Performance Modifications

Air filters HID headlights
Brakes Steering Rack
Chips Styling
Differential Suspension
Exhausts Tyres
Engine Wheels

Here's a pic of my dream engine!

One serious M42!

Many people have asked for a page on performance mods for the 318is - so here it is! The guidance here is gleamed from listening to many peoples' observation along with my own experience.

I fundamentally believe that the E30 is a well style car, so I personally don't like too many cosmetic alterations. Anyway, body alterations are not specific to the 318is and plenty of other sites are available for help, so I'll barely touch on them here.

What is presented here are improvements for road use and perhaps occasional track use. I won't describe extreme mods as I believe that few people need them (and I really don't have enough knowledge either). The mods here are those I feel are worthwhile - too many people modify their cars for the sake of the modification and rarely get value from the increased performance - and the 318is is pretty good car stock anyway!

Brake upgrades

The standard disc brakes fitted to the 318is are fine for normal road use. The performance of the system is mostly related to the quality of pads and brake fluid used.

I would recommend using top quality DOT 4 fluids (such as ATE Super 200) and high quality pads from Pagid, EBC (Green Stuff seems best), Mintex or Ferodo. The EBC Greenstuff part numbers are 2463/2 or DP2779 for the front and DP2447 for the rear. Some people say that stainless steel brake hoses offer improved feel too. Other than this, I see little point in spending huge money upgrading the braking system for normal use. Money is better spent on the upkeep of the system, good quality tyres - or even some advanced driving lessons!

A great value upgrade, when the time comes, is a pair of ATE PowerDisc rotors for the front. They have an ellipsoidal groove and are cheaper than BMW parts but only a fraction dearer than OEM discs from the direct suppliers.

These slotted discs offer slightly improved brake cooling and allow pad gases to escape. This reduces the likelihood and effects of fade, especially where high speeds are involved. Drilled discs extend this capability even further but have significant negative effects in terms of a reduced cross sectional area (= increased brake pressures and faster disc wear) and a proneness to cracking at the drilled holes.

If you only do occasional track days, slotted discs are an excellant idea but I would steer clear of drilled discs unless I was a serious competitor.

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Engine improvements

The engine is only mildly responsive to low cost tuning as so many of the basics are right. Stick with the stock multi-electrode plugs - there seems to be no benefit of going to platinum or +4 plugs with the M42 (although BMW have now recommend a 4 electrode platinum plug for extended service, with max. 100,000 miles life, BMW part# 12 12 9 071 003 or NGK BKR6EQUP). The individual coil packs and the specific plugs do a good job. I have never heard of a worthwhile upgrade of the spark plug leads either on this engine.

Always use really good oil. A semi or fully synthetic branded oil from Mobil, Castrol, Amsoil, Redline, Shell, etc. is really obligatory for this engine. Not only do they provide greater protection but they also clean the internals, last longer and offer better cold start protection. They also are generally lower in friction and so will put up less resistance to the movement within the engine which can actually increase available power! Unless climate dictates it, try not to use lower than a 10W oil on these engines. Forget any PTFE/Teflon oil additives as they risk blocking the oilways in the head and hyraulic tappets.

Oh, by the way, that lube stuff goes for the tranny too!

Many people rave about Shrick camshafts, available for many cars. The stock cams have low overlap (for good idling and low down power) with high lift for good breathing as they are but the Shricks can improve top end power. However, I am led to understand that a flat spot occurs in the mid range if the cams are installed on their own. Apparently the inlet manifolds support low down power and the Shricks maximise high end power - but nothing helps the bit in the middle! The engine has a dip in the power curve as it is (see the graph below). They are alo very expensive (something like us$1200 for the pair!

Some people change the manifolds for racing - but we are getting out of our depth now! A similar logic applies to enlarged throttle bodies whereby the potential benefits outweight the effect on low-medium power. Ultimately, for most drivers, BMW have got their issues pretty well balanced.

There is scope to lighten the flywheel to reduce spin up inertia in lowergears. I believe this a major contributor to the cars' relatively poor acceleration from standstill. You can buy expensive modded flywheels but I would really like to hear from someone who has managed to shave 1-2kgs off the stock one - any guinea pigs?

