Interesting Dyno Day
#16
So Bruce, if I read you correctly, you're saying that if I had exactly the same motor and mods as Dana in this case and we were running in similar temps on the exact same dyno setup, I would have to run approx 3 psi more to reach the same power figures?
In which case the results are even better than the average bear.
Conversely, if I ran the same psi I would get lower numbers? Or have I got that backwards?
EDIT: I see that I did indeed have this backwards. So this is an even greater set of numbers!!
In which case the results are even better than the average bear.
Conversely, if I ran the same psi I would get lower numbers? Or have I got that backwards?
EDIT: I see that I did indeed have this backwards. So this is an even greater set of numbers!!
#17
Turbo cars lose power at altitude, just not as much as non turbo cars because we can increase to compensate for some of the loss.
#18
Probably the "best" answer is the NHRA.
http://www.nhra.net/tech_specs/altitude.html
Here is what the NHRA says about correction factors for 1/4 mile times for turbo cars:
"NOTE: Supercharged and/or turbocharged cars (i.e.: AA/A, AA/AT, BB/A, BB/AT, A/PM and AA/PM) use half factor"
Generally, the dyno shop sees about 30% correction factor SAE. When I first started going I had this discussion (I am the only client that wants uncorrected numbers, everyone else likes seeing big numbers) that their SAE was too high for a turbo car (of course they do tuning and big numbers sell). They then saw the light and started going with a standard 1.15 correction to approximate the half correction.
#19
Here is only ONE example of how things can get really mixed up. The original poster noted that he was pushing 19 psia. I am sure he meant to say that he was running 19psi (19.9 or 20psi on the Zeitronix computer screen) over atmospheric pressure at his current geographic location. Because if he meant a true 19psia, (PSIA = psi absolute = gauge pressure + current geographical location atmospheric conditions - 12.2psi according to calculator link below) that would mean he was only running 7.7 psig, which is clearly not the case considering this set up and power numbers given.
However, you must realize that a the MAP sensor is NOT like a boost gauge. A boost gauge references to atmospheric pressure. So it shows a differential pressure from atmosphere.
A MAP sensor is sealed in a vacuum and references to zero. So at 14.7psi atmospheric pressure ("zero boost" at sea level), the MAP voltage is 1.52. I was at about 3.60V so 19psi above 14.7psi.
Yesterday we were at 12.18 absolute atmospheric pressure. I was 19psi above 14.7. To my gauge pressure was 19+ (14.7-12.18) = 21.5 gauge. However, I had cylinder pressure equivalent to 19psi at sea level.
Yes the psia is confusing but most people do not equate 33.7psia pressure to 19psi boost.
The key word in this was boost which means above atmospheric pressure.
Hope that clears it up.
#20
using today's conditions here in Houston, - 93 deg. F and 40ft alt. on the same calculator gives me an atmospheric pressure of (slightly rounded up from 14.67) = 14.7 Add in 19.9 psi of pressure over that = 34.6
So there you have it, two entirely different absolute pressures even though our gauges read the exact same thing!!!! (psig)
What does this mean? It simply means that I have the boost turned up higher than the original poster if our gauges are reading the same thing!
Here's the math;
Houston 19.9 psig = 34.6 psia
Original Poster 19.9 psig = 32.1psia.
Difference in pressure = 2.5 psi!!!! So to truly compare apples to apples, the original poster is running an absolute psi that would read 17.4psi on my gauge here in Houston.
what does this mean for Horsepower difference? It gets a lot more complicated from here, but it's obvious that 2.5psi less or more of boost will make 2 entirely different numbers on a dyno. I suggest turning up the boost 2.5psi to match the same absolute pressure I run when I see my 22-23psig numbers. Which for this original poster would mean running 24.5 or 25.5 psig. - Well, those that have a turbo that can handle it anyway. Of course, you will then only adjust your dyno to correct for about 3-6% or 103-106% depending on humidity, etc. - not 126%. Keep in mind, this is the great debate I keep having, and just my opinion, not proven fact (yet.. lol) That is truly only for an NA vehicle. (1.26% correction factor) And in this case, not quite that. Here's my math for that.
