Dyno #'s bogus with high stall converter

[glhs875]

Kevin Davis and I discovered for ourselves anyway, others already knew, that a high stall converter can really throw off the readings from a dyno. A stall converter will cause the #s to read high down low if the converter is flashed, and low #'s up top in both torque and HP. The dyno can still be used to tune in gains or losses with, but the #'s themselves are not true and should be ignored. The Dyno would have to be reprogramed to work correctly during this senerio, because dynos are programmed to work under a 1.1 locked up condition. So if you have a high stall converter and go to the dyno and you feel the #'s are off because of your torque converter being inefficient, and then go to a lower stall or even a manual trans to bring the #s up, that doesn't mean you will run quicker at the track. You could end up running slower. So when I dyno my car I probably won't ever get the high # I'm looking for either, because I have the same converter. But I won't be changing the converter out, it works too darn good at the track. And the track #'s vs. weight of the vehicle is a more accurate way to determine HP on a car with a high stall. Just thought I would pass this along. I'm not going to post any #'s on Kevin's car, that's up to him. But I will say that 2.4 16V in is car is very strong!! Even with the #'s reading low, he still showed well over 400 WHP! And even though he had his combo tuned pretty darn good already, we were able to find an honest 30 to 40WHP more!

[slasky]

Sounds like a ricer excuse for low numbers to me.
j/k
Dynos are so far off from each other the numbers really don't mean much anyway. I agree that basically they should just be used for tuning. The only numbers that really matter are the ones that show up at the end of the track.

[glhs875]

Sounds like a ricer excuse for low numbers to me.
j/k
Dynos are so far off from each other the numbers really don't mean much anyway. I agree that basically they should just be used for tuning. The only numbers that really matter are the ones that show up at the end of the track.

He compared to 2 different dyno's on the same day. One of the dyno's was reading alot higher #s. I think there was a 60WHP difference at 20psi. Might of been more than that. Kevin needs to post. But the dyno that was reading the higher #'s could not hold the power due to massive wheel slippage on the rollers with the boost set as low as 23psi. I'd be willing to place a bet on the #s being at least 500+ wheel torque and 525 to 550WHP if a manual trans were used to dyno with on his combo. There was a Honda Civic hatch (B20 w/ B16 V-tec head and turboed), there, that dynoed to 450WHP on the same dyno. I out ET'd that Honda at the track with my 2.2 8V with me on 300 treadwear tires and the Civic on DR's. And I know Kevin is making way more power than Iam!!!

[87csx2.4]

Yeah the guy was supposed to email me the runs but hasnt yet and now he wont answer my phone calls.The guy that runs the shop has a honda that makes 420 whp at 22 psi and it runs 7.60 in the 1/8 mile,at that boost on his dyno my car made right at 340 whp.Ok my car is 900 pounds heavier than his and at the same boost level at the same track making supposedly 80 whp less ran 7.44 I dont get and I dont think he did either.Here is a good article though.http://www.forcefedperformance.com/TechDynamometer.asp

[SebringLX]

Interesting... just curious, what's the stall speed your torque converter is set at? The HSTC in my 41TE is set at 3400 rpm, which should be full boost for me. I'm still a couple weeks away from even being able to drive the car, and I'll have lots of 1/4 mile times before I ever get it on a dyno (there aren't any dyno's in Montana). I have a lot of people that are waiting for dyno numbers on my car. I could care less about the dyno numbers, I'm looking for 1/4 mile times in the 11's, but no faster than 11.5 (don't want to put a roll bar in). Although I would like to know if I hit my 400whp goal or not. I'd hate to spend the money getting a dyno done, and have unusable numbers and messed up graphs.

[glhs875]

Interesting... just curious, what's the stall speed your torque converter is set at? The HSTC in my 41TE is set at 3400 rpm, which should be full boost for me. I'm still a couple weeks away from even being able to drive the car, and I'll have lots of 1/4 mile times before I ever get it on a dyno (there aren't any dyno's in Montana). I have a lot of people that are waiting for dyno numbers on my car. I could care less about the dyno numbers, I'm looking for 1/4 mile times in the 11's, but no faster than 11.5 (don't want to put a roll bar in). Although I would like to know if I hit my 400whp goal or not. I'd hate to spend the money getting a dyno done, and have unusable numbers and messed up graphs.

The numbers will still be unusable. Just tune for gains and then go track testing to get more accurate HP #'s. One thing with an auto trans. Always load the car the same way when making pulls. Varying when going WOT can vary the numbers.