From analysing the BMW ETK, I have found out that '89 models were fitted with the M40 9.973kg flywheel but were changed to a 11.45kg (aircon) or 12.25kg (no aircon) from 1990! So there's about 2.5kg saving to be had at a fraction of the cost of a performance part ! BTW, M20 engines have a 8.5kg or 9.98kg flywheel but will not match the M42 starter motor teeth, nor pressure plate, nor gearbox input shaft...and, if you fitted a M20 pressure plate you would be ~0.5kg up again (M40/M42=1.26kg, M20=1.674kg).

Here's another tip - BMW have recognised a potential momentary power reduction after a gear change followed by full throttle - due to partial contraction of the air intake boot. A support ring, p/n 13 71 1 734 359 can be installed at the first pleat in the boot! This seems to be a US only part though... I made my own! You need some rod, ~5mm diameter and 400mm long. Start by folding it to a curve to suit one end of the bellows. It should be about 90mm across. Continue to shape it using the outside of the bellows as a template. When about 95mm off the curve is done, start shaping the ends as they need a very pronounced bend. Once the general shape is right, cut off the excess on the ends and file any burrs. Fine tune the shape so that it fits into the 2nd fold without jutting out. It should be under a slight tension when installed.

Get the top curve and width right Use the outide as a guide Start the turn ups at the ends Cut back the excess and fine tune the shape so the ring is fully recessed

Don't forget the breather hoses when you put everything back in. BTW, I didn't notice any change - but you never know!

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Air Filters

A cheap upgrade is to replace the air filter with a free-flow design. I use a Jetex panel filter but those from Pipercross, RAM-Air and K&N are good too. Filter cones and induction kits are popular but I am not convinced they give much additional benefit over the panel types. The air route for the M42 is fairly straight anyway and is plumbed to a point at the rear of the headlights. I think they can add ~1-2bhp at higher revs but can give a more throaty induction sound.

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For real horsepower a new ECU processor, or "chip", is a great value upgrade. The stock M42 chip has been criticised for not being well optimised - so the potential for improvement is high.

They work by having the fuel map modified so that the timing and duration of the injection process is optimised. Chips are designed by car manufacturers to take account of different fuel grades, poor maintenance and extreme environments, hence having compromises that can be removed. Obviously, the flip side is that mid-high octane fuels (95 in Europe, 92 in North America) and regular maintenance will be needed.

The most commonly rated chips are from Jim Confonti (US), Dinan (US), Authority (US), Wetterauer (Germany) and Superchips (Europe), although there are a number of other company's provide good service too. Installation is a simple plug out - plug in swap.

Consideration should be given to custom chips, if an option. These can be tailored to your specific car my fine tuning the map to your particular engine. Costs can be up to 60% more than off-the-shelf chip, may require the car for a day or more but may help liberate an extra few bhp.

I have a Superchips chip installed. Have a look at the graph of before & after so I can explain its affect (the graph will launch to a new window).

Rolling road printout, before & after Calculated torque & power curves after superchip was fitted.

The first improvement is at low revs. From around 1250-2000rpm there is about 5 bhp extra available. This is noticeable by the improvement in the ability to move off slowly in traffic. Previously, the car needed a bit of throttle to get going or else the engine would bog down. It is now easier to get the car moving slowly with less risk of stalling or flying into the car in front!

In the midrange from ~2000-3500rpm the benefits are less pronounced and not as easy to detect. I can best summarise the improvements as a marginally improved ability to pick up speed when cruising.

The top end is where the real benefits lie. From ~4000rpm the two graphs really diverge. By summation, the peak power has risen from ~144bhp to ~163bhp (although I really believe it is actually closer to 154bhp due to wind-down inaccuracies of the dyno) - a nice improvement. The power peaks at about the same rpm but is wider, and the rev limit is raised by ~500rpm. The extra power is really noticeable when 4th gear overtaking - the act is much more effortless and less time consuming. A nice additional surge is noticeable in 2nd and 3rd too.

The fuel consumption has barely changed (maybe worse by 5% - or is that just my heavier right foot?) and emissions are not a problem. The old chip can be retrofitted any time.

Pop over to the "Me & My Car" page to see the acceleration figures - in summary the car is about a second faster to 60mph.


