333pg333

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!!

DanaT

SAE correction is VERY optimistic for a turbo car. The SAE correction would have been about 450hp. We know a 951 on 19psi absolute boost is not making 450hp at sea level.

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.

DanaT

355 was uncorrected. 405 was a correction below SAE (that was 1.267 yesterday). Correction factors for turbo cars is fuzzy. His dyno was actually showing a 35% SAE correction because he had a swamp cooler running in the shop (high humidity and still high temp)

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.

DanaT

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.

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.

DanaT

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

DanaT

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.

DanaT

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.

fast951

Good dyno session Dana. There is more in there
The Boost Control MAP needs some work, we'll take it off-line

DanaT

Well once again, Johns support is great!

I think some of the spool problems are do to user error (me). Some minor changes might fix this right up. I just wont have the dyno data...

333pg333

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?

Duke

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.

333pg333

But when we're discussing altitude isn't this an absolute?

onspeed

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.

95ONE

Too true, big numbers do certainly sell. 355 uncorrected is a great number For a Stage 2 turbo and stock intercooler. - And - to be clear, I'm not doubting it. It's also nice to see the number at the same altitude as Bandimere. - 5010ft. So, Doing a calculation on 355 whp on a 3000lb car should get you right around 113-115mph tonight. It will be nice to see what it actually Traps in MPH since this is a proven horsepower level at the exact altitude as the track.

Boost above which atmospheric pressure Yours or mine? But yes, true, and I understands mafs quite well. So many read differently at different voltages, that it is impossible extrapolate any information from voltage and just the word MAF.. and I don't remember you mentioning it in your first post, so I apologize for missing earlier information given. Also, I read 19.9 psi in the ZT-2 chart. Was that just a quick spike or should we just call it 20psi? It looked like an insanely flat line.


I also understand those numbers (Boyle's law, Gay-Lussac's etc. ) and know that the compressor you're using should be far and above more efficient than the K27/6. less heat will be transferred in the compressor maps. It would be interesting to see both, but I don't think John V would offer one up? What pressure were you running off the 27/6 that gave you close to 400 deg F!? 25psi? (before it just turned into the blow dryer you're describing and lost psi at peak rpm) I wish you would have used another example because I could have worked with it a bit better. I just can't sit here and agree to that comparison at all. I would guess your new turbo is hitting around - doing math now..325-350 deg f max. On a side note, the NHRA correction factor is a, "too many variables, just throw this out there as a suggestion" kinda correction factor. BOOSTED (not just turbos) set ups are way too varied and unique to give a "all in one" correction number. They're including in there old and horribly inefficient supercharger's that can't hold a candle to a modern turbo charger set ups. So I take the NHRA suggestion with a grain of salt. NOW... on to the intercooler.

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. .....

agreed. But still reference my statement above 100% efficiency for use of ice or dry ice in a quarter mile run.

Patrick, what Dana's number are trying to tell you is if your altitude is near sea level, your current boost level would be fine and not needed to be dropped. He has just explained that the 19PSIA was a small mistake, BUT he defined it as the fact that his set up was already correcting for the 2.5psi difference and was indeed running at a 19 (19.9) psi that would equal to one at your altitude if you are at or near sea level. So you would compare your dyno numbers directly to his corrected 400whp. So if your 23psi is making 365whp, his 20 is making 400. As mentioned in many posts, the Australians Dynos probably read lower, and no two dyno set ups or conditions are the same.
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.

DanaT

Approximately, yes.