Safety vs power to weight ratio (long)

[ZR8ED]

Ok this might sound like a rant, and maybe it is. After a lot more reading here and other sites, as well as many conversations here at work/car club etc etc. The topic of weight and safety, and the search for the all mighty power to weight ratios.

 

Over the years I have seen well built cars, poorly built. super tough and rigid, wicked fast cars with more flex than their owners care to openly admit, and lots of variations in between.

 

I like to drive my z hard. Always have. I have a very strong safety work ethic. It has been driven into me by the company I work for, and I have come to understand and actually practice this mindset. My long time mechanic and friend is a long time racer who understands the importance of safety on and off the track. When I first started playing with Z's I just wanted to make the car go faster, and safety was not much of a factor "its a sports car, the brakes must be good" or so i thought. After my first few mods, my mechanic started to talk about safety (I was also a young driver at that time) He really stressed about making sure the car was safe BEFORE taking it to the track..heck before making any high performance mods.

 

We worked on making my car (13 years old by then) mechanically sound. we worked on handling and suspension. We worked on minor upgrades to the brakes (ss lines, better pads, remove dust shield etc) We upgraded the tires and rims to aid in handling and braking. THEN we built a kick ass 8000rpm redline killer N/A engine. This was over a period of 6 years at least. Yes we upgraded the engine slightly during this time, but not extreme. We shaved the head, put in a hotter cam, headers, and other minor mods.

 

Over the years, we had taken lots of what I thought were unneccessary weight out of the car. I had it down to 2780 with me in it. After that, the car started to get real quick, and the thoughts started to turn to "what if i crash this thing at 140+mph?" and i knew the answer. and I didn't like it. I added 4 point harnesses, i added a 12 point cage, I added 5 strut braces, I added other triangulating braces where reasonable on a mainly street car. I added even larger brakes and rotors. Even larger rims and sticky tires. More ground effects and aero mods for some level of safety margin.

 

Well since then, the weight has crept back up, and it sits at 2900 with out me in it. I've also made the car quieter and more comfortable at the same time so that has also added weight. but I degress.

 

My point I'm trying to get accross here is a high power to weight ratio is great, but does nothing if you twist up the car, or worse DIE when this 30year old car folds up around you. The crash testing done back then is not even remotely comparible to what is done these days where they build crumple zones etc to save the occupants of the car. etc etc.

 

I am every bit as guilty for doing this as well. I've learned, and all I want to do is pass this info on so someone else might learn. I have had friends have their 2 ton early 70's Chevelle stripped down and have 500hp and stock brakes fold it up and be lucky to be alive after a normal speed car crash.

 

Our little z's came with 135-150hp depending on year. Many of us are easily doubling these numbers, and many more tripling or even more the stock #'s. getting past the stock 120mph top speed is a piece of cake with minimal investment in mods.

 

I have personally talked with Z owners who run much faster 1/4 mile times than me confide to me they would not want to try and follow my Z around a road course for fear of falling off the road, not being able to brake properly, and possibly twisting the car all to hell in high G turns. To make it clear, their cars are wicked fast, but other wise stock in other areas, and if they crash, many have removed bumpers, side door crash beams, sway bars, as well as all the other kinds of things we can remove from our cars to make them lighter.

 

I am not saying what they are doing is wrong for them. Knowing your cars limitations is very important in keeping you out of situations your car can't get you out of.

 

What I am saying is that (me, you, and people in general) should consider safety when building a high power exotic from a 30yr old sports car. Doing 160mph is no fun when the car is getting floaty and practially air borne, and you have no bumpers, stock brakes etc..

 

Sorry if this sounds preachy. I just thought I should put this out there for all the new guys that come here with money to burn on their car, or who have wild aspirations for their car. Putting on high performance brakes on your car is not just for bling bling. They are there to stop that rolling steel NOW!! when you need it most. Bragging rights for brakes is cool and everything, but it has a very practical use as well.

