Supra Forums banner

101 - 120 of 133 Posts

·
A zone of danger.
Joined
·
1,175 Posts
Sounds good.

Looks like I'm being bullied in to going to the dyno tonight. I wasn't prepared to make a run at 750+, but I've got a group of guys pushing me to swap plugs, drain the 93 and shoot the moon on 114. I'll warm it up before leaving and take a stab at the idle correction and report back...
 

·
Premium Member
Joined
·
2,887 Posts
Sounds good.

Looks like I'm being bullied in to going to the dyno tonight. I wasn't prepared to make a run at 750+, but I've got a group of guys pushing me to swap plugs, drain the 93 and shoot the moon on 114. I'll warm it up before leaving and take a stab at the idle correction and report back...
Sounds good, I will leave my laptop at home and enjoy not working for once! :beer: Should I have fresh mop water waiting? :love:
 

·
A zone of danger.
Joined
·
1,175 Posts
Sounds good, I will leave my laptop at home and enjoy not working for once! :beer: Should I have fresh mop water waiting? :love:
What'd you say the record is again? Six feet? Pfft....I'll toss a rod at least 8ft if I don't have to go thru the fender. :D I changed the catch can routing, but still might need that mop n bucket for the FMS. :p

I'm good for this weekend if you are, though. Driving the car today and tomorrow to burn up the fuel.
 

·
A zone of danger.
Joined
·
1,175 Posts
My suggestion is to zero out that ign vs idle table temporarily, set the idle dead band to +/- 1000rpm(to kill idle fb) and set the idle% vs target table. After this is set, then put the those things back like they were. When done, I think you'll see your desired idle rpm at close to what your main ignition map is calling for, and the ign vs idle table working close to the zero point.
Hey Kurt,
I quickly gave it a shot this morning before leaving for work...not the results I was hoping for.

Set the dead band to +/-1000rpm and watched the idle. Target: 1000, actual: 1020, so that indeed is where the timing pull was coming from. I lowered the idle% table by 2% for a 995-1005rpm idle. Ign timing is still at 7deg ATDC. Idle AFR is still around 12.7 at this point, so I start adding timing. By the time I hit 0 degrees, the more complete burn pushes the AFR's up to 13.5-14.5 and the idle gets rough again. On top of that, its hunting badly...both RPM and AFR. This may take a while...

However, I'm only going to fight it for so long before I chose comfort over efficiency. Even with the retarded timing and running fat (13-13.5:1) under heavy vacuum at idle, I really can't be putting more than 20-30degC into the manifold - a drop in the bucket considering what WOT or even cruise EGT's are. And the car gets less than 5k mi/yr...far from a daily driver, so fuel consumption at idle be damned. I don't have any implied feedback from the power steering pump, etc. so at some point I'm going to stop worrying about it. I'm just being picky because it's good experience, fun to learn, and to see how close I can get to a goal. :)
 

·
Registered
Joined
·
2,189 Posts
Just noticed your response. :) Well, if it's working for you then it's not that big of a deal! lol I've always found that there's value in trying something even if you don't immediately get what you want, though. There are a lot of tables and options at play for idle, so it's a matter of disabling them so you can change one thing at a time.

I mentioned earlier that I was going to make a pump93 map using the automap feature. I've found it to be a pretty good tool for tuning the fuel table on the street. Others have not! lol I only use this for the low load, cruising portion of my map. For the WOT stuff, I just use the O2FB value to make adjustments. Please review page 135 of the AEM User's Guide to get the basics on it. It's fairly well explained, but they could have done a slightly better job on it!

This function works on the computer, not within the ems. You must disable O2FB for this to work. It's also a good idea to disable accel fuel enrichment as well, but if you're very easy with the throttle while doing this, it's not essential. The Automap Fuel Log is always working when you have it open, but when you're not "automapping" it's just recording data. No changes are made to your fuel map unless you "Start Automapping" or select all the logged cells and "Program Changes".

