Surrey Rolling Road results - 11/11/10

[Ewan]

Thanks to NoelWatson for arranging the Surrey RR evening - (http://www.nsxcb.co.uk/testvb/showthread.php?t=8430). We had Noel, Simon (NSXGB), Paul (NSX2000), me, Paul (CrazyMixedUpKid) and Kare (SilverSurfer). Markc came for moral support but not in his NSX :)

Here are my results:

7914

7915

Not bad given that the only power mod is a Larnini exhaust on standard cats & intake, except with a K&N filter element. I had a blown O2 sensor but the dyno chap (I think it was v1xpy from PH) said he thought it was running just fine.

Now over to the others to brag/moan etc about their results :)

Ewan

[NoelWatson]

Thanks to NoelWatson for arranging the Surrey RR evening - (http://www.nsxcb.co.uk/testvb/showthread.php?t=8430). We had Noel, Simon (NSXGB), Paul (NSX2000), me, Paul (CrazyMixedUpKid) and Kare (SilverSurfer). Markc came for moral support but not in his NSX :)

Here are my results:

7914

7915

Not bad given that the only power mod is a Larnini exhaust on standard cats & intake, except with a K&N filter element. I had a blown O2 sensor but the dyno chap (I think it was v1xpy from PH) said he thought it was running just fine.

Now over to the others to brag/moan etc about their results :)

Ewan


After replacing my air filter, my numbers have gone from bad to worse. When I went with just intake and exhuast, I got 321bhp with power being maintained almost to redline. Fast forward to running with cats on and with dirty air filter and I got 307bhp with power tailing off very sharply after 7000rpm. Last night car was running very lean (due to increased airflow from replaced filter), and I was getting 295 bhp at around 6400rpm, with power tailing off slowly. ECU is not happy with cats/ECL, so they are coming off at next opportunity.

Another visit will be planned for those of us that needs to fix things!

[AR]

Noel at what AFR where you getting MAX power before ( 321 hp ) and after ( 307 hp )?

[NoelWatson]

Noel at what AFR where you getting MAX power before ( 321 hp ) and after ( 307 hp )?

I will dig them out, but IIRC, the car likes running rich when in VTEC.

[greenberet]

After replacing my air filter, my numbers have gone from bad to worse.

LoveFab in the US developed a new exhaust system for the NSX in 2009 and measured the horsepower gain it provided. As a baseline, they first measured the horsepower of the car in stock form and came up with 229.0 rwhp. Then they built their new exhaust system, installed it on the same car, and went back to the same dyno. Their results this time: 274.5 rwhp, or a gain of 45.5 hp at the wheels.

To confirm the results, they decided to carry out before and after measurements on the same dyno on the same day. This time they only measured a gain of 22.3 hp at the wheels, however. The "stock" measurement was higher than before and the "modified" measurement was lower.

LoveFab’s lesson learned was, “The best comparison results can only be gathered by testing components as close to back-to-back as possible.”

A dyno day like the one you guys just attended is great for checking how much power different NSXs put out compared to each other. But since almost no dynos are regularly calibrated, they’re not so good for measuring changes in horsepower over time. The air/fuel ratio AR mentioned is probably a better indication whether your engine really is leaning out than a change in measured horsepower.

If it makes you feel any better, the measured rear wheel horsepower for my NSX has dropped from 408 rwhp to 238 rwhp with the car in the same state of tune. However, I take comfort in the fact that the top speed hasn't dropped, the compression readings are all good, the engine doesn’t burn any oil, and an exhaust gas analyzer says everything is still as it should be.

[AR]

Agree 100% greenberet, dynos can vary soo much is just a slight reference.

[NoelWatson]

Agree 100% greenberet, dynos can vary soo much is just a slight reference.

But we weren't really looking at absolute numbers, we were looking at the shape of the power curve. I'm not sure how a dyno could that bit completely wrong.

[markc]

I didn't get to see all the results but it was looking like the late model LEV cars didn't like the "race cats". The AFR traces I saw could be seen to hit a certain point (about 5K revs) and react by leaning right off. You could even hear it in the exhaust note!

I believe that, in theory, provided the throttle is wide open the ECU runs Open Loop mode i.e. ignoring the post CAT O2 reading and just running the pre-defined fuel/ignition maps so it shouldn't make a difference... but it plainly does. Do LEV cars use differant O2 sensors or is it just the ECU/program?

