XJOSHX

OK my friend is 100% hooked on running his car on the gtech on the street and insist it is the most accurate thing in the world. Today he was telling me his gtech is more accurate than a dyno for horse power ratings. What do you guys think??? I think the gtech is a great toy for the street but not something to live by.

25THRSS

ummm, if you friend really believes the g tech is more accurate than a dyno then he is an idiot. They're cool little instruments, but there is no substitute for a real track or dyno.

ShiftyCapone

iTrader: (7)

Agreed. He needs to visit a dyno and see how far off his g-tech is. To many changing parameters for a g-tech to be as accurate as a dyno. I would not trust the power numbers it gives you at all. They are failry accurate as ET's go but seem to be about.1 to .2 off and about 3 to 4 mph off. You can have two cars that run the same times even though one has more power. A dyno does not lie and takes away some of the varying parameters that a g-tech relies on.

XJOSHX

Me and my buddy and his 94 cobra (all the bolt on's) went to the dyno and he put down 252 horse and 299.8tq (I just called to make sure i had the exact numbers correct) and he said we are liars. He said the car is a 240 horse car that makes 216 horse at the wheels and we should put it on the gtech to see what it really makes. This is madness!!!!

AlkyIROC

A dyno will give the exact HP to the wheels. It doesn't measure HP but torque and does calculations to determine the HP. It can't give an accurate ET because there are too many factors that can affect a 1/4 mile pass.

G-tech just measures accelleration and calculates HP based on what it measures and correct data inputs for the results. Lie to it that the car is lighter than it really is and it will tell you that you have more HP than you really do.

Personally I'd rather believe the dyno if I want to know the exact HP getting to the rear wheels. The g-tech is just a tuning aid. Like a weather station, no 2 give the exact same results.

bandit454

All the answers are correct. A dyno (depending on which type) will give you true HP to the rear wheels without wind drag and tire drag. There are some dynos made that will take that into account, and even one that you can input your car type and it gets the factory wind drag coeficent where the factory tested them and inputs that into the equation. The GTech Pro Competition, not the early GTech, will give you true HP including the wind drag of your vehicle and rolling tire resistence that you don't get on dynos. A GTech Pro Competition, not the early ones, if you set it up correct, including calibration, with correct weight of vehicle it will give you accurate measurments. I know some will disagree but I have the luxury of getting to test auto products like that and they are very accurate if set up correctly. The difference in the speed at the end of a 1/4 mile turn is on the GTech tells you the speed at exactly at the end of the 1/4 mile, where a track estimates your last few feet. I tested 6 different Gtech,(and others), and every one of the GTech Pro Competitions gave me the same results within +- .01. Thats pretty accurate. So it all depends, the dyno and other measuring devices both have pro and cons, and either one will give you good results. They are both correct measurments, all depending on what you want to see.

XJOSHX

It's the early gtech he is speaking of too btw

vwdave

I dont trust something that doesn't take gearing into consideration.

bandit454

Gearing only effects how fast you reach peak HP/TQ. Has nothing to do with total HP/TQ.

vwdave

Do a dyno pull in 1st gear and tell the computer its in 3rd gear and see how insane your power numbers will be.

25thmustang

Thats why you run in 1:1 to take care of the gear factor.

vwdave

Exactly my point, it wont "add" horsepower, but it will trick the dyno into thinking you have more.

A 2.73 car is not going to accelerate as fast as a 4.11 car (for instance.) Therfore, the 4.11 will show having higher horsepower numbers on the GTECH than the 2.73 car will.

bandit454

It will not show up on GTech that a 4.11 car has more horsepower than a 2.73 car if you do it correctly. You do all horsepower and torque runs in your 1:1 ratio. As you said above if you put it on a dyno and tell it is in 3rd gear and your in 1st gear, it will mess dyno readings up. Same on the Gtech. If you run in first gear and not your 1:1 gear then you will get incorrect readings. The GTech Pro Competition if set up correctly and ran correctly will not show different horsepower on a 4.11 car versus a 2.73 car. If your in the 1:1 gear ratio, no difference in gear ratio. A dyno does not care what gear your in nor does the GTech, but if not done correctly you will get wrong readings on both as you stated above. Look at Horsepower equation and no where will you see gear ratio as being a factor. Look at how a dno figures Horsepower and you will find nothing that has anything to do about gear ratio.

vwdave

I have one, and on my old 305 TBI, I got a 130hp in 1st gear, then 80hp, then 25 hp in 3rd gear with the GTECH.

(I have the regular GTECH Pro)

bandit454

The regular ol Gtech were not all that accurate. The GTech Pro Competition is light years ahead and if it is run properly will give you good results. It just depends on what you want to see and how much money you have. Either one will give you something to look at, I have done dynos and the Gtech Pro Competition and they both have pros and cons. Both all depend on the operator, thats why they say when ou are tuning go to the same dyno and not different ones. I have got 3 different results at 3 different places. But they all let me know what I needed to know, I was improving. The real test is the track though, thats where it all counts.

vwdave

Next time I goto the track, I am going to bring mine and ask them if I can run it at the same time just to see what the difference really is.

bandit454

I took my Pro Competition model and ran at the track, they have what they call a midnite madness at the local track on Saturday nights. At 11:00pm until-???? they let anybody run, race each other, etc. all they want and for only $10.00. They did this to stop street racing and a good idea. I ran I don't know how many times but mine was accurate, never more than .07 off the time. Of course the spped was different, the Gtech will give your speed at the end of run, where as the track estimates the last few feet to get speed, so the miles per hour was off most of time around 4 -5 miles an hour. But the time was what I wanted to see.

