I bought a '91 900T a few months ago that was for the most part very well taken care of. The previous owner had a 2.1 head installed when the head gasket needed some love a few years ago, and I asked if they did the intake manifold to match at the same time.

He said they did.

They did not.

So my question is has anyone had a car with this setup, and what did it drive like? Mine is acting weird, and I've fixed a bunch of things already but I am wondering if I'm chasing a symptom of the airflow just going turbulent at higher RPM...

At high RPM and moderate to full throttle it falls on it's face, knocks a little but. Feels sort of like the timing is super retarded, but it's fine.

Any experience?

I did the opposite, 2.1 intake and 2.0 head and it ran sort of like that you described. It was many years ago at this point but I remember it being pretty bad right around the transition from vacuum to boost, once it got going it was ok but it definitely did not run correctly. Do you need a 2.1 manifold? I'm pretty sure I have one laying around you'd be welcome to..

BTW if you remember that nutjob that used to post on saablink with the convertible that he systematically took apart of spray painted, I believe he was running a stock 2.0 intake manifold with a n/a b204 head, so anything is possible

I was going to put a wanted ad up for a manifold actually. I think I have a 2.1 fuel rail kicking around somewhere, but if you have one to go with it I'd happily throw you some money. It's pretty irritating to have a nice C900T that I can't stick my foot in when I'm driving around town.

Thanks for sharing, I wasn't looking forward to probing out all the sensors and checking fuel pressure under load and all of the other upper level diagnostic crap that I was starting to worry was going on.

To follow this up, changing the manifold made a huge difference. Pretty much totally got rid of the low boost / misfire / hesitation symptoms. Huge thanks to hutch for the manifold!

Before re-assembling I fit checked the 2.1 gasket to the manifold and block, and all of the ports on the gasket were too narrow by 1-2mm, so I did my best to gasket match the intake with a razor blade. I feel like it was 5-10 mins very well spend what with how much of a pain it is to get the intake off.

The offending 2.0 manifold, and a B202 missing it's induction system....

I realized I don't have any photos of this car. I need to get the fleet together to get a few shots of everything!