Ive done a conversion on a mk3 1.8D Fiesta top speed 96mph. I put a new TD engine in, goes through the gears quite quick now but still the same top speed. Im using a Fiesta Si mk3.5 gearbox as i thought it would be better than a 1.8D box. Would say an RST, RS1800, OR XR2i box be better for a higher top speed?

 

if thats the case you prob have an IB5 gearbox, ideally for top end you want an mtx75. The ib5 is only good upto 100 really. Mtx75 boxes are found on endura td engines or 1.8 silvertop engines ie escort

I think the mtx 75 has a longer 4th and 5th gear