 

Consider this when you are trying to keep your car light. Buy light weight parts if you like.. go on a diet. Dropping 30lbs from you may be much easier than dropping 30 lbs from your car. Don't sacrifice safety to increase your power to weight ratio.

 

And if your really building up an engine (300rwhp)++++ don't worry so much about weight... worry about safety first.. do what I do now...turn up the boost to compensate for the added weight of my safety equipment. hehehe

 

Peace.

 

I'd hate to hear about one of you guys getting seriously hurt or killed in your Z after making it your dream car only to have it fold up around you.

[Guest ON3GO]

very awesome and well thoughtout rant!

i for one was like that, and im glad im not now.

at 1st i just wanted to run 11's and thats it..

well i saw that was a stupid way to even consider building a car, even worse building a Z-car.

Now i have a Z car that has every single suspension mod you can think of and HUGH brakes and good tires and wheels.

and no motor.. well ones being built but still.

and as soon as i get money a roll bar is next!

 

but yes i dont want to see somebody on here lose there lifes because of these cars we are building..

heck i worry were some of us are, like Brad D and others... havent seen him and a few others on the site for a LONG time.

 

mike

[datsunlover]

Funny... I have lots of similar thoughts on this.. After the past few months welding up my Z, I came to the realization that "If I crash this car and anything over say.. 40 MPH, I'm really gona get hurt..cause it's gona fold up around me,," At that point, I welded in a subframe of .100 wall 2.5" square tube. In adition to that, I am going to weld a tube across the front bumber-shocks and paint it black; I like the no front bumper look, but I have visions of my hood coming through the window if I hit something with my front end! And as for mods, the first one on my list is definatly front brakes! And before I take my engine past stock performance (or drop in the 302 I want..) I am going over the entire suspension system and replacing..well, probly evrything! I have been in a few crashes, and in LOTS of 'near misses' (one just last night in my truck) and I fully understand what can happen in an emergency situation if your vehicle isn't "up to par". I need front brakes on my truck, and I was lucky enough last night to slow down in time (rear end was starting to drift around ) and I missed the moron turning left in front of me, but not by much!

[technicalninja]

Saw a picture of a 76 that got slideways and hit a pole at about 45 mph. Took the hit 6 inches aft of passenger door forward edge. Crushed body all the way into transmission tunnel. If a passenger had been present legs would have been totally crushed and they would have been lucky to live. Driver was not hurt and walked away.

A cage would have helped alot and will give nice stiffening gains. I don't think a 6 point would have helped. Lucky driver!

[Guest Nic-Rebel450CA]

Oh come on now, what's wrong with stripping it down to a tin can and stuffing 2500 HP under the hood? It will be sooo fast!

 

Hell ya it will be fast, it will be so fast you wont even need life-flight cuz you'll already be dead. They'll be cleaning you up with a pooper-scooper and a vacuum.

 

Very good post ZR8ED, nice to have good opinions and information posted

[johnc]

Safety is much more fundamental then what even ZR8ED posted above. Its doing things like:

 

1. Periodically checking EVERY fastener on the chassis and suspension.

 

2. Replacing ANY fastener that has even one damaged thread, rounded heads, galling, etc. with NEW OEM or better.

 

3. Properly torquing EVERY fastener with a torque wrench (you'll need two torque wrenches, a 1/2" and a 3/8" swivel head).

 

4. Periodically checking every suspension and steering bushing.

 

5. Replacing ANY bushing that is cracked or worn with NEW OEM or better.

 

6. Constantly inspecting all parts of the car with the thought in your head that your life depends on the proper functioning of that part at all times.

 

When I'm working on a customer's car, I'm constantly throwing away fasteners I take off the car. I sometimes get complaints about having to pay for new nuts and bolts, but after I explain my thinking, my customers realize the benefits of my "wastefulness."

 

Remember, these cars are 30 years old and in most cases, we have no idea what the car has gone through before it came into our hands.

[gramercyjam]

I think the post is WAY preachy. Bumpers aren't a safety item. Power to weight ratio is not a crash worthyness issue.