The stock exhaust is ~2" right through so is superbly functional if not so resonant. Performance gains from putting an aftermarket system in are minimal unless the catalyst is being removed. Selecting a system is really based on sound, looks and quality. There seems to be few which are commonly recommended:

  • Supersprint: A high value for money system which if mid-priced, well made and with a sound which is more bass the normal, although the volume of the system is not particularily loud. There are a 70x90mm oval (#783105) and a 100mm diameter (#783124) rear boxes available. They have a matching header (#785701) but I do not know about its benefits.
  • Sebring: High price but top quality. I think there is a small number of tail pipes available.The overall sound is noticeably more agressive without being ostentatious.
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With a slightly lowered stance and the shadowline kit on the 318is, I think the car looks pretty good as standard. Of course, styling though is a matter of taste and an easy way of customising a car and marking it out as ones' own. I think many German cars are styled with a certain boldness yet cleanliness, which is too easily spoilt. Mercs, Audi's and BMW's can be really messed up with tacky spoilers, poorly choosen wheels and superfluous addenda. The E30 is no exception, looking best as a sleeper.

The M-Tech kit was optional and is a good retrofit. The side sills add depth and the M front bumper/spoiler assembly looks aggressively sporty without being frivolous, although I could live without the arched rear spoiler.

Here's an M-Tech kit

Most 318is cars now have the extended front spoiler lip - approximately 5mm deeper than standard with a 20mm extension at the sides and front corners. It certainly adds a purposefuless to the front view by appearing to lower the car. While down there, a set of foglights combined with the brake ducts balances the symmetry of the main lights.

I think stripes and stickers are no-no's on any E30. A top tint windscreen is a better alternative to a sunstrip. A simple M badge on the grill looks good, as are clean reg plates. Cars, other than black or white, can look good with clear front and side repeaters although I would stop at replacing the rears. Eyebrows are not suited to Euro models with side (parking) lights at the top - and I think they make a car look dozy.

Have a look around the "Pics" page to get an idea of what other people have done.

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Decent alloys, like most Bimmers, can make all the differance. I think 14" wheels look too small while 17" or more compromises handling and ride. I still favour the 15" BBS basketweaves (cross-spokes) which were optional - I got a shadowline set from BMW directly, which look like the rims fitted to the Ceccotto and Ravaglia M3's.

Here's one of my shadowline BBS 15x7

I also like the "Hockenheim" and Alpina styles too. Avoid 3 spoked wheels and rounded "Stealth" 5 spoke designs - they don't do the rest of the car justice. I think that styles that are chunky or detailed look best. Click on the "Pics" page to get some ideas.

Given the relatively low weight of the car, the best performance size seems to be 15" although 16-17" are often fitted for looks. Bigger sizes are possible but if widths go above 8-9" then there are serious possibilties for contact with wheel arches. The fronts will certainly foul the splash guards. Offsets are critical too, note...

6" rim width: 35mm offset
6" rim width: 30mm offset
7" rim width: 25mm offset
8" rim width: 15mm

...although this should be double checked with the suppliers. The wheel bolts are 4x100mm and the hub centre diameter is 57mm. I would recommend getting wheels with the correct offset and hub diameter - there can be complications in terms of strut/wing contact with the former and vibration with the latter.

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The suspension can be tweaked without sacrificing too much comfort. Springs can be selected for personal preferances in handling - and anti-roll (sway) bars to tune roll and gas dampers to control rates. One simple adjustment that can be considered is to reduce negative toe. Running 0 to -10 minutes can help turn-in slightly without sacrificing too much straight line stability.

One effective way to improve handling in one swoop is to install the Bilstein Sprint kit, part number SE5-8600. This it is specific to the 318is and includes springs (~-25mm) with matched dampers. It guarentees properly matched damping for the springs and the correct stiffness for the weight balance.

Antiroll bars
The only upgrade within the E30 family is the convertibles' front ARB, it being 21mm diameter compared to 20mm of the 318is, this being a useful 20% stiffer. The M3 uses 19mm on the front (but a different design - although the mounts can be welded onto the struts) and the exact same size on the rear (14.5mm) - so a custom bar is the only option for the back.

Hartge produce replacement ARB's which are stiffer and adjustable, however, I can see no reason why the front stock ARB could not be made the same by a competent welder. The bar is made stiffer by moving the tierod towards the bushings.

