OST Dyno Day # 3

[Wildsupra]

The way I see it. You car makes much more "true" HP. From the start to your peak power you are making up to 65-70HP more at any given speed than Nigel in the same gear.
Its only after you hit your top HP that he starts to catch up. The end number is not what is most important when comparing your two supras.

ie For the entire shaded section your car is faster.

also agree with this, similar to what i was saying about a laggy car.

Matty

[GeneSPIDA]

Some very interesting points.

And glytch, I'll be trying to apply the same theory this weekend's MaxAction to see if I can consistently reduce my runs.

Get the boost on early, get the boost on early...

[rustyP]

^^ so that means ur car is gonna be putting our more hp and acceleratin faster from the word go all the way to 170k in 4th (which, if im not mistaken, is not something your gonna be doing in most practical situations)
therefore, on the road, ur gonna be well ahead of him before he manages to make almost the same hp (in 5th, doing like 200 clicks)

just goes to show max HP aint everything.

edit: PS. Nigel - no offense! im sure no-one here is trying to bag you out for havin a slow car!

[EldarO]

Todd, how did you come up with the 100mph and 106mph figures? have they actually been run, or using a calculator? (im assuming run).

even then, driver skill plays a massive part in it, and you cant assume that they're the same in the slightest.

of course, you dont care, but i thought id mention it.

Eldar.O.

[JZA70 R]

I think ill get the 2 cars strapped to another dyno, where the dyno operators actually know where to place IT sensors. It might prove my point a little better.

If they both make the same HP a 2nd time in the row ill just shuddup .

but for now my bet is on my car making at least 20hp more on a different dyno.

Thats the point im trying to get across.

[chris davey]

I agree with what Glytch has said regarding the power curves. More area under the curve is what will accelerate the car quicker. I believe that as the runs continue and both cars will be in the upper rev ranges and making similar hp and torque then from there it should be fairly even.

However, as the IT seems a lot higher on Nigel's car I do think that shootout mode may have over compensated e.g. if Nigels car was at 29 deg intake temp also then it would have registered a lower curve in general. (I don't know what the actual correction figure is per degree celcius) Say it then made 7.5% less throughout the whole curve and had 240rwhp peak and less torque down low as can be seen by the shape of the hp and boost curves then I could see how if both of these cars weighed the same and both had the same gearing and no traction issues jza70r should pull away from the start line ahead of Nigel's car because of more torque down low and then it would continue to pull away for a quicker ET and faster trap speed. I don't know if this has happened in real life or not but that is what I suspect would happen.

I do think the dyno has over corrected if the 106mph trap speed and 100mph trap speed were done with similar weights.

It would be really helpful if the graphs were in rpm rather than speed IMO. Then you could see where the cars would be during most of a run.

My 2.2c

Also, agree that dynos are tuning tools. Dyno days are just for run and unfortunately no claims can really be based on them. True measure is at the drag strip unless you want to pull the engine out for an engine dyno to compare penis size j/k

Also, sorry to those who aren't SF.com members but I can't copy and paste this as it is too big. It is the physics of how a car with less torque down low can out ET and trap a car with low down torque with the correct gearing and gear change to optimise the torque curve.

BIg read and very technical
http://www.supraforums.com/forum/sho...d.php?t=387509

[chris davey]

ALso, here is another to compare


Different weights and gearing. As both of these cars will make more hp and torque in the lower revs than my car (if they were the same weight for comparisons sake) they would out accelerate my car off the line and then my car would catch up. Unless, (as stated in SF thread) I can launch at optimal revs to make decent torque off the line (which is what I can't do presently). Then the higher hp (and torque depending on rpm) can be utilised earlier in a race and a car with higher hp, higher revs but lower torque down low can out accelerate a car with masses of low down torque.

[JZA70 R]

Thanks Chris, both cars weigh basically the same. both ran in full street trim with stereos and big wheels. Nigel runs 100 mph i run 105 on average.

if both of these cars weighed the same and both had the same gearing and no traction issues jza70r should pull away from the start line ahead of Nigel's car because of more torque down low and then it would continue to pull away for a quicker ET and faster trap speed. I don't know if this has happened in real life or not but that is what I suspect would happen.

Pretty much what exactly happened.

[JZA70 R]

Also i remember Eldar talking about how torqueless and gutless the 1JZ is, and how the 7M is some crazy torque monster hence being a superior motor?

Well...

[WA_TRD_83]

This is turning out to be quite the technical thread.. I like it.. I think I'm learning stuff!

Unfortunately I still have no idea what all these curves and numbers mean on my graph.. I'll have to post a pic of it tonight so people can analise it for me and tell me what needs to be fixed - cos on 1.3bar (17psi) it should have been making more power than it did..

Damo
TRD83

ps. collected disk from Dean with pics & video of the day.. will also try and upload them tonight..

[chris davey]

It is very easy to get hyped up over dyno numbers.

I know I was comparing mine to other 2.5L engines the other day. I know that there are so many variables but you still want to do it

My first dyno with a stock 1jz, 62mm compressor, large turbine a/r (low back pressure) and 20psi through the auto got 192rwkw or 255rwhp. Came down to lack of timing control. (backed up by 108mph trap speed in 2800lb car)

If you can optimize afr’s, with ignition timing to suit (safety margin to knock), keep the charge air cool and have a free flowing system post compressor and post turbine then you should make good power.

[Fish]

yes don't look at the numbers look at the area under the curve. Thats what matters.

