[laynlo15]

Originally Posted by JSH

Yes I will post my ETs but they will reflect a 3925# car with 830-850 or so uncorrected hp. I'm guessing 9.80s.

But back to dynos. Everyone here posts corrected hp and trq figures. And I'm guessing 5% correction is the median.

I think that would be pretty stellar at 5000 ft but I think you have the power to do that also. We both have to get thru winter to get back out there to lay down some new numbers. You have a cool build and making tons of power. Congrats.

[JSH]

Originally Posted by laynlo15

I think that would be pretty stellar at 5000 ft but I think you have the power to do that also. We both have to get thru winter to get back out there to lay down some new numbers. You have a cool build and making tons of power. Congrats.

I plan to make at least one trip off the mountain to Topeka or St. Louis in the spring when the air is good. Do you race at the track (can't recall its name) across the river east of St Louis?

[laynlo15]

I race at WWTraceway in Madison, Ill. Just 5 minutes outside St Louis, Mo. That track is about 450 ft elevation and a great NHRA track that they prep really well. Topeka is about 1150 ft so you'll run slower there but much faster the on the mountain. I haven't raced at Topeka in a while, I hate going thru KCMO, its 3.5 hours towing for me where STL is 2.5 hours and much easier trip since my daughter lives there also. Your car should really haul ass at 450 plus the DA. Hell even if its 1000 or 1500 your still going to run fast. I usually try and get out first event in March. Weather can sure screw that up but we still try.

[JSH]

Originally Posted by laynlo15

Your car should really haul ass at 450 plus the DA. Hell even if its 1000 or 1500 your still going to run fast.

I'm still using the OEM high side pump and am not sure if it will safely make 950 whp, so higher elevation tracks like Topeka and Vegas are probably wiser choices until I put a BBFP on it next year.

[JimGnitecki]

Layinlo15 is right that dragstrip performance is a better indicator of actual power than corrected dyno sheets, BUT even dragstrip performance is affected by actual temperature, pressure, and humidity of the air at the time.

Trying to predict EITHER sea level dragstrip performance or sea level dyno performance based on high elevation dyno charts is inherently dangerous, and usually optimistic, because even The SAE organization, who developed and maintain the formulas used to correct horsepower to standard temperature, pressure, and humidity, says that any correction beyond about 5% should not be assumed to be accurate.

This is because the correction formulas assume that an engine can PERFECTLY handle the air it is handling, regardless of how cold or hot, how humid, and how pressurized that air might be at that location on that date. i.e. the formulas assume that the engine can get 100% of the theoretically calculable power for the current ambient conditions under ANY conditions.Anyone who has built a performance engine knows this is NOT actually what happens. Engines have significant shortcomings in their ability to work optimally under ALL conditions.

One very simplistic and deliberately exaggerated example shows why:

There are engine and vehicle combiantions that do VERY well in producing power at moderate temperatures and humidity, but put them into 95 degree weather, they overheat instead. So, if you do dyno runs with those vehicles at both the moderate and the 95 degree conditions, the UNcorrected results will be very different, and so ALSO will the CORRECTED results. The corrected results will usually be "less" different, but will still be different.

Also, the accuracy of the formulas depends upon the accuracy with which the ambient conditons are actually controlled and measured. One simple example of erroneous data being fed into the calculations:

- The outside temperature is 40 degrees F. The outside door to a dyno room is left open because vehicle tuning on the dyno has heated up the indoor room to 85 degrees. The dyno is physically near the outer door to help get exhaust out of the building easier. But the ambient temperature in the dyno room is measured by the temperature sensor, which is located by an inside wall that is further from the open door than the point where the air is inducted into the engine. The temperature sensor is also rather close to the heating system register for the room, and ebcause the outside temperature is 40 degrees, you KNOW that the building furnace is sneding air into all the heat registers - even the one in the 85 degree dyno room - that's why the crew has opened the outer door in the first place. So, the engine is getting colder air than the temperature sensor is reading. So, the engine's corrected power is inflated by the erroneous input that says it is getting 85 degree air when it is actually getting air that is "somewhere" between 40 degrees and 85 degrees. That actual temperature is even affected by whether the hood is open or closed. Think this scenario is unlikely? It's more common than you think.

