What all can you do with an intake manifold. I've got a 90 prelude, b20a engine(no relation to the rest of the b series, sadly enough). Had a b21, blew a rod, dropped a jdm b20a in. No vtec 6500 redline.

I should've put the b21 intake manifold on, but honda didn't have the gasket, so I just left the b20 IM on. Before I get my car inspected, I need to put the b21 manifold back on. Edit: B20 manifold has dual runners, but I don't have the vacuum lines to make them work? Thats what I was told, anyhow. b21 manifold(the one I would have modded) is single stage, one runner.

But while its off, what can I do to it performance wise? The runners, plenum and throttle body are all off, and in one piece.

I know I can get the throttle body bored out a little bit, but can anything be done with the plenum? I'd imagine that could be bored out a bit as well. I'm mechanically stupid, so bear with me, and please correct me.

A throttle body is just the piece with the valve in it, connected to the speedo cable. When you press the pedal down, it opens the valve gradually, controlling the amount of air into the engine. So when you bore out the throttle body larger, more air can enter the engine at lower rpm, giving better engine response and a little bit of power. So it effectively simulates a heavier foot on the acceleration pedal?

Now, you could also bore out the plenum(The tubular airbox thing between the runners and the intake IS the plenum, right?). But doing some quick math, it only increases internal volume by a few percent. Is it worth it?

Next are the runners. Again, you could bore those out some, polish them too. Would it be worth it? I know runner length is important, but what are the attributes for shorter and longer runner lengths(Can it be generalized that simply?)

There aren't any aftermarket intake manifolds for 3rd gen preludes, so that option is ruled out. And can't quite drop an h22 in yet. Although GSR IM are fairly easy to make fit. But seeing as how the stock redline is 6500, and cams are pretty much only designed for up to 7000, I'd be worried that manifolds designed for GSRs wouldn't match the powerband of a b20a.

So, the original question again-before I put my intake manifold back on the engine, what can I do to it performance wise? And where would yall have it done?

I'd also dearly love to pick yalls brains about ITBs, but thats for later!

Thanks yall.