[mr0077]

Wayne,
Okay, here's the deal. Bob and I were addressing Kim's original question: he DOESN'T want a 4- or 5-point harness, so he's asking if a 3-point street-style system is better than an lap belt only [yes, it is], and if so, where does he install his upper attach point. None of us (not even YOU) know enough about his car to say with certainty how the installation should be configured. All we have to go on is empirical data, similar installations, and published data/guidelines. You need to read the posts more carefully, and not twist words or mischaracterize what people say. I never advocated the use of a 3-point over a 5-point system...I said go with a 3-point over a lap belt, and I tried to say that the 5-point system would only be marginally better than a 3-point system unless the 5-point system was installed with proper modifications to take advantage of the superior capabilities of the 5-point. Read my post and tell me where I said: "a three point without study is actually safer than a properly installed five point system"; "a five point system will tear out of a car (but a three point won't)". Once again, read the post...I said that "without roll cages and other...safety upgrades" the 5-point is only marginally better than the 3-point.
As a student of automotive safety for the past 40+ years (it started before I put seatbelts in my '61 Studebaker!) and a forensic engineer, I will tell you that I tend to trust the seat belt designs of the major auto makers (for their intended application), knowing the effort they expend in both design and testing. I also think that simply following NHRA guidelines for mounting a restraint system without properly strengthening the attach points is false security.
Quoting a rule book does not make anyone an expert. You didn't provide any backup for your information. You didn't note where NHRA got their requirement. Does anyone know? When someone complies with the NHRA rulebook attach geometry, how does a safety inspector know that the structural integrity of their framework is suitable without an analysis of their frame? Why not make them crash it to prove it is acceptable? That's as absurd as saying we would be better off to follow the NHRA rules blindly as a "known commodity than to attempt to creat a system by way of presumption".
Note that the early experiments in what a human could withstand (Navy rocket sled, 0-2500mph in 5.6 seconds, 2500-0 in 2.5 seconds over 400 foot distance, at average of 45+ g-force), and subsequent military restraint designs by Lockheed, General Dynamics, etc., use systems similar to NHRA, while General Aviation (Mooney, Beech, Cessna etc.) use systems similar to GM, Ford, etc. What's up with all that? Maybe it has to do with intended application, like Kim's original question...
For race purposes, NHRA et al is the way to go; for street use, I'll go with the auto industry. I agree with Bob P...for street use, a 3-point system with properly strengthened attach points, and with upper point at or above shoulder, or as high as possible if not above shoulder, is better than a lap belt only.
I guess we can agree to disagree.
Cheers
Ken Smith