I always like to look carefully at the ambient conditions, which, at a scrupulously careful dyno facility, are recorded right on the data graph, along with the "SAE Corrected" peak hp and torque. That at least gives you an idea of how large or small the errors in the corrected power and torque might potentially be, even if the dyno oeprator has scrupulously observed bast dyno practices.

Jim G

[JSH]

Originally Posted by JimGnitecki

... any correction beyond about 5%... [/B]

Jim G

Those of us that live, test, and race on and off the mountain know that CF between 18 - 26% are common for Denver conditions depending on the time of year. My dyno pull here used a CF of 18% because it was a cold dry morning. A pull back in August used 22%. And we also experience power increases and lower ETs when we race at lower elevation tracks.

But the main value of the dyno for me is to be able to use the same dyno to measure power output from build to build, A-B. For example, we'll tune it with 104 in the near future and test it on the same dyno to measure any hp/trq changes. DynoJet says this is the primary purpose of a dyno.

[JimGnitecki]

Originally Posted by JSH

Those of us that live, test, and race on and off the mountain know that CF between 18 - 26% are common for Denver conditions depending on the time of year. My dyno pull here used a CF of 18% because it was a cold dry morning. A pull back in August used 22%. And we also experience power increases and lower ETs when we race at lower elevation tracks.

But the main value of the dyno for me is to be able to use the same dyno to measure power output from build to build, A-B. For example, we'll tune it with 104 in the near future and test it on the same dyno to measure any hp/trq changes. DynoJet says this is the primary purpose of a dyno.

Totally agree with you on this - for as far as you went. My own Camaro dyno sheet done At Davenport in Calgary showed a very high correction factor. Yes of course, high correction factors are unavoidable at our altitudes. As long as we use them to measure improvements or losses versus our local baseline results, no problem.

BUT, when we try to compare our results to other people's results, whether taken at high or low altitudes, and claim that we have either more or less power than they do, we are using the data way outside its probable accuracy range, for the reasons stated in my last posting.

Even for dyno "shootouts" where all the cars are being tested on the same dyno on the same day, if the testing is not being done in a climate controlled building where the ambient conditions are being kept exactly the same all day, it's not really a fair "shootout". Most of those shootouts are done on portable dynos parked for the day in a parking lot, or at best, inside a shop whose doors are open all day in an effort to get the heat out of the building as the cars heat up the room one after another.

So, smart and competitive owners show up early to get their car tested at cooler ambients in the morning versus the hot afternoon or evening, because that's going to give their car and advantage over another car with an identical engine.

And guys with larger radiators, higher capacity coolant pumps, and large dual fan setups get higher power readings when all the vehicles being compared are strapped onto a non-mobile platform instead of getting the airflow they get on a street or highway. (Regardless of the fans that "look large" but are puny compared to 40 mph airlfow on the road).

Dyno operators who are SERIOUS about absolute accuracy have VERY expensive and detailed dyno environments, and control-freak protocols.

The best that I have personally seen was the one I saw (and used) about a decade ago, owned by my friend Micah Shoemaker, who runs AF1 (motorcycle) Racing, in South Texas. Micah's 2-step dyno room (small tuning room inside a very large outer room) was HUGE to dampen temperature swings during tuning sessions, is heated and cooled to automatically maintain a specific temperature. His dyno was a steady state dyno, not an inertia dyno like the much more common Dynojet, so the constant ambient control is important for the extended tuning sessions he was running at multiple steady state rpms.

I had my Honda 1800cc v-tiwn dyno-tuned by Micah personally. One of the things I told him before the dyno session was that the bike made my stomach a bit queasy at a moderate specific speed range on the highway in top gear. This was a huge problem because I spent most of time on the bike in that speed range.

During the session, he pulled me into the tuning room and pointed at the rpm (2200 rpm on this large displacement 5500 rpm engine) and at the battery box located under the seat. At this SUSTAINED 2200 rpm, the battery box welded into the frame was vibrating like crazy. It was the result of a vibration resonance that the Honda factory testing had apparently not uncovered.

Micah told me that day that he himself often felt queasy when dyno testing the 16,000 rpm 600cc 4-cylinder Japanese Supersport motorcycles (like the one I have now) when holding them at specific rpms for tuning. You'd never detect such an issue on the typical inertia dyno because the rpm "sweep" occurs too briefly to see or feel it.

The quality and detail level of dyno testing, just like the quality and detail level of automobiles, varies. When evaluating the precision of either, look hard at the details and protocols used by the operator or builder.

