Hi - A bunch of us recently used a GTech meter to measure rear wheel horsepower on our cars. I was expecting to see about 290HP to the wheels from a mostly stock C5 (1999) Vette, but the result was much less (235 peak HP).
The other two cars (MR2 Turbo, and EVO 8) produced numbers that seemed more reasonable, and because of that I think we were getting good values from the GTech meter.
Here is the graph from the Vette:



We did take some measurements of the spark plug wires and noticed that one wire was at 1500ohms, while the other 7 were at 500. The spark plugs all look good (no cracked insulators). From the graph the torque bounces up and down a good bit - perhaps from a breaking up ignition?
The rest of the graphs (and video) are here:
http://lovehorsepower.com/forum/index.php?topic=192.0

We did manage a 0-60MPH time of 5.3 seconds (see video):
http://www.lovehorsepower.com/Videos...vember2007.wmv

Any other ideas on what could account for the missing power? Does anyone have similar data using a GTech meter on a stock C5?
Thanks for any help!

-Joe

 

It could be the weight that you put in for your car. How much did you put in? What gear was that pull in. My gtech said I had about 280 which I suspect is low. Unless you have it perfect then the hp and tq will be off. The pitch setting may also affect the reading. You also have to figure that wind resistance is going to affect the reading as well.

 

In looking at the graph two things come to mind immediately.
1) There is a note shown that the firmware in the G-Tech unit is not up to date. Software / firmware incompatibilities can cause all sort of crazy readings. Download and install the firmware upgrade from their web site and try again.
2) The 0-60 ft time is horrible 3.7 seconds ---- a reasonably hard launch with street tires should show around 2 seconds and with drag radials less than that.
How hard did you launch on the run recorded ??

 

your chart in your post shows a 0-60 of 8.5 sec which is more consistent with the low hp.Which 0-60 is correct?

 

The chart's 0-60MPH time is different because a horsepower test is different than a 0-60MPH test. In a horsepower test, you don't launch the car, you just start out 'normal' in 1st gear, switch to second gear, and then floor it up to red-line.

The latest firmware has been uploaded to the GTech meter. I think the reason the software shows that it is out of date, is that perhaps support for this meter is lagging behind the RR and SS versions? It is the GTech Competion meter:


The other two cars were tested on the same day, same conditions, and the results seemed correct - ie similar to results previously tested, and to actual dyno numbers. I've tested my own MR2 many times using the GTech meter, so I'm sure the method was correct. Sure the GTech meter isn't perfect, but 50-60HP is a lot to be off by. We ran the test multiple times, and this was the highest recorded values.
Even on different days and very different conditions, I"ll get similar results of HP/Torque with the meter - never is it that far off.

I'm guessing something is wrong mechanically - ignition, fuel, something. Any ideas?

As to the weight entered, we actually specified a higher weight than we should have, which would result in a higher reading, but since we got a lower reading, we figured something else (mechanical) must be wrong.

Please keep in mind that the data shown is for the horsepower test, not the 0-60MPH test.
Here is the data from the 0-60MPH test:



See video for the 0-60MPH test:
http://www.lovehorsepower.com/Videos...vember2007.wmv

 

Joe,
I tested my old OEM wires (only two were bad-a spark plug change gone bad). If I recall correctly they tested at near 600 ohms. I could send you the one one closest to 500 ohms for free if you want to swap it in.

 

Why did you let that evo and mr2 beat you!? Gotta work on traction.

 

Just to clarify, Joe is my brother and this is my car we are discussing. As far as the GTech goes, both the MR2 and EVO have been to a 1/4 mile track, and on several dynos and the meter was always almost exactly what the dynos and track times were.
Thanks for the plug wire offer, but I'm going to get a new set from Gene. One last thing, the video of me with the burnout was not my best time, I got the 5.3 time doing much less wheel spin.

 

Yes! Please help my brother figure out what's wrong!


Beside new plugs wires, what else could it be? Fuel filter / pump? Bad air flow sensor? There are no codes stored.

-Joe
http://videos.lovehorsepower.com

 

I think your horsepower is normal for a gtech. Here's a shot of mine on street tires. The upper is supercharged, the lower is stock. Gtech's are different than dynos, in that, the gtech is more of a real world number. It takes into account drivetrain losses, rolling resistance, air resistance. I've got a stock dyno pull of 358rwhp, significantly more than the gtech shows. I've also got 2 dyno pulls with the supercharger showing 507 rwhp, also significantly more than the gtech. Dont try and compare gtech hp to dyno hp.

 

itchynackers - thank you for posting your results.

