toyota_scion_tc

I took my car to the dyno today. I finally got my flanges to add in my cat on the midpipe and re-installed the header then drove 1hr to the dyno. Cel was on and the humidity was very high. I didn't disconnect the battery to let the ecu learn the engine. I am hoping that this affected my dyno. This was done on a dynojet and in the correct gear (4th) for the dyno. Also this was by the SAE not the STD correction.

I will have to get a digital camera to show you the graph but the Power at the wheels are

154.1 hp

158.1 tq

Beantowntc

That's decent, nice numbers right around what everyone with the same mods are getting...

dp-_-

No it isn't.....I got about 8 hp and 1 tq higher....and he has a pulley....

toyota_scion_tc

What gear did they dyno yours in? Did they use SAE correction or STD? Was there a load on your dyno?

Beantowntc

I didn't even notice he had a pulley too....most are getting closer to 160 with just i/h/e and s pipe.....hmm

toyota_scion_tc

I think the humidity and the cel screwed my dyno up.

dp-_-

I dunno.

I don't know jack about dyno's

can you tell me?

https://www.scionlife.com/forums/viewtopic.php?t=103795

Whocares05050

Wow, Thats no were neer what you should have gotten with all the mods listed in ut profile. Are you going back to try again?

senseiturtle

Please see my post about dyno misconceptions.

His numbers should NOT be used for comparison.

dp-_-

sorry if it seems like I'm hijacking, but it's good info if this can be answered!

So I spoke with the dyno shop I went to. The dyno is not loaded but explained that they ran in 3rd gear b/c due to the torque and weight of the vehicle, 3rd gear would produce higher numbers.

He also went on to say somethign about a 6500lb inertia something or another while most use 3500lbs.

Question though....

based on seeing senseiturtle's post about dyno's, is there a standard method to dyno? As in, is there any assumed "correct way?"

senseiturtle

Treat it as a scientific experiment...

1- Must have an independant and dependant variable. These are locked... engine RPM vs. Torque at the wheels. (Horsepower is computed later)

2- Must be repeatable.

Therefore, an unloaded dyno is just as valid as a load dyno. However, they are NOT to be compared. The thing is, people are using dynos to come up with a peak HP figure, and then trying to claim they have the "best setup" for maximum gains based off of that final number. This is something parts companies do to sell their products, occiasionally at the expense of accuracy.

This is how you're supposed to use a dyno:

a- Baseline the car.
b- Make a change.
c- Re-run the car, compare to original baseline.

Repeat as necessary to maximize your numbers for the day, and that's it ! If you want to see how fast it is, run it down the 1/4. MPH determines car strength, and E.T. determines both strength and driver in combination. Those figures are valid comparisons worldwide, since they're theroetically repeatable worldwide (with a correction factor.)

If you gain 5% from your changes during the dyno, then you can be safely assured that your car is definitley 5% stronger than it was before. However, you cannot compare to some other car on some other dyno due to the fact that it's a new day with a new set of conditions, a different dyno, etc..

Nick06tC

sensieturtle sounds right. You can find a dyno that says you have 3000 hp base. Yes that number wont compare to someone who is on an accurate dyno. But if you make a change( install header turbo or whatever) then redyno it and now dyno at 3035 hp. The dyno worked. The number pretty much means nothing but bragging rights of whose dyno ran higher. Unless 2 cars are ran on Identical dynos on the same day with same conditions, the comparrison means nothing.
BUT, It is good to get a general idea of how well the car is doing comparitively. but within say 10 hp i would THINK you cant say my car has more horsepower than yours and be 100%true.

just my thoughts.

Nice setup and numbers.

senseiturtle

A thought hit me as I was getting in the car, I don't think I answered the question posted to me above.


A dyno is run in either 3rd or 4th gear in order to ensure "smoothness" by being able to take more readings over a larger timeframe. The computer can only measure torque every so many fractions of a second, so if the car takes longer to go through the whole rev range, there are more data points entered... and therefore, a smoother graph.

Balance this with the fact that the computer can only store so many data points, and we dont want to take entire minutes to do one run... that's why we don't do it in 5th.

