Z4 Performance Modifications

[Chris_Geezer]

Well after my day on the track Saturday I'm looking into performance mods. I stood my own and the car went supprisingly well.

Has anyone on here actually done anything for high gains? And before anyone tells me to just sell and buy an ///M model the answer is no, I want to mod mine, lol.

Have looked at a few supercharger kits but to get a comprehensive one including manifold I'm looking £7000+, so pretty much a no go. I'm pretty handy with a set of spanners so will probably carry out most of the work myself over time and there's no rush for this project initially I am just looking into things. Have debated going the whole nitrous route so as I can just turn it off for everyday driving, but there still aren't many experts in the UK who I can pick the brains of (even though nitrous oxide has been installed into cars for more years than I've been born). Loads of places offering to fit a kit, but none of which I would actually call an expert.

Anyway, who's done what? Cams? Turbo conversion? Head work? Anyone?

 

[mmm-five]

As a fair few of us on here will say, the most cost-effective performance mod you can do is to get some driver training.

If you haven't had any track/race driving training then do some, as it will make you faster everywhere whilst reducing the strain on the car's components.

If you've done all that, then I'd go down the performance braking, road legal track day rubber, and adjustable suspension route before adding any power, as it will let you brake later, carry more speed into/through/out of the corners, and give you much more confidence in the car to go along with your driver training.

After all that, the supercharger route may sound expensive but you'll probably find that it's excellent value-for-money, and is quite an easy/quick fit.

Cams, valves, throttle bodies, injectors, exhaust, intakes, remaps, etc. are all pretty poor in £/bhp stakes, and can take time to set up correctly.

I'd also look into insurance before you start modding, as I know a few will raise your premium for simply fitting the nitrous kit installed even if it's only used on track (and have seen a nice 928 with twin 100bhp shot nitrous on the rear parcel shelf).

Although for much less cost/trouble/time you might simply want to buy an ///M version and put some decent brakes & track rubber on.

 

[Chris_Geezer]

I've been racing and modifying for years... to buy a car with all the power in the first place just isn't me. Some say I'm daft, some say I'm just darn right stupid, but I like to play and tinker and I can't stand to think that someone else might have the same car/set up as me. It's more of a hobby than anything.

I know all about insurance don't worry there, I've had cars with complete custom engine builds before, and a Jaguar XJ with nitrous, oh and a fibreglass kit car running near on 400bhp from an SW20 engine through the rear wheels (tip... tooooo much power for a fibreglass car as you can't get the power down).

The braking/general handling is easy to sort, so just really interested if anyone had done any high gain power mods.

Question:
How did a car have twin 100bhp shot nitrous on the rear parcel shelf? Was there some form of controller limiting the flow to 2 "shots"? Or did the driver tell you this?
The power gain (shot) is down to the jetting (as far as I know, unless times have changed and systems have totally been re-designed) which is hidden away amoungst all that iron mongery under the bonnet. If you mean he had 2 bottles on the parcel shelf then I'm guessing they were reletively small as a standard 10lb bottle takes up the majority of the boot on my mates Elise. The bottle size also doesn't have any link to the "shot" size. So don't get too impressed with people trying to be flashy by having their bottles on display.

 

[mmm-five]

Question:
How did a car have twin 100bhp shot nitrous on the rear parcel shelf? Was there some form of controller limiting the flow to 2 "shots"? Or did the driver tell you this?
The power gain (shot) is down to the jetting (as far as I know, unless times have changed and systems have totally been re-designed) which is hidden away amoungst all that iron mongery under the bonnet. If you mean he had 2 bottles on the parcel shelf then I'm guessing they were reletively small as a standard 10lb bottle takes up the majority of the boot on my mates Elise. The bottle size also doesn't have any link to the "shot" size. So don't get too impressed with people trying to be flashy by having their bottles on display.

I say 'parcel shelf', but they were more correctly attached to the roll cage/rear strut brace where the parcel shelf used to be.

I believe that each bottle handled one bank of the V8, and he had some electrickery to warm the bottles and to manage flow. But I didn't get anywhere near the engine bay to see how complex it looked so it could have simply been straight to the intake manifold(s).

The twin 100bhp was what I was told, but he didn't use it on track, only on the strip.

He also claimed to have a water injection system.