So there you have it, two entirely different absolute pressures even though our gauges read the exact same thing!!!! (psig)
What does this mean? It simply means that I have the boost turned up higher than the original poster if our gauges are reading the same thing!
Here's the math;
Houston 19.9 psig = 34.6 psia
Original Poster 19.9 psig = 32.1psia.
Difference in pressure = 2.5 psi!!!! So to truly compare apples to apples, the original poster is running an absolute psi that would read 17.4psi on my gauge here in Houston.
what does this mean for Horsepower difference? It gets a lot more complicated from here, but it's obvious that 2.5psi less or more of boost will make 2 entirely different numbers on a dyno. I suggest turning up the boost 2.5psi to match the same absolute pressure I run when I see my 22-23psig numbers. Which for this original poster would mean running 24.5 or 25.5 psig. - Well, those that have a turbo that can handle it anyway. Of course, you will then only adjust your dyno to correct for about 3-6% or 103-106% depending on humidity, etc. - not 126%. Keep in mind, this is the great debate I keep having, and just my opinion, not proven fact (yet.. lol) That is truly only for an NA vehicle. (1.26% correction factor) And in this case, not quite that. Here's my math for that.
pv=nrt
so p1/t1=p2/t2
I have long ago measured air coming out of my old K27/6 and I think temps were near 200C (392F). Lets use this number. It wont be too far off for the sake of discussion.
Houston 19.9 psig = 34.6 psia = 2.385 bar
Original Poster 19.9 psig = 32.1psia. = 2.213 bar
2.213/473=2.385/t2 ---> t2 = 236C (457 F)
So just to make that extra 2.5 psi I have added 65 degrees. It doesn't really matter if I start with an outlet temp of 150C or 250C. If I start with 150C then I gain 32C in temp.
Also, I have 20% less air mass flowing over my intercooler to cool that air. This means that I am heating the intake charge more to make the same boost (and more heat in the same volume actually shows up as more pressure on a gauge) and I have less cooling of the intake charge to get rid of it.
This is why the NHRA uses a "half correction factor" for turbo cars. It is not as simple as turn up the boost.
-Dana
#21
Like I said. This is just ONE of the many things I would have to explain on truly getting a firm grip on what is happening or has to be done to make a true apples to apples comparison from one altitude to another... on a turbo car.. Naturally aspirated is just plain and simple, and easy to explain. Turbo car, MUCH more complicated.
#22
I figured out one the "issues" with my boost coming on late. I am getting old and memory loss is occurring. I do not have an LSD and not super sticky tires. On high boost setting, if I do a second roll on, i start spinning tires when boost comes on. I have tried to massage a gentler boost curve to minimize wheel spin. I probably need to work on it some more. Maybe actually bringing boost on sooner would help??
But essentially here are my boost settings:
The red arrow points to 90. This is the duty cycle required to run the boost level that I desired.
As you can see, below 4200 rpm, I am not running full boost. This was an attempt to make boost roll on as to not spin the tires. Maybe I need to re-think that an bring boost on sooner to make a "smoother" power delivery to help with wheel spin.
I am also starting to drop power by 5500 rpm. I can probably increase the boost at 5700 and 6100 to keep getting a smooth power curve all the way past 6000. I really don't want to run higher boost beyond 6100rpm because in my mind that is my safety margin against over-revving by dropping boost off.
Also, if you look at my map, if I hit past 21psi, I drop boost off immediately and hard. This again is safety that I have put into my tune. Probably not the ultimate power setup, but I also want the engine to live.
But essentially here are my boost settings:
The red arrow points to 90. This is the duty cycle required to run the boost level that I desired.
As you can see, below 4200 rpm, I am not running full boost. This was an attempt to make boost roll on as to not spin the tires. Maybe I need to re-think that an bring boost on sooner to make a "smoother" power delivery to help with wheel spin.
I am also starting to drop power by 5500 rpm. I can probably increase the boost at 5700 and 6100 to keep getting a smooth power curve all the way past 6000. I really don't want to run higher boost beyond 6100rpm because in my mind that is my safety margin against over-revving by dropping boost off.