Paal Berg's Hartge adjustable ARB

Note that these adjustment on their own may increase understeer and reduce oversteer.

There is a company in America called Suspension Techiques who provide a 22f/19r ARB for the car with good reported results. Be aware that a very stiff rear ARB, as in this case, can rip off the mounts, so enquire about strengthening too! This setup will dial extra oversteer into the handling of the car.

Eibach also have an adjustable bars (20mm front / 16 mm rear) for E30's which is reported to be quite good. Part # 2003.320.

For a modest increase in spring rate consider Eibach's for general fast road use. H&R Sports are a similar quality spring which are a good bit firmer if you do some competitive driving (part #'s 3VA=~40mm drop and 5VA=~60mm drop). I find that these springs reduce understeer by lowering the front roll axis more than the rear - and there is also a larger proprtional rise in spring rate at the rear which causes the same effect. There are then H&R Race springs for a really stiff set-up. See picture below of my car with -60mm springs on the front.

-60mm H&R on the front

If you come across them, the M3 springs are a not such a great upgrade. The front springs are identical and the rears are just a little stiffer. The main difference on the M3 to the 318is is just its front antiroll bar...

The M-Tech springs are about 15mm lower than normal. Unless you are going for a very stiff spring, I would not lower too much more than this, perhaps a further 10mm maximum. Lowering by 40mm or more will cause front and rear negative camber to increase; OK for track use but is liable to eat tyres on the road. K-Mac camber adjustment plates are really required for the front with offset bushes (available from BMW) for the rear trailing arms.

Dampers tend to wear out by 100,000 miles and a worthwhile upgrade is to fit firmer models from the big manufactures such as Bilstein or Koni. For the 318is, an overwhelming amount of people have good things to say about Bilstein Sports (Europe) / Sprint (USA). Part numbers are P36-0335 for the front and B36-2027 for the rear. Do not get the HD listed for the 318i as the shaft lengths are longer.

The Koni dampers are 8641-1210 Sport for the front and 80-2641 Sport for the back and are adjustable. Koni are reported to be a little less reliable but a little less jiggly than Bilstein, possibly due to their lower gas pressures. It is said that they should be run in at their softest setting.

Generally it is better to match springs and dampers together - adjustable units are not particularily beneficial for most. There usually is a damper setting that best controls a particular spring rate. As a rule of thumb, it better to have a slightly overdamped system. I'd also not advise coilovers for normal use unless you have access to very specialised equipment and skills to match corner weights, ride heights, damping, etc. To be honest, a standard suspension system can be tweaked to handle nicely without the cost and complexities of coilovers - can and do most people know how to drive their cars to take advantage of these?

The rear damper mounts can (and should) be upgraded with the suspension. The best is the OEM E46 convertible units which are much more resilient without being harsher. Part number is #33526754096 with the sealing gasket #33521128734.

The M3 front control arm bushes are a must have upgrade if the arms are being replaced. They cost a little more than stock, but this cost is reasonably insignificant in terms of the overall cost. The bush is offset, changing the castor of the front strut (and toes in slightly) and is completely solid. This has the effect of improving steering and braking feedback enough to notice it. However it can cause more harshness to be transmitted too.

I have written an article on installing this, Click Here if you want to see it.

Strut Braces
Some people swear by them, some people don't see any advantage, I personally think that if you can get something that limits positive camber changes in hard cornering for a small cost then it is worthwhile - however, springs and ARB's are the normal route and a brace should be low on the shopping list! There are braces out there at good prices - and there is certainly no harm in installing one. Most people recommend one piece (non-hinged, non adjustable) from companies such as BMP, Sparco, Hartge and AC Schnitzer.

Please note that I have a write up for the procedure for changing spings and dampers here!

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The E30 has the handling of a sports car - but that means that it pays only token respect to normal, lazy driving. Lift off oversteer and inherent understeer can catch the unwary out. Power oversteer is another normal trait. So, buy the best brands to mitigate the chances of an accident.

And I'll give ye all a little secret. Tyres affect your handling much more than minor suspension upgrades. Good tyres brings real excellance to the handling by further sharpening reflexes and providing greater on the limit control in addition to the pure grip they provide.

