Like it says, when you put your lights down does your car speed up? Yes, no or not sure.

Mine does. I was wondering about this because there always seemed to be a subtle thrust when I put them down. So I tried a scientific experiment. On a flat road at cruising speed (70 mph on the interstate) I put the lights up, then down, carefully measuring the small thrust change with my internal thrustometer. Sure enough, two out of three times I got a good reading (the other might have been a problem with a crosswind).

So I was wondering if any of you guys were seeing the same thing?

 

My only guess is headlights put a strain on your already weak alternator, thus robbing you of a bit of power.

 

i go with this one but i doubt that would be something you could ever actually feel

 

Internal Thrustometer? Hmm... Ray are you making up old school tools again? LoL

Maybe those headlights really slow you down in terms of wind resistance, I find it hard to believe that its that noticeable, but I've heard of weirder stuff with our cars.

 

I'm going to try it next time I take it out. If there is a resistance,I'm leaning toward aerodynamics, try holding something the size of the headlight, or 2, out the window at 70mph. Probably the combo of the aero, and the alternator.

 

I remember reading somewhere for the first gens the headlights up increase wind resistance from .36 to .38 so it could be attributed to that, I do know when I put my headlights down whilst cruising on the highway I can feel it ever so slightly.

Stevan, I love that bumper in your Avvie...would make for some nice night time driving so you wouldn't have to put the headlights up in the first place.

 

Is there some medication that you are supposed to be taking three times a day that you have been skipping Ray?

 

Putting the headlights up does add wind resistance as stated but I would
serisously suspect your ignition Ray. Let me know if you want to build one
like mine. Ford and Chevy ignition parts FTW!

 

I agree with many above....
It's obvious that the car is more aerodynamic with the headlights down, but you'd have to have a very sensitive "thrust-o-meter" in order to actually feel a difference.
I'm not buying the added drag from the alternator either.

 

I should have mentioned, this test must be done on a perfectly tuned car with no mechanical issues such as a weak alternator or an ignition issue, neither of which my DD the Silver One has, of course.

Tim you know my ignition is always in perfect condition! GM parts in a 1st gen, in a mint SA, no less? Sacrilege I say!

Also, for useful results, the driver must be completely free of mind altering medications.

It helps if you really know your car really well, drive it daily for many miles so you are sensitive to it's most subtle changes. That's the case with the Silver One and I've discovered that she prefers her headlights down.

 

Maybe my "thrustometer" (which is external, btw since I am male) is faulty, but I'm not sensing it at all. I would think this might be caused by a slightly weak battery, forcing the alternator to carry the full load while the lights are on. Maybe a weak ground could do the same thing.







.

 

Ha - Ha!
External thrustometer vs internal.....I wanted to be clever in my post, but totally missed that pun....Well done!

 

Well, physics dictates that any energy emitted from a free object must exert an equal and opposite reaction, and the headlights are emitting 110 watts worth of photons out the front of the car...

That equates to a 0.15 HP rearward thrust.

 

We can rule out the whole electrical issue by putting them up manually with the
little toggle switch in the console and leave the lights off.

You should get one of those portable performance thingies with the built in GPS
and force sensors so we can measure this. Sounds like a great experiment for
the track at ZoomFest!

Ray, your ignition is weak, you just don't know it

When my hoods closed you can't tell there's anything unusual under there,
so its ok in my book.

I voted yes in the poll just so you know.

 

I used to notice it in my GXL. However, since I had removed my ac, I was driving around NM with the windows down (hot) and there would be a lot of wind buffering inside the cabin. However, with the headlights up, the buffering was much lower as the headlights would deflect the air around the car and not billowing through the cabin, so I know it does make a difference on low powered cars around 80mph.

Please reference my highly tenical drawings below:
Headlights down: |II|
Headlights up: /II\
(*Note: The above drawings do not acurately portray anything and are not to scale)

I would be interested in a MPG test as I think that is more accurate than an internal or external thrustometer. On a side note, try placing the thrustometer out the window at 80mph and see what happens.

 

There's your problem right there Ray!! Sorry, I couldn't resist. I used to notice this in the first 1985 GS that I owned. It was really noticeable when I was on the interstate. I think it is probably just attributed to wind resistance. I never noticed the problem unless I was on the interstate. Cruising around town at night with the lights on at lower speeds had no effect. It was only high speed operation on the interstate, that I noticed change. That car had quite a few performance upgrades too, so I don't think it was ignition related in my case.

 

exactly!

a couple of my friends have 89 civics, and since those only generate .2hp stock, the .15hp the headlights use is significant!

oh and the power is so low on those things you actually do need an internal thrustometer to measure it

the Rx7 is different of course...

 

It makes perfect sense! I can't argue with those maths.

 

i think ray's smoking something.

 

ahahahah

 

Michael, I was on my way home from work, fully eligible to conduct the test.

I think that DD has found the explanation, the speed up is mostly caused by the Forward Photon Force (FPF). Here's what he claims:

"Well, physics dictates that any energy emitted from a free object must exert an equal and opposite reaction, and the headlights are emitting 110 watts worth of photons out the front of the car...

That equates to a 0.15 HP rearward thrust."

DD's FPF, combined with the Streamline Efficiency Index (SEI - exquisitely refined by the Mazda engineers in the 1st gen design) probably accounts for the increased Forward Thrustometer Force (FTF) that I'm seeing.

FTF = [3(FPF + SEI)] x URC

where URC = Universal Rotary Constant

Nice work DD!

You guys who say there's no effect probably haven't done the test, can't get your headlights down or have the sensitivity of a Neanderthal with a dysfunctional thrustometer.
__________________

 

That wouldn't be a good 1:1 comparison of the effect as the headlights are preceded by the bumper which will alter its incoming airflow.

Saw someone post a diagram from a brochure showing the pressure zones of an FC once, was pretty interesting but didn't really understand it.

 

So, I'm making a new **** for my headlight switch that says FIRE RETROS

 

Could be useful DD, kind of like that pass button they're using in Formula 1 these days.

So the poll results are in and they confirm that putting your headlights down causes your FB to speed up noticeably (11 yes, 9 no, 4 don't know). Thanks guys, time to send this thread to the archives.

 

Sorry to put my nose in where it probably doesn't belong, but I found this thread pretty interesting. I have noticed the reverse phenomenon in my various FC RX-7s to what mikeric described. Namely, with the windows down, there seems to be just a hint more cabin buffeting with the lights up vs. down. I always thought this was neat because it verified the assumption that raising the lights on a car with pop-ups actually impacted aerodynamics, if only slightly.

Incidentally, since this is a first gen question, I refrained from voting lest I corrupt the important scientific data collection.