An example is to 90Hp gemini motors gearing is exactly the same. One is a DOHC and the other SOHC. the DOHC makes more top end power and slightly more torque. The SOHC makes more mid range and top end power kicks in early. Torques peaks early too. Which one wins? the SOHC does. why? more power early and the area under the curve is better.

[chris davey]

for those who can't see it.

Here are the 2 dynos compared on SF link.

We'll use these two rather extreme examples for this experiment:
First, we have a car that peaks at around 430 ft/lbs at about 4200 RPM, with a peak HP of 395 at about 5700 RPM. 200 ft/lbs is crossed at 2700 RPM, and torque falls to 210 ft/lbs by it's redline of 7300.





Both cars are on 26" tall slicks, with identical, perfectly shifting 93+ LSD transmissions (with a drivetraid loss of, lets say, 16%), ATS Axle cages, 4" skinnies up front, and both cars weigh the same. Both cars weigh 2801.4 pounds, or 87 slugs.
____

Using the E153 gear ratios of-
1. 3.23
2. 1.91
3. 1.25
4. 0.91
5. 0.73
Final gear is 4.28

The following is the process to get the true wheel torque constant.

1st gear: 3.23 x 4.28 = 13.8244 ____ / 1.08333 = 12.26215422 _____ * .85 = 10.423
2nd gear: 1.91 x 4.28 = 8.1748 ____ / 1.08333 = 7.545969463 _____ * .85 = 6.414
3rd gear: 1.25 x 4.28 = 5.35 _______ / 1.08333 = 4.938461554 _____ * .85 = 4.198
4th gear: .91 x 4.28 = 3.89 ________ / 1.08333 = 3.590769232 _____ * .85 = 3.052

___

Fir the first car, using shift point calculations, I have found that the optimal shift points are as follows:
1st > 2nd: 7102 RPM
2nd > 3rd: 6418 RPM
3rd > 4th: 5769 RPM

The optimal shift points for car Two for each gear are past redline, so we will have it shift at its redline of 9100 RPM. This is simply because even at redline where the engine is making only 280 ft/lbs of torque, the wheel torque due to gear multiplication is higher than at any RPM in the next gear higher.
___

Fowl smoke billows from behind the cars as they smoothly reverse back to the starting line. With tires now hot, they begin to rev their engines. Car one, with the aid of 2-step technology, builds boost at 5000 RPMs, while car two builds boost at 6000. The pair of identical robotic drivers, programmed to drive, shift, and react exactly alike, slowly release their clutches as the last yellow dims.

We have seen cars on drag radials and slicks lift the fronts from a dig. If these MR2s weigh 2801.4 pounds, and have a wheelbase of 94.5 inches, with a weight bias of 42/58, that would take 1176.588 pounds of force to lift the front wheels up. With the fulcrum of the car being at the rear wheels, it would take 9265.6305 pounds of force at the contact patch. Speaking that neither of these cars is capable of producing that much torque, we will say that these tires, in this case, are unspinnable (although they technically are spinable, it is not relevant to the case.

As they launch, both cars slip the clutch at their launch RPMs, with, say, approxomately of 300 pounds of torque making it through the clutch, at which time the clutches are fully released and full torque is applied. This means that up until 4200 RPM, both cars have a linear force at the contact patch of 3126.9 pounds, and accelerate at a rate of 35.94 ft/s^2. 4200 RPM in first with these tires is 23.5 MPH, or 34.467 ft/s. Between 0 and 23.5 MPH, the cars both cover a distance of 16.527 feet, in a time of .96 seconds.

At this point, car One's clutch is fully released, with it's full 430 ft/lbs being forced through the drivetrain. Car Two still has it's same 300 ft/lbs at the wheels due to the still slipping clutch. while car one remains at 3126.9 pounds with the same acceleration of 35.94 ft/s^2. At 5000 RPM, it's clutch is also fully released. 5000 RPM in these cars is 28 MPH, or 41.067 ft/s. Between 23.5 and 28 MPH, car Two covers 6.94 feet in .184 seconds. At the same time, car One, with an average force of 4325.545 pounds, has accelerated to 29.74 MPH, and covered a distance of 7.18 feet.

snip

T: 10.444 seconds.
Car Two has finished the race at a speed of 141.046 MPH at 7105 RPM in 4th.

Car One, with an average acceleration of 11.050 ft/s^2, in the additional 344.007 feet required, reaches a speed of 195.821 ft/s (133.514 MPH) in a time of 1.854 seconds.

T: 11.101 seconds.
Car One has finished the race at a speed of 133.514 MPH at 6720 RPM in 4th.

Conclusion:
Even though car Two had 80 ft/lbs less torque, it still made 105 more HP. It seems many would say that this doesnt matter, but I beg to differ, and have shown why. You don't feel horsepower like you can feel torque. Still, in any physical scenario, power (given the name "horse"power in the cause of automobiles) determines overall acceleration of a mass through a given speed range, while torque only determines instantaneous acceleration at a given point. Also note that the car's acceleration is determined by the average torque that the wheels see through multiple gears over several speed ranges, and not just the peak, or even average torque at the crank.

[WA_TRD_83]

owwww ... my brain hurts ...

now becomes too technical for my simple mind to comprehend

has anyone got a picture book which shows what Chris just said!

[chris davey]

Hehe, I skipped all the bits in between starting and finishing!

I think that is the first time I have seen physics as a useful tool