 

[PawnSacrifice]

I've been racing and modifying for years... to buy a car with all the power in the first place just isn't me. Some say I'm daft, some say I'm just darn right stupid, but I like to play and tinker and I can't stand to think that someone else might have the same car/set up as me. It's more of a hobby than anything.

Good man, nice to try different things... just document and photograph everything please

Oh, and while not many performance upgrades done here you'll struggle to find a stock car, so you're not alone

 

[ChawenHalo]

As a fair few of us on here will say, the most cost-effective performance mod you can do is to get some driver training.

If you haven't had any track/race driving training then do some, as it will make you faster everywhere whilst reducing the strain on the car's components.

If you've done all that, then I'd go down the performance braking, road legal track day rubber, and adjustable suspension route before adding any power, as it will let you brake later, carry more speed into/through/out of the corners, and give you much more confidence in the car to go along with your driver training.

After all that, the supercharger route may sound expensive but you'll probably find that it's excellent value-for-money, and is quite an easy/quick fit.

Cams, valves, throttle bodies, injectors, exhaust, intakes, remaps, etc. are all pretty poor in £/bhp stakes, and can take time to set up correctly.

I'd also look into insurance before you start modding, as I know a few will raise your premium for simply fitting the nitrous kit installed even if it's only used on track (and have seen a nice 928 with twin 100bhp shot nitrous on the rear parcel shelf).

Although for much less cost/trouble/time you might simply want to buy an ///M version and put some decent brakes & track rubber on.

Driver training is top top advice. "it not the ride, its the rider".

When you tune your car you make it will first of all and in all probability go slower than stock. Thats the usual learning curve. Laslty, one you've got it set up nicely you'll find the limits a little higher but it'll snap too. ie: not be as progressive.

Manufacturers spend astonishing ammounts of money setting up their cars to be communicative and balanced.

Personally, I think that until you've experience and explored the full limits of your car's handling (and they are high of the Z coupe), by tuning you'll be making your life harder not to mention more expensive.

Decent set of tires (not the softest and stickiest) and some instruction will make you progress real fast. Then you can effectively pick the upgrades you want.

I regularly get my own arse handed over to me by far more experienced drivzers ion the track driving far less powerful cars.

have fun!

 

[bimster]

Has anyone on here actually done anything for high gains? And before anyone tells me to just sell and buy an ///M model the answer is no, I want to mod mine, lol.

Anyway, who's done what? Cams? Turbo conversion? Head work? Anyone?

I'm always surprised that differential/carrier swaps (a.k.a. the poor man's supercharger) don't show up in most top-of-mind lists. They are by far the best performance modification for the cost on naturally-aspirated BMWs and they produce truly large acceleration gains without any engine modifications or their associated affect on insurance rates, emissions testing, maintenance cost, or warranty.

For example, replacing the 3.07 ratio carrier on a manual 3.0i with the 3.64 ratio carrier from a 2.5i automatic will cost only a few hundred quid and will increase wheel torque by 18.5% in each gear across the full rpm range. Compare this to the isolated 2% or 3% peak dyno gains from many popular and equally expensive engine mods and you'll understand why they generally don't add points for racing group classification whilst this mod does.

 

[mmm-five]

I'm always surprised that differential/carrier swaps (a.k.a. the poor man's supercharger) don't show up in most top-of-mind lists. They are by far the best performance modification for the cost on naturally-aspirated BMWs and they produce truly large acceleration gains without any engine modifications or their associated affect on insurance rates, emissions testing, maintenance cost, or warranty.

For example, replacing the 3.07 ratio carrier on a manual 3.0i with the 3.64 ratio carrier from a 2.5i automatic will cost only a few hundred quid and will increase wheel torque by 18.5% in each gear across the full rpm range. Compare this to the isolated 2% or 3% peak dyno gains from many popular and equally expensive engine mods and you'll understand why they generally don't add points for racing group classification whilst this mod does.

However, the downside is reduced gearing, so you top out at 140mph, are doing 4500rpm at 70mph, and have to change 4 times to get to 60mph

 

[bimster]

However, the downside is reduced gearing, so you top out at 140mph, are doing 4500rpm at 70mph, and have to change 4 times to get to 60mph

These are certainly important issues to consider, however, the actual performance measures are simply not as bad as these exaggerated numbers imply. If they were, absolutely no one would buy a Z4M or M3 with their 3.62 gear ratio.

