i might pick up a 90 civic DX monday with a blown engine. I have a d15 with the MPFI swap already done to it that i can swap in, but i also have a rebuilt D16a6 (SI) head that i can put on it... I'm planning on using a zex kit or a low boost turbo kit and so i have a few questions...

1. What will my compression ratio be?
2. Will the head give me more hp than just the MPFI swap?
3. If its not worth swapping the head on, will the SI cam be worth swapping in?

I searched but couldn't find any answers

 

I'm pretty sure the DX and SI heads are the same, it is just the blocks and electrical stuff (dpi/mpfi) stuff that is different.

If the head is rebuilt, it might be worth replacing, but I guess I'd wait till I broke the old one.

I'm not sure if the cams are different.

 

1990 Civic SI:
108hp @ 6000rpm
100ft/lbs @ 5000rpm

1990 Civic DX:
92hp @ 6000rpm
89ft/lbs @4500rpm

That would be a big gain just from the MPFI swap, i know the cam is better but i'm not sure about the head... i've heard that the DX has higher compression?

 

Where did you learn that the cam is better? It is more than possible, just some info that I have never heard.

You are right that increase is big for just having MPFI. The other main difference is the entire bottom end. I believe the pistons and rods and definatly the crank are different in the DX engine. This contributes to the power gain, but I believe that the better injection system (MPFI) is responsible for most of it.

review: head is the same, blocks are different
DPFI vs MPFI differences

If you are sure about the cam, then go for it and switch it.

 

The head is the same, but the cam and valvesprings are different. So, there will be no difference in compression, unless you use a D16Y8 (96-99 civic EX) head gasket, it is thinner, and will give you about a .2 bump in compression. also, when the head was rebuilt, was it shaved any? that will give you a C/R gain as well.

If you don't want to increase C/R, then just swapping in the cam and valvesprings will be worthwhile.