the Intake runners are a little differnt,
but an entire 2.1 intake runners and plenuim , even throttlebody ,will 
fit onto a 1.9 ..or vice versa. ..
not that there's anyreason the put 1.9 parts on a 2.1
  I put 2.1 stuff on 1.9's all the time....'everything'  actually. Every 
single 2.1 part from throttle body to tail pipe will bolt onto a 1.9 block.
How the plenum bolts to the top of the block differs a littlesometimes.
there are two kinds of  1.9 plenum, 83/84 is one type, 85 the other.   
Only one version of 2.1 plenum.

You weren't trying to put a left intake runner onto the right side , or 
vice versa were you ?

scott
turbovans

On 2/10/2013 11:44 AM, J Stewart wrote:
> The manifold pipes from a 1.9 and 2.1 are not interchangeable. How did I come to learn this? Well, I am (slowly) cleaning up a 2.1 to stick into the Blue Star I bought back in October. I've torn it down to the block and cleaned and/or painted everything, and one challenge has been cleaning out the threads where the a/c compressor and p/s pumps mount , as the engine I bought had neither. Anyway, the intake pipe on the left side was kinda crusty, and I had a set of pipes of a 1.9 that were in great shape. So, for the left side I decided to use the 1.9 pipe-I held it up to the 2.1 pipe and it looked to be identical. So I cleaned and painted that one. Went to install it today, and it would not line up to the airbox. It was just a bit off, but off enough that it won't work. I still had the somewhat crusty 2.1 pipe in the garage, test fit it and dropped right in. So... it looks like I'll be cleaning up and painting that one.          Jeff
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