Apeiron

Horsepower won't change at all, of course, but neither will torque because it's not dependent on gearing the way the dyno measures it. You don't "tell" the dyno what gear you're in because it doesn't really care. The total torque multiplication is inferred from the difference in engine and rear wheel speeds. That way it doesn't need to know anything about rear-end ratio, transmission ratios or tire size.

25thmustang

Testing in a different gear will give you wrong number because the multiplication through the tranny isnt factored in. You have to run in 1:1 gear to get as direct power numbers to the motor.

Screw this, lets just run on an engine dyno, instead of trying to figure RWP the proper way and then using a made up percentage to get engine power!

Or screw power and worry about track times, the real measure of power!

daverr

iTrader: (1)

25thmustang

as Apeiron said
gearing does not change hp no matter how much gear multiplication u use.for example

if u had a motor that made 300tq at 5252 rpms connected to a direct drivetrain(1:1 total drivetrain gear ratio) lets say its a perfect no loss drivetrain.so u get 300 hp at the wheels

lets say u change the total gear ratio to 10:1

so now u spin the motor up to 5252 rpms which it makes 300 tq so after the drivetrain multiplication its making 3000tq at 525.2 which = 300 hp ( (tq x rpm)/ 5252=hp)


Ive been to a few chasis dynos .there are couple of reason why they do the pull in direct drive.

1. direct drive= the least power loss from the trans.
2. power will be graphed alot broader on paper as apposed to a very steep graphed first gear(harder to read).

dave

LUVmy92

If a Gtech is more accurate why the hell do big companys who make the parts to make cars go fast spend all that money on engine and chasis dyno's??? Your friend is riding the short bus on this one.

pre

XJOSHX

I could not have said that better my self!!!!!

383backinblack

first off....the g tech is an acclerometer......it measures acceleration, then extrapolates that data into the numbers it reads for whatever it might be your measuring.....

secondly, aerodynamic drag has absolutely nothing to do with the true wheel HP made by a given vehicle......

its absolutely a factor in how fast the car will run the 1/4, top speed etc......which are all forces that are pushing in the opposite direction.....

but a dyno will give you a very accurate reading of how much power your making where the rubber meets the road.

i mean come on people, you dont tune your car on a dyno because they dont read accurately do you?

i know i wouldnt be caught dead tuning my carburetor or changing my gears based on info i got from a gtech

gen3z

well i love my g-tech it shows to be about 5mph fast but then again there is not a beam to cross,it works off of inertia once you realize this point it will be easier to undrestand the way it retreives its info,my 13:77@the track is a 13;74/MPH at the track is103 and the g-tech shows108 i am very satisfied with my g-tech,i should say (used to,that car was hit x-tremely hard by a dodge aries K car)

383backinblack

the gtech tries to give you an absolute mph.....

on the track, the end segment has speed sensors every so many feet, and the mph on the timslip is an average over that semnt of the track

bandit454

Then why do some dynos, especially the high tech ones, have inputs for factory wind drag coefecient to make up for wind loss? Been there done that too.

383backinblack

because wind does not affect how much HP there is at the wheel.....come on.

if your trying to simulate a run, or a pass, or a top speed pull on a dyno (which you can also do, not just measure power)

then wind resistance is a pertinent variable, because the top speed of many cars is drag limited, and how fast the car will accerlerate especially at high speed, is very dependant on drag.

for that purpose, those factors are useful on a chassis dyno, but drag in no way effects the amount of torque thats present at the rear wheels, which is what the dyno is measuring.

thats like saying, this motor has 500hp.....but only 450hp when theres a 50mph wind blowing on it....

besides, SAE correction factors on dyno's to compensate for atmospheric conditions arent very accurate in the first place, so i wouldn't trust any correction provided by a dyno with a drag coefficient either.

a Dyno is a tool, and a very useful one at that....it will give you the most accurate reading of wheel HP that you can possibly obtain (unless someone knows of other equipment that measures wheel hp)

which aids in tuning immensely.....especially right now when you cant get to the track.

while the dyno will tell you how much power you have, it cant tell you how fast your car will run the 1/4, you need to run it and find out.

bandit454

Then the flywheel horsepower is the correct horsepower also. Wind drag will reduce the HP overall. It depends on how you look at it. If you loose HP, you will lose speed. Some measure from the flywheel, some from the rear wheels. I am not going to argue but it all depends on what you want to see. I know for one thing, the Gtech Pro Competition, not the old Gtech, if I see an increase in HP, I gurantee I'll see it on the dyno. Did too many test on them to see. A Gtech Pro is a GREAT tuning tool for those who don't have the money to run to the dyno anytime we feel pleased.

