So I pulled the inlet manifold off my FD. I noticed it has 2 sets of secondary butterfly valves. One set mechanical, the other solenoid/vacuum controlled. The mechanic set don't fully open and get to I would say 85 - 90% open. There doesn't see to be any way to adjust this and it doesn't seem like anything is really wrong. Is this just how they come from the factory. Is there a fix for this or does it not make a huge difference? The vacuum activated set get to 100% perfectly well.

Thanks

 

Yeah, its pretty normal on FDs and worse as the plastic bushings in the primary to 2ndary plates connecting link and throttle shaft bushings/seals wear.

I have corrected this on both the FD throttlebodies I have modified for flow in a couple different ways.

On my first TB I made new connecting links for 1:1 opening ratio instead of the primary first throttlebody movement.

On my 2nd TB I just smashed the 2ndary shaft linkage relief stops so the primary plate doesnt move without the 2ndaries moving and tigtened up the shaft nuts with the slop biased toward 2ndary opening.

Same result- looks OE.



The awl is pointing at follower that is attached directly to the 2ndary shaft. The cam on the lower side of the fllower is bent up against it. You can see the slot in the connecting link which no longer gets used. The linkage is adjusted so the primary shaft pulls the 2ndary shaft from the start instead of sliding up that slot.

 

This is the 1st TB with new linkage, but my OE linkage one works same.



The mods are porting, halfshafted primary plate with flathead screws, contoured 2ndary shaft with flathead screws and the 1:1 opening timing.

On the OE linkage TB I did the same, but used low profile buttonhead screws instead as it is very hard to center the throtle plates in the TB bores with the tapered fit of flathead screws (they want to self-center on taper as tightened).

 

You're describing normal operation. It's fine. Make sure your tps is adjusted properly and press on

 

Thanks for the reply. Interesting it looks like it's quite warn here. It might not be too hard to make a new linkage. Probably take a few tried to get the length right though. Mine is stock, I'm trying to make it run at a little better than it does now.

 

You're likely right, I can imagine much difference from 90% to 100% throttle but I guess every little bit counts.

 

Depending on the trajectory of the entering air, 90% "could" flow better or as well as 100% open - you'd need to flow test the assembly to be sure. Somebody (Howard Coleman?) has likely done that.

 

+1 the old timey road racers would have tested throttle opening vs either air flow vs power. on an NA there probably would be a butterfly angle that worked best, and it might not be 100% open.
but FD's have turbos, so its less important. if you hit the Advanced Search "Speed of Light" has done some airflow testing on the FD stuff, and posted results

 

for the most part it's a non linear relationship between the opening area of the throttle and the amount of air that flows through it. going from 10-20% open moves a lot more air than going from 90 to 100%.