Obviously, the first step is to fill in the Fuel Target table with what you want a/f to be. See pic below for an example. The User's Guide outlines what to do pretty well here. Some values that I use when starting off are 10 for "Weight before change" and .5 for "Target accuracy". Use the percentage option with -7 as the multiplier. Put the range for % change from 20 to 20. I'm not 100% sure if the negative sign is needed for the minus side, but I have it without the (-) infront and it works for me. I'm usually starting from the rich side, though. These settings will make adjustments very quickly, so they're applicable if you know your map is way off.

The tuning method is simple, get to the rpm breakpoint center (what the aem is showing) and see what the tach says. See the image below where the target is on the bottom left. While watching the tach and the road, keep it right at that rpm at various loads using the brakes to keep you at a constant speed and the throttle to change load. Do this in whatever gear is necessary to get you to the rpm breakpoint you are tuning at a reasonable speed. Do everything very very gradually and you can get a lot of samples for each load point and give the automapping a chance to make good changes. Maybe 20 seconds to go from low to high load for each rpm breakpoint. (up to zero psi) When you've gotten through all that, "stop automapping".

Your fuel map will have peaks and valleys when done. Simply use some logic and smooth it out. What you have is a roughly close fuel map, so an extra automap tune with tighter tolerances will help. Go back to "initialize auto mapping" and set the weight before change to 20, target accuracy to .2, the mulitplier to -3, and +/- range to 10%. Select all the logged values in the automap fuel log, right click and "set weighting" to zero and also "reset states". This gets you back to zero, with fresh data to work with. Now, go out and repeat the method described above.

After this, your map will likely have peaks and valleys again. You can leave it like that or smooth it out some. It's up to you, but either way, it'll be pretty close. Remember to turn O2FB and accel fuel back on after you've finished everything.



 

·
Registered
Joined
·
2,189 Posts
For those with the new Series 2 box, this may help you set up the boost by gear feature. If you look under tabs>hidden tabs in AEMTuner, select "gear".

The main parameter to monitor is "Gear Ratio". Here's a screen shot of a log I made the other day when setting this up. With the Series 2, the inputs are Vehicle Speed and Engine Speed. It's Crank and Vehicle Speed for those with the Series 1. Turn "TC Gear Ratio" on, and set GerCal M to whatever you like. I chose a multiplier of 3 and this put the Gear Ratio number I recorded for 6th a little below 256 (highest value). The Vehicle Speed channel is rather jumpy and I was told this might be addressed in a future update. Just note the highest and lowest value of Gear Ratio for each gear. You set the Gear Ratio table with the data from your log. 1st gear is 1-1.5. 2nd is 2-2.5. ect... In my case, the lowest value I saw for 1st gear was about 45.5 and the highest was 49.5. So, i set 1 at 40 and 1.5 at 50. 2nd was 75.5 to 81, so I entered 74 and 82 for 2 and 2.5 respectively. Just set a little bit wider range than what you record and that's it.



 

Attachments

·
Registered
Joined
·
1,192 Posts
Discussion Starter · #107 ·
Kurt,

What does your fuel map look like after O2 feedback automapping? I tried it a few times, but it really only is applicable for a small portion of the fuel map. I found best performance by having someone drive during cruise at various speeds/loads and bumping the fuel map up/down and then smoothing it out for best results.

-scott
 

·
Registered
Joined
·
2,189 Posts
It's been effective for me from 1800 to 4000rpm and my lowest load up to 0 to 2psi. It would be great to have someone else driving while I make adjustments, but this is a very good solution to do it on your own. What settings did you use when you tried it?

Here's an image of the peaks and valleys I was talking about. And after smoothing it out.



 

Attachments

·
Function over form
Joined
·
2,465 Posts
i am glad to see that my fuel map is looking very similar to yours kurt, so i must be doing something right =D

i've been able to achieve a very close stoich AFR during cruise and light accell without o2 feedback and automapping, though i did try using both of those features in the past and just found them to be confusing. my tuner had told me it is possible to achieve a stoich AFR in cruise without those 2 features though they obviously will only help if you use them correctly. oh well, i'll probably experiment with it more on a dyno when i go for a retune.

kurt, are you familiar with accell enrichment? i'd like to send you my map if possible so you can tell me if my settings are normal or within some kind of normal range. i am noticing a split second delay on delta throttle changes. nothing serious but i'm just curious if it's possible to increase the response time to sensitive throttle changes? seems like my AEM wideband is always a second or 2 behind the EMS reading.
 

