How significant is the performance difference between a 2nd gen(s4 if it matters) upper intake manifold and a FD upper intake manifold? I have a FD upper laying around and have been wondering if it would be worth making it fit. I know I would have to port match to my s4 lower, match the bolt holes, and use a FD throttle body. Not sure if the gains(if any) would be worth the effort. Any help with my decision will be greatly appreciated!

Derek

 

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I believe the S4 lower manifold is not suitable for this conversion, as it's too different to the FD upper manifold. The S5 lower manifold is a bit bigger than the S4 one and can be ported to suit the FD upper manifold.

There wouldn't be much in it for a mildly modded engine, but as power increases it'd be a worthwhile conversion as the FD's TB is quite a bit bigger than the FC's.

 

There is no physical differences in size of runners or locations, between a S4 lower and a S5 lower.

 

Soul Assassin gained 30rwhp, but he also had it ported. But he had a lot of mods. I plan on doing it in the future.

 

The S4 and S5 lower manifolds can easily be made to work with the 3rd gen upper. Lots of people do it. The 3rd gen manifold flows much better than the S4 or S5 uppers. The intake runners themselves are physically smaller in the 3rd gen manifold much like the n/a's. This is strange since the throttlebody is so much larger. It promotes higher velocity and therefore more usable torque throughout the rpm range. Bigger isn't always better! The gains should be noticable with the proper fuel management system. I have retrofitted different size throttlebodies to factory ecu equipped cars with good results but they were all n/a's.

 

Two quotes from this thread by BlueTII about the putting the FD UIM onto FC LIM's:

"Here is the bottom of the 3rd gen UIM. You can see how I milled the holes to match up to the 89+ LIM studs (which is much closer to 93+ than 87-88 pattern is!)"

"Well, my car is Series 4. The engine is S5 "block" w/ S4 rotors. If you mean adapting the 3rd gen UIM to S4 LIM-that would be much harder as you cannot simply mill the holes out; they are very far off. It would probably have to be done w/ an adapter plate like Garage Vanna uses. I picked up my S5 LIM cheap- you could as well (plus the 2ndary runners are a little bigger in S5 LIM.)"

I didn't mean it couldn't be done using an S4 LIM,just that it's more work and the end result won't be as good. I figure if you doing to all the trouble of doing this, sourcing an S5 LIM is no big deal.