I'm planing on making an intake plenum from carbon fiber and kevlar. It is for a turbocharged car, so it needs to withstand some pressure!

I mean I'm not necessarily recommending using a 90 Tg resin for a 350C application, rather just pointing out that your parts aren't going to melt and fall apart. What will happen is that if they are exposed to heat above their capabilities then the resin will soften a touch, which will certainly lead to print through. If the parts are under load and are unsupported, they may distort quite badly depending on their geometry and the degree of load etc. For example on something like a plenum, if you had a hose clamp on the inlet piping, this may distort the mouth of the plenum. Or if you had your intake piping bolted onto a throttle body, and this was unsupported weight that was 'hanging' off the front of the plenum, then this may distort the entire plenum.