[ShelGame]

FWIW, If you were to datalog RPM and MPH, you could still find your actual HP and torque. The dyno measures actual torque at the wheels. And then calculates the HP vs. RPM assuming a 1:1 drive ratio. But, you can use the RPM and MPH to generate the actual drive ratio (which can be far from 1:1 on an auto and will vary with both speed and RPM). And then use that to scale the torque reported by the dyno and calculate a more accurate engine HP. The calculated HP will still be considerably off at high drive ratios (ie, low MPH, high RPM) due to the low efficieny of the converter at these ratios.

I actually don't understand why the dyno software doesn't do this automatically. It's really a no-brainer. They already measure RPM, MPH, and torque...

[glhs875]

FWIW, If you were to datalog RPM and MPH, you could still find your actual HP and torque. The dyno measures actual torque at the wheels. And then calculates the HP vs. RPM assuming a 1:1 drive ratio. But, you can use the RPM and MPH to generate the actual drive ratio (which can be far from 1:1 on an auto and will vary with both speed and RPM). And then use that to scale the torque reported by the dyno and calculate a more accurate engine HP. The calculated HP will still be considerably off at high drive ratios (ie, low MPH, high RPM) due to the low efficieny of the converter at these ratios.

I actually don't understand why the dyno software doesn't do this automatically. It's really a no-brainer. They already measure RPM, MPH, and torque...

Yea, I feel that would get things closer. We know that Kevin's torque converter has at least 19 to 20% slippage in the upper R's. Adding that 20% slippage to what was reported on the dyno gives a 525WHP #. We feel that is real close to what he actually has for WHP.

[sdac guy]

One variable that shouldn't make a difference, but does even with the same car on the same dyno, is what rpm the run is started at. Whether it is a fluke in the dyno software, or the car's reaction I don't know. And I don't know if it would happen on every car either.

I found this out by looking for a missing 8-10 hp on my nearly stock VNT Daytona. I ran it stock when I bought it in 2000, and again after I got the 2.5" exhaust on it, both times at the same shop.

A couple years ago my turbo went south (at just over 100K miles) and I got a deal on a new warranty head, cam, turbo package. Everything new except the valve cover. So after I changed it all out I tried the car on the dyno again to see if it improved with all the new parts.

It lost 8-10 hp. How could this be??? I went back to the old runs (which were archived on the shop's computer) and looked at them. I noticed those runs started at about 1800 rpm where the ones he was doing that day he was starting at about 2500-2600 rpm. I asked him to start the next run at 1800, and guess what? My 10 hp came back. He did another run starting there to make sure it was consistent and it was. We both scratched our heads on that one.

Whether this would apply to other cars, I don't know. My Daytona starts building boost at about 1600 rpm and is at it's full 14psi boost at 2100 rpm. When he started the runs at 2500 rpm, it went to full boost immediately, while it was still building boost when starting at 1800.

The peak tq/hp were at the same rpm ranges for all the runs. They just measured higher when the runs were started at a lower rpm.

Barry

[sdac guy]

And to be more on topic ..

I worked in a dyno shop for a while in 1998. I saw a lot of high hp hi stall cars run on the dyno. Indeed the torque is down low (that's why the hi stall converter was purchased). But remember as a rule of thumb, it is torque that accelerates a car, while it hp that accounts for top end.

And as most folks who have any experience drag racing can tell you, the first 60-330 feet really make a difference in ET. So it is very possible that a car with a lot of bottom end torque will ET better than a car with 100 more hp but whose torque is all mid-range or upper end. The car with more hp should have a better trap speed if all else is equal.

Barry

[glhs875]

The peak tq/hp were at the same rpm ranges for all the runs. They just measured higher when the runs were started at a lower rpm.

Barry[/QUOTE]


I agree. That's why I said be sure to load the car the same for all pulls. Kevin told me he was rolling into the throttle and didn't go WOT untill about 3000rpm. He will do differently next time he goes. I think why he did that was to cut down the torque spike from the converter and turbo spooling. But I feel that was alot of cause of the false readings he got.

[8valves]

One of the most important questions is what manufacturer and model of dyno is this on?

Barry, the difference in overall peak due to starting point is the building of load on the turbo. Think of it like trying to pull someone out of a ditch, you get better results because the tires and engine are being gradually loaded more and more if you gently bring the rope taught and apply more and more throttle rather than just yank and hope. Make sense?

Turbo cars should have their runs started in my experience at least 1000 rpms short of full boost to give it a gradual ramping into boost.