In reality, top speed on a Z4 3.0i with a 6 speed manual transmission and 3.64 gears will still be electronically limited to 155mph; 70mph will require 2700rpm; and, since there is sufficient torque to start briskly in 2nd gear, 0-60mph will only require one shift (at 59mph). This latter feature makes shifting during one's daily drive altogether less bothersome by virtually eliminating the high rpm 1-2 shift.

 

[mmm-five]

If they were, absolutely no one would buy a Z4M or M3 with their 3.62 gear ratio.

But they've also got different gearbox ratios to match the diff and their different powerband profiles.

 

[ChawenHalo]

I've been racing and modifying for years... to buy a car with all the power in the first place just isn't me. Some say I'm daft, some say I'm just darn right stupid, but I like to play and tinker and I can't stand to think that someone else might have the same car/set up as me. It's more of a hobby than anything.

I know all about insurance don't worry there, I've had cars with complete custom engine builds before, and a Jaguar XJ with nitrous, oh and a fibreglass kit car running near on 400bhp from an SW20 engine through the rear wheels (tip... tooooo much power for a fibreglass car as you can't get the power down).

The braking/general handling is easy to sort, so just really interested if anyone had done any high gain power mods.

Question:
How did a car have twin 100bhp shot nitrous on the rear parcel shelf? Was there some form of controller limiting the flow to 2 "shots"? Or did the driver tell you this?
The power gain (shot) is down to the jetting (as far as I know, unless times have changed and systems have totally been re-designed) which is hidden away amoungst all that iron mongery under the bonnet. If you mean he had 2 bottles on the parcel shelf then I'm guessing they were reletively small as a standard 10lb bottle takes up the majority of the boot on my mates Elise. The bottle size also doesn't have any link to the "shot" size. So don't get too impressed with people trying to be flashy by having their bottles on display.

Impressive! Dude have you thought about dropping a E90 V8 in it? Hartge do this regularly but I would lovr to see this on a Z4C

 

[Wondermike]

However, the downside is reduced gearing, so you top out at 140mph, are doing 4500rpm at 70mph, and have to change 4 times to get to 60mph

These are certainly important issues to consider, however, the actual performance measures are simply not as bad as these exaggerated numbers imply. If they were, absolutely no one would buy a Z4M or M3 with their 3.62 gear ratio.

In reality, top speed on a Z4 3.0i with a 6 speed manual transmission and 3.64 gears will still be electronically limited to 155mph; 70mph will require 2700rpm; and, since there is sufficient torque to start briskly in 2nd gear, 0-60mph will only require one shift (at 59mph). This latter feature makes shifting during one's daily drive altogether less bothersome by virtually eliminating the high rpm 1-2 shift.

I'm with bimster

Diff swap is the first mod I would be doing

 

[F1ADAM]

This is an interesting one.

Bimster, aside from increased wear and tear on the engine and associated components (but other performance mods will also have this effect?) is there a reason this hasn't been a more popular route?

How much does somthing like this cost? And, based on your ratio calculations, what would you estimate the 0-60 and 0-100 times be compared to the standard 3.0?

 

[cj10jeeper]

I've done more diff and ratio swaps than I care to remember, but all on Jeeps (some final ratio, some transfer case which has the same effect). Purpose is simple to gain overall lower ratio's an in effect increase the torque in all gears.

The result in the real world makes for a horrible drive on normal roads. My biggest engined Jeep has an effective crawl ratio of 160:1 !! May well pull up mountains and accelerate faster than most road cars but tops out at 80 with a 6 litre V8

For daily drives the downside (and why I'd never do it) is it runs at higher revs for any given gear, drinks more fuel and is generally not as well matched to the engine as the OEM combination of engine torque, gear ratios, final drive and tyre size.

Still for a track focussed car then it has to be the cheapest real performance mod

 

[F1ADAM]

CJ,

Wouldn't other performance mods have the same side-effects? Namely, a mismatch to the OEM settings?

Also, is there a reason why the 2.5 and the M use the 3.64 and the 3.0 has the 3.07 ratio, as suggested by bimster?

 

[Lower]

If you want more performance on track from the car (and not the driver) i would concentrate on brakes, tyres and suspension in that order before you even start playing with the engine.