·
Registered
Joined
·
2,189 Posts
That's assuming that I'm actually doing it right! lol I think automapping might be a little bit more difficult with an auto due to the torque converter slipping. I guess you can set it to remain locked during the process, though.

Accel is explained really well in the user's guide, actuallyt. The only thing I can add is that the Accel Warm Up Enrichment Table is much much higher for e85 than 93 gas. All of the starting and warm up tables are massively different for e85.
 

·
Registered
Joined
·
2,189 Posts
Series 2 Boost Control

AEM provides a pdf in the instructions folder (AEM Series 2 EMS setup notes- Advanced Boost.pdf) that explains the new boost by gear setup pretty well. There was a change with 01v17 firmware, though, so it looks slightly different. Hopefully this will make setting up the target tables a little more clear.

Boost by gear is not too difficult. You have to set up the Gear Calculated table first. There's actually a Wizard for this, so it's not hard. See attached pic for my settings, which work perfectly for me. After that, set up the Boost WG Base Duty table, which is explained very well in the pdf. There are actually two ways to set this up, depending on how you want to set the Boost Target Comp table. I have that table set to zero across the board and have a different duty level for each load row in the Boost WG Base Duty table. Alternatively, you can set the entire Boost WG Duty table all to the same value, like 20 or 50, and then set the Boost Target Comp table to adjust up or down from this base value based on what your boost target is. If tuned right, either way will work the same.



One thing you'll notice in the Advanced Boost tab, is that the RPM, TPS, and Gear tables all start at zero, whether using kPa or PSI units. It may help to think of these as the additive tables. The VSS table also starts at zero, but if you look at it in PSI units, it starts at -13.xx (whatever the offset of you MAP sensor is). So, this table should be set to zero PSI, or 100 kPa (same thing). You can think of this as the base target table.

Boost target is the summation of these four target tables. Lets say you set each of them to zero, even the VSS one which would be around -13.xx PSI, or 0 kPa (whatever the MAP sensor offset is). In this case, your target would be -13.xx Psi, or ~0 kPa. If you enter 10psi (69kpa) in the RPM, TPS, or Gear target tables, your target will be around -4.7psi (69kpa). You'll be scratching your head when you want 10psi, but you're getting your base WG Spring pressure. The point is, set that VSS target table to zero psi, or 100kpa and the other tables will make more sense. So, with the VSS table set to 0psi (100kpa) and any of the other three tables set to 10psi (69kpa), then your target will actually be 10 psi.

I've got a mix of boost by gear, TPS, and RPM. VSS is set to 0PSI across the board, TPS is set to zero from 0% up to 50%, and increases linearly from 0psi to 8.5psi at 100% throttle. So at 100% throttle, my target is 8.5psi. 1st and 2nd gear are set to zero, 3rd is 7.5psi, and 4th+ is 9.5psi. So, that gives me a target of 8.5 for 1st and 2nd, with the ability to vary that target with the throttle. 1st has to be part throttled anyways even at my WG Spring boost level of 7psi. 2nd can hold about 8.5psi, 3rd 16psi, and 4th+ are set to my max boost of 18psi. In any gear, pulling throttle will lower boost target and this helps a lot with getting traction down. I also gradually add an extra psi of boost as rpm gets over 5200 to help with torque drop off, so it feels like a flatter torque curve.

 

Attachments

·
A zone of danger.
Joined
·
1,175 Posts
Great work as always, Kurt. We appreciate your efforts! :)

I read somewhere that you could actually control the Series 1 with the Series 2 software, but something tells me there would be a conflict with the firmware. I haven't tried this myself, but an interesting thought for anyone else who may be interested in trying??? :dunno:

...and I still owe you TC data! I'm sorry, but I'm not sure you could have picked a worse time - if we haven't gotten a couple inches of snow, it's been freezin-ass cold here (20's-30's...which is low for OR). The only time I got to take the car out on the new tune, we made two vids at 28psi, then as soon as I moved up to 30psi I shot the hotside elbow clean off the IC end tank. Hopefully this weekend I'll get the new coupler, my TRD sways, and steel driveshaft in and I can try again...weather permitting.