[JMortensen]

I've got 2 things to add to this:

 

One, I was rear ended by a Firebird doing about 50 mph in my 1st Z. She said she never even saw me, never touched the brakes. She pushed my car into head on traffic where I was hit by an Acura Legend head on, about 25 vs 25 mph would be my best estimate on that one. Not one of the windows in my Z broke. Not even the hatch. The Firebirds low nose hit in the right rear tail light area, and pushed the car in at least a foot. The front folded up to the rad support, then only about 1" farther. These cars are pretty tough. I had a broken nose, and my wife hit her head on the dash. A guy I know got T-boned in his 510, took it right in the driver's door by a Ranger at about 35 mph. He walked away sore but no serious injuries.

 

Two, a badly designed or built cage is potentially disastrous in a crash. I don't think a full cage should be put into a car that isn't driven with a helmet, just because of the potential head injuries. Even with padding, I think they just aren't safe. A helmet is the only way to make a cage work to your benefit. Maybe if the seats were lowered and 4 point or better harnesses were used, it might be ok, but IMO the roof of a Z is too close, especially with stock seats, to a 6' tall person's head for a cage to be used on the street.

 

Jon

[BillZ260]

I like the post, keeps what is important in our heads. I would like to see some diagrams on where and where not to modify your chassis. I don't want a full cage in my car, but I think it could benifit from having more than strut tower braces and and autopower SCCA bar in it. So has anyone posted any structural mods that can be easily and inexpensivly added? I currenly have the Paraska style sub frame connectors and the above mentioned items. What else can be done to keep me SAFER in a front or rear end collistion.

 

Also, the bumpers on these cars really will NOT make that much differnce in a collision. If you think so, then you are kidding yourself. They are a minimalist attempt at meeting the current safety standards of the time.

 

my .02.

[SleeperZ]

All excellent thoughts and points, including grameryjam's.

 

I know my Z isn't particularly safe structurally. I do not intend to increase power by much more, if any, but what I've got now is dangerous enough. The brakes are good, but brakes are limited by reaction times and tires, which is why I seldom speed in the car faster than my trap speed. And I limit how much driving I do, reserving it for track events and the occasional weekend cruise. And I have no bumpers, but I agree, they were installed by the insurance companies wanting to limit their costs in low speed bumps. They are not a structural or major energy absorbing element in the car, and they are ugly.

 

I'm welding impaired, so just welding in a cage or supports is beyond my abilities - I guess my take on the safety element is to limit my exposure in the car, and to be defensive as all-hell when driving. Sort of like speeding through stop signs to minimize the time in the intersection??

[ZR8ED]

Yea I suppose it can sound kinda preachy to those that know better. I just want people to think about it.

 

I do agree the bumpers are a joke, it was the general idea of taking some element of crash protection out in the name of lightening the car.

 

I don't agree with the no cage/ or roll bar stuff.. except if your tall and it is not padded or intrudes into the compartment too much.. as far as hitting your head on the metal, have you looked at the door openings or the roof around the window? its metal right?.. not much padding there... might be sheet metal, but a human head makes a poor mallet for shaping sheet metal.

 

I do FULLY aggree that a cage should be professionally built/installed and designed.

 

Roll bars asside, for the average street car can be a bit much...but if you have a 500hp street car..that could be considered a bit much as well.. safety to match the threat..

Sooo crash avoidance is extrememly critical. brakes, suspension, wheels, tires, steering, proper seat belts to hold you in so you operate the car properly..

 

I don't even have to get into driver training...nuf said on that one.

 

Thanks John you are absolutely right, I just barely touched on safety.

 

I would think these kinds of considerations should be the first thing you consider when planning a project. might make a good sticky.. (once some of the preachy stuff is removed ehehehe)

 

I may not be all that young anymore (33), but I have WAY too many dead friends/family/aquaintences/co workers from auto related mishaps, and this topic passes through my head from time to time..