Also, if you look at my map, if I hit past 21psi, I drop boost off immediately and hard. This again is safety that I have put into my tune. Probably not the ultimate power setup, but I also want the engine to live.
#23
Good dyno session Dana. There is more in there
The Boost Control MAP needs some work, we'll take it off-line
The Boost Control MAP needs some work, we'll take it off-line
#25
The maths is too high for my brain but I'm still wondering if I read this correctly. To do a fair comparison regarding psi, should I be dropping my boost to approx 2.5psi below yours to do this directly? Therefore, if you're running 20psi, I should run 17.5psi and then we're running even as far as that is concerned?
#26
The math only gives an estimation. The exact results will always vary depending on the setup such as the turbo compressor map and how the engine air temp compensation tables have been setup etc.
#28
Thanks for the answer.
Honestly, I was just mistakenly thinking that the SAE correction accounted for boost, but it doesn't, so that's good to know.
I understand the concept of different air densities with altitude and etc, but good info for those who might not.
Honestly, I was just mistakenly thinking that the SAE correction accounted for boost, but it doesn't, so that's good to know.
I understand the concept of different air densities with altitude and etc, but good info for those who might not.
#29
355 was uncorrected. I had this discussion (I am the only client that wants uncorrected numbers, everyone else likes seeing big numbers) that their SAE was too high for a turbo car (of course they do tuning and big numbers sell). They then saw the light and started going with a standard 1.15 correction to approximate the half correction.
No its a mixed absolute/gauge. I have described incorrectly.
However, you must realize that a the MAP sensor is NOT like a boost gauge. A boost gauge references to atmospheric pressure. So it shows a differential pressure from atmosphere.
Yesterday we were at 12.18 absolute atmospheric pressure. I was 19psi above 14.7. To my gauge pressure was 19+ (14.7-12.18) = 21.5 gauge. However, I had cylinder pressure equivalent to 19psi at sea level.
Yes the psia is confusing but most people do not equate 33.7psia pressure to 19psi boost.
The key word in this was boost which means above atmospheric pressure.
Hope that clears it up.
However, you must realize that a the MAP sensor is NOT like a boost gauge. A boost gauge references to atmospheric pressure. So it shows a differential pressure from atmosphere.
Yesterday we were at 12.18 absolute atmospheric pressure. I was 19psi above 14.7. To my gauge pressure was 19+ (14.7-12.18) = 21.5 gauge. However, I had cylinder pressure equivalent to 19psi at sea level.
Yes the psia is confusing but most people do not equate 33.7psia pressure to 19psi boost.
The key word in this was boost which means above atmospheric pressure.
Hope that clears it up.
But what you are still missing from your 103% -106% correction is that I am having to compress my air 2.5psi more.
pv=nrt
so p1/t1=p2/t2
I have long ago measured air coming out of my old K27/6 and I think temps were near 200C (392F). Lets use this number. It wont be too far off for the sake of discussion.
Houston 19.9 psig = 34.6 psia = 2.385 bar
Original Poster 19.9 psig = 32.1psia. = 2.213 bar
2.213/473=2.385/t2 ---> t2 = 236C (457 F)
So just to make that extra 2.5 psi I have added 65 degrees. It doesn't really matter if I start with an outlet temp of 150C or 250C. If I start with 150C then I gain 32C in temp.
Also, I have 20% less air mass flowing over my intercooler to cool that air. This means that I am heating the intake charge more to make the same boost (and more heat in the same volume actually shows up as more pressure on a gauge) and I have less cooling of the intake charge to get rid of it.
This is why the NHRA uses a "half correction factor" for turbo cars. It is not as simple as turn up the boost.
-Dana
pv=nrt
so p1/t1=p2/t2
I have long ago measured air coming out of my old K27/6 and I think temps were near 200C (392F). Lets use this number. It wont be too far off for the sake of discussion.
Houston 19.9 psig = 34.6 psia = 2.385 bar
Original Poster 19.9 psig = 32.1psia. = 2.213 bar
2.213/473=2.385/t2 ---> t2 = 236C (457 F)
So just to make that extra 2.5 psi I have added 65 degrees. It doesn't really matter if I start with an outlet temp of 150C or 250C. If I start with 150C then I gain 32C in temp.