And I need to do a write up on my first dyno tuning experience on big boost! The results were good. :)
 

·
Registered
Joined
·
2,189 Posts
I think you can use AEMTuner with the Series 1, but it would be with FW 1.19, so you wouldn't have all the new features. It's a lot better to stick with AEMPro with the Series 1 box! I'm starting to get used to AEMTuner, but there's a lot about Pro that I miss.
 

·
Registered
Joined
·
2,189 Posts
I've noticed that there is no option for limiting the WG out to only be active at high throttle%. With boost by gear set up, you have a boost target of, let's say, 18psi in 4th gear and your error table is going to add or subtract duty to attempt to get actual engine load to the target. Problem is, when you're just cruising around, the solenoid is going to be going full blast trying to attain the target but it's never going to get there. It's just running all the time and getting hot. I don't know how long the solenoid would last like this, but it bugs me! lol

To kill the solenoid below 50% throttle, I've set up my boost target switch using the software switch #8. (under setup in display explorer) I've got the boost switch to be active when Switch #8 is OFF with a target of -13psi. Above 50%throttle, the boost switch is off (Switch #8 On) and boost target is then taken from the rpm,tps,gear,vss tables. Of course, this isn't the best solution if you were actually using a switch for a different boost level, unfortunately. I've suggest that AEM add a new TPS option in the boost control settings but I haven't gotten any feedback on it yet.

Edit: Use Analog Switch #8. #7 is used for the air conditioner request (a/c button) and using this as your boost switch will cause your a/c to stop working. Found this out when my a/c would never turn off! lol Ignore the Switch #7 attachment.

Here's how I've set the switch up.
 

Attachments

·
Premium Member
Joined
·
2,887 Posts
I've noticed that there is no option for limiting the WG out to only be active at high throttle%. With boost by gear set up, you have a boost target of, let's say, 18psi in 4th gear and your error table is going to add or subtract duty to attempt to get actual engine load to the target. Problem is, when you're just cruising around, the solenoid is going to be going full blast trying to attain the target but it's never going to get there. It's just running all the time and getting hot. I don't know how long the solenoid would last like this, but it bugs me! lol

To kill the solenoid below 50% throttle, I've set up my boost target switch using the software switch #7. (under setup in display explorer) I've got the boost switch to be active when Switch #7 is OFF with a target of -13psi. Above 50%throttle, the boost switch is off (Switch #7 On) and boost target is then taken from the rpm,tps,gear,vss tables. Of course, this isn't the best solution if you were actually using a switch for a different boost level, unfortunately. I've suggest that AEM add a new TPS option in the boost control settings but I haven't gotten any feedback on it yet.

Here's how I've set the switch up.
The other thing you can do is control the other side of the solenoid with a HS output, giving you a whole new set of parameter to control the overall solenoid operation with. Then you can keep it locked out till boost starts to build, etc. Works great!
 

·
Premium Member
Joined
·
46,551 Posts
Chassis Dyno Testing - How Bogus Is Your Local Chassis Dyno?
That Depends. How Serious Are You About The Numbers It's Spitting Out?
From the March, 2011 issue of Hot Rod / By Mike Finnegan / Photography by Mike Finnegan
Our domes are on fire thanks to one seemingly simple idea we had for a great story. We wanted to go undercover at five different performance tuning facilities and test each of their chassis dynos using the same car in a short period of time. We hoped to uncover bogus numbers. We wanted to find the root of the problem for so many skeptical hot rodders who don't trust dynos as far as they can throw them. We were looking for a smoking gun or two. After hours of testing and days spent studying the data, we ended up with more questions than answers and decided we could write a book about the differences between dynos, test facilities, and data interpretation, and at the end of it all, we'd still arrive at the same conclusion: There is no smoking gun. The numbers just don't matter. That is unless you get off on having the biggest dyno graph on the Internet.