[Scottie-GNZ]

Excellent post!! I have been preaching the same thing but only in a different manner and that is to understand the power you have and respect it. I know this is hard to understand and accept for some of the young 'uns and I suppose when you get to my age you start thinking about more important things, like losing your life.

 

After my feet came back to the ground last night I was thinking about the same thing! That pass factored out to 518+hp at the wheels based on the 1/4-mile formula so I would guess maybe somewhere around 540 peak on a dyno. That's a mind-boggling 5lbs/hp and I will openly admit that scares me sometimes. Despite a decent cage, good handling suspension, a beefed-up chassis and massive brakes, I would never ever run my car flat out in full race trim mode on the street. Not only would I not survive the crash I am dread the thought of how many other lives I might take with me. After a certain point in your life you understand and accept the fact this could actually happen to you.

 

So, Richard, preach on. You have my full support on this issue/discussion

[zero]

I have a quick Z, nothing insane, but not slow. I bought it that way. The first modifications I plan to do are structural. I want to weld in subframe connectors, doorbars, a cage, and what else is necessary to stiffen up the car. Just out of curiosity, what part of the Z do you think is most prone to injury from accidents; where should I focus my attention. Thanks

[Guest bluex_v1]

I've been giving the cage without a helmet issue a lot of thought recently, because a forward cage is extremely integral to my plans for the car, and I will be driving without a helmet on the street.

I have a modified SW kit mostly installed, but that crappy halo piece really has me nervous...its just way too in the way. I don't even know if I'd have room for a helmet as is.

 

What I'm thinking of doing is cutting out the horizontal part of the halo that goes back to the main hoop and replacing it with some 1x2 rectangular tubing bent so that it tightly hugs the arch of the roof beam above the door. The two inch wide flat of the tube would be perpendicular to the path my head might take toward it. To do this, I'll have to cut the A-pillar downtube free so I can do a good job on the round to rectangle transition and then weld the 3 sided bar back in place. In theory, I will just have a 1 inch extra encroachment toward my head versus stock.

 

The question of course is, does the added strength of the forward cage offset the increased risk of head or neck injury due to the additional encroachment? What if I also removed the seat sliders to lower myself and moved the seat and steering wheel inboard an extra inch to reclaim that spacing?

 

Of course I would also be getting some high grade impact foam for this piece and trying to blend the foam into the roofline to make smooth transitions.

[JMortensen]

I don't agree with the no cage/ or roll bar stuff.. except if your tall and it is not padded or intrudes into the compartment too much.. as far as hitting your head on the metal, have you looked at the door openings or the roof around the window? its metal right?.. not much padding there... might be sheet metal, but a human head makes a poor mallet for shaping sheet metal.

 

That's a perfect example. I did a snap spin at an autox once. Turned into a full 360. When the car stopped spinning it grabbed really hard and I smacked my head (inside a helmet) so hard on the door frame that I saw stars. The last thing I would want on the street is another 3" (2" + padding) of room taken away so that I would be even more likely to hit something with my head, especially since I don't drive around town with a helmet on . Might make a good case for adding padding to the stock vehicle, but IMO this doesn't prove your point for putting a bar in that already limited space, padded or not.

 

The SW bars I've seen have the bar over the door WAY too low as bluevx1 mentioned, I'm not sure about any of the others. I've seen "custom" cages with Petty bars 4" from the driver's head with no padding, and halo bars that were pretty close too. The worst was a friend's rock buggy that he built. Awesome machine, but sitting in the driver's seat you had about 2" between your head and the cage which directly above the driver was just a small rectangular hole. Not even a chance of putting a helmet on and getting in the thing unless you were 5'7" or less, I'm betting. If that thing were rolling it with me in it my head would be bouncing off of all 4 sides of that rectangle, no doubt.

 

rc240z's cage is about the best I've seen. The bar over the door is very high and tight against the roof. http://www.classiczcars.com/photopost/showphoto.php?photo=6553&password=&sort=7&thecat=500 I wish I saw more that were like his, but most of the others that I've seen don't seem to take this stuff into consideration.

