. There are only three common 1st gears - 3.45, 3.25 and 2.92. The later is obviously what you want and they come from Mi16's or 1.9L GTi. The most common is 3.25 and it's not the end of the world as you're rarely in 1st anyway. The 3.45 is just a pita.
 

natumbri

New member
Hi everyone (@PeterT), given there are a few things that I'm doing to the front end, is there any reason not to
  • build up a new front subframe with everything I want on it, cleaned and/or refreshed (including, eg, brakes and struts)
  • drop the existing subframe out
  • put the refreshed one it
It seems better to try to not do this stuff under the car, given I have a subframe and am replacing/refreshing lots of the bits...?

If I disconnect the brake and pas hoses, unclip the clutch cable, disconnect gear linkages, disconnect the steering column, unbolt the struts, unbolt the subframe, unbolt the bottom engine mount, can I then pull the whole lot out?
 

schlitzaugen

1000+ Posts
Yes, you can do it, but you also need to either disconnect the suspension arm and control arm at the subframe or the suspension arm at the wheel hub carrier. I would suggest you disconnect the suspension arm at the hub carrier, it's just a ball joint and you might want to replace that with everything else.

Just before you start the whole thing I would also suggest you check the spare subframe is in good nick otherwise you might find it's not by having weird issues with the steering geometry. Get the tape out and measure some stuff and compare with the one on the car.

After the swap you might need a steering alignment anyway because of the tolerances of all the bushes you will replace but if the spare subframe is not in good nick (distorted, bent, etc) this alignment may not be enough to bring the car back to proper working order and it will be difficult to chase what's wrong. Cheap insurance to check now rather than later.

Also, be careful how you press the suspension bushings out. The arms are pressed steel and easy to distort and the bushings are a very tight fit and give you bugger all to push against.
 

PeterT

1000+ Posts
Hi everyone (@PeterT), given there are a few things that I'm doing to the front end, is there any reason not to
  • build up a new front subframe with everything I want on it, cleaned and/or refreshed (including, eg, brakes and struts)
  • drop the existing subframe out
  • put the refreshed one it
It seems better to try to not do this stuff under the car, given I have a subframe and am replacing/refreshing lots of the bits...?

If I disconnect the brake and pas hoses, unclip the clutch cable, disconnect gear linkages, disconnect the steering column, unbolt the struts, unbolt the subframe, unbolt the bottom engine mount, can I then pull the whole lot out?
Yes, it's definitely more manageable to drop the subframe out. Separate and leave the struts hanging if you like, then take them out after. Leave the rack on the subframe and separate at the pinion. When it's out on the ground, you can swap the power steering rack over.
 

natumbri

New member
While I'm accumulating bits and pieces for the car, I spent some time making a very simplified mathematical model of a Peugeot 205: https://205.si/simulator

The RPM v Nm curves I'm using are just guesstimates I found on the internet. Has anyone got a real life actual dyno of a motor (or wheels), together with relevant car stats (mainly gears, FD, weight, tyres, 0-100, and top speed) so I can check (and tune) the model?

Looking at what it spits out using the internet torque curve, it doesn't seem like it is wildly off...?
 
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