Repeatable results are the only ones that matter, and the only ones that can be used for A-B testing of performance gains or losses. Anything else is just hype, assumption, and fodder for ego stroking. When tuning for max power or verifying baseline performance, you need to be able to spot subtle trends. These trends are only valid if you stick with the same shop every time you want to verify a change to your car or engine. Oh, and one other thing: The numbers are no good if the shop alters its test protocol from one test to the next.

We borrowed an '11 Ford Mustang Shelby GT500 Super Snake, a 750hp demon of a car that costs around $90,000 and has enough rear-wheel power to break loose a set of 275/35ZR20s from a 50-mph roll. The Super Snake is Shelby's limited-production car that starts as a GT500 and gets a bigger Ford Racing supercharger, suspension bits, and other stuff to make 750 hp at the crank, and it comes with a warranty. Our test car had a six-speed stick transmission, as a manual is more repeatable on a chassis dyno than an automatic.

We hit five shops, one with a Mustang dyno, another with a Dynapack, two with Dynojets, and finally, one with a SuperFlow unit. We played dumb, showing up at each facility to have baseline dyno pulls made with a car our dad supposedly just bought. The Shelby wouldn't be tuned, "Dad" just wanted to know how powerful it was. Real data extrapolated from the car's performance at that shop, on that dyno, at that particular time is what we were after. Each shop took the bait and tested the car as they would for any regular customer. That's where it all went sideways.

How powerful is the Super Snake? We can't say for sure. If you believe the one-shot hero pulls that two shops gave us, then the Shelby makes more than 662 hp at the wheels. If you put more stock in the pulls that repeated more than once, then this is either a legit 630hp, 650hp, 600hp, or 577hp car. Follow our plight.

Dyno 1
Our first stop was Muscle Motors in Canoga Park, California, which works exclusively on Fords and had already tested several Super Snakes. We dropped $200 for four pulls on its Dynojet 224XLC. The Dynojet is an inertia-style dynamometer that measures the horsepower at the rear wheels and then uses a math formula to derive the torque. The horsepower is determined by the number of revolutions the tires spin the 3,000-pound dyno rollers during the time it takes to accelerate from 2,000 to 6,000 rpm.

Muscle Motor's dyno area is located in the back of the shop, positioned to the rear of a drive-on hydraulic lift. Like most facilities, this one leaves the hood up and places a fan in front of the radiator and supercharger heat exchanger to keep the water and air inlet temps in check. The Dayton 2MV56 48-inch fan will move 21,200 cfm of air on its highest setting.

Since the Super Snake was backed against a wall, an overhead fan built into the ceiling worked to flush out the exhaust fumes from inside the shop. After allowing the car to cool off for 20 minutes with the fan running, the tech made a full pull in Fourth gear. The peaks were 651.3 hp at 6,075 rpm and 611.1 lb-ft of torque at 4,914 rpm using the SAE STD correction factor. We snuck our Altronics PerformAIRE weather station into the shop to verify the weather information the dyno was using to make its computations and found the info to be solid. The dyno was applying a 1.02 percent correction factor to the raw figures to arrive at its final numbers.

After a 10-minute cooling session, the second pull at Muscle Motors shed light on a common problem with chassis dynos everywhere. The computer said the Super Snake put down 662.61 hp at 6,059 rpm, a gain of more than 10 peak horsepower with no changes to the car from the previous test. But, looking closely at the dyno graph, the peak horsepower figure came from a spike at the very end of the run right as the dyno operator ended the pull and pushed in the clutch. The spike was likely the result of tire slippage. With the exception of the spike, this pull mimicked the first one. The final pull backed up the first one with 611.59 lb-ft and 656.32 hp. Shop owner Jack Abraham offered a tuning session that would reportedly boost the car's output by 50 hp while improving driveability and throttle response. The cost-$1,000 plus the price of a handheld programmer. The Super Snake needs no help in any of those departments and we politely declined and headed to the next shop.