383backinblack

oh my *** man...no offense buy you are absolutely insane....HP at the wheels or any otherplace is independant of rolling resistance, wind resistance, or anything else other than driveline friction......

wind will slow your car down, but not reduce power.....because it is lowering the ratio of HP/unit force in the opposing direction.

but i guess we're all morons, and professional race teams should all start using the gtech to tune their race cars

bandit454

Apparently you are a moroon (no offense). All I'm saying is, if I have 325 HP on the dyno, and another car has 275 HP, and he blows me away, what good does the dyno do me. Bragging rights that I have more horsepower. If I put them on GTech and see the car that beat me is only pushing 250 HP (ie 25 HP less than Dyno) and mine is showing 250 HP on Gtech, I know that I have some work to do with wind drag, etc. A dyno would do me no good what so ever in the EXAMPLE above. The Gtech is a good tuning tool just as the dyno is. All depends on what you want to see and believe is absolutly true horsepower, but a dyno showing me that I have more HP versus someone else does me no good what so ever if I'm not beating him. As far as professional teams using them, I know some that are, just for the same reason stated above. They can take in account wind drag. Either one is a useful tool, to me, I could give a hoots a$$ what a dyno is telling me as far as HP, the end line is getting down the road and winning. The dyno number to brag about means nothing to me after I have all I got, I need something useful to work on the wind drag etc.. Maybe thats why I win more often now, might not need to let my secret out. Geesh.

383backinblack

lol ok man, whatever toasts your pop tart.

if you tune your car to produce more power at the wheels, and all else is the same with chassis setup and what not,

its going to go faster down the track, period. your not changing wind resistance lol......maybe you should get a job at nasa, they like to talk about drag too

bandit454

Whatever you think. There are many many things you can do to a car to reduce wind drag and it will make a difference. I tune for power at the wheels and anything to reduce wind drag. I go for total tune, not just bragging rights on Dyno HP. Thats why you see cars with less HP win over higher HP cars. As far as NASA, I do work for them.

25THRSS

NASA has a facility in Alabama?

Apeiron

The Marshall Space Flight Center is in Huntsville.

I'm with 383backinblack on this one... how do you "work on" wind resistance?

gen3z

with a clean car and a smooth coat of maguires wax LOL

383backinblack

you use your nasa spec'd dyno windtunnel gtech pro......

you sit in your car and fool with the playback tach until the gtech reads infinity horse power......then you get out and adjust the hood stops and the hatch stops and alignment ....then start duct taping the seams until you achieve a drag coefficient of 0.....

then you go to the track, run 4 sec 1/4 miles and tell everyone you have 22hp at the wheels and your car runs on schlitz.......

this concludes todays "new math" of HP tuning tips

bandit454

383, since you want to be such a smart a$$, the next time you roll through Alabama, stop by and you might learn a few things. There are many many things to do to improve wind resistence of a vehicle. Same on motorcycles. Maybe thats above your head and too technical because the dyno doesn't show you what to do. I was trying to make a point, but as usual there is always a smart a$$ in the crowd. You would not happen to own a Mustang would you?

383backinblack

nope, im retarded

aerodynamics isnt really that important for what we do i guess.....we dont get that far south too often, but if i do, i'll let you know and you can come down and see how your car stacks up to what we bring lol

check the links in my signature and find out

bandit454

I'll be waiting, going to be so much fun. Just be sure to bring money, the only way I race.

383backinblack

lol you better bring your insurance policy, cause you aint gonna race.....you're gonna get run over.....i really think you should look and see what your up against lol

even if you do race it, its got 1500hp of blown methanol fury

bandit454

Already looked, (why do you think I'm so confident?) like I said, bring a large money order.

CobraKiller

hahaha you guys are like children..It's good fun entertainment keep it coming!

25thmustang

Agreed, dyno is only there to help tune a car. If you make 600 hp and run 12s it means nothing but bragging rights... it allows you to tune the car so in the same situations (IE conditions) it will run better times.

Anyone who races dyno numbers needs to head to the track...

LUVmy92

The whole point was that the guys friend is saying ACTUAL horsepower ratings were more accurate on a GTech than a dyno, I would say anyone who thinks a 350 dollar piece of equipment is more accurate than one that costs thousands of dollars needs their head checked and a good slap upside the head.

25thmustang

Thats stupid, might help if you were testing a mod, and you ran it to get the power... added the mod, and ran it in the identical conditions.

Otherwise will never be accurate! Dyno numbers suck.

383backinblack

the point is there is no way a gtech any where near as accurate as a chassis dyno.....

and if this bandit 454 guy thinks his car is gonna take out our 10,000lb fire breathing monster truck with 6' tall tires.....

hes smokin the reefer a little too often.

25thmustang

Your gonna race him in the Monster truck, hahah!!!

LUVmy92

No hes not gonna race him.......hes gonna crush him!
Monster trucks = Kick ***!:rockon: :hail:

bandit454

383, What makes you so confident in your going to win???? You have no clue what I have, as I said, come on down and we will go to it. BTW, why wasn't you at Huntsville this weekend?