zoom44

ok thats what i want. now is this the formula that is used to derive hp from trap speed?

((.00426 times x MPH) to the third power) times a weight of xlbs

dmp

I have no idea if that is the formula to make iced tea...I'm doubting a formula can accurately predict or dictate the HP a car makes, based on it's weight and trap speed.

zoom44

but thats what you did by link the thread and telling me to read it. as if it bolstered your opinion and not mine. that was incorrect.


i am not trying to talk down to you. you brought up the relationship between trap speed and hp as many have in the past. i want to know what the relationship is and im tryign to get you to say yes this is the one or no this isnt here is the correct one. that first calculater was incorrect in its statement as i have shown with the other 5 calculators that say whp and calculate the same hp.

this is really irritating for me because i am usually on the other side of this kind of discussion. there is a freind of a freind who is always geting on my nerves. hes an engineer. like this one time he says "if you take a rifle and levle it with the ground and fire- whichwill hit the ground first the bullet or the shell" my answer was is and always will be that the shell hits first. but he and all sorts of physics students and engineers will tell you they hit at the same time. i show him many scenarios in which his math doesn twork but he insists that it does. that time i ended the discussin by saying " my bullet isnt going to hit he ground because i always hit what i was aiming for and thebullet will still be in the dead body.



but in this case we have to use the math why? because YOU said trap speed indicates hp and said your trap indicates that it is not reaching advertised hp. using the math i have shown you that it does within 5%. i agree that the simple formula doesnt take into account every factor thats why we have the 5% window.

so either trap speed does indicate hp and your car is making the advertised power or you dont believe that trap speed indicates hp.

zoom44

then how do we verify your intial statement?

dmp

Negative - I posted that article as 'information on the topic' - and you can clearly see in the article several opinions.

The relationship is this:

Two RX8s run the 1/4 mile. One traps at 95mph, the other at 90mph. The car with the 95mph trap speed is making MORE power.

(shrug)

It only hits within 5% if one believes the car is losing 20-25% of it's engine's power thru the drive train.

186/.8 = 232 crank HP, or 3% less than the rated number. The Miata forum thread I linked to shows pretty clearly that it's not that simple, as to simply subtract a percentage from the engine's rated HP, to get rear-wheel hp.



Again, I've maintained Trap speed shows the power one's car is making, relative to the model of car. My car traps at 4-6mph less than 'test cars' from Mazda. It's not a huge leap to believe their cars are making substantiall MORE power than mine. It's not a huge leap to believe PoLaK's car is making substantaill MORE HP than my car based on HIS trap speed, too.

The variable is: What kind of trap speeds would my car make if it ran with those test cars, or with PoLaK's car, at their tracks, on those days?

Since we can't do that, for logistical reasons, we use dyno numbers. But even that isn't reliable, as different dyno's run different ways.

What do we do? If we're zoom44, we believe Mazda is honest and forthright in their rating of 238hp, and this car has a pretty inefficient powertrain. If we're dmp or others, we believe Mazda is full of crap, and needs to deliever as promised.

But for the sake of argument, lets assume that all these rx8's which dyno at 185whp are making within 5% of what Mazda claims.

Why doesn't mazda simply acknowledge the car makes 5% lower HP than thought, and advertise 226hp for the RX8?

Pride? Embarrasment? Incompetence? Lack of controls in place to ensure we all have engine's tuned like Warren's 200-206whp car?

dmp

Well, my statement was flawed, slightly...

My car, with me, and gas is 3255lbs...

but we verify it based on practical experience.

BlueEyes

maybe a little late to the party, but 100 lbs lost generally shows a 0.1 sec improvement in the 1/4 mile. so 10 hp = .1 sec improvement.

zoom44

no the one with the 95 mph trap has a different driver. there could be something wrong with your car but that doesnt mean Mazda is lieing about hp. if there is a problem and you fix it and then you run 95mph that proves the car does make advertised power. if soemone else drives your car adn hits 95 mph same outcome.

lets go with the miata threas opinions. 2 guys are adamant abotu 25 hp and the otehr is adamant about using percentage. the math on there showed 25hp to be 19% yet you claim 20% is higher than you've ever heard. you chose 17% from thin air but that percentage comes from atual testing of the engien in and out of a car. actually 3 engines. besides we arent subtracting here- we are measuring actual whp and trying to add to bhp

actually thats not the case. i am not believing Mazda. I am trying to get you and others to prove your claims that your car isnt making advertised power. and you just said that other peopl's cars trap faster so there is something wrong with your car. that doesnt mean Mazda is lieing to you or anyone else that means something is wrong with your specific car. either a mechanical problem or a driver error.

because as you have pointed out it is impossible to make every engien make the exact same hp as ever otehr engien even went built and tested at the same time. they are allowed to be within 5% because of all the variables that you yourself have pointed out. they have provided timeslips and otehr evidence to show the cars make whatthey advertise within 5%. i want people who believe other wise to prove their claims.

dmp

Trap speed isn't as influenced by the driver as you may believe. Hence my faster trap speed coming from a 'worse' launching/driving performance shows.

25hp to be 19% of what? There's evidence that the 240hp motor still lost that same 25-25hp. In that instance, it's not so much a percentage, as it's a fixed number. Yes - the 3 engines which were dyno'd on an engine dyno, then in a car...one of those, if I recall, was the 240?hp engine which still lost the 25hp. Thus, the loss thru the drive train was 11%. I picked 17% as a compromise between what I expect (15%) and what you believe (20 or more %).