 

I am going to put a cage in my Z, but I almost never drive it on the street anymore. Pretty soon it will be on the street only to bed in brake pads and stuff like that.

 

Jon

[johnc]

What I'm thinking of doing is cutting out the horizontal part of the halo that goes back to the main hoop and replacing it with some 1x2 rectangular tubing bent so that it tightly hugs the arch of the roof beam above the door.

 

No racing sanctioning body that I know of allows rectangular or square tubing of any size or wall thickness in the construction of rolls bars or cages. Its OK for the frame itself in a tubular framed vehicle and maybe OK for a formula car of some type, but its not allowed for driver protection in a production based vehicle.

 

For a 240Z used on the street I would only install a roll bar and, maybe, some type of door bar but I would have to spend a lot of time figuring out a good design for the front mount of the door bar.

[ZR8ED]

Jon, I guess you are talking about typical cages with the forward hoop (around the windshield area) I do agree that most bolt in cages, in fact every street cage I have seen is not much better as far as bars encroaching into the cabin. Ie at the MSA show last year, I don't think I saw one car that had a really good roll cage in it. Lots of pretty ones though..hehe

 

I only have my own cage as an example and it is totally custom and is VERY tight to the roof and door opening (lucky to cram a finger between it and the body at the widest point.) That, and I'm only 5ft 7, and have lots of room in there for me.

 

Though to clarify further, a street cage to me is a proper roll bar with the extensions that link to the strut towers, and maybe some side bar intrusions. Anything more is pretty extreme for a street car.

 

And banging your head on metal in a 50mph crash from a distance of 6" or 3" is negligable in the end.

 

Proper design is critical to elimate or reduce these risks. Saying all cages for the street are dangerous is way too general. I'd rather think of the risks and using the best resources and info I can find do what I can to reduce the risks, as opposed to saying it can't be done, and doing nothing.

 

I'm not talking about joe normal in his 200hp Z. I'm talking about joe crazy with his 500hp street Z. Less crazy...less safety required.

 

Glad to see the responses and I hope it makes people think about it for even a second. After that, safety is your choice and responsibility.

 

Peace.

[JMortensen]

Though to clarify further, a street cage to me is a proper roll bar with the extensions that link to the strut towers, and maybe some side bar intrusions. Anything more is pretty extreme for a street car.

Not trying to beat a dead horse, but you are describing a roll bar here, not a cage. I agree with almost everything you said though, particularly this:

Ie at the MSA show last year, I don't think I saw one car that had a really good roll cage in it. Lots of pretty ones though..hehe

 

My main point is that if you don't wear a helmet you don't want metal next to your head - padded or not. I had an Autopower roll bar in my Z, and my old boss scolded me for not having padding on it in the middle between the seats. I asked "Why would I need padding there" and he got even more emphatic that your head will whip all over the place in the event of a serious accident. He's been roadracing for 30 something years, so I think he has some pretty good insight on what's going to happen if you crash.

 

Since you are 5'7", if you wear a 4 point harness your likelihood of hitting your head on a good cage (which by the sound of it you have) is pretty minimal I would guess. I don't think that likelihood should be underestimated for people 6' and taller though. Especially with some of these cages I've seen where the bar above the door isn't even as high as the door frame itself. I don't have definitive proof, but I'm SURE that the reason that rooflines in cars keep getting higher and higher is to prevent head injury.

 

I just don't want someone to spill gray matter in a botched attempt to make themselves "safer".

 

Now I'm probably the preachy one...

 

Jon

[Pop N Wood]

Might as well throw in my admittedly uneducated opinion as well.

 

IMO, if you drive you car on the street in such a way that you think you need a cage to be safe, then the safety problem lies between your ears and not with your car. Most street cages are for looks and not performance (my opinion). And like the one guy's signature says, who needs to explain why you have a roll cage to the officer who has just pulled you over for a traffic violation?

