induction

Gav, if you want to see if it's running lean, you could always take it to an MOT station and ask them do do an emissions check.

One thing though-does your car have a catalytic converter? If it does, then you can't check mixture strength this way cos the cat will confuse the readings. If you've got the M50 24v straight-six, then it'll have a cat.

Having said that, however, the system only operates under closed-loop catalyst control on idle or part-throttle openings on a warm/hot engine.

When you go to full throttle the system switches to open-loop for maximum engine power, and the cat doesn't function, so a good dyno shop/rolling road can monitor mixture strength under full throttle conditions.

Sounds like it may be running lean though, if more air causes it to stumble. Sometimes the fuel pressure regulator gets weak with age and drops pressure in the fuel rail that supplies the fuel injectors, weakening the mixture.

A good fuel injection specialist should be able to confirm this though.

One more thing-I have an E34 525i also with the M50 24v engine, and it used to 'stumble' off the line, and had a flat spot. Then it failed the MOT emissions test, and I found out that the oxygen sensor down by the catalytic converter had died.

If you get an MOT station to do an emissions test, if it fails on high emissions and you get the occasional stutter, it may be the oxygen sensor.

I replaced mine myself and it cured the fault-no stutter or flat spot, and it passed the MOT

Alex

Cheers guys, i'll get the emissions checked when i get back down south! It's always had a little stutter, but never had the 'pop' before? As long as it's an easy fix though!

Gav

I designed my own induction system for my 635csi.

This was done to remedy two problems. Firstly the air box sits on the manifold and gets very hot and secondly the induction intake varies in size from 76mm - 62mm - 72mm - 62mm - 76mm.

The work started from going to a rolling road day and finding out that the car was running rich under full acceleration and thus potential power was being lost.

So i looked at all the kits out there and could not find something that i felt would benefit the engine, namely reduce induction temperrature of air, increase airflow which was in standard form fairly good and increse intake diameter. So i looked into making my own at considerable exspense. I had a fabricator make me a 76mm induction pipe to the back of the headlight assembley so i could keep the filter away from the engines heat. I then built a heatshiled and i lined this with neoprene to reduce engine temperatures further.

Now i can not verif the benefits yet on a rolling road, but my impression is there is at least a 10bhp increase in performance and possible more. Beforehand the car got very sluggish after it had been sitting in traffic. Now as soon as there is any airflow the car takes off. Fuel consumption has increased. Prior to fitting the best i achieved was 28mpg. Recently on a trip back from Leeds i gained 31.6mpg and that was driving normally and not trying to be economical. I now get 24mpg in town. Performance wise the car revs much faster and feels like it has a shorter diff or a lighter flywheel. I will be able to prove the results in february. The only problem i have is that a couple of parts have died since it's instalation in August namely the Manifold and just recently the ECU. Now the hope is that there will be no difference with these new parts, but the best indicator is the Lamda reading at the same revs and comparing these as this measures the lean/rich ness of the fuel.

Please see a photo below of the kit and instalation in the bottom right corner of the engine bay

For what its worth my thought on induction are if the kit increase intake temperatures then performance will drop. If intake diameters are smaller performance will drop. However if intake temperature is reduced and intake diameter is increased then performance will raise. Also if the route the air has to travel has less corners performance will increase as intake air speed wll be faster. Modern ECU's should be able to adapt quickly especially those with Air mass sensors. BMW intake are genrally fairly good, but they are designed to work in desert climates and hot temperatures with dusty conditions to Artic conditions and snow and water. They also have to meet noise regulations. Thus baring this in mind i believe there are gains to be had, but what you put on needs to be considered bearing a number of factor into consideration.

I hope this helps / is usefull

James

Just followed that link on the M5 vs 540i debate. Interesting that they mentioned that intake restrictor on the V8, until I remember the good old German bhp/tax thresholds.