If you go in halves with me, I'll pay to have the engine pulled out of the car and put on an engine dyno. (shrug).

Unless you go in with me on the engine-pulling, we'll have to look at the evidence, and draw conclusions:

Racingbeat hit 216hp on an engine dyno.
My car trapped at 91mph, max
My car weighs 3255 when I hit that trap speed.
My car dyno'd at 186whp

186whp shows anywhere from 215-240 'crank' HP - although it's nearly impossible to be sure...

Based on the evidence i've seen online, the RX8 - at least MY RX8 should be trapping in the mid-upper 90mph range if it really had 238hp. Based on Dyno evidence, MOST RX8s are 'under-powered' to some degree.

Perhaps mazda should start rating their cars as "215-240hp, depending on how well your MAF works with your ECU, and other variables - like 'driver error'"

army_rx8

^^hehehe i like that new HP rating system :D

zoom44

racign beat results doesnt matter- you said your car doesnt make the hp. we have to stay with what we know about your car.

the weigth was from a different day yes? but its an accurates measure so lets plug that into the formula

(.00426 times * 91 mph) to the third power) times a weight of 3255lbs = 188.66

pretty close to the dyno. which again puts to rest any claims of safe mode on the dyno.

so now we are just stuck on what is an acceptable drive train loss. how can we decide on that?

dmp

I bring up Racingbeat as 'evidence' to show issues with Mazda's claims...nothing more.

Yes, different day, but within 1/16th of a tank of gas, as shown by the gauge, no other changes.

I have had NO worries of dyno 'safe modes'.

But that calculator is flawed - so the fact it is pretty close to the Dyno isn't any more relavent than Racing Beat's 216hp number, now is it?
fwiw, some online calculators, show 191.4 horsepower - the gordon-glasglow shows 183.8hp. Are they using different formula? And it doesn't take into account the innacuracies with my two OTHER cars, either.

What I'm trying to get you to see that you're using inconsistant math/calculators to argue HP. I have verifiable dyno results showing 242hp on my car, then a timeslip showing 106mph, then a weight slip showing 2885, without me. Your calculators suggest my car had nearly 20hp MORE than what I really did; albiet on a different day.


And it's not 'acceptable' drivetrain loss i'm looking for...it's finding 'accurate' drivetrain loss. That can't be found unless Owners pull their motor, or apply 'perponderence of the evidence' however circumstantial.

zoom44

http://www.wrc-tech.co.uk/services-rolling-road-faq.htm

read that very interesting especially from
"Is it possible to measure the true transmission loss of a car?" down

RX8-TX

mmmm....maybe because we still like the flavor and we couldn't find a bag with the full 5lbs. :p

zoom44

whats crazy about this whole thign is that there are alot of people on this board who often use math and measuring to prove their points and yet here are two people who dont like the math(generally) in the discussion. with none of the experts chiming in to help either side. where are they?

Nemesis8

iTrader: (3)

They are out driving their 8's

zoom44

really kevin? thanks for the input that helps alot

richard paul isnt driving his, rotarygod doesnt have one, wakeech doesnt have one etc etc.

have you run yours in a 1/4 mile? what was your trap speed?

zoom44

really what about this statement?

arent you saying there tha the driver was the reason for the difference in trap speed from run 1 to run 2?

zoom44

forget that lets try it another way around.

you say your car is not making 238 because a 3300 lbs car with that much hp should trap better than your car did. yes?

ok then at what speed should a 3300 ilb 238bhp car trap?

zoom44

eyah yeah forget that ill delete it if you want. what should your car trap at to get the advertised power

dmp

a 3300lbs RX8, with 238hp/160lbs-ft should have no difficulty 95? 96? 98?mph...mine 'does' have difficulty doing that. It makes me frustrated to think I didn't get what I paid for, but I bet at least part of my frustration is because I wasn't able to turn good times. There's a decent amount of 'emotional response' in this thread - especially the first couple posts...A few days, and one GOOD drive have calmed me a bit; however, I still believe Mazda is less than truthfull about the engine's power numbers - my car's trap speed is just 'one' indicator in my mind.

...but keep in mind, the higher trap speed was on a run where i drove 'worse'

:D

zoom44

ok ok so we have time slips from 8 or ten cars on this site. most, say 8 out of ten, have traps of 94.x to 96.x . yours and maybe one other show 90.x-91.x.

so by your own numbers most of the cars hit the hp advertised. do you want to continue to believe your car doesnt "because mazda lied to you"? or do you think, maybe, there is something wrong with your car and go find it and fix it?

dmp

If there is something wrong with my car, it's going to be hard to find, that's for sure. The dealer tells me "All we can do is drive it, and compare it to others on the lot."

(shrug)...that's like saying "you're stuck with it".

r0tor

iTrader: (1)

I have a fairly accurate model in a simulator called Car Test.

Stock with a perfect launch it traps at 96.4mph. Bogging or excessive tirespin can drive it down almost 2mph. Playing with the shift times and effect it another 1-2 mph. Also another big factor in trap speed is if you had to shift right before the line. While trap speed is more consistant then ETA, its not fool proof.

It also estimates parasitic losses based on some general driveline guestimates. The difference in 3rd gear between 7k and 9k rpms in parasitic losses is around 10hp.



and why in the world is this a sticky???

guy321

Check your plugs and test your coils. Your plugs will give you an indication of how your engine is burning.