 

People go on about a "properly installed cage designed by a professional cage builder". Yeah, nice words but truth be known that anyone with an ebay account, a chop saw and a tubing bender can become a "professional cage designer". Even the established cage manufactures build "kits" that fit a class of cars. And unless you want a lot of returns, you are going to design that cage slightly undersized to ease installation on slightly out of dimension cars.

 

Also the idea that by installing a cage you somehow have made your car too unsafe to drive without a helmet just doesn't make sense to me. Like ZR8ED says, steel tube or stock sheet metal the effect will be the same. So the issue comes down to one of encroachment. I have said this before, but I feel many people (not all) have a naive belief in the safety benefits of helmets. If you think wearing a helmet will overcome the impact of a poorly designed cage or reckless driving....

 

As for rectangular tubing, may not be sanctioned but if you only want to stiffen the chassis without calling unnecessary police attention to yourself, then I am thinking this might be a viable option. Auto manufactures build safe cars using only sheet metal stampings. I don't have enough tools for that, but I'll bet I can strengthen the stock sheet metal with some subframe connectors, strut bars and some yet to be designed bracing of the rear hatch area. One Austrailian HybridZ member posted he got rid of the body panel creaking and paint cracks on his 240 with a formed sheet metal brace.

[TimZ]

Man - it's really nice to see that I'm not the only one that is concerned about the street cage issue. Regardless of where you fall on the issue, it's good to see that people are thinking about it.

 

Several people have commented along the lines that it doesn't matter whether you hit your head on the steel cage or the steel door frame - metal is metal, right. I'd contend that this is dead wrong. It's not the material, but the shape of the material, it's proximity to your head, and how it's going to effect the motion of your head when it hits it. Shouldn't take a rocket scientist to see that there is a huge difference here.

 

First off - the shape of the cage will most likely be a round bar. The convex shape if the bar will concentrate the energy that is transferred to your head to a very small area, and WILL do much more damage to an unprotected head than the more convex shape of the door frame/roof interface. Think about it - would you rather get hit in the head by a baseball bat or a tennis racquet (the flat side, not the edge )? Yes, at some point either one will kill you, but that point comes up much sooner with the bat.

 

The idea of using square tubing will most likely be a better approach in this area, but I'd be very careful about the construction of such a cage. It has already been mentioned that such tubing isn't as strong as round tubing, and it will be even less so when you start trying to make it follow a curve, instead of using a straight piece. It would take some serious consideration to make sure that if the cage deforms it does so away from the occupants.

 

The issue of proximity to the head should be pretty clear - as has already been pointed out, there isn't too much room in the Z's cockpit to begin with, and I have yet to see a solution that keeps the 'halo' section of the cage without encroaching into your head's normal range of motion.

 

Just to add some anecdotal 'evidence' here - one of my development vehicles at work is a Lincoln Navigator. We anticipated having to do some limit handling work with the vehicle, so we outfitted it with a full cage, custom designed and installed by a VERY respected local fab/prototyping shop. Pretty much EVERY time this car gets driven on the street (it's about an hour's drive to get to the proving grounds), somebody inadvertently hits their head on the damned cage - often hard enough for the pain to be a major distraction to the driving tasks at hand. This is in a Lincoln Navigator being driven normally in normal city traffic, folks. If you think you have more headroom than that in your Z, you should really consider putting down that crack pipe.

 

The other thing that makes me very nervous about the 'halo' section is that the section that goes across the headliner is often in a very bad location. I have seen many that are located such that during hard longitudinal decel a loosely belted (i.e., not using a racing harness) occupant's head will naturally contact the bar at right around the forehead area. The effect of this will most likely be to snap your head back severely and compress your spine.

 

I won't sit here and argue that there aren't any situations where a full cage wouldn't help. However, it's patently clear (to me, at least) that there are many more situations where having a full cage on the street (where you almost certainly will not be using a full harness and helmet) is a liability.