Okay! After some anticipation, I have finally completed the challenge!
I realised that the issue was gearing. Everything else was fine. I had the gearing set to my needs, but then as I changed other things, I just left the gearing as it was, so after changing that my economy went from 4.98 to 4.47, and acceleration went to 9.8, and I just refined it from there!


Damn, I was so worried that I'd fail, but I'll just put that behind me
Here's the challenge for Hermann95!As I took too long to complete the last challenge, I won't put much thought into a story to go with my challenge for Hermann95.
Cottam Auto Group has just released a new GT car. The Cottam Parslow. It's a comfortable car with massive acceleration - 0-60 in just 3.2 seconds! And boasts an impressive 41mpg (6.9 lt/100km).

It is now up to you - the cheap sub-brand of CAG, to make a cheaper version, with equally decent stats.
RequirementsCost £20,000 or less
Man Hours 240 or less
Tameness 60+
Sportiness 40+
Comfort 30+
Prestige 45+
Safety 50+
Eco 6.5 lt/100km
Car Reliability 70+
You CAN'T Change:Bodyshell (But feel free to change the fixtures)
Chassis Type
Engine Placement
Drive Type
Platform Quality
Anything on bottom end
Head and valves
Head material
Anything on turbo except for max boost
Fuel system/config/intake
Fuel type
Fuel quality
Anything on exhaust except exhaust diameter
Gearbox or ratios (you can change spacing and top speed)
Gearbox quality
Tyre compound
Brake calipers
Number of seats
Anything in suspension
You CAN Change:Anything not mentioned in the above section.
If there's anything I haven't covered, or you are unsure about something, just ask! As far as I know, this challenge should be absolutely possible. I only tried it for about 20 minutes, but by that point all I needed was economy, and I think that will be the main challenge here.
Good luck!