can I use a 6 point harness as a 4 point? just don't install the sub belt???

 

No, that would not be safe - for a variety of reasons.

1) You greatly increase submarine risk by omitting the 5th and 6th point on a harness.
2) You will not have correct mounting points for the shoulder straps unless you install a harness bar (in conjunction with a roll bar).
3) You will not have sufficient rollover clearance with the factor roll hoops (unless you have a very short torso).
4) Stock seats are not designed to work properly with 4-, 5-, and 6-point harnesses (no holes for shoulder straps or sub-belt(s).

Please read this thread to see why it is a very bad idea to change any part of your factory restraint system without changing all elements (seat, harness and rollbar) together.

 

 

I'm confused... what do points 2-4 have to do with his question? He didn't ask about using the harness w/o a rollbar/rollcage or harness bar. He only asked if he had to use the submarine straps on a 6-pt harness.

I'd say, "no you don't have to use them, but you are compromising safety by not using them".

 

If you want me to ignore a potentially hazardous situation, then I will admit that only point 1 is directly relevent. Furthermore, point one is enough to absolutely, positively not install the system in the car (unless he has purchased a Schroth ASM 4-point harness to which someone else added the other 2 points).

However, due to the serious (fatal) consequences of the improper installation and use of 4-, 5- and 6-point harnesses in street-driven vehicles (that is all too common), I wanted to add more value to my answer in case those points had not been considered. I assumed that owenxguo's car is stock and he was considering the addition of a modified 6-point harness. If that is not the case, then all irrelevent points can be ignored.

Adding an aftermarket harness should not be about style, there need to be substantial risk assessments made and intelligent systems integration to make it work properly and safely.