The good news, for me, is that my car should be OK on it's new CATS :) (Better get to a dyno then)

Cheers

Mark

[greenberet]

But we weren't really looking at absolute numbers, we were looking at the shape of the power curve. I'm not sure how a dyno could that bit completely wrong.

Dynos that measure driveline losses can get the overall shape of the crank horsepower curve wrong due to inaccuracies in the coast-down measurement. The coast-down drag measurement is added to the rwhp measurement to come up with a crank hp figure at each rpm. Since the coast-down drag increases exponentially (not linearly) with rpm, problems with that measurement have the potential to change the overall shape of the calculated crank hp curve.

ProcarSpecials put his NSX on a rolling-road dyno that did coast-down measurements. 24.0% driveline losses at 218.3 km/h were measured for his car. A different rolling road dyno measured 10.4% driveline losses at 216.0 km/h for my car. Either Detlef's transmission was filled with sand and mine with teflon, or the measurements were wrong.

If our rwhp curves had been completely flat, Detlef's crank hp curve would have had a different shape than mine simply because of that dubious coast-down measurement. Mine wouldn't have increased as nicely towards the redline even if our cars had put the exact same hp to the road at every rpm.

If one dyno measures the exponentially increasing coast-down drag to come up with a crank horsepower figure and another dyno doesn’t even measure it but simply adds a fixed percentage to the rwhp measurement, that will also change the shape of the crank horsepower curve.

Also, the shape of the rwhp curve itself is impacted by the amount of tire slip. Increasing the rollers' coefficient of friction (for example) will reduce tire slip and allow the car to transmit more power to the dyno, producing a nicer horsepower curve up top. A dyno that measures at the hub is of course the ultimate way to do away with tire slip completely, impacting the shape of the curve up top even more.

That being said, I look forward to seeing more results from the Surrey Rolling Road dyno day. Tests carried out on the same dyno on the same day should allow the cars to be compared with each other very well and hopefully, conclusions to be drawn - like markc's.

[NoelWatson]

Dynos that measure driveline losses can get the overall shape of the crank horsepower curve wrong due to inaccuracies in the coast-down measurement. The coast-down drag measurement is added to the rwhp measurement to come up with a crank hp figure at each rpm. Since the coast-down drag increases exponentially (not linearly) with rpm, problems with that measurement have the potential to change the overall shape of the calculated crank hp curve.

ProcarSpecials put his NSX on a rolling-road dyno that did coast-down measurements. 24.0% driveline losses at 218.3 km/h were measured for his car. A different rolling road dyno measured 10.4% driveline losses at 216.0 km/h for my car. Either Detlef's transmission was filled with sand and mine with teflon, or the measurements were wrong.

If our rwhp curves had been completely flat, Detlef's crank hp curve would have had a different shape than mine simply because of that dubious coast-down measurement. Mine wouldn't have increased as nicely towards the redline even if our cars had put the exact same hp to the road at every rpm.

If one dyno measures the exponentially increasing coast-down drag to come up with a crank horsepower figure and another dyno doesn’t even measure it but simply adds a fixed percentage to the rwhp measurement, that will also change the shape of the crank horsepower curve.

Also, the shape of the rwhp curve itself is impacted by the amount of tire slip. Increasing the rollers' coefficient of friction (for example) will reduce tire slip and allow the car to transmit more power to the dyno, producing a nicer horsepower curve up top. A dyno that measures at the hub is of course the ultimate way to do away with tire slip completely, impacting the shape of the curve up top even more.

That being said, I look forward to seeing more results from the Surrey Rolling Road dyno day. Tests carried out on the same dyno on the same day should allow the cars to be compared with each other very well and hopefully, conclusions to be drawn - like markc's.



Dynos that measure driveline losses can get the overall shape of the crank horsepower curve wrong due to inaccuracies in the coast-down measurement.


Maybe SRR do things differently, but I didn't see any coast down measurement - they measure at the wheels power, then apply a fudge. If I were to look at the at the wheels power, I would see the same thing, just scaled down.

[NoelWatson]

(Better get to a dyno then)



Reckon in a month or less for rematch!

[greenberet]

my numbers have gone from bad to worse.

