From knowing nothing to having a Thunderbird supercharger on an m20b27i

[Ether-D]

After some research, it's actually off of a 93-2000 saab 900 or 9-3 2.5l.

[Victell]

I had always thought that BMW throttle body linkage was designed to have an exaggerated early throttle opening curve as to make the engine feel stronger. This would be the opposite of what you want. My guess is that the tbird throttle body is simply too large for your smaller engine so it has difficulty modulating lower-volume airflow.

These are my guesses and I could be completely wrong about all of it.

[Ether-D]

The factory m20b25 one is reduced at first and then increased as the plate opens (Saab one is the same). The ford one is about the same size as stock, but it has no increase or reduction, just a lever on a throttle plate. That's what I think the issue is.

[The Dark Side of Will]

My dad has a '75 Jaguar XJ6 with Chevy TPI V8, 4L60E trans and 3.31 gears. The TPI throttle cam was like the Thunderbird throttle cam you described... It was actually difficult to leave a stop light without chirping tires. He swapped the throttle body from a '90's LT1 that was identical except for a progressive throttle cam. The car was much easier to drive slowly and smoothly after that.
I had the same experience with my Caddy Northstar in my Fiero... The OBDI throttle body I had to use with my first engine computer had a pretty linear throttle cam. When I swapped to my current computer I had to install an OBDII throttle body, and it had a more progressive throttle cam. The car's much easier to drive slowly now also.

[Ether-D]

Wait a minute, that north star-ed fiero was you, Will? Awesome.

Also, I decided to go ahead and try to mount up the new TB to the old u-turn for now. I've got about half of it done. Throttle cable stuff and tps calibration left to go.

[Farbin Kaiber]

Or an air restriction in the intake system somewhere, like the intercooler or that 180 degree bend. I think this is most likely.

This, I still think that my original question and concern was well rooted in logic, and I think it's the issue as well.

Plus, since I am not modeling the flow, just spitballin' but the tightness can hamper flow, right?

[Ether-D]

This, I still think that my original question and concern was well rooted in logic, and I think it's the issue as well.

That may have an effect on overall air flow, but this particular problem isn't at all about too little flow. It's about too much air flow too soon. It needs to be slowed down at first. That's what I'm working on currently. I'll let yous know *when* this fixes this problem...:)

[Ether-D]

What Lorin was referring to was the belt slippage and subsequent trailing manifold pressure, btdubs.

[Ether-D]

I'm letting the silicone cure up nice over night. I'll wrap it up in the morning. It looks so much better without that damnable Ford TB in there. So now my car only has BMW, VW, Saab, Eaton, and Mini parts in it. Awesome.

[agent]

And a realty sign.

[Ether-D]

And a realty sign.

Yeah bro, but that shit's custom...

[Ether-D]

OMgoodness. That totally fixed the jumpy throttle problem. The first 2/3 of pedal travel opens the plate about 1/3. Progressive throttle opening, what a fuckin concept…FORD! So much better. Before, I couldn't raise the rpm up to 1500 with the pedal. It would jump to 2000-2500 then I'd have to beg it to come back down even a little. Now I can go to 1100, 1150, whatever I want. Never use a non-progressive throttle body if you want to retain factory drivability.

[The Dark Side of Will]

Wait a minute, that north star-ed fiero was you, Will? Awesome.

Also, I decided to go ahead and try to mount up the new TB to the old u-turn for now. I've got about half of it done. Throttle cable stuff and tps calibration left to go.

Which Northstar-ed Fiero? There aren't many, but there's more than one.

[Ether-D]

Which Northstar-ed Fiero? There aren't many, but there's more than one.

Didn't you post a link to one? If not you, someone did. Maybe Q5Quint. That's the one was talking about.

[Ether-D]

On another note, I'm noticing that my AFRs have been creeping up again after the TB swap. Not so much at low RPM, mostly when I start to go into boost. Then today, after re-calibrating my TPS and IAT sensor, it's gotten really high. Coincidence? Probably. I know that in the past, my cars have loved to try to trick me. So I guess I'll replace the fuel filter to see if that helps. If not, I'll need to buy a fuel pressure gauge to see if the pump is taking a shit. And it's two weeks to the Brodeo. FOCK!

Ideas?