[Savage GT]

The PCS chassis is the easiest way to go, but obviously chassis cost+ motor pod cost + axle cost + gear cost.
If you are lucky to have round wheels and carful removing them you can remove and reuse the wheels on slot it axles with a drop of glue.
Re-use the stock motors.

Pendles part No.s if you wish to go that route:


SIGI27BZ x2
Slot.it Inline Crown 27t Bronze
C8547 x2
Scalextric BMW E30 M3 PCR Chassis
SICH110 x2
Slot.it Inline Motor Mount 0.5mm Offset Classic DTM
SIPA01-45 x2
Slot.it Steel Pro Axle 45mm
SICH106 x1
Slot.it Motor Mount Screws M2.2x4.5mm
SP101003 x1
Sloting Plus Universal EVO Guide PCS

With discount and postage, will work out around £20 per car.
Granted, this now makes each (in your case) a £50 car, but it will at least perform adequately.
You will need to trim the length of the guides down.

I have done this on my Sierra/BMW E30 pair, but I also added alloy wheels and an SRP 16k motor