I am wondering if this wouldn't be a far more fun, and far less expensive option to a standard three dyno pulls to measure your actual power output($24 total for unlimited runs on Test and Tune nights at Tulsa Raceway Park vs. $150-odd for three pulls at Toyspeed). If you know your true weight, gearing, and rpm range and can do a little math it ought to be pretty real-world accurate. Opinions?
If you are ok with burning some runs, shift to 4th as early as you can, and do as much between 2-3k up to redline. For things like spark, that should show you more with the curve shape.
But other than that, yes, you can do that. Take a lot of data, and know how it should look.
Be aware that you will get more of a power estimate vs a hard and fast number.
Tuning, though- good stuff!
Wouldn't wheelspin play a big factory in how accurate that would be? I'd guess you'd be better off with the usual accelerometer based solution (e.g. Torque app), which could be applied well at the 1/4 mile.
Check out the calculators, I think Wallace racing? Has a bunch.
With the little bit of drag racing I have done, they have impressed me with accuracy.
Plus, it's measuring what actually matters (acceleration or time).
BrokenYugo wrote: Wouldn't wheelspin play a big factory in how accurate that would be? I'd guess you'd be better off with the usual accelerometer based solution (e.g. Torque app), which could be applied well at the 1/4 mile.
Wheelspin is pretty much a non issue once you get to the end of the track.
I know some of the online calculators were pretty accurate with my capri and its crate motor. Although changing cam and heads at the same time as tire size made it seem a bit off.
Depends on your goal.
Yes, 1/4 mile trap speed will let you estimate the hp of the vehicle because it's relatively insensitive to things like shifting time and launch technique. If your goal is to compare power numbers with your buddies for bragging rights, then it's great.
Where it falls down is if you want to use that data to try to tune the car to improve the power because for that you need something that is more detailed than a single number, specifically a dyno chart which shows power/torque across a range of RPMs. You can use the car itself as an inertial dyno, this is the basis of the "virtual dyno" software out there.
Compared to a real dyno, virtual dyno has a number of significant disadvantages. It's sensitive to the car's weight, aero drag, tire drag, and road inclination. You also typically want to dyno a car in the 1:1 gear, which requires a lot of speed. My Miata (6-speed, 3.636:1 rear end) redlines 5th at 135 mph, which is serious go-directly-to-jail territory if you do it on the street, and probably too fast to hit in the quarter mile.
BrokenYugo wrote: Wouldn't wheelspin play a big factory in how accurate that would be? I'd guess you'd be better off with the usual accelerometer based solution (e.g. Torque app), which could be applied well at the 1/4 mile.
That's the beauty of it. A good and bad launch will still net very similar trap speeds. ET will change a lot.
I do my "dyno testing" at the dragstrip for exactly the reasons stated. It's a lot cheaper and it's a lot more fun.
Really, you don't even need a calculator, just tune for the highest trap speed.
Moroso used to sell a pocket dyno that used trap speed, vehicle weight, and gear ratio to tell you how much power you are putting to the ground.. I recall it being less than $5..
If you have an ACCURATE race weight, your trap speed will tell you your horsepower. If you don't have an accurate race weight, i would not consider it any kind of substitute for a dyno run.
Knurled wrote:BrokenYugo wrote: Wouldn't wheelspin play a big factory in how accurate that would be? I'd guess you'd be better off with the usual accelerometer based solution (e.g. Torque app), which could be applied well at the 1/4 mile.That's the beauty of it. A good and bad launch will still net very similar trap speeds. ET will change a lot. I do my "dyno testing" at the dragstrip for exactly the reasons stated. It's a lot cheaper and it's a lot more fun. Really, you don't even need a calculator, just tune for the highest trap speed.
This was my thinking! I don't actually intend to ECM tune much on Test and Tune nights, just use it as a progress gauge and for rough improvements. When the final build is finished I am absolutely taking it to Toyspeed for a full on-dyno spark and fuel sweep and steady-state full and part-throttle tuning session to get every last 10th of a horsepower and best throttle response out of it, because road racer.
Vigo wrote: If you have an ACCURATE race weight, your trap speed will tell you your horsepower. If you don't have an accurate race weight, i would not consider it any kind of substitute for a dyno run.
I figured as much, and I do.
Knurled wrote:BrokenYugo wrote: Wouldn't wheelspin play a big factory in how accurate that would be? I'd guess you'd be better off with the usual accelerometer based solution (e.g. Torque app), which could be applied well at the 1/4 mile.That's the beauty of it. A good and bad launch will still net very similar trap speeds. ET will change a lot. I do my "dyno testing" at the dragstrip for exactly the reasons stated. It's a lot cheaper and it's a lot more fun. Really, you don't even need a calculator, just tune for the highest trap speed.
That makes sense, for some reason I had it in my head that overcooked launch=low trap speed for ET, not the other way around.
Yes and No.
The MPH=HP correlation is more of a system efficacy and less of a HP/Wt=MPH outcome.
Why? Well here are 3 examples
Our 3,814# 1960 Studebaker runs thru the traps at 123 mph. It is moving an estimated 153 HP worth of air out of the way. The same drivetrain would produce the same HP in a modern slickmobile, but would run 7-9 MPH faster.
Our $2015 Challenge Bugzilla ran 105+ MPH at the 1/8 and only 122 in the quarter. The challenge is a time based event so we do everything to sprint out of the hole, and then make a peanut butter sandwich waiting for the finish line. Based on those MPHs, we are at 95 less HP from the 1/8 to the 1/4. In reality, its gear bound. If I optimized the gearing for ET and MPH, we would be .10-.15 less quick, and 5 MPH faster.
If you are not gear bound, a MPH/HP calculator will tell you if a change had a net benefit. At 2700#, 10.3 HP equals 1 MPH. On our $2006 Datsun, I modified the air intake multiple times and ultimately made 1.7 more MPH. That calculates to 17.5 HP. In reality it was more because the positive effect is only at higher speed and you run out of track before you see the whole benefit of the power increase. Regardless, the calculation said 17+ and I was happy.
Simply stated - Not being gear bound or aero stalled allow the quarter numbers to be translated into practical reference numbers, but not absolutes.
For tuning look at your 1/8th to 1/4 incremental times. That takes 95% of the error out.
Paul_VR6 wrote: For tuning look at your 1/8th to 1/4 incremental times. That takes 95% of the error out.
Ahhh, for tuning look at your plugs. Lean is fast for a little while. Just sayin'.
what about power under the curve?
I know for autocrossers that's more important than peak power or trap speed.
To what Mr Nelson was saying, it IS a lot more accurate on slower cars. Aero becomes a huge factor at higher trap speeds.
Mister Fister wrote: what about power under the curve? I know for autocrossers that's more important than peak power or trap speed.
Unless you're data logging and using virtual dyno, there's no curve being plotted, just a single point. If you tweaked something that added power between 3000 and 5000 but lost power between 5000 and 7000, you might well get the same number out.
I use a programmable/datalogging ECU system on my Hayabusa-powered sports racer, and have an AIM Solo GPS lap timer. I did my initial tuning at Summit point and used turn 10 exit @ X rpm to braking at the 300' board, looking at maximum speed at the braking point. It was easy to see what AFR gave the highest trap speed, and I used my familiarity w/ Summit to judge how well the car was getting off the rest of the corners.
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