924Board.org

[Porver9two4]

I have a track prepped 924 for fun on track days - it's just a toy, no serious racing or competition.
It's a real blast, a HUGE amount of fun. Mechanically stock, so robust and easy (and cheap!) for bits and surprisingly quick - it's no rolling roadblock and often embarrasses much more expensive machinery.... Partly because I can push it right up to 10/10ths in the knowledge that if I get it spectacularly wrong, come off the track or really break something expensive I am not so deep into it that I can't just throw it away.
Part of the secret to making it competitive (cheaply!) has been an extreme diet.... less weight = more power (to weight), the old Colin Chapman (of Lotus) adage of "add lightness".
I am about to embark on the next round of weight loss ahead of some planned brake upgrades (better brakes will really improve it) and as part of that the Bosch CIS has come in for scrutiny

I am not concerned about cold starting or warm up running as the engine can be as much of a bitch as it likes whilst it warms up in the paddock - I wouldn't go out on track with it cold anyway and once warmed up it will spend the rest of the day at operating temperature until being shut off at the end of the session. Consequently I am looking at stripping ALL the warm up kit out of the CIS system, the WUR, the Idle Air Valve, the thermo-time switch and anything else I can find..... just leaving the metering head and the 5th injector.
I then plan to live wire the 5th injector with a dash mounted push button 'on' switch and tap an adjustable fuel pressure regulator onto the old WUR fuel lines so I can set and adjust the control pressure in the metering head. I will use the 5th injector combined with deft throttle operation and moderated button pushing for rudimentary cold (and hot) starting enrichment...... or that's the plan anyway.

Question is, has anyone stripped a CIS system down to it's bare minimum before and have any comments? has anyone replaced a WUR with an adjustable fuel pressure regulator and got any experience? or thoughts?

I am guessing most of you are thinking 'why bother'? The answer is 'for fun'; because I can; to see what happens; to shave a few grams off the weight (every little helps!) and to liberate a few Bosch CIS parts that can then be sold to raise funds for more time on track

I would also welcome any suggestions on where I might be able to get some more weight out of it, some more speed or some more power for minimal outlay. This is just a fun project folks, so we can go as mad as we like!

[Eric P]

I don't have experience modifying the CIS beyond what was intended by the factory so I can't answer your question, but I did want to pose another question: does your racing class mandate that you need to keep the stock injection system? Why not ditch the entire CIS and go carbureted? There are a lot of parts to the mechanical injection system. Ditching it all together would probably give you a significant weight savings and maybe better throttle response too.
_________________
1980 924 NA, US model
1987 924S, US model

[924-76]

[RC]

[Porver9two4]

To answer some questions....
I am not competing in any racing class, so all and any modifications are permitted. I did think about switching to bike carbs or Webers, but there is the issue of cost and fabrication - I would need to make a suitable manifold (which I have the kit to do, it's just a bit of a faff). Besides, the CIS actually works really well in general and is a super simple, reliable system - it's been great on the track so far.

The car is a standard Euro spec 1983 2.0L, non-sunroof, so nothing special but a good base for a track car. Off the top of my head, lightening so far has included ALL the interior, just some lightweight race buckets and the instruments half of the dash left... although all the instruments have gone and been replaced with lighter ones. The fuel tank and all the boot floor, which has been replaced with a smaller under-floor fuel cell, some strengthening bars and the floor re-skinned in aluminium. All the door internals and all the glass (still has the OE windscreen, but no external trims) - just the door catches left and 2mm lexan windows. The bumpers front and back, replaced with lighter alternatives. The headlights, changed to CarreraGT style with lexan covers. Plus anything else I could find to take off yet keep the car roadworthy (technically it can still be driven on the road).

Future plans and weight saving I am revving up for now includes, CIS components strip, a re-work of the dashboard (in CF hopefully as I want to have a play with the material), a bespoke wiring loom and switch gear, lighter radiator fan and starter (if I can find one cheap), a shorter, lighter, free-er flowing side exit exhaust, removal of any brackets and steel I can get out of it, even lighter LED front and rear lights etc. etc. .... basically anything I can do to cheaply shave weight from anywhere I can... If I can find some glass fibre wings, doors or bonnet then great (although I am also tempted to have a go at these in CF). This is just for fun and I can go as mad as I like here, raiding junk yards for parts (hence the Mercedes S class 4-pot Brembos I have on the shelf to engineer on). Thinking laterally for cheap and free power is what it is all about


RC - thanks for your comments, that's good to know. Junk yard hunt is ON

[Cedric]

The cis would be the last thing to touch, since it works well.

Have you swapped the rear hatch? Easily one of the heaviest components on the car.

Lightweight alternator from a Daihatsu or similar

Make a tube manifold and thin walled exhaust.

Light weight wheels like the super light citroen wheels, cheap and light

Carbs, since you get rid of lots of parts including cast manifold, lots of effort though.

Modern Alu Radiator, stock brass one is very heavy.

The cast mirrors are super heavy, i guess those are of already..

Lightened flywheel, ads some acceleration aswell.


Swap rear torsion bars for gaz coil overs, can save many kg, and you can cut away lots of metal from the rear suspension after that.


Please post some pics, would be fun to see the car
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[MikeJinCO]

Cedric, Can you recommend a lightweight alternator option ? On my slowly being built track car I'll only have 4 or 5 circuits so a high power one is not necessary. Only lights are for brakes, fuel pump, ignition, instrumentation and a manual operated rad. fan.
_________________
Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)