Were the three runs you mentioned (321bhp, 307bhp, and 295bhp) all done on SRR’s dyno?


Last night car was running very lean

It’s strange that your engine is leaning out on the dyno. The PGM-FI should be in open loop mode at full throttle, ignoring the O2 sensors. The fuel should simply be injected based on the fuel map in your chip, modified by the short and long term fuel trims the PGM-FI has learned. Those short and long term fuel trims are learned when the car is at idle or part throttle. The PGM-FI injects fuel based on the map and then with the feedback from the O2 sensors, it learns whether it needs to richen up or lean out the fuel map to be at lambda 1. That can compensate for the fuel pump no longer pumping quite as hard as when it was new, the fuel filter perhaps being stopped up a bit, etc. When you go to full throttle, the PGM-FI ignores the O2 sensors but applies the fuel trims it has learned.

Did you pull the clock fuse or disconnect the battery shortly before the dyno run? Maybe the PGM-FI hasn’t had time to learn the proper short and long term fuel trims for your engine with its current modifications. Or maybe your modifications have increased the airflow so much that it is now beyond the PGM-FI’s range of adjustment.

[NoelWatson]

Were the three runs you mentioned (321bhp, 307bhp, and 295bhp) all done on SRR’s dyno?



It’s strange that your engine is leaning out on the dyno. The PGM-FI should be in open loop mode at full throttle, ignoring the O2 sensors. The fuel should simply be injected based on the fuel map in your chip, modified by the short and long term fuel trims the PGM-FI has learned. Those short and long term fuel trims are learned when the car is at idle or part throttle. The PGM-FI injects fuel based on the map and then with the feedback from the O2 sensors, it learns whether it needs to richen up or lean out the fuel map to be at lambda 1. That can compensate for the fuel pump no longer pumping quite as hard as when it was new, the fuel filter perhaps being stopped up a bit, etc. When you go to full throttle, the PGM-FI ignores the O2 sensors but applies the fuel trims it has learned.

Did you pull the clock fuse or disconnect the battery shortly before the dyno run? Maybe the PGM-FI hasn’t had time to learn the proper short and long term fuel trims for your engine with its current modifications. Or maybe your modifications have increased the airflow so much that it is now beyond the PGM-FI’s range of adjustment.





Were the three runs you mentioned (321bhp, 307bhp, and 295bhp) all done on SRR’s dyno?


Yes, and the curves aren't too different until past 6000rpm



Did you pull the clock fuse or disconnect the battery shortly before the dyno run?


We deliberately didn't to see how the car was running with the CEL light on. After getting the new air filter fitted, and pulling the fuse, the car felt very strong (the exhaust was far noisier than before), but definitely wasn't as sprightly yesterday after light had been on for a few weeks.

[markc]

Were the three runs you mentioned (321bhp, 307bhp, and 295bhp) all done on SRR’s dyno?

I shouldn't speak for someone else but as I know the answer I will, Yes all runs were done on the same dyno (SRR).


The PGM-FI should be in open loop mode at full throttle, ignoring the O2 sensors. The fuel should simply be injected based on the fuel map in your chip, modified by the short and long term fuel trims the PGM-FI has learned.

That's what I thought.


Those short and long term fuel trims are learned when the car is at idle or part throttle. The PGM-FI injects fuel based on the map and then with the feedback from the O2 sensors, it learns whether it needs to richen up or lean out the fuel map to be at lambda 1. That can compensate for the fuel pump no longer pumping quite as hard as when it was new, the fuel filter perhaps being stopped up a bit, etc. When you go to full throttle, the PGM-FI ignores the O2 sensors but applies the fuel trims it has learned.

It's not just one car though. Two late model LEV NSX's running the same CAT/Exhaust systems showed the same issue i.e. leaning out at high revs.

It wouldn't appear to be the dyno equipment at fault as the other NSX's in attendance showed nice smooth AFR plots.


Did you pull the clock fuse or disconnect the battery shortly before the dyno run? Maybe the PGM-FI hasn’t had time to learn the proper short and long term fuel trims for your engine with its current modifications. Or maybe your modifications have increased the airflow so much that it is now beyond the PGM-FI’s range of adjustment.

It sounds like the LEV ECU does in fact read the post CAT O2 sensor at full throttle. It doesn't like what it sees, because the race CAT isn't reducing CO/NO2/HC emissions enough, so responds by leaning out the fuel mixture?