Also, your peak gain can be attributed to getting to a higher TQ number quicker. Your big torque 4 cylinder will appreciate starting lower, such as 1800 like you stated because it's already getting close to peak torqe at 2600 rpms... you've passed some of the cars powerband with no load! Now it needs to try to catch back up to itself by building power up to where it should be by that rpm, and it will constantly play catch up the whole way up the graph.

This is also why getting gains in the midrange can prove beenficial to overall peak numbers. You can make an alteration in the midrange that will bring the numbers up a bit and no changes up top, yet the car will continue to take those midrange gains and carry the line higher all the way to peak resulting in some small gains.

Brian- a legit 450WHP LS/VTEC setup is usually a 125-128 or so MPH car... also right around mid to high 11's.

[Vigo]

The HSTC in my 41TE is set at 3400 rpm, which should be full boost for me

A little OT but did anyone discuss with you the possibility that you wont be able to brake-stall that converter without going into limp mode? too high of an input rpm in gear at 0 mph =ratio error code = slip = limp mode= dumped into 2nd gear. I have spoken to a few people with high stalls, and it seems it only happens to the people who brake-stall on launch to build boost, rather than the n/a people who tend to do it shorter or flash-stall on launch.

i am building a 606 with a supposed 3500 rpm stall from precision and im going to try a neon 2.0 converter behind my 3.3 so ill have some opportunity to straighten it out but make sure and post somewhere or pm me when you get it going.. i want to know if that stall is going to end up being too high for the tcm's taste

[t3rse]

why does it take 450whp to get a honda in the 11s?? there was a guy at the 1/8 last week with 268whp supered stock interior integra on slicks cutting 7.6s.

[8valves]

why does it take 450whp to get a honda in the 11s?? there was a guy at the 1/8 last week with 268whp supered stock interior integra on slicks cutting 7.6s.

Because your blower car on slicks will be just about done for anythign brilliant in acceleration just past that 1/8th.

It's not that it's not possible to get them into 11's with less power... just look at the all motor world of Honda's... but most boosted LS/VTEC cars that make 450 or so WHP will run mid 11's at 125-128 mph.

Area under the curve of the blower car will be quite a bit different than most boosted (turbo) setups.

[sdac guy]

One of the most important questions is what manufacturer and model of dyno is this on?

All of mine were done on the DynoJet at Advanced Chassis, which is the dyno originally purchased by PowerCurve.

Barry, the difference in overall peak due to starting point is the building of load on the turbo ....

Excellent explanation, thanks Aaron.

Barry

[8valves]

All of mine were done on the DynoJet at Advanced Chassis, which is the dyno originally purchased by PowerCurve.

Excellent explanation, thanks Aaron.

Barry

Which is where I dyno at as well! Andy is a good guy. That dynojet is particularly accurate, posting results only 11 WHP off of a local Mustang dyno. That's pretty much unheard of in the world of Dynojets.

[glhs875]

Because your blower car on slicks will be just about done for anythign brilliant in acceleration just past that 1/8th.

It's not that it's not possible to get them into 11's with less power... just look at the all motor world of Honda's... but most boosted LS/VTEC cars that make 450 or so WHP will run mid 11's at 125-128 mph.

Area under the curve of the blower car will be quite a bit different than most boosted (turbo) setups.

Well at least that lets me know where I'm getting to with my ride!! I've never ran the 1/4 with it, only in the 1/8th.

[Anonymous_User]

A good quality hi-stall converter should not affect the high rpm numbers too much. A good converter will flash to desired stall, multiply torque down low, AND minimize slip up top. I have run several converters in my RWD car from cheap off the shelf converter to multiple custom converters. Even with the same stall rpm, I can tell the quality converter by my trap speeds. The better converter will not slip as much above flash stall, the cheaper ones will and thus reduce the power put to the ground.

[glhs875]

A good quality hi-stall converter should not affect the high rpm numbers too much. A good converter will flash to desired stall, multiply torque down low, AND minimize slip up top. I have run several converters in my RWD car from cheap off the shelf converter to multiple custom converters. Even with the same stall rpm, I can tell the quality converter by my trap speeds. The better converter will not slip as much above flash stall, the cheaper ones will and thus reduce the power put to the ground.

Kevin is using the $900.00 FM (Saturn based 8") torque conveter. And has sent it back a couple of times having it adjusted to get the best ET out of it. When a well built 2.4 16V shows 438WHP @ 7000rpm with a maximum wheel torque reading of just over 280 ft lbs, something is not right. 2.4's usually have peak torque numbers that pretty much match peak HP numbers. And I would think if the torque numbers read low on the dyno, then HP numbers will be reading low as well, because HP numbers are gotten from the torque.