I bought a 3.0si Coupe to convert to a race car - so many questions...

[Liam22]

I know - they're too nice to go racing with - but I had an itch that wouldn't go away...

And this was the result!

20181213_102248_HDR.jpeg (285.32 KiB) Viewed 1829 times

My plan is to convert this lovely thing into a race car, for one of the 45-minute race series, such as 750MC Roadsports, MSVT SuperCup or CSCC New Millennium. I currently race a Mazda RX-8 in Roadsports and the E86 should take me to the next class up. Before that I raced an E30 320i in the Production BMW Championship

I'll be doing the conversion myself, and I've been reading lots of FAQs and threads on here for info. Learnt a bunch already, but have a few newbie questions that should help to avoid expensive mistakes. If you can answer any of these I'd be very grateful.

Wheels/tyres
I plan to sell the lovely 19" CSLs and switch to 17" for more affordable track tyres. Will I get away with 8J all round (square) on 225 or 235 section tyres? Will I really need wider rears for corner exit traction with sticky track tyres? What is the max wheel offset that will fit nicely without screwing up the scrub radius. My current favourites are E89 rims (8J ET29) or E90 rims (8J ET34).

LSD
Am I really going to need one? E46 M3 subframe swap looks like a reasonable option (I'll have the subframe out to replace bushes anyway). Are there other options that will fit in the OEM diff case?

Steering rack
The steering is the only disappointing thing about the car so far. It sits there, tugging away randomly, providing zero feedback. It has to go! Plan A is to figure out whether I can fit a hydraulic pump once I've deleted the aircon compressor. If not, then I may just run a PAS rack without the hydraulics. Alternatively, I wonder if it's straightforward to remove the electrics and motor from the OEM rack and just convert it to manual.

Oil cooler
Looks like there might be a tiny water/oil heat exchanger next to the oil filter. Are there any aftermarket kits for a regular radiator-style oil cooler? Is oil temp a problem for track work?

Coding
I'm new to the world of fancy electronics and BMW coding. Is the car going to have a fit when I remove all of the airbags, and slim down the wiring loom? I see talk of various apps for dealing with this. Any recommendations for my use case?

Exhaust
The car has had the mid box removed, which is nice, but it still looks kinda heavy. What's the lightest exhaust system available? I'll be keeping the standard exhaust manifolds for now. Power tuning will happen later.

Thanks!!! I'll start a build thread once I get going. Is there a separate forum section for projects?

[buzyg]

Welcome to the forum. She will be a fine looking race car.

[Doddsy]

Welcome mate. Now this sounds like fun

[philbo909]

Welcome to the forum,
Machine monkey, a member on here, swapped in a hpas so it might be worth dropping him a message, I think there's a thread on it
I run 225 square set up and I like it, with sticky tyres I see no reason why you couldn't do it on track.
E46 rear subframe would be the way to go for an Lsd I think, then you get a mechanical diff, it's that or a quafe/alternative brand on the 3.0Si subframe
I'm sure someone more knowledgeable than me will be along soon

[MrPT]

Not the happiest ending, but this might be of interest:

viewtopic.php?f=2&t=97050

[Zedtastic]

WRT scrub radius, the standard front wheel off-set is ET47, so I would have thought sticking as close as possible to this would reduce the possibility of screwing it up.

[Liam22]

Not the happiest ending, but this might be of interest:
viewtopic.php?f=2&t=97050

Thanks. I already found and read that thread with interest. I've done a lot of searching on here! It's an impressive build. I know of Gary Feakins and I'm pleased to see the Z Cars series was revived.

WRT scrub radius, the standard front wheel off-set is ET47

Thanks. On what width? It would be useful to know the OEM front and rear wheel sizes. I haven't been able to find definitive data for that.

[NickDE]

If you want BMW 17" wheels, go for Style 32. They are lighter than other BMW wheels, and cheap to get from ebay as were an option on E36 and E46 3-series, which have the same sizes and offsets as the E86.

[rally-chris]

You may find the following site useful, wrt to OEM wheel dimensions:

http://www.bmwstylewheels.com/Z

Chris

[Mr Tidy]

Lovely looking Coupe, Liam.

I'm looking forward to seeing how you get on.

If you can find one the M Coupe had an LSD as standard so might be the easiest fit. But a few forum members have had a Quaife one fitted by Birds.

Standard wheels on a Sport Coupe are 8J x 18 fronts with an ET of 47 and 8.5J x 18 rears with an ET of 50.

I've got 18" E89 wheels the same widths on mine and they sit a fair bit further out as the fronts are ET29 and the rears are ET40, but no rubbing (so far)!

Good luck with your project.

[srhutch]

Welcome to the forum,
Machine monkey, a member on here, swapped in a hpas so it might be worth dropping him a message, I think there's a thread on it
I run 225 square set up and I like it, with sticky tyres I see no reason why you couldn't do it on track.
E46 rear subframe would be the way to go for an Lsd I think, then you get a mechanical diff, it's that or a quafe/alternative brand on the 3.0Si subframe
I'm sure someone more knowledgeable than me will be along soon

MM swap to hydraulic steering was on a M54 though. N52 will be harder I believe as the engine didn’t use hydraulic steering in any car it was used in.

Quaife did is the easiest option as I think you’d need a different prop due to length. Also not sure on driveshaft lengths as ///M axle is shorter.

[mr wilks]

If you want BMW 17" wheels, go for Style 32. They are lighter than other BMW wheels, and cheap to get from ebay as were an option on E36 and E46 3-series, which have the same sizes and offsets as the E86.

Only the 18s are lightweight.
No idea why that is but the 17s weigh like any other oe bmw wheel set

[Mr Tidy]

MM swap to hydraulic steering was on a M54 though. N52 will be harder I believe as the engine didn’t use hydraulic steering in any car it was used in.

No, my E91 has an N52 with HPAS - it was an early one though! Build date was 29 August 2005.

And sadly it steers so much better than my E86.

[Liam22]

You may find the following site useful, wrt to OEM wheel dimensions:
http://www.bmwstylewheels.com/Z

Wow! This is exactly what I needed. With weights and everything...

E89 style 290 were my front-runners. But now I think they will sit too wide, and probably foul the wheelarches once lowered.

I had previously earmarked E90 wheels as plan B but these now look ideal (ET34). Style 284 and 285 look OK and are also about as light as I can find on the OEM market. +13mm is not going to screw up the scrub radius too much - hairpins are rare.

No, my E91 has an N52 with HPAS - it was an early one though! Build date was 29 August 2005.

This is great news. I will be scouring realoem and eBay for more info/options. Although I will need to compare mounting points and steering column compatibility. Electric motor delete, or E46 rack without hydraulics is probably a simpler plan A, until my forearms become the weakest link!

[Mr Tidy]

Mr Tidy wrote: ↑Sun Jan 20, 2019 10:53 pm
No, my E91 has an N52 with HPAS - it was an early one though! Build date was 29 August 2005.

This is great news. I will be scouring realoem and eBay for more info/options. Although I will need to compare mounting points and steering column compatibility. Electric motor delete, or E46 rack without hydraulics is probably a simpler plan A, until my forearms become the weakest link!

Great news, I'd love to know how you get on with that - if there is one thing I don't like about my E86 it's the steering. And every time I drive my E91 it reminds me of how good it could - or should - have been!