I wish we could get into these OBDII ECU's to understand and adjust settings/maps for this sort of thing but I realise that it's not cost effective for any commercial companies to do so.

Cheers

Mark

[greenberet]

I wish we could get into these OBDII ECU's to understand and adjust settings/maps for this sort of thing

As far as I understand it, for USD 100 you can at least monitor what's going on in the engine. See here (http://www.nsxprime.com/forums/showthread.php?t=112530).

That's the one thing I would prefer an OBDII car for. It would be great to check the air/fuel ratios while driving, how the manifold pressure is affected by different air filters, how the ignition timing is affected by different octane fuels, etc. That would make it much easier to check whether modifications really have any benefit.

[NoelWatson]

As far as I understand it, for USD 100 you can at least monitor what's going on in the engine. See here (http://www.nsxprime.com/forums/showthread.php?t=112530).

That's the one thing I would prefer an OBDII car for. It would be great to check the air/fuel ratios while driving, how the manifold pressure is affected by different air filters, how the ignition timing is affected by different octane fuels, etc. That would make it much easier to check whether modifications really have any benefit.

I have this one

http://www.easyobdii.com/

but difficult to know what to look for.

[NSX 2000]

Here are a copy of my graphs.

For people who don't know Noel and I have the 02+ cars, (these are the 3.2 litre LEV engines), both have a Procar airbox and scoop with brand new Apexi airfilter fitted a few weeks back, Tiatec GT exhaust, Prospeed Hi flow sports cats. Both cars have the yellow/orange engine management light on caused by the post cat O2 sensors. These are sending a reading back to the ECU which think that both CATS have broken.
(Hope the above makes sense)

Paul

[NoelWatson]

Here are a copy of my graphs.

For people who don't know Noel and I have the 02+ cars, (these are the 3.2 litre LEV engines), both have a Procar airbox and scoop with brand new Apexi airfilter fitted a few weeks back, Tiatec GT exhaust, Prospeed Hi flow sports cats. Both cars have the yellow/orange engine management light on caused by the post cat O2 sensors. These are sending a reading back to the ECU which think that both CATS have broken.
(Hope the above makes sense)

Paul

Paul,

I spoke to Charlie about

1. Renault vs Honda
2. Diesel vs petrol

when we get bored of testing the NSXs.

[AR]

I have a feeling that those cats are not up to the task due to the quality of cores, but that is just my .2p.

[Justin]

I have this one

http://www.easyobdii.com/

but difficult to know what to look for.

Some peeps are plugging a bluetooth OBDII head and leaving it in situ for live feed to an iphone (running something like DashCommand) whilst driving...

Though I think that the biggest piece of info I would pull from such a set up is "you have just wrapped your car around a tree" :no:

[greenberet]

Here are a copy of my graphs.Interesting! It seems most naturally-aspirated engines produce peak power at air/fuel ratios around 12.5-13.0:1 and in both runs, the air/fuel ratios were within that range from 5800 to 7400 rpm. However, in the second run the engine was running leaner than that at lower engine speeds (closer to the stoichiometric ratio of 14.7:1) and richer than that at higher speeds.

What markc wrote sounds very plausible - that the PGM-FI saw that the CATs weren’t doing their job properly at full throttle so it adjusted the air/fuel ratios closer to stoichiometric in the second run, trying to give the CATs an easier job of getting the emissions under control. Since the peak power produced above 5800 rpm was within 1 hp of each other during both runs, I’d guess the PGM-FI left the ignition timing alone. What happened to the fuelling above 7400 rpm - God only knows.

An OBDII gauge and someone who knows in detail what feedback loops the 2002-2005 PGM-FI has in open-loop mode (Kaz?) would be very helpful in diagnosing exactly what’s going on. But if you swap your old CATs back in, the check engine light goes away, and the air/fuel ratio at full throttle goes back to where it should be, you'd have your solution even if the "why" remains somewhat unclear.

As an aside, if the S_HP in the first picture refers to the calculated crank horsepower and the HP in the third picture refers to the measured rear wheel horsepower, SRR may have assumed a 17.6% driveline loss for the NSX instead of the more usual 13.5%.

[Ewan]

I have this one

http://www.easyobdii.com/

but difficult to know what to look for.

