Rear Diff Swap info...

[e34.535i.sport]

I've Been searching around for some time as you may have noticed for an upgrade that will give some noticable increase in acceleration for relatively low cost. Difficult to find? Maybe not.

Upgrade Options:

1. Turbo - Way WAY too expensive for most!

2. Supercharger - See above.

3. Engine Swap - See above.

4. MAF conversion - Relatively cheap at around £250 but mixed opinions on the improvement of acceleration and reliability of the unit. I also don't like the idea of splicing the original wires to make it fit. Tempted to go for this one, but too many if's and but's.

5. EAT Chip - Clearly a positive upgrade for £120 or so. Everyone running one reports a marked improvement in acceleration and power. The only negative i can see is the need to run on higher octane fuel.

And finally,

6. Rear Diff Swap (Higher Ratio) - Now, this is an interesting one which i have researched thoroughly, and according to my calculations the best bang for the buck. I'm confident you could pick up a used Diff for anywhere between £100 and £200, and get it fitted for around £150. The theory behind the swap is with a higher ratio acceleration will improve as the revs at speeds will increase (how much depends on what ratio you go for), but top end will decrease. My car is limited to 147mph, which is a speed i will probably never see living in this oppressive country. However, I would either way sacrifice top speed for more low end acceleration. Gears will be shorter too, but that won't bother me. The only negative point i can find is an apparent reduced mpg on a run.

I Quote from Bruno's Site: "a 3.91LSD diff. from a 525iA installed to replace the stock 3.46LSD in the 535i will give you a mileage loss of about 2/3 mpg on the highway. But it is more than justified by the drastic increase in acceleration."


Now, the way i look at it the chip is the obvious choice due to the small initial outlay but it seems that in the long run the diff swap would work out cheaper. Example: Lets say it costs me £350-£400 for the diff swap total. The EAT would cost £120 to purchase and then an extra 8p per litre for the higher octane juice. an extra 8p per litre equates to an additional 36.4p per gallon, and lets say i'd average about 16mpg (about right for 95% city) doing 12000miles per year - using 750gallons of petrol, that would mean an additional cost of £270 in fuel PER YEAR! I make that £390 in the first year, then £270 the next year and so on and so forth. *And thats not taking into account any increase in fuel prices.

If you look at it closely it seems that the rear diff would be less costly in the long run, and obviously give you a serious increase in acceleration. I am looking at this clearly from an external point of veiw as i have not done the swap yet, and others will be able to shed more light on the situation.

What do you think?

[Sam-Son]

after having an auto with a 4.10 open diff going to a 5-spd with a 3.15 LSD the car feels like a rocket. But I also have a TMS chip, and a B&B Triflo if that makes a difference

[Barney Paull-Edwards]

There is a a complete rear end from a 518 on Ebay. That should be a pretty low ratio.Agree with your thinking,doing a JonK in UK would cost more than the car by miles,to be honest, even with friends in low places, my twin turbo set up that was too fierce cost £3400,and that was cheap.You will loose a lot of top end but if that doesnt matter then a numerical higher diff is the cheapest way to get out of Toxteth in a hurry!

[leicesterboy15]

The EAT chip may be the ultimate but how about a compromise with another chip that doesn't need high octane? I have a superchips chip and you can fuel it normally and the MPG is the same if not ever so slightly better. My 535is was fine between 3000 - 5500 RPM, it delivers what it promises but out of this band it could be slower that you would expect and the chip really helped with this.

Bottom end it would pull well from just below 2k (no more getting caught out by torquey diesels around town) and at the top end there was power right up to the red line where as previously there was no point going over 5500RPM.

It might be a good compromise for a budget if you can actually source an alternative chip. If you decide later to trade up you can usually get what you paid for a used chip as they don't really depreciate or wear with time.

Maybe worth a punt?

[Dave M]

a 3.91LSD diff. from a 525iA installed to replace the stock 3.46LSD in the 535i will give you a mileage loss of about 2/3 mpg on the highway

Yeah, the chip will cost you extra $$, but so will the diff. If Brunos calcs are correct (its likely decreased by 1/3, not 2/3, and that seems extreme), you stand to spend a lot more on pertrol with a 3.91. The relative ease of chip installation and removal should also be considered. My vote is for the chip.

Dave M

[e34.535i.sport]

Hey guys. Dave its funny you should say that because i've just been discussing the ease of chip installation in comparison with a friend of mine CaptainGoSlow. He's also considering upgrading his e36. Really I would love to swap the diff out with the help of the captain to make sure its done correctly, but because of the weather and lack of daylight at this time of the year its putting me off. I also like to research things thoroughly before i go ahead and do them. I'm looking out for a 3.73 or 3.75 ratio at the moment out of a 89/90 525i for a good price, I wouldn't really want to stretch to a 3.91 as first gear can already feel a bit short at times. I know motorway mpg would decrease but i was under the impression Bruno meant you would lose 2 or 3 miles per gallon when he says that? If he means you'd lose 1/3 or 2/3 of fuel economy i could never afford it! At the moment i'm getting about 16-16.6 around town, and about 23-26motorway according to the OBC. I don't mind this too much as i knew what i was getting into when i bought the behemoth!

Just done a bit of research on the superchip, and from what you say Rak it does sound worthwhile. According to their results an additional 18BHP on the 535i and obvious torque gains lower down like you have. Priced at £293 its steep but if the difference lower down is noticable i'd definitely pay that price on your recommendation. I just can't seem to find a link to buying one - anybody help me out here?

If i were to buy a superchip would it then be ok to change the diff at a later date with the chip?

[leicesterboy15]

£293 sounds really steep! Especially considering the EAT is what? £120? Maybe try and source it from the US as it may well be $293 (£140 ish) which is more reasonable or scour the classifieds for a second hand one because as I said if treated correctly they will not degrade.

Another option is to 'copy' a chip so get hold of a non original one - or shouldn't I have said that?!

[leicesterboy15]

How about a custom mapped chip? That is likely to cost less than £293!! Don't know what these guys are like bu its worth a phone call...

http://www.chiptuners.co.uk/index.htm

[Barney Paull-Edwards]

That price is fair when you consider the developement costs, better idea than diff swap unless you are lucky enough to find a good one.

[e34.535i.sport]

Those guys seem like a professional outfit, and i've come across another called paramount performance that also looks good. These places cost more than the chip, but I would assume similar results... The good point about a remap is that it's apparently undetectable (i.e to insurance companies)

I have a superchip dealer not too far from me, so I will pay them a visit in the week and see if i can get some more information and maybe a deal on one!

I'm really excited... Like a kid at Christmas!