If you add engine power, all you will do is arrive at the corners quicker but not be able to go round them any faster. So your brakes will take even more punishment, as will the tyres.

Increase your corners speed and your lap times will drop substantially more quickly than if you just add engine power.

 

[cj10jeeper]

CJ,

Wouldn't other performance mods have the same side-effects? Namely, a mismatch to the OEM settings?

Also, is there a reason why the 2.5 and the M use the 3.64 and the 3.0 has the 3.07 ratio, as suggested by bimster?

Putting smaller wheels on with lower profile tyres would have the same effect

Each model has it's ideal ratio for road use based upon engine and gearbox characteristics, fuel economy, etc.
Swapping one bit can make a real mess of a roadcar. Track is very different and I bet it's a great mod and real value for money.

 

[bimster]

CJ,

Wouldn't other performance mods have the same side-effects? Namely, a mismatch to the OEM settings?

Also, is there a reason why the 2.5 and the M use the 3.64 and the 3.0 has the 3.07 ratio, as suggested by bimster?

All the E85 & E86 Z4 transmissions have essentially the same gear ratios. The only significant exceptions are the "si" automatics. Here is a link to the most comprehensive listing I've found:
http://www.bokchoys.com/differential/GearRatios.htm

The automatic transmissions use a higher ratio differential gear set (typically 3.46) because they lose torque through their torque converter and transmission. The 2.5i automatic uses a 3.64 ratio differential because it would feel a bit underpowered with a 3.46.

The Z4M also uses a 3.62 ratio to give it faster acceleration, but also to enable it to get to higher rpms faster. If you look at it's torque and power curves on a dyno chart you'll see that it only has about a +20 ft-lb wheel torque advantage over the M54 engine found in the Z4 3.0i through about 4,000rpm. With the 3.62 ratio this is increased to a 65 ft-lb advantage, which registers nicely on the customer's butt-dyno and helps justify paying the higher price.

I've gone to a 3.64 ratio in my Z4 3.0i 6 spd. manual (5 years ago) and 3.46 (+ Limited slip) in my 530i 6spd. manual (this year) and they both benefited enormously from these changes. I use both as daily drivers at different times of the year. There is no adverse affect on OEM tuning or system function. In fact the OEM tuning seems to adapt quite well.

There is also no increase in maintenance cost. Engine speed at cruising speed is unchanged except in high speed driving, although the selected transmission gear may be different.

Perhaps this is why fuel economy does not change except that you can expect to lose about 2mpg or so during sustained high speed driving. To be fair, of course, there is the constant temptation to drive more aggressively just because you can, which may also affect fuel economy.

What’s also great about this improvement is that it comes without the weight penalty or appreciable loss of fuel economy associated with adding a couple cylinders to the engine or with building the engine to run at 8,000 rpm, without the maintenance issues associated with a high pressure direct injection fuel pump…or need I even mention NOx injection ...the crystal meth. of the automotive scene?

BMWs typically come with differential ratios that permit high top speeds and high speed fuel economy at the expense of maximum acceleration and lower speed performance. That’s probably important to anyone using the Autobahns in Germany, but most of us who value our driving privileges and continuing car insurance coverage don’t care much about performance at those speeds. What we do care about is the performance available 0-85 mph to accelerate from a stop, through a curve, when passing or merging into traffic, when climbing a hill, and so forth. The differential swap is ideal for improving performance in these daily driving situations as well as at sports car track events. Subjectively, it absolutely feels like the car was intended to drive like this. It most emphatically does not feel like it's some kind of specialised off-road racer being taken on the street...although it certainly could feel that way if supplied with a much higher ratio custom gear set than what we have been discussing.

If a diff. swap is this great, you ask, why don’t more people do it? Well, for one thing, it’s not commercially promoted. Why should someone selling proprietary engine performance modifications like engine tuning for higher octane fuel, exhaust systems, or cold air intakes that deliver 1-4% improvements at selected engine speeds promote non-proprietary alternatives giving 12%, or 18%, or more, real torque improvements at all engine speeds? Likewise, why should automakers promote this option when customers will pay several times as much for more powerful engines? For example, my 530i with a 3.46 ratio differential will accelerate as quickly as a stock 535Xi because the somewhat higher wheel torque on the 535Xi is accompanied by much higher weight.