I know one is at 192 bhp, and there's another one at 286 bhp-always wondered why the 540i made exactly the same power as the original M5/M6 and early E36 M3's.

Looks like that restrictor was there for a reason on the V8. Even with my paltry 5-speed slushbox the car is now noticeably livelier at the top end with every intake restriction I could find removed.

There's power and torque all over the place and the noise is much meaner now. I personally prefer the guttural bellow of the V8, and all these little tweaks have cost nothing but time and made a real difference that you don't need a dyno to prove, as the top end is livelier now without losing anything at the bottom end.

You don't really have to try to access the V8's torque, and the only criticism is that the very long 2.93 diff means the auto gets stuck in the standard 2000rpm stall speed torque converter 'hole' from standing starts, although the big V8 masks it to some extent.

Once on the move it really flies, and on a dry, cold crisp winters day it feels VERY rapid .

I feel the other reason the M5 3.8 six-speed goes harder once roused is that it has a much shorter diff-shorter than even the 3.6 M5's unit.

If you strapped the 3.8 M5's 3.91 diff in place of the 540i's 2.93 diff, even the auto 540i would blow your socks off.

The fact that the 540i is so rapid even when pulling such a long-legged diff bears testament to the wide spead of torque.

I once did a diff change on an auto E28 535i, from 3.07:1 to 4.1:1. I sacrificed the long-legged overdrive top, but acceleration was storming, and lopped nearly a whole second off the 0-60 time.

Sadly it wasn't a heavy-duty diff, and soon wore out and started whining very loudly very rapidly and had to be replaced with the original unit, which just killed acceleration by comparison.

The 540i will pull a lower rpm on long-distance cruising as it's barely ticking over-I get 2000rpm at 70mph in mine, and 30 genuine mpg on long summer motorway runs. I checked the mpg by brimming the tank, and ignoring the trip computer figure, which was reading 9% optimistic anyway, and has since been recalibrated by me.

At the end of the day, it's horses for courses. If you want an all-out racer then get the M5 but expect to have to work for the results and pay a big price for the car in the first place.

I found that some insurers impose special conditions before giving cover for M models, whereas they see the 540i as just a pumped up 520i and less of a threat to their claims department.

I live in the centre of a town and drive down miserable slow plodding roads to work in the dark and wet, with occasional long trips when the weather's nice, so a racer with the M5's abilities would be a big waste of money for me.

In my case the autobox and big, lazy V8 play a great tune, and with the little mods alllow for more fun than a standard 540i when the sun comes out.

My next door neighbour has just bought himself a 1969 Chevrolet Camaro SS with a race-tuned 5.7 litre small block American V8 with twin exhausts, and that makes my 540i sound like a gnat farting in a thimble by comparison, and even a screaming M5 3.8 would be humbled by the rumbling Chevvy V8, which my neighbour says has been dyno'd with 340hp at the WHEELS, never mind the flywheel

Mind you, he's too scared to use it on our wet roads cos it's the 4-speed manual, and he got wheelspin in all 4 gears bringing it home from Manchester a few weeks ago, and hasn't yet got used to changing gear with the window winder hand

Good point, but could you find a mechanically sound Alpina B10 3.3 for the same price I paid for my E34 540i 2 years ago (£4500 with 88k miles, full history and replacement Alusil engine at 43k miles).

The Alpina's an expensive, rare, precision scalpel for surgically slicing roads to pieces whereas the 540i is a cheap old blunderbuss for barging through the bends and rumbling lazily along the motorways at 2000rpm and not requiring anything other than bog-standard parts to keep it going

Thanks-I do really like all the Alpina's, M models and tasty BMW machinery from all ages and model ranges and don't dislike any of them, but I had to stick to a limited budget when I was on the car hunt, so chose the E34 540i as it was the best all round package for cost, power, space, spares prices and insurance ratings that I could find.

In 2 years and 30,000 miles it's been nothing but fun

I think we all own the best car, or we'd have bought a different one!!!