Dyno 2
Hours later, on Granatelli Motorsports' Mustang all-wheel-drive dyno in Oxnard, California, a location just a few hundred feet above sea level, the Super Snake put down 568 hp and 617 lb-ft of torque using the SAE J11349 correction factor. The first shop was located 790 feet above sea level, and this one was near the ocean. The dyno was using a 0.98 percent correction factor that actually reduced the raw numbers from 577.5 hp at 5,451 rpm and 626.9 lb-ft at 3,633 rpm. We were stumped as to why the Super Snake seemingly was down 87 hp (the equivalent of two air-cooled VW Beetle engines) and up 15 lb-ft of torque after travelling just 41.7 trouble-free miles from one shop to the next. More curious was that the Mustang dyno showed peak torque and horsepower occurring much earlier in the power curve than it had that same day at Muscle Motors.

We are fairly certain the tach signal was accurate, so that means the numbers were being skewed by another factor. After the test, we contacted the shop and the dyno manufacturer, eventually determining that a programming filter was inadvertently left on after the last calibration session and that was affecting the rpm readings. The Super Snake ran fine and we still have no idea why the horsepower numbers were down. The good news is that the Mustang dyno repeatedly said the car made 599 lb-ft of torque and 577 to 579 hp, so it was consistent, although different from every other dyno we tested.

Granatelli showed us another interesting thing: Simply by altering the dyno location's altitude from near sea level to 6,000 feet in the computer, the results climbed by 150 hp. It reveals that user methodology is critical and results are easily skewed.
 

·
Premium Member
Joined
·
46,551 Posts
Dyno 3
It was pure luck that our next appointment was at another shop with a Dynojet . We hoped this test session would back up the first one the day before. At Superior Automotive in Anaheim, California, we found a large shop filled with an engine dyno, a machine shop, and a bunch of high-performance muscle cars. The chassis dyno area was generous in size, with large bay doors at each end. Superior ran the car with the hood open and not one, but two fans facing the grille area.

The first pull was aborted at 4,500 rpm when either the clutch or the rear tires began slipping-we aren't sure which, but you could clearly see the problem in the Dynojet WinPEP 7 software, which showed the engine rpm climbing disproportionately from the drum speed. That was a wasted pull.

The shop made three more tests, which was considered a baseline dyno session with no tuning involved. The cost was $75, and had we only been interested in obtaining a peak number, it would have been a hell of a deal. But a problem reared its head when the Super Snake produced more power and torque on each successive test. Pull number two netted 564.40 lb-ft torque at 5,629 rpm and 638.77 hp at 6,070 rpm. After a seven-minute cooling session, the third pull generated even greater numbers, 585.3 lb-ft of torque at 5,368 rpm and 653.7 hp at 6,100 rpm. The Super Snake sat with the cooling fans blasting the radiator and heat exchanger for 12 more minutes before the fourth and final pull commenced, yielding 599.3 lb-ft of torque and 664.3 hp. The Snake was putting up bigger numbers every time a pull was made, but why?

The employee running the dyno said the car's computer was learning from each pull and that it was probably the first time the car had really been driven hard. But we had personally driven it very hard. It's a long shot, but perhaps it's because this dyno session required the shortest drive to get to, an 8-mile jaunt in bumper-to-bumper California traffic, which likely didn't give the rear differential, transmission, and engine oil enough time to adequately warm to operating temperature. Once at the shop, the car sat for almost an hour before testing commenced. The ambient temperature at this location was 10 degrees cooler than any other location we visited, and the car benefited from nearly twice the external cooling fan capacity as well, which certainly helped power production. Had we been running the test ourselves, we would have made several more pulls until we obtained repeatable numbers. As it was, the test was over and so we motored onto the next shop.

Dyno 4
EDO Performance Tuning is a Huntington Beach, California, shop that specializes in parts sales and installation for popular import cars like the Nissan 350Z, Subaru Impreza and WRX, and Mitsubishi EVO. We picked this shop because it has a Dynapack all-wheel-drive dyno, which bolts right to the axle hubs instead of using tire rollers to measure the acceleration rate. The dyno is located at the back of the shop with the exhaust pointing out the bay door and with three small fans facing the car's grille.