Tyre pressures are also critical, most enthusiasts seeming to run 2-6 psi above the manufacturers recommendations. Driving style, suspensions mods and tyre size will all dictate the actual pressure. I run 35-38psi on the front and 2-34psi on the rear (32f/30r recommended) on 205/55/15's. Generally the wider the tyre and the more regularily you corner hard, the more air pressure you should run but, using a tyre depth gauge, monitor your tyre wear at the inside, middle and outside of the thread and adjust pressure to get an evenness.

Balancing can also be a problem - very often due to a out of roundness of the tyres (another reason to buy good ones). Watch when the tyres are being fitted and balanced for a up and down motion. The wheel may be balanced according to the machine but will still result in vibration on the road.

Tyres, as of 2004, which seem to work well on the E30 are:

  • Bridgestone Potenza S03 Pole Position (Probably the best all round tyres in the world)
  • Bridgestone RE730 and 930 (Good value all rounder)
  • Good Year Eagle F1 (Good in the wet)
  • Dunlop SP9000
  • Yokahama A520 and A539 (Good for dry)
  • Toyo Proxes T1S
  • Falken Azensis
  • Fulda Extremo

My Bridgestone Potenza S02 Pole PositionsMy Bridgestone Potenza S03 Pole Positions

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The 318is came with a 4.10:1 differential in either an open or a limited slip design. If you have the LSD then KEEP IT! It is rare so maintain it well.

For those with an open diff, an excellant upgrade is to fit a LSD from another E30. Generally speaking, the ratio should be kept near stock but a 3.91 is excellent if the engine's power has been increased. The E30 LSD provides 25% lockup when one wheel begins to slip. This is beneficial because of:

  • Increased traction as both rear wheels will always receive some power
  • Stabler cornering as the power to the ground will not suddenly drop when traction is lost
  • Less likely to get one wheel locking up during braking

Remember that a diff effects the overall gearing of the car, either raising or lowering the speeds across all gears. If you race your car against a particular fixed parameter (e.g. 1/4 mile, 100m, 0-60mph) then the diff can have an important effect by maximising the time near peak power (and limiting to amount of gear changing).

For example, the stock 318is pulls about 53mph flat out in 2nd. For a 0-60mph run, the car will have to be in third for, at least, the last 7mph - adding on the time of the gear change and the slower acceleration in 3rd. A ratio of around 3.6 would allow the car to reach 60 mph in 2nd gear - substantially reducing the time even though the overall rate of acceleration would be a little lower (the effects magnify as the gears rise).

Designers generally match top gear and the diff ratio to the engine's powerband and car's aerodynamics so that top speed is reached in top gear at peak power. A 3.6 diff, in this case, would have the engine away from its power peak - reducing its overall top speed and hurting the absolute acceleration too.

Generally a narrow power band requires a high ratio diff with lots of gear changes to ensure sufficient in gear acceleration (like a motorbike) while broad power bands can run low diffs with few gears (like dragsters). So picking a diff is really a balance depending on power and performance needs.

For the 318is, I would stick to 4.10 for a stock setup, although the 3.91 will not effect it too much - but the 3.91 ratio is ideal if the engine has been modified. Usual sources are the US E30 M3 (4.10), the European 325i Sport (3.91) or any 318i/is fitted with a LSD.

The 6 cylinder models had beefier diffs - they will fit, but double check the need to change the output flanges against the original.

The Z coupe/roadster has a rear cover that has cooling fins which can be bolted on to E30 diffs too to help keep the oil temperature down - handy if a lot of high speed driving is done. It also comes with an uprated top bushing.

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Steering Rack

The E30 has been rightly criticised for its slow geared steering. At around 4 turns lock to lock for the powered rack and over 4.4 turns for the manual rack, it can get be a handful on Autocrosses or even in town! The M3 rack has a much more useable 3.5 turns, but no use for right hand drive models.

Zionsville, in the USA, have a nice article for fitting the powered E36 M3 rack in - click here to get it. I am not sure why they didn't use an E30 M3 rack???

It is also possible to change the rack & pinion for track use. I have heard of 2.5 or 2.7 turn rebuilds being available through Demon Tweaks and TransAutoSport (0044 1772 454647) in the UK. I am trying locally to find out if it is possible to fit an M3 rack and pinion into existing racks - if I ever succeed in confirming this I will let you know!

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