....I'm sad to find out that I have one of the wimpiest corvettes in this forum. I went to Westech Performance Group today for my first dyno test. They were great and talk about friendy folks! Great people.

I was all excited because I was finally going to have my very first real test of how many ponies my C5 has. Granted, I haven't made a lot of modifications to the car but you know how it is when you change the windshield wiper blade and they tell you that you just gained 10 HP just by doing that!

Well, my biggest mistake was never doing a baseline test before doing anything on the car. That way I would've known exactly how much each modification was getting me. But, too late for that now. I went and got my black beauty strapped up and tested.....boo hoo hoo .......it is with great pain and sorrow that I hereby announce that my C5 only has 332 HP to the rear wheel. They couldn't tell me exactly how much I have to the flywheel because they would have to dismount the engine and test it separately. Similarly, they could not measure exactly how much total power my car had.

I asked them to give me an estimate and they said I had about 392 BHP (using some complicated formula). Lee would probably know about that. I couldn't even break 400! [][]

Ok, I need to go get some Ben & Jerry's right about now! .... and if you see me driving down the street in my C5...please try not to pass me up too fast....it'll just hurt my feelings [][][]


Additional Data:

332 HP at 5774 RPM. Speed of 134.2 mph in 3rd Gear. (4-speed automatic transmission). Top Speed = 145 mph (this part I didn't understand....especially since they didn't take the car into 4th gear......I thought my car could go a lot faster than that). My Air/Fuel Ratio = 11.4 @ 5774 RPM and 14.7 @ 3333 RPM.

 

rufaryif
don't beat yourself up too bad. Actually not bad at the rear wheels. Now I'm curious what mine would put out, just being stock with no modifications yet.
I'm just curious, if you don't mind me asking how much did they charge you?
I've been looking for a shop here in my area, and have'nt found one yet, but hoping there's one here in the area somewhere.

 

gorichb,

I live in Southern California. The place I went to charged me $125. It took about 1-1/2 hours to complete. They also have engine dyno testing but you have to take the engine out of the car for that. I think those run about $650 for the dyno test.

 

That's not bad at all for an automatic.

 

This is pretty good. You car is running about 387 HP at the flywheel.

Some comments:

First 332 HP at the RW is pretty good. You have an A4 and stock it probably did about 300 to the rear wheels (meaning it had about 50 HP lost in the drivetrain from flywheel to rear wheels, or 14.3% of the stock flywheel rating of 350 HP).

The shop got its estimate of of 392 this way. They used an assumed 18% driveline losses, and applied the formula:

Estimated flywheel HP = (measured rear wheel HP)*118%

And, 392 = 332 x 118%. Hence the figure they gave you.

About a week ago in the General Tech section, I went over how to accurately convert RWHP to estimated flywheel: it is a bit more complicated than that formula. As I said in that earlier post, shops and speed-part vendors always use the most optimisitc figures and formula they can reasonably quote: and the higher the assumed driveline losses, the higher the estimated flywheel HP reading they get by applying the formula to any actual RWHP test. For example, with that same formula above, if you assumed your car had 20.5% instead of 18% driveline losses, the formula would give exactly 400 HP: that would really please you if the shop told you that and you believed them. But 20.5% is way too high -- a lot of people would know the shop was BS-ing them with such figures. However, many people accept and assumed 15% driveline losses figure as reasonable for manual trans cars, and 18% -- the figure you shop used -- for automatic trans cars.

These figures were valid many years ago for most cars, but not today. Modern low-viscosity oil, and modern efficient (if big) tires reduce driveline losses, as does the type of torque tube driveshaft and rear end design in the vette.

But in actuality, "vettes have only about 11.4% driveline losses for the manual trans cars and about 14.3% in the automatic (at least A4 automatics, I do not have enough experience with the new 6-speed autos in the latest C6s to know what its losses are).

So, the correct way to estimate HP on your car from now on is:

First, convert the 14.3% driveline losses to percentage of measured rear wheel HP, the 50- HP lost is 16.6% of the 300 HP stock rear wheel reading most A4s give.

Estimated flywheel HP = (measured rear wheel)*1.166 --> 387 HP

Thus, I'd guess your car has 387 at the flywheel, meaning you have picked up a solid 37 flywheel HP over stock. That's pretty good. Not knowing what mods you have, I would assume you have headers, a very good cat back exhaust, and a good cool air intake to make that, and a very good tune, as it would take all that to make this much additional power.

Finally, the 145 mph top speed is the top speed the shop ran the car up to on the dyno., keeping it in third gear. If 5774 RPM was 134.2 mph in third gear, then 145 mph would be 6250 RPM, meaning that, as they should, they ran the car past the power peak (5774 RPM) and on up to the redline in the dyno test, so they got the full RPM range HP curve. Your car has a top speed around 170, but will get to 145 in third, as it did in this test.

 

I just looked at the mods you list.

'02 Black, Auto, Bassani Cat Back,
Vortex Ram Air, Big G Performance Chip,
Mass Air Flow Sensor W/ Cold Air Tune,

Assuming the shop's 332 RWHP reading was correct (some shops dial in a loose dyno so its reads a bit high, but let's assume this shop is pretty legit, as it probably is), you are getting an impressive amount of power for a car that does not have headers on it. I would expect only about 15 RWHP from these mods, 20 max. Are you sure you do not have headers on that car? Generally, it takes headers, and an average cat back and cold air box, plus a re-tune, to give in the neighborhood of the 30+ RWHP you have.

 

Well, Lee....the headers are stock....all I did was replace the computer chip, install the catback, replace the air intake and add the mass air flow sensor.....the final dynojet figure was 332 at the rear wheel. The SuperFlow WinDyn figure was 314 at the rear wheel. They gave me both readings SuperFlow WinDyn and DynoJet. They vary by about 18 horses. Each system (they told me) uses a different formula for computing the HP......I, of course, elected to go with the DynoJet figure!!!! Can you blame me???

I guess it depends on which testing method you think is the better system. Of course, I could always just split the difference and come up with:

Estimated flywheel HP = (323)*1.166 --> 377 HP!

But then you would really be doing some serious harm to my fragile ego

Please Lee....don't do it.....don't do it!!!!

It sounds much better to say;

Estimated flywheel HP = (332)*1.166 --> 387 HP ..... now doesn't that sound much better?

 

Lee....like I said in my previous post.....my headers are stock.... I did replace the computer chip, install the catback, replace the air intake and add the mass air flow sensor.....what would you suggest be my next "bolt-on" mod? I want to reach 350HP at the rear wheel without having to invest in supercharging it. Your thoughts?

 

I'd go with the 387 figure, based on the 332 reading on the Dynojet. The 300 RWHP data I was using to compute the losses and the formula was based on Dynojet readings on stock A4s I've seen, so it is consistent: you would have to develop a different formula to convert the Winjet readings.

 

What correction factor did they use with the Dynojet? SAE correction will generally be lower than STD correction. My C5 with only intake and exhaust put out 328 RWHP (STD), which is the equivalent of 320 RWHP (SAE). The nice thing is my torque of 352.2 lbs-ft (STD) and 346.6 lbs-ft (SAE). That torque is higher than the torque of most stock C5 Z06s. I was very happy with that.

Dave