We got four full pulls for $125 and paid an additional $20 to have an O2 sensor attached to one of the tailpipes to give us air/fuel data. The first pull was made within two hours of the last one at Superior Automotive. The shops are 10 miles apart. The Super Snake put up nearly identical torque numbers during all four pulls. The best was 569.4 lb-ft, and the rest were within 5 lb-ft. However, we saw radically different peak horsepower numbers as the data plots veered away from each other from 5,000 to 6,000 rpm. The first pull showed 602 at peak, while the second, which was made less than five minutes later, showed only 580 hp. The car sat for about 10 minutes before the third pull commenced and the Snake put up 598 hp, then a fourth run showed a dramatic drop to 561 hp.

So, how powerful is the car? Does it make 598 to 602 hp at the wheels or 561 to 580? Was the problem that the blower was heating up? This test session was not conclusive.

Dyno 5
Our last stop was to a familiar shop, Westech Performance Group in Mira Loma, California. The guys there obviously knew Dad didn't buy the car, but we did not reveal exactly what we were doing. We wanted to add another dyno brand to the mix, and that was a SuperFlow AutoDyn 30 that can operate in inertia or eddy-current mode. The room is large, with the dyno built into the floor at the front of the shop. The car sat on the rollers with the exhaust directed outside and a large Dayton fan in front of the open hood. Westech prefers to "hot lap" the car on the dyno, making several runs within minutes of each other to simulate on-road performance.

The first pulled showed 624.4 hp at 5,944 rpm and 622.7 lb-ft of torque at 4,381 rpm using the SAE STD correction factor. The second and third pulls were right at 632 hp and 608 lb-ft, and since they repeated, the operator let the car sit twice as long before making another backup pull. That next pull showed the car picking up power, peaking at 638 hp and 641 lb-ft of torque. Since that was a new high, the operator immediately made another pull and heat soak knocked the power down, resulting in just 624 hp and 608 lb-ft of torque again. Satisfied with the numbers, that's where the test session ended and we were handed a bill for $175.

The Super Snake put up six runs that were all within 14 peak horsepower of each other, and twice it repeated the peak number and average power numbers. This is good, usable data. Ignore the hero pull and focus on the others and there's only a 7hp difference among the other five.

So How Do You Get Repeatable Results?
Every brand of dyno in this story can provide consistent test data. If you see big variances from pull to pull, you need to look for answers in one of three areas.

First, seek mechanical problems in the test procedure. For example, low tire pressure can affect chassis dyno results and must be consistent from test to test. The same is true for how tightly the car is ratchet-strapped to the rollers. If a shop tests with the hood open on one pull and closed on another, that can change output, as can being inconsistent with the cooling fan or the oil and water temps. Cars with automatic transmissions have a torque converter that is not a fixed coupling to the wheels, and especially in the case of drag race converters, they can lead to wonky results-even more so if the operator does not "drive" the car the same way each time.

Second, there could be input-data inconsistencies. Make sure the same data is in use every time you visit the dyno. Look for oddly out-of-range weather correction factors; they typically fall between 0.9 and 1.09. Also ask what weather correction factor is being used, as it varies from shop to shop. Some dynos plot the power numbers versus mph rather than rpm, but those with the preferred rpm curves need some way of reading engine speed. This could be through math (tire diameter versus gear ratios-very difficult with an auto trans) or more likely through direct reading from the engine. The rpm could be read from a tach lead, a plug-wire inductive pickup, CAN output, or a strobe on the harmonic damper. Make sure the method is the same each time. Don't forget that torque and horsepower always cross at 5,252 rpm. If they don't, raise a red flag.

Finally, there can be mechanical problems with the car. To keep better tabs on this, many shops will supply data about air/fuel ratios, and you'd like to have that at the least. Big variances in air/fuel can change power (and hurt engines), as can air inlet temp. With the Roots-blown Super Snake, inlet temp changes in both directions likely led to many of the pull-to-pull inconsistencies we saw, but only one of the shops provided that data; they might have been able to had we asked. In the end, you don't care what the numbers say as long as you can get consistent results from test to test. Without that, you never know which way is up.
 