Also, I have 20% less air mass flowing over my intercooler to cool that air. This means that I am heating the intake charge more to make the same boost (and more heat in the same volume actually shows up as more pressure on a gauge) and I have less cooling of the intake charge to get rid of it.
This is why the NHRA uses a "half correction factor" for turbo cars. It is not as simple as turn up the boost.
-Dana
If you have a stock intercooler, I might understand your loss of 20% cooling capacity, BUT.. if you have an upgraded intercooler that runs at say 20% more efficient.. not a stretch by any means. I did not say 20% bigger. I said 20% more efficient, which I could easily get 20% more efficiency than the stock thick brick that sits in the car from the factory. more front surface area, thinner core, smoother flow path designed for higher pressures etc. You now have an intercooler that negates any argument for less power because of loss of cooling potential. You might have a slightly larger area to compress which is also nothing to be considered for power numbers, it only slows spool by a tiny margin that would probably not be noticed.
What Am I saying? If you still have the stock intercooler - yes, you are correct,
but, if you plan your set up correctly, and buy the proper intercooler for your boost levels and delta P (pressure differentials - Plural) the power loss will be extremely small to zero. Now throw in a water to air with dry ice. Now you're working at over 100% efficiency, which brings me to your next statement. .....
Yes. As I explained, air mass over an intercooler matters. Just the difference in running a water to air intercooler vs an air to air makes a difference in correction factor . The mass of water in Denver doesn't change much...so a water to air we would have essentially the same cooling as sea level....for a while. Again, at some point the air mass has to remove the heat from the water, but that wouldn't occur in the time it takes to make a dyno pull. You would see that during a few laps on a road course.
The maths is too high for my brain but I'm still wondering if I read this correctly. To do a fair comparison regarding psi, should I be dropping my boost to approx 2.5psi below yours to do this directly? Therefore, if you're running 20psi, I should run 17.5psi and then we're running even as far as that is concerned?
That said, here in the states, I had my NSX dynoed on about 5-6 different dynojet dynos and they were never more than 3-5hp different. - I owned a shop with a dynojet and knew other shop owners so I had the privilege of testing out many for free. - Also to see if they were fudging numbers. A couple were NSX dyno days that were just fun to go to in other city's. One in Dallas and another in San Antonio. Within 2-3 hp of each other. I just can't possibly state any information about anything in Australia as I have absolutely no experience there.
If he is running a Vitesse Stage 2R and 19psi. (supporting fuel and tune an obvious necessity) I highly doubt the correction would equal 400whp. - I'm not saying his combination is anything less than fantastic, - Which I think some might see my cold calculating words are trying to do - they are not.. I am just trying to shed light with an opposing INTERNET OPINION based on first hand experience. Whether it's an apples to apples comparison is really the trick.
I had a GT30R that took 23psi to get to 406 whp. Also a fully upgraded intercooler and piping. I was also running E-85. A 3" downpipe and straight
through 3" exhaust. Tial 44mm dual port wastegate, MoTeC, larger throttle body, 044 Fuel pump. Lightened flywheel, no power steering or AC accesories to bog the motor. I also tried to obtain 400whp on E-85 - summer blend - with 880cc injectors. I could not get past 360whp at 100% duty cycle with the fuel pressure throttled to 70psi at vacuum. 880's or something close is what DanaT is running. - This alone is a more telling story - The uncorrected numbers match my experience. - Almost.. 90% duty cycle on propably 880cc's injectors at 355whp. vs my 360whp at 100% duty cyle at 70psi fuel pressure at vacuum, 880 cc injectors. Not dead on, but very close.
So you might see / understand why I might doubt his specific combination would make the same rwhp as the above combination because a correction factor deemed it so. - that said. 355whp sounds about right, and I say -hell yeah- for Dana to post the uncorrected numbers.
Last edited by 95ONE; 06-21-2012 at 02:32 AM.
#30
The maths is too high for my brain but I'm still wondering if I read this correctly. To do a fair comparison regarding psi, should I be dropping my boost to approx 2.5psi below yours to do this directly? Therefore, if you're running 20psi, I should run 17.5psi and then we're running even as far as that is concerned?