This may sound a little strange, i may be looking into this a bit too much and it may be alot easier to sort out than i am making it but here goes...
So i have written a song that is quite heavy and upbeat for the majority however it has a quieter chilled out clean intro. Now when i wrote it and i sit and play it alone on my guitar it all sounds fine but when i came to record i noticed that the intro is in 4/4 time and the remainder of the song is 3/4. i have done this on a couple of other songs and it has just been a case of a change in drum beat.
when i worked out the bpm for the main bulk of the song it needs to be at 163bpm. this though then makes the intro sound really slow and laboured due to the extra beat so i tried playing the intro to a 3/4 beat but this just isnt working. I then tried increasing the tempo for the drums on the intro (i am using a drum machine by the way) but it is really noticable when it changes to 3/4 that there is a tempo change.

so does anyone know how to solve this or is there a way of setting a faster tempo for the intro but calculating it so it sounds right?
Thanks for your help in advance.

(that probably makes no sense but its the best explaination i can give. sorry)
its probably best to just go with your first instinct
you will probably need to post a sample so people can have a better idea of what your trying to do.

i have no idea how to help tho

best i can do is bump back to front page and maybe someone will help
you consider 163 bpm slow? 163 bpm in any (conventional) time signature isn't slow.

honestly, i'm not sure what you're asking for.
Anfangen ist leicht, Beharren eine Kunst.
I'm not sure what you mean either.

As long as the bpm stays constant and you're counting the same type of notes (for example quarter notes, in the case of 3/4 and 4/4) there won't be any tempo changes. Keep the bpm constant and you should be fine switching back and forth between 3/4 and 4/4.

Unless I'm missing something, like you want the 3/4 measures to take up the same amount of time as the 4/4 measures, but that's a different story.
Only play what you hear. If you don’t hear anything, don’t play anything.
-Chick Corea
Listen to Dethsupport by Dethklok. The intro switches from 7/8 to 6/8 and back every measure.

Really, I'm not sure what your problem is. You say that it sound heavy, so I'm assuming you're writing metal. Which means that all convention is thrown out the window. Change the tempo mid-song. Change the time signature. It'll allwork out, if you do it right.

There's no problem, as far as I'm concerned, with having the intro in 4/4 and the rest of the song in 4/4.