Jim G

[laynlo15]

Originally Posted by JSH

Those of us that live, test, and race on and off the mountain know that CF between 18 - 26% are common for Denver conditions depending on the time of year. My dyno pull here used a CF of 18% because it was a cold dry morning. A pull back in August used 22%. And we also experience power increases and lower ETs when we race at lower elevation tracks.

But the main value of the dyno for me is to be able to use the same dyno to measure power output from build to build, A-B. For example, we'll tune it with 104 in the near future and test it on the same dyno to measure any hp/trq changes. DynoJet says this is the primary purpose of a dyno.

No doubt using the same dyno and I've made close to 200 tugs between my 16 SS, my C7 and my new 2022 Lt1. To be honest I've felt like I made some bad choices on the numbers I've gotten off my dyno pulls after mods I've done. So here is a fine example of that, I did SE long tubes 1 7/8s, no cats and we probably did 10 pulls on the dyno making minor changes and made like 12 or 13 rwhp and was dissappointed to say the least. I drove the car home which was about 30 miles from my house to the dyno and immediately knew it was much faster. So we loaded up that weekend and went to the track and this is when I was tuning my own car, never touched the trans or any of the stuff. The first pass it goes 11.12@124. My fastest pass prior to that was 11.58@120. So I made a couple changes cause it was running right up against the rev limiter and a buddy of mine who tunes helped me figure that out and next pass I had to run him in his Charger Srt, it was a fast car. I ran 11.06@124 and he went 10.99@125, the old man was quick on the lights and I won the race and went to the second round. So the moral of the story is don't get bent out of shape on bad numbers on the dyno. If the dyno operator is the tuner or he knows the tuner be wary, if they ask you how much you'd like to see it make, don't fall into that trap. Just say I'm not worried so lets just see what it makes. Just take what they give you and go to the track. You may be disappointed are like me many times happy a shit.

[JimGnitecki]

Below is a photo I took at the Davenport Motorsports dyno room.

Note that the dyno is in its own wing of the building.

Note the generous size of the room.

Note the cleanliness (other than where client cars have left oil deposits under the engine bay).

Note the bright lighting that makes it easier to detect sooner if something is going wrong (smoke or steam) and stop a run before big damage is done.

Note that the dyno is built into the floor, so the car is at normal height above the ground, not on an elevated platform, so closer to real world airflow from the fan blowing into the grill and under the car.

Note that even the fan shown here is really tiny compared to what the airflow of fresh, unrecycled air is on the street. A negative. (I think the large caged fan at the SIDE of the dyno is likely there to help cool the drive wheel tires.)

Note that the bench with the display screen is right near where the engine bay of the car is going to be. Since the dyno is under the floor, I hope the temperature sensor that feeds the dyno calculations is insstlled at or near the bench, not under the floor (I never thought of asking while I was there, but I think Davenport is pretty smart about proper dyno protocols).

I asked Steve what gear they dynotested my car in, and I got the answer I hoped for: They used a gear low enough to keep the top speed during the dyno run low enough to prevent the tires from overheating. Yes, this depresses the reported power on an inertia dyno like the Dynojet, but it prevents doing heat damage to the tires.

Details are important.

Jim G

[ZL1Atlanta]

Originally Posted by laynlo15

I think I'm going to just post ET and MPH next year. This is not pointing to anyone but the dyno numbers just confuse people and really don't mean anything at the drag strip. Yes, you should tune on the dyno, but you should also log at the track and make changes to go faster at the track and on the dyno. Now I may post after the track of what it made on the dyno and then everyone can have their concerns about that. Wallace racing really has a good calculator for HP/Weight/ET/MPH. Just because a car makes 800, 900 and up it only shows that on the track, I caclulated my DT and I should have only run 137, however I ran 142. So even though I will still dyno I'll let the ET and mph speak for itself. Everyone should post what they want after they start their thread, still proof is in the pudding at the track. JSH, I don't know what a 950 plus rwhp run a the mile high but I'm hoping you'll post some numbers next year to let us know.

I have also moved from talking about my dyno numbers and just say on "on that pass it made roughly x" and use all of the variables in a calculator before commenting. I do use the dyno number to have an idea of what's left to throw at the car. As an example, we tested the car up to 24 psi on the dyno and know it has the fueling for it, no belt slip, etc., but have only ran it at 19-20 to make sure everything past the engine is holding up. So when I look at my PB to date, I have an idea of where we should land at 24 psi, assuming other variables stay the same.