I got a new USB scanner off ebay, and it came with PCMScan -http://www.palmerperformance.com/products/pcmscan/index.php (http://www.palmerperformance.com/products/pcmscan/index.php)

Looks a tad more comprehensive than the freebie ones.

rgds
E

[Silver Surfer]

Here's mine

SS

[NoelWatson]

I got a new USB scanner off ebay, and it came with PCMScan -http://www.palmerperformance.com/products/pcmscan/index.php (http://www.palmerperformance.com/products/pcmscan/index.php)

Looks a tad more comprehensive than the freebie ones.

rgds
E

Looks better than easyOBD. I've gone as far as observing that the car goes to open loop at WOT, and that the speed that comes out of the port is different than that shown by the speedo.

[NoelWatson]

Here's mine

SS

Very good numbers. Will be interesting to see what difference the power makes at high speed

[NoelWatson]

I have a feeling that those cats are not up to the task due to the quality of cores, but that is just my .2p.

Because the cell count is too low (200?), or not of adequate quality?

[NSX 2000]

Here's mine

SS

Show off :D

[CrazyMixedUpKid]

And the runt of the litter ... poor old P26 ...

I have the Dali "stealth" Apexi filter - no scoop - DC sport headers and exhaust and Prospeed cats (no CEL lights for me - but mine a 3.2 non LEV)

... so not sure whats going on here. Maybe I should go back and fit the scoop ... maybe my timing is off ... maybe I have a compression issue ... maybe she's just 'tired' ... 133K miles on the clock ... any tuning gurus out there please chip in. Seems to be a lack of torque out of VTEC compared to others ...

Knew it was a bad idea to get this done! I was perfectly happy before I went ;-)

Great to see (and hear) the other cars ... my exhaust is MUCH quieter than the Taitec and Larinis ... maybe I need more noise to get more power!

Cheers
Paul

[NoelWatson]

And the runt of the litter ... poor old P26 ...

I have the Dali "stealth" Apexi filter - no scoop - DC sport headers and exhaust and Prospeed cats (no CEL lights for me - but mine a 3.2 non LEV)

... so not sure whats going on here. Maybe I should go back and fit the scoop ... maybe my timing is off ... maybe I have a compression issue ... maybe she's just 'tired' ... 133K miles on the clock ... any tuning gurus out there please chip in. Seems to be a lack of torque out of VTEC compared to others ...

Knew it was a bad idea to get this done! I was perfectly happy before I went ;-)

Great to see (and hear) the other cars ... my exhaust is MUCH quieter than the Taitec and Larinis ... maybe I need more noise to get more power!

Cheers
Paul

Paul,

This was from when my car was standard

http://www.noelwatson.com/blog/content/binary/SRR-AFRatio.jpg

and as you can see, the AF ratio is pretty flat until around 5500rpm, until it starts to run richer. My theory is that the ECU likes the car to run rick in VTEC. Your A/F ratio is completely different to mine. If it were me, I would go back to standard, and see how it looks, but not sure if you want to go through all that effort.

[havoc]

the AF ratio is pretty flat until around 5500rpm, until it starts to run richer. My theory is that the ECU likes the car to run rich in VTEC.

On the assumption that the NSX mapping is similar in principle to the ITR mapping, I agree - that certainly seems to be the consensus from the ITR community (those that have dyno'd and/or re-mapped their cars).

[AR]

Because the cell count is too low (200?), or not of adequate quality?

Quality I will say Noel, I doubt those cats have passed any EPA, Carb, or Euro tests.

I wonder if an NSX-R ECU is an LEV one???

Perhaps a non LEV ECU might fit and allow use of sports cats?

[NSXGB]

Finally got my scanner working...
My humble results.
3.0 (93,000 miles)
DC Sports Headers, De-cat, Larini Exhaust.
OEM air filter, Downforce snorkel intake.
95 RON fuel.
ECU reset before drive to SRR.

Made a bit more than I was epecting.

794079417942

:cool:

[AR]

I reckon that dyno is not reading right IMHO.

[NSXGB]

I reckon that dyno is not reading right IMHO.

