Tii Intake Manifold

[tomphot]

I’m in the process of rebuilding the original engine for my ‘72 Tii. 
The engine in the car has an E12 head and aluminum intake  and runners.

I’m going back to the original manifold intake and plastic runners and 121 head. 
I just took off the aluminum intake and noticed it was a good bit bigger than the one that’s used for the plastic runners, both in length and circumference.  
What effect does this have?  

[Conserv]

Tons more power…. ?

 

Actually, I haven’t a clue, Tom. But I’m not aware of a measurable/advertised horsepower increase accompanying the changeover to the aluminum intake runners et al. 
 

On the other hand, this increase in the plenum size feeds into the need for the firewall notch on E12 cars…

 

On my ‘73, I had the intake manifold and four aluminum intake runners (and the exhaust manifold, for that matter) extrude honed for improved flow. But when I took a look at the cavernous plenum, I thought, “No, a smoothed interior surface probably can’t improve flow in such a large vague space!” (OK, these mods weren’t necessarily dyno-tested! ?)

 

Perhaps someone can tell me now why my instinct was wrong and why I should have that big ol’ plenum extrude honed.

 

Best regards,

 

Steve