Well there selling a APEX-I n1 universal exhaust brand new in box for $90
and
there selling a 13b racing beat lower half intake manifold for side draft for $100
what should i get

I have a 1991 N/A rx7 M/T

 

Are you talking about the DCOE racing beat *upper* manifold? I don't think they make a lower except for peripheral ports.

It's the upper half in this photo:
http://racingbeat.com/photos/18101.jpg


to use it you would need a DCOE style carburetor or DCOE throttle body and fuel injection, otherwise you have a paper weight... so it will require more investment to make use of it, significant investment. RB sells it for $130, and it's actually not a very good piece anyways, I have it on my car and it required alot of attention.

Apexi N-1 I don't have experience with nor am I familiar with their going prices so I'm not gonna touch that.

 

In response to your PM, asking if it really isnt worth it to go the RB DCOE route...

I will answer here so others can possibly use the information.

If after considering the price of it all in the end, you still wanted to go that route (I highly doubt it, it's one of those if you ask yer probably not type of things.) I would say do not bother with the RB upper, it's junk

The pre-renesis star mazda race cars ran sealed 6 port motors with DCOE carburetors, they have a specific one piece manifold that is a better solution than the stock lower bolted to the RB upper. You can get it for $300 from moses smith racing parts, heres a photo:


the site is:
http://www.msrparts.com

go under engine, then look for the one piece manifold.

It's better partially because it's one piece, theres no seam / gasket nonsense in the middle, and theres no 6PI actuator bullshit, no bushings, rods, all that junk is gone it is much better flowing, it takes alot of work to get the stock lower intake manifold to work this well, ALOT.