The track is a little tricky for gauging a cars power as well because of the changing conditions from day to day, and even the tuning or mechanical limitations of parts when using more than one gear. As an example, I trapped 169-170 MPH on a couple tracks in over 3k DA, but in 1k DA it went almost 174 MPH. No other changes occurred on the car. I am definitely eager to go find the negative DA some of these guys are running in for this reason! Also, in our struggles to keep the 10L90 alive, we have had times where it randomly short shifts, hits the limiter, slips, etc. that resulted in a lower MPH, but not because the car made less power. The transmission was just done or a tuning change was needed.

[JSH]

Originally Posted by ZL1Atlanta

I do use the dyno number to have an idea of what's left to throw at the car.

We're doing the same. We put this 100-octane version of the car together in August and dyno'd with the 3" upper and made 965. We then put a 2.75 on it and made 981 on the first and only pull that day (for $100). No dyno tuning.

We'll dyno with 104 soon to, as you say, see what's left in it.

If the track were open, we wouldn't dyno, but would instead be making hits and editing tunes in much the same manner, except we could accomplish a lot more in a shorter time.

The dyno has value and is typically just the first step in tuning followed by track tuning. For some who never track their car, the dyno is the sole power benchmark (except perhaps for a dragy 60-130).

I'm 100% confident you know all of this though.

[Z OH 6]

Originally Posted by ZL1Atlanta

I have also moved from talking about my dyno numbers and just say on "on that pass it made roughly x" and use all of the variables in a calculator before commenting. I do use the dyno number to have an idea of what's left to throw at the car. As an example, we tested the car up to 24 psi on the dyno and know it has the fueling for it, no belt slip, etc., but have only ran it at 19-20 to make sure everything past the engine is holding up. So when I look at my PB to date, I have an idea of where we should land at 24 psi, assuming other variables stay the same.

The track is a little tricky for gauging a cars power as well because of the changing conditions from day to day, and even the tuning or mechanical limitations of parts when using more than one gear. As an example, I trapped 169-170 MPH on a couple tracks in over 3k DA, but in 1k DA it went almost 174 MPH. No other changes occurred on the car. I am definitely eager to go find the negative DA some of these guys are running in for this reason! Also, in our struggles to keep the 10L90 alive, we have had times where it randomly short shifts, hits the limiter, slips, etc. that resulted in a lower MPH, but not because the car made less power. The transmission was just done or a tuning change was needed.

Bottom line, its always hard to compare vehicle performance from one dyno to another, also one track to another due to so many variables.

[USAFS197]

Originally Posted by Z OH 6

Bottom line, its always hard to compare vehicle performance from one dyno to another, also one track to another due to so many variables.

FWIW, it goes beyond that to different vehicles, different drivetrains, different ways of making power, etc., etc.

[JimGnitecki]

Originally Posted by Z OH 6

Bottom line, its always hard to compare vehicle performance from one dyno to another, also one track to another due to so many variables.

Yeah, the whole world has become very complicated in recent decades. Have you ever examined the various obscure numerical components of your cable TV, cellphone, and municipal utility bills recently? Scary.

I have an absolutely true story about just HOW ridiculous things can become when theoretical rules get applied far beyond the intended and envisioned usage:

Here in Canada, the latest creative profit center for the Canadian Postal System is a cute add-on called "fuel surcharge". I recently mailed a regular Number 10 envelope with 10 sheets of letter sized paper to U.S. Social Security, and needed both tracking and a signature. The postal clerk told me that would cost $29 (!!) as a base charge, which I thought seemed very excessive already. But then the computer system added the $6 "fuel surcharge", for a total of $35. So, $35 to send an envelope containing 10 sheets of paper 2200 miles.

Also, the adhesive-backed printout that the system required the clerk to glue to the Number 10 envelope was TOO LARGE to fit on the envelope. She had to trim the borders off with scissors, being careful to not remove any vital information (like the huge bar code required for automated routing).

By the time she was done, a lineup of about 15 people had formed behind me.

This is what sometimes happens when theoretical formulas get applied beyond the logical boundaries.

So, be careful with those high altitude dyno charts.

Jim G