Cars Help with car mod engine swap

[SonicMarmalade]

Hi, I've always had a curiousity that the version 2 of the BAC Mono should have had a hayabusa style V8, like the ariel atom v8 or radical sr8. I tried doing an engine swap in Assetto Corsa car tuner, (from the ariel atom v8) and it is as fast as I expected, but handles completely differently. The duratec and rpe-v8 have similar torque, and can use the same gearbox, and weigh a very similar amount, so I understood it would be more difficult to drive, but expected it to be maybe 25-50% looser. It's completely different though, and now understeers off the throttle, and wildly oversteers on the throttle. I've checked the torque and power curves against dyno sheets from real H1-V8/RPE-V8's, and they don't look massively different from the real engines. Am I doing something wrong?

PS. I realise this is a pair of mods someone else made, and have no intention of uploading them for anyone else, and would 100% ask permission if I did decide to do that.

 

[SonicMarmalade]

Oh, another thing, the tyres drop almost all temperature in seconds, down to 15-20 degrees, and only ever get up to around 40-50 degrees, which seems unlikely for something of this speed. The original mono does it too. Any ideas why, and what can I alter to stop it?