guy321

well re-do your calculations with 3255?

Still, normal people only weigh 160 (im normal :p )

Remember this is an asian car!!! Im heavy for an asian too!

dmp

I haven't weight that little since...hm...7th grade.

guy321

It's ok.. I have about 60 lbs of speakers in my trunk, plus golf clubs , one of those battery starter things, and a bowling ball..

zoom44

no i DO believe it. i even provided calculators that use the formula mentioned in the quote i posted. you then questioned whether they are accurate and said you believe car guys over scientists. i quoted a car guy giving the formula. i am asking you whether or not you now believe this formula and the calculators or if you have some other means of proving/showing that hp can be figured from trap speed.

guy321

He needs to recalculate using 3255lbs instead of 3300..

SEE!!! It has even LESS HP !


Conversions:

weight = 3255 pound = 3255 pound
velocity = 90 mile/hour = 90 mile/hour


--------------------------------------------------------------------------------

Solution:

horsepower (hp) = 185.19572143833 horsepower

dmp

Still, I listed two of my previous cars - one was off by 50hp, the other by about 5...to point out how math doesnt always relate to what actually happens. Read that dyno-thread from MiataForum.... :D

dmp

I did recalculate - just didn't post the results; although I mentioned those numbers in a few posts since i got home from work.

BlueEyes

this is a fun thread.

dmp

I agree.

dmp

Side note, the weight drops further - thus the 'power' in the calculators, when you remove the 2 JL 10" subs in a box which weighs probaly 50lbs...

guy321

You have subs also? me too, so your weight was with the subs? do you have base or GT?

THe weight would drop (thus the calculated HP ) BUT if you remove the subs, you may have gotten a higher trap speed to compensate

dmp

I have a Sport with apperance package and rear wing...

One can kinda hear my system, especially towards the end of the vid...

http://www.d-mphotos.com/movies/rx8audio.wmv


that is possible...but I doubt ?50lbs? would affect the car to the tune of 4-5mph in trap speeds.

guy321

I thought someone said every 10 lbs is equivalent to 1mph..

Not sure if 4 or 5 HP will give you a 4 or 5 mph increase.

"Yep, the old "standard" is that 100lbs. = 10hp or so..."

http://web.ask.com/redir?u=http%3A%2...nip&Complete=1

r0tor

iTrader: (1)

EXCEPT that driveline losses are determined by inertia, friction, AND RPMS's and RATE OF CHANGE OF RPM's. A miata does not rev to 9k or go through the rev band nearly as fast as the 8 does.


Also trap speeds are not nearly as independant from your launch as you appear to think... a friend of mine gained something like 5mph by switching to drag radials on his 11sec Firehawk. I guess he picked up a lot of power with those tires . Think about it, the longer your car is hooked up at full power, the faster it will be at the end of the 1/4 mile - if you bog or spin the tires like crazy you have less road/time to accelerate.

dmp

2000rpms makes a the kind of difference some of you would have us accept?


Negative - perhaps your buddy spun the tires at the 660ft mark?

The concept is this:

All things being equal, the car with more Power will have a higher trap speed.

That's it. You can toss that around, or try to find 'an' instance where it may not apply, but it's a sound concept.

dmp

I'd bet 5hp would give somebody a ~.5mph increase...the difference would likely be too small to accurately measure; small enough of a difference to fall into the margin of error between runs. I gained about 1mph just by shifting differently - not quite to redline. And reducing weight won't give your car more power - it'll just accelerate as if it did have more power.

:D

guy321

Yes, that's what the word EQUIVALENT was there to quantify

lurch519

the operative phrase is "all things being equal". if you are spinning off the line, you are not accelerating, so you should have a lower trap speed. you claim your 60ft time was 2.5, and you ran 90 mph. the timeslips that were posted on rotarynews showed about 2.2 to 2.4 60ft times with trap speeds of around 95 mph.

take a top fuel dragster for instance. when they launch, the tires barely spin, allowing them to accelerate all the way down the track, getting them 300+mph trap speeds. now, if for some reason they lose traction off the line, their trap speeds are generally under 300.

dmp

On the 90mph run, it was 2.3. On the 91mph run it was 2.5. I'll double check those when I get home tonight. You're making my case for my car missing HP...

RX8-TX

2003 All Over Again!

dmp

it's a 2004.

(shrug).

I'll never get why those who pay for a 5lbs bag of potatoes settle for 4.5lbs.

zoom44

dmp so we have establishe dthat you believe there is a way to figure hp from trap speed. you dont think your trap supports the advertised power. but you dont believe the math is accurate in the real world.

so you dont believe trap speed is an accurate measure of hp?

eitehr you believe it or you dont.

here is the formula- ((.00426 times x MPH) to the third power) times a weight of xlbs

do you agree or do you hav some other way of figuring hp from trap speed?

no more rhetoric answer the questions.

dmp

I beleive Trap speed is an indicator of a car's relative power. What that power number IS, however, is up for debate. Your online calculators match pretty close with my dyno-verified HP numbers - except the one which clearly states ENGINE HP...

What trap speed shows, between two of the same-make cars, is which has 'more' power available. My 240whp Probe GT trapped about the same as a C5...Of course the c5 has MORE power to the wheels - so that comparison doesn't work. But compare MY RX8's 90mph trap speed with those RX8s you posted of 94-95, and Polak's 96mph trap speed, AND coupled with my dyno numbers, it's pretty clear my car is missing some of the HP I paid for.

I plugged in numbers from two other cars i dyno'd and raced - one was pretty close, the other was off by 40hp. What's that tell you about math? About those calculators? They are accurate 2/3rds of the time with what i 'know' my cars to be.


What do you want?

zoom44

if you want rhetoric without support than here is some from your miata thread-

your 17% is too low and rOtor is correct about rpm-
oh look not 17% but 19%
etc etc

dmp

uh? okay? I can pull a number of opinions out of that thread - my goal was to provide INFORMATION, not to further a specific Agenda. If you'd like to take parts and opinions of that thread and use it to back up your and others, what is in my opinion, naive belief that every RX8 puts out it's advertised HP, and we should just believe the car consumes THAT MUCH power thru it's drivetrain, then I can't stop you. I can, however, remind you I liked you much more when I didn't feel as though you were trying to talk down to me.

You remind me of a guy I knew who was in School at the Univ. of FL, gainsville. We were talking about Air Intakes. He showed me math formula after formula stating a 2" diameter intake on his KL-powered MX3 would help INCREASE the air's velocity - MUCH better than my 3.5" diameter. I had no math to show him - no nifty online calculators; but what i did have was practical experience building and dynoing and using air intakes for KL engines.

After three days of his 2" snorkel, he emailed me, dumbfounded..."Math is NEVER wrong!" he proclaimed. In spite of his very solid math, the 2" intake was horrible.

I don't know much about math - but I do have a firm grip on reality. By preponderance of the evidence, my car's engine is having trouble making 238hp.

Look at my car's dyno.

Look at my car's trap speed.

Ride in another car with similar weight, gearing, and rated HP.

When I have to chose between equations I likely don't understand, and what I see 'really happen' on the track or on the street, I choose what i can feel, see, and measure. Hands-on.