As far as recognizing the difference between 3rd and 4th gear, the dyno is usually able to determine a RPM per MPH measurement per each gear by attaching a sensor onto one of the spark plug wires. This RPM/MPH figure is then used to determine torque at the wheels, which is then converted to HP based on the formula ( HP = [TQ*RPM]/5252 )

dp-_-

So does that mean that since the engine spins up faster in 3rd, therefore a 3rd gear pull would yield higher scores than 4th?

toyota_scion_tc

a third gear pull yields more because your engine turns one turn to 1.33 turns of your transmission creating a higher hp and tq even though it isn;t true. A fourth gear pull shows your engines true power it is almost equal 1 engine rotation to 1 transmission rotation, meaning a 1-1 ratio. That is why you need to do a 4th gear pull and not a 3rd gear pull.

toyota_scion_tc

Read again! CEL was on and I didn't reset my ecu. I am going back. I reset my ecu today and installed my o2 sensor on my cat so I won't ever set another cel. I am planing on going again when the weather is nice and the humidity is a lot lower the humidity on that run was extremely high.

ivandrios

sorry for the noob question guys but whats the diff. between whp and hp. how would you read 160whp into reg. hp? and how much does a dyno usually cost to do?

senseiturtle

Well... sorta.

What toyota_scion_tc is trying to illustrate is the effect of gear ratios on true torque output at the wheels.

Let's create an example scion tC, which produces 150 lb-feet of torque at the wheels. The formula for torque comes down to (force)x(distance), so if you give a strong guy a 2-foot lever attached to the axle, and he pushes on it with 75 lbs of force, he should technically produce the same torque as your motor does.

While the above is statistically correct... it's totally un-feasable. 6 guys couldn't push your car 1/4 of a mile in under 15 minutes. So how is your little 4-banger able to accelerate your car to such high speed?


The answer my friend, is leverage. Let's compute overall gear ratios for each gear... this is determined by multiplying-- (final drive ratio)x(gear ratio)x(axle/differential ratio).... since the tC doesn't have a rear differential with another gear multiple, its just (final drive)x(gear ratio).

Final Drive - 4.24
Gear.............. Gear Ratio..............Overall ratio
1st ................3.54:1..................... 14.98:1
2nd ................2.05:1..................... 8.66:1
3rd.................. 1.33:1.................... 5.65:1
4th ..................0.97:1 ....................4.12:1
5th................... 0.78:1 ..................3.28:1

Physics is now our friend. Since our motor puts out 150 torque, the actual force at the wheels is equal to = (torque)(Overall ratio)

(150)(14.98 ) === 2247 !!

Yes, your tC has 2247 wheel torque! This should be enough force to get things moving along quite nicely....

Let's do second gear--
(150)(8.66) = 1299
Still plenty of force, but a significant reduction. This makes sense... you accelerate slower in 2nd than in 1st.

Now, to go back to what toyota_scion_tc was saying... If you truly wanted to get as close as you can to a 1:1 ratio of driveshaft revolutions to crankshaft revolutions, then you'd want to dyno in 5th... where the crankshaft rotates 3.28 times for every 1 rotation of the drive wheels.... but again, this isn't done for 2 reasons-

1- The computer will determine the RPM/MPH factor (read, gear ratio ) for each run by measuring spark pulses in conjunction with wheel speed.

and 2- The sheer number of datapoints of torque measurements taken every 0.1 seconds over a 30-second run would overwhelm most low-grade computers used as dyno computers... in addition to absorbing valuable dyno time.

Hope this helps.

senseiturtle

whp = horsepower measured at the wheels, includes losses due to friction-

bhp, advertised hp = horsepower measured at the crank, does not include friction.



160 whp on a dynojet = about 188 bhp, assuming 15% drivetrain loss.

160whp on a load-bearing dyno = about 200 bhp, assuming 15% drivetrain loss and another 10% or so for engine load factors in the dyno itself.

My friend charges about $75 for 3 pulls. This is about the going rate. Sometimes they do it per-hour, check your local shops.

dp-_-

So, to round things up, essentially, all dynos are crap except the one that you use...so long as it's the same one....

yes?

lol.