It looks like you launched the car and then plotted out horsepower using the GTech meter. This will not result in valid horsepower numbers.
To measure horsepower with the GTech, you start out gently in 1st gear - just enough to trigger the meter;
then switch up to 2nd gear and floor it from a low RPM until red-line.
Assuming you do not have wheel spin in 2nd gear, you should get valid results. Anytime there is wheel spin, you will not have valid horsepower and torque figures.

Check out the support page on the GTech site on how to run horsepower tests:
http://www.gtechprosupport.com/support/HP1.htm

In my own experience, a real dyno has been close to the GTech meter. Here is the GTech results on my own MR2 turbo:


Here is the horsepower from a real dyno:


The GTech did show a higher peak horsepower, but the overall shape of the HP and torque curve is very similar.

Assuming that the meter is not invalid, and the test we performed is not invalid, what could be causing a loss of 50-60HP?

Thanks!

-Joe
http://videos.lovehorsepower.com

 

I lose traction at the top of second gear. I have an older G-tech but was considering upgrading since I was very happy with the old one but would like the memory and charting features on the new one.

Have you guys tried a 3rd gear pull and are the results correct? I would think the G's would be less, but for a longer time...so it would still chart correctly....or would it?

 

You can certainly do the runs in 3rd gear - as long as you have enough straight road to complete it. Just start off in 1st to trigger the meter, switch up to 3rd gear and then go WOT until red line.
Check out the HP instructions here:
http://www.gtechprosupport.com/support/HP1.htm

It says:
"# Before doing any runs, you must decide in your head which gear you are going to use for all your measurements:

* A general rule of thumb is that you should use the lowest gear where you won't experience any wheelspin/wheelhop/clutchslip under full throttle acceleration. For many unmodified cars, even sports cars, 2nd gear is fine for this. You will have to see for yourself. Some higher powered vehicles might need 3rd gear to get clean, smooth acceleration throughout the entire RPM range."

Looks like you have one of them 'higher powered vehicles'!


-Joe
http://forum.lovehorsepower.com

 

I've done hp runs only, and the results were the same...

 

Accurate weight is an important factor. I just guess-timated mine and my HP reading was 280 also, but a few weeks earlier had it at 340 rwhp on a mustang dyno. Looking in the book I believe it mentions it will be less then rwhp, but I think it's still a good measuring stick to see how your mods are progressing.

 

Yep Stock 3.42 gears, textrailia Oz700, and ~420rwhp = wheelspin after ~4000rpm. My torque curve jumps from ~360ft lbs to 395ft lbs between 4000-4200rpm and that's where I usually lose traction every time.

Of course according to forum policy I'm supposed to say that I'll be doing my 3rd gear 100+mph pull somewhere off public roads (a nearby track). I'll see what gifts I get for Christmas, might be a good gift certificate purchase (G-tech).

 

It's an excellent device - very valuable for tuning and measuring the effectiveness of modifications. I love it!
Accurate weight is very important. I've found that local recycling places will sometimes measure your car's weight for free.

So - assuming the GTech is giving valid information (we'll probably re-run the test again), does anyone have any ideas on what the cause could be for being down around 50HP?

Thanks.

-Joe
http://forum.lovehorsepower.com

 

If the car hasn't been beaten on (high revs for a long period..eg a dyno pull or WOT run on highway) the engine will carbon up and you'll get a TON of knock retard the first time your do your pull. After cleaning out the carbon, your knock should dissipate and you'll magically "gain" hp in subsequent runs. If not, might be time for some SeaFoam treatment (there are tons of threads on how to do this).

Also your tune could be off. You say "mostly" stock...but if you changed the air filter OR intake OR exhaust, etc...your stock tune could be lean enough to cause knock retard and also lose big power. Lastly, a dirty MAF will also throw off your tune and provide lousy performance.

Those are just a few reasons off the top of my head why your performance is significantly different than what you expect. They're all free or almost free (except for the professional tune) so you might as well rule out the cheap stuff first.

 

Thanks Billdog350 - We'll take a look at the MAF, and I'll talk to my brother about any modifications. I believe it has an intake, exhaust, and headers.

From a dyno, I would expect to see a rise in power and then a sharp decrease if there was detonation. But I'm not familiar with how GM's engine control system works - perhaps it responds very quickly.

Thanks again - I'll post here with what we find.

-Joe
http://videos.lovehorsepower.com

 

Hard to tell from your chart since its not a "true" dyno chart...but look at 4750rpm...there is a dip that doesn't fully recover...and then several other ones that reduce your peak. Again it could be just your software but you should be seeing a SMOOTH chart all the way to peak...any dips can mean air/fuel issues or spark.

So he has headers, intake and exhaust and no tune? You're VERY likely running lean and getting significant knock and/or a bad AFR at WOT. That can account for most or all of your performance issues.

Don't get a hypertech! Make sure to bring it to a respected tuner or buy HP tuners/EFI Live and tune it yourself on a dyno.