gearing

kingprawn

Newbie
Points
51
Car
bmw525td
Hi I have a 525Td it has a custom intercooler and the chip has been mapped specifically for my car and on my car it has a standard 5 spd box and a 2.64:1 diff. the engine produces 190 BHP but I'm not sure of the torque increase but it is significant.

I have a six spd box from an e60 BMW530d and a lsd of 3.23:1, I intend to fit; the gear ratios in both boxes are the same with 6th gear being 0.8:1.

can anyone advise me if lowering the diff gearing will provide better driveable acceleration across the range or is the higher gearing as standard the better option?

regards Andy
 
Hi and a warm welcome to TorqueCars. I would say with the BMW range as a whole they are built as Bahn cruisers and have quite high gearing.

For the ultimate setup I would get a fairly close 1-3rd and then go standard ratio towards the top end gears. As a compromise just go with closer gearing across the entire box.

Bear in mind that your wheel size will alter the gearing as well so if you plan to put some massive 22inch rims on it :lol: get some very close gearing.
 
Hi and a warm welcome to TorqueCars. I would say with the BMW range as a whole they are built as Bahn cruisers and have quite high gearing.

For the ultimate setup I would get a fairly close 1-3rd and then go standard ratio towards the top end gears. As a compromise just go with closer gearing across the entire box.

Bear in mind that your wheel size will alter the gearing as well so if you plan to put some massive 22inch rims on it :lol: get some very close gearing.

My wheel size is 16" with 225/55x16 tyres would like to keep it there;

Without altering the gearbox ratios do you think the 3.23:1 diff would be an advantage or a drawback? the overall ratio withn 6th gear and the 3.23 diff brings it back to more or less std.
1st is 5:1, 2nd is 2.88:1, and 3rd is 1.75:1, 4th 1.20:1. in both boxes!
 
It depends on too many factors. Ideally you need to match your gearing to your power output peaks. Personal driving style comes into it a lot.

My gut feeling is that you will prefer the car with the 3.23:1 diff ratio and it will feel quicker.
 
The change to a 3.23 diff,

will increase your acceleration ability by the percentage change in overall ratio.
 
The change to a 3.23 diff,

will increase your acceleration ability by the percentage change in overall ratio.


Hi thanks for your input another thing I'm going to try is removing the catylizer I'm going to make a dummy intermediate straight through pipe I have heard some people say you can gain up to 20%? not so sure about that! I will soon find out!

regards Andy

P.S. I will change the diff first which will let me know what gains can or cannot be made?
 
Hi thanks for your input another thing I'm going to try is removing the catylizer I'm going to make a dummy intermediate straight through pipe I have heard some people say you can gain up to 20%? not so sure about that! I will soon find out!

regards Andy

P.S. I will change the diff first which will let me know what gains can or cannot be made?

Removing a cat might net you around 2 to 3%. Assuming it's in decent working condition. They are made quite well now. Removing it might get you tagged for emissions non-compliance. It may be better to look for an after-market high-flow cat with larger inlet and outlet pipes than you have.
i.e. if the cat entry and exit pipe diameter is 2" increase this to a 2.5" type with a high-flow core.
 
I'd agree there, a sports cat will give almost the same power gains without the emissions issues.
 

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