·
Premium Member
Joined
·
46,551 Posts
Correcting the Correction Factor Confusion
Every shop we visited provided dyno data that showed horsepower and torque numbers altered with a weather correction factor. The raw power figures are multiplied by the correction factor, giving us the ability to adequately compare engines tested in varied conditions of temperature, pressure, and humidity. Because engines make more power at oxygen-rich sea level locations than they do atop the Rocky Mountains, or in dry and cool climates as opposed to hot and humid ones, it's necessary to have a formula that takes into account these conditions to level the playing field between different dynos, or even different test days on the same dyno. The Society of Automotive Engineers developed several correction factors for dyno testing, and it's important that if you compare numbers from one dyno with the next that the factor be the same. Two of the dynos we tested used the SAE J1349 correction factor, which utilizes the following numbers for reference: 77 degrees Fahrenheit, 29.234 in-Hg barometric pressure, and zero percent humidity. The other three dynos used the SAE STD factor, which references 60 degrees Fahrenheit, 29.92 in-Hg, and zero percent humidity. Using the STD factor usually pushes the raw power numbers approximately 4 percent higher than the J1349. Keep in mind that weather correction factors do not change the rpm points at peak power.

LOCATION DYNO TEMP BAROMETER HUMIDITY CORRECTION FACTOR
EDO Performance Dynapack 73°F 30.6Hg 30.3% 1.015% SAE J1349
Granatelli Motorsports Mustang 71.6°F 29.8Hg 45% 0.98% SAE J1349
Muscle Motors Dynojet 72.0°F 29.2Hg 25% 1.02% SAE STD
Superior Automotive Dynojet 63.0°F 30.0Hg 53% 0.99% SAE STD
Westech Performance Group SuperFlow 76.5°F 28.9HG 36.5% 1.06% SAE STD


Types of chassis dynos
Dynos can be categorized as either inertia, hydraulic, or electric. An inertia dyno can only do full-throttle acceleration runs, but the best load-bearing hydraulic and electric dynos can do step tests, constant-speed pulls, and even part-throttle testing so that full road-load simulations can be conducted right on the dyno.

Inertia Dyno: These extrapolate rear-wheel power output by analyzing the dyno drum's acceleration rate using a sophisticated accelerometer and computer software. A vehicle is placed on the dyno with its drive wheels sitting on heavy roller drums of known mass. The car is placed in gear and accelerated at wide-open throttle. It takes a certain amount of time and force for the tires to accelerate the rollers. The acceleration rate is directly proportional to how much power the tires place on the heavy roller to get it to rotate. Inertia dynos have the reputation for reading "high." Generally, with mainstream vehicles in the 3,500-pound class, they'll yield consistent results with minimal setup time. They may have trouble obtaining accurate results with extremely heavy or light vehicles. Turbocharged engines won't build boost as they do in the real world. Dynojet is the most common pure-inertia dyno (some of its newest models have an eddy-current option).

Hydraulic Dyno: Like most engine dynos, the hydraulic or water-brake chassis dyno relies on a constant speed brake or absorber coupled with a rotor with a rotating element and a stationary element. On most hydraulic chassis dynos, the tires turn rollers that in turn couple with the rotor. An exception is the Dynapack, where the load brake attaches directly to the axle, removing the tires and rollers from the equation. Either way, the rotor elements generate braking force using water or hydraulic fluid to absorb or match the powertrain output. Usually a strain gauge measures the torque reaction between the rotor's rotating element and a stationary element. Again, Dynapack is unique: Instead of a strain gauge, it measures the hydraulic fluid power required to hold a vehicle at a constant rpm. Potential hydraulic dyno problems are impeller lag when you snap open the throttle and the need for periodic recalibration.

Electric or Eddy-Current Dyno: This type of dyno controls the brake/absorber using electric current instead of fluid, measuring torque output and calculating power based on a strain gauge. Electric current provides much more precise control and minimal spool-up lag time, but you need a gonzo electric supply and the dyno itself is more expensive than other types. Electric dynos are best for sophisticated R&D, emissions testing, and calibrating electronic engine management systems under heavy vehicle loads, but achieving their full potential requires a high degree of skill and setup time. Mustang and SuperFlow are among those marketing high-end, eddy-current dynos. Some electric dynos can also be run in full-inertia mode, but then they have the same drawbacks as any other pure-inertia dyno. -Marlan Davis HOT ROD MAGAZINE
 
101 - 120 of 133 Posts
Top