Ahhh...Casper I'd love to hear your explanation as to how you know the gtech reads off on 0-60...? In fact the numbers stack up great as compared to the mfg stock numbers for 0-60, considering my mods and drag radials, 4.77 is right on, better...!

Have you ever even used a gtech, and if so why aren't giving us your numbers as opposed to mouthing off.

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99 SS, Dark Metallic Blue, M6
SLP lid, KN, TBB, SLP Y-pipe, SLP loudmouth
ported MAFs, Nitto 315 DRs
Currently: 1/4 13.06@113.8 (gtech runs high in mph by about 4mph), 0-60 4.77 (w/passenger) Gtech'd
12.99@110.2, 2.06 60ft - Tazzo.

 

Wow, this is an old one. However, the TAzzo is now $99.99 and I think i'm going to get one. How far off on the MPH is it? I know the G-Tech is 4 or 5 MPH high but how does the Tazzo compare?

 

The g-tech gives you net horse power there is a system you have to put in to get the air drag, road drag, such to get close to the right horse power,there is a web page on the system they use.it wont give you rear wheel, or flywheel horsepower. Only net horsepower
This form will calculate the HP that is lost due to aerodynamic drag at a given speed

http://www.gtechprosupport.com/support/index.htm

Also the mph is higher because of wheelspin or wheel hop and im pretty sure at the track it gives you an average of the last 60 to 80 feet. somewhere in there anyway. I have the g-tech pro, which I love . I took it to the track also and it is as they say, very very close even in 60' times. as long as you get a good launch. Most important the road has to be as flat as it can be and not a lot of bumps.Here is a forum if you want to know anything on g-tech..

http://www.gtechproforums.com/forums/index.php?s=

 

The MPH is off because trap speeds are averaged over a distance. Not from wheel spin.

Wheel spin, clutch slippage, or converter not flashing will throw off a chassis dynos also. It also can be manipulated as well as the G-tech. It also can't measure gains from a CAI or ramair. Neither are really 100% correct.

BTW, WHP = NET HP. Gross hp is measured @ the flywheel.

 

The Gtech, on the other hand, does just the opposite.... it calculates HP from velocity, acceleration and vehicle weight, and then (with knowledge of RPMs) calculates TQ from HP, using the same formula listed above.
The Gtech measures NET horsepower, which takes aero drag and the rolling resistance of the road into account. A dyno does not have to contend with aero drag but the Gtech does. This often accounts for a large part of the difference between a dyno slip and the Gtech results.

The Gtech calculates HP & TQ by mathematical calculations based on the output of its sensors (the accelerometers.) Therefore, the extent to which the sensors measure the true output of the vehicle is the extent to which your readings will be meaningful.
The previous item, "in English", means that you MUST take every step possible to ensure that the Gtech is subjected to no external factors that will impact your vehicle's acceleration. To point:
There must be no wheelhop or wheelspin during the measurement
There must be no clutch slip during the measurement
There must be no headwind/tailwind during the measurement
There must be no slope / grade to the road or track surface, i.e. it must be level and flat.
Losses or "slop" in torque converters (for vehicles that have them) can wreak all sorts of havoc. Just as a slipping clutch will not deliver full power from the engine to the transmission, some torque converters really convolute the power delivery curve.

This is taken off the g-tech page. You will not get the right wheel or flywheel horsepower readings.

Also I had a post in the g-tech forums about a higher mph.. They told me if you get any wheel spin it will read higher mph.. A lot of people had this problem/concern.

 

Like I said, each can be manipulated and each has its pros/cons ofor what it does and can't measure. I personally haven't used the g-tech for hp measurements yet. Probably will if I can find a suitable place.
Net HP is still wheel HP.

If I let off the clutch easy and then get on the gas w/out wheel spin, I still get the same trap speed from the g-tech as I do by spinning. I've tried it both ways in 3 cars. Its been consistantly 4-5 mph high when compared the track trap speeds.

I still only use the g-tech as a tool to see how/if mods are working.

 

Ummmm BTW no.
rwhp is rwhp.
gross hp is the flywheel hp with no exhaust and no accessories, no alt, no ps pump, sometimes not even a water pump.
Net hp is the flywheel hp with all of the accessories on and functioning with a full exhaust.

 

Drivetrain loss is also factored in for Net HP. Guess it depends on if you want Net HP at the flywheel or at the wheels. Go check out some of the HP calculators and they'll figure net hp as whell hp.

 

So is it safe to say that the G-Tech units and the Tazzo will all read roughly 4-5 MPH too high compared to what you would get at the track? Assuming you don't have a track within 200 miles of you and you want to go by one of these units for your times, of course.

 

yes

 

Ok I guess someone should post in the g-tech forums this info, because all the techs that made the g-tech are wrong.. What they say about horsepower is it will be low on the g-tech because it does net horsepower,,not flywheel or rearwheel.. pretty simple. i will leave it up to you to explaine to them how their product works..

http://www.gtechproforums.com/forums/index.php?s=

Here is the link,,

 

The horsepower at the wheels is the horsepower at the wheels. There is no net rwhp or gross rwhp. Any calculator that figures net hp is figuring flywheel hp from rwhp with all accessories and exhaust. People can dream up all the calculators in the world to try to guess what hp here would be if hp there is such and such. But there are only 3 real hp ratings gross fhp, net fhp and r(or front)whp.

 

Net is NET FLYWHEEL HORSEPOWER.

 

Net HP is not the same as Wheel HP
Net HP (or Road HP as I like to call it) includes aerodynamic drag and rolling friction. To get to Wheel HP (WHP) you need to adjust net HP for aerodynamic drag HP (ADHP) and rolling friction HP(RFHP).

Net HP = WHP - ADHP - RFHP

therefore.

WHP = NetHP + ADHP + RFHP

WHP is what dyno's usually measure.

As an example see:

Sample HP Breakdown (Audi '01 S4 Stage 2+)

Bruce

http://pictureposter.audiworld.com/4...est_bej_s4.jpg

 

But that is all a fantasy number. And it means nothing. It can NOT be measured. It's an if the road is absolutely dead level and if there is absolutely no wind. Never happen for a long enough time to measure anything.
Net hp IS flywheel hp with accessories.
Gross hp IS flywheel hp without accessories.
RW(FW) hp IS the horsepower generated at the wheels.
All of these are measureable under controlled conditions.

I'm not arguing that friction and aerodynamic wind drag aren't real numbers. But they have nothing to do with horsepower ratings. Cars don't make horsepower, engines and motors do.