What would happen if I were to only port the intake and not the exhaust on a turbo engine? Whether it be a small and or large streetport?

 

not much...

it really depends on the rest of the combination, particularly the turbo. all the pieces have to work together. my friend has 2 port templates, and he built 2 cars (basically). the car with the mild port makes good power everywhere, it did something like 380rwhp@15psi. the car with the big port made 370@15psi. the big port car really needs a larger turbo to take advantage of the port.

so you you had a big turbo, a mild intake port might help. going too big without opening up the exhaust as well probably will not be good. also if you had a stock turbo, any port at all is likely to do almost nothing, the turbo is the limiting factor

 

^^
I agree the exhaust porting has the most potential to really f-up (uh, change) the engine's power band.

So if you want mild street porting with as little downside (and upside) just doing the intake ports is a decent idea.

If you started to go into the large/wild street ports or bridgeporting without porting the exhaust you would be going down the path of getting all the downsides of porting and no upside.

Real world examples-
No one talks about how much more power the S4 TII engine can make over the S5 TII engine (because it doesn't) since it has primary intake ports that open up 13 degrees sooner.
An early opening street port gets you about 6 degrees sooner opening than S4 TII.

No one talks about how much more power a 6 port turbo-ed engine makes than a 4 port turbo (because again, it doesn't) even though it has a whopping 30 degrees later intake port timing.
A late closing (oops had to epoxy my side housings) monster street port 4 port will get you about 15 degrees later port timing than the stock TII port.