Tuning suggestions for 728i

[tommo163]

Hi,

Does anyone have any suggestions for tuning/modifing a 728i for a bit more ooomph without breaking the bank or stepping too far away in terms of originality?

I am looking at a custom fuel pressure regulator and a new exhaust but I'd welcome some other suggestions.

Many thanks in advance.

[Hit Man X]

Diff swap will be the biggest difference, 728i came with a 3.64:1 as I have read. Since these are Ljet controlled with an adjustable distributor, I would try adding a touch of ignition timing. Unsure if the 728i was designed to burn lower octane fuel or not, if so, add 2-4° and run high octane fuel. This has always yielded nice gains for me in the past on vehicles. My old Ljet turbo specified 27° BTDC @ 2300rpm, when I bought it the timing was severely retarded around 19-20°, pathetic. Just bumping back to OE spec helped immensely in how the vehicle drove.

I am unsure if they run an oxygen sensor or not, I lean toward no. If so, they should idle around 1.5% CO when hot at idle. If you are too lean, this will change throttle response and part throttle power.

Playing with fuel pressure is not going to help and the stock exhaust is very free flowing.



Just my thoughts.

[andyleonard]

I put a 745i LJet turbo on my 84 728i and left the diff. Goes well. No oxygen sensor except for wideband.

[Thradya]

Look for euro high compression m30b34 and swap the block leaving ljetronic in place? That's my plan anyway.