Yeah, a bit too low :)

[AR]

Yeah, a bit too low :)

O'RLY :)

IME Max BHP for 3.0 NA with mods = 290 +-5

[NSXGB]

O'RLY :)

IME Max BHP for 3.0 NA with mods = 290 +-5

I like to think mine's special :)

What do you think happened to the dyno on my run?

[AR]

I can't say as I don't know the particulars, but for a 3.2 to read 321bhp and a 3.0 307bhp it all sounds too high.

[vtecdirect]

Guys, as greenberet says, a rolling road is really just a tuning tool and should be used as such. They will all differ in their readouts. If you intend to make some modifications to your car get it dyno'd before and after the mods on the same dyno and if possible on the same day with the same operator.
Other than that the figures produced on almpost all rolling roads i have seen have been simply pie in the sky.
I use a hub pack dyno for all my tuning etc and this is as accurate as you can get, but as a one off readout i doubt the figures are truly correct.
If you just want to see if your car is healthy, put it up against a similar modified and mileage vehicle, if they are similar all good.

[Silver Surfer]

I reckon that dyno is not reading right IMHO.

My car has been dyno'd in 2 separate rolling road prior to SRR and on both occasions it read 367 and 368 bhp respectively.

SRR gave me 386bhp..nearly 18-19bhp more than previous.....
If you minus 18 to 19bhp form the other cars...It could be what the 'alternative true' power level for each of the car tested on that day....:dunno:

CMUK's still acchieved 284bhp despite the tester suggesting that it wasn't fuelling at optimum...I thought 284 wasn't bad at all considering manufacturer suggests 290bhp as standard for a 3.2l if the RR was accurate.

SS

[NSXGB]

I can't say as I don't know the particulars, but for a 3.2 to read 321bhp and a 3.0 307bhp it all sounds too high.

The 321bhp run was not taken that night.

I agree that the figures are too high for mine ( I was expecting 280-285 ), but what happened to the 3.2's on the night?

Maybe the Dyno's atmospheric error correction was not functioning...

[NoelWatson]

but what happened to the 3.2's on the night?



They were lulling you into a false sense of security

[greenberet]

Last night car was running very lean ...What air/fuel ratio did you have from 6000-7500 rpm?

What’s strange is how differently shaped the air/fuel curves were on this day if everyone had stock engine management systems except for Silver Surfer. Either Honda completely changed the air/fuel ratio curves in the PGM-FI for different model years or something else is going on.


… for a 3.2 to read 321bhp and a 3.0 307bhp it all sounds too high.I agree but the three rear wheel horsepower measurements mentioned so far:

NSX 2000’s 2005 3.2: 251.7 rwhp with airbox/air filter, cats, and muffler
CrazyMixedUpKid’s 1997 3.2: 233.0 rwhp with air filter, headers, cats, and muffler
Silver Surfer’s 1991 3.0: 322.3 rwhp with supercharger
look rather conservative. However, the assumed driveline loss was very generous and perhaps that's what raised the calculated crank bhp figures.

[NSXGB]

NSX 2000’s 2005 3.2: 251.7 rwhp with airbox/air filter, cats, and muffler
CrazyMixedUpKid’s 1997 3.2: 233.0 rwhp with air filter, headers, cats, and muffler
Silver Surfer’s 1991 3.0: 322.3 rwhp with supercharger
NSXGB's 1993 3.0: 253.3 rwhp

look rather conservative. However, the assumed driveline loss was very generous and perhaps that's what raised the calculated crank bhp figures.

Roughly 19% drivetrain loss seems to have been added to those figures. From what I've read, 15% drivetrain loss is closer to the norm, which would be closer to the truth maybe?

[greenberet]

I agree. From what I’ve read, adding 15% to the rwhp figures of an NSX is probably a more accurate way of estimating the crank bhp than adding 19%.

In any case, your car seems to be running very well and it produced peak power at an air/fuel ratio of 12.9:1. The air/fuel ratio curve of your car looks quite different than, for example, Ewan’s. Is your engine management system stock?

[NSXGB]

I agree. From what I’ve read, adding 15% to the rwhp figures of an NSX is probably a more accurate way of estimating the crank bhp than adding 19%.

In any case, your car seems to be running very well and it produced peak power at an air/fuel ratio of 12.9:1. The air/fuel ratio curve of your car looks quite different than, for example, Ewan’s. Is your engine management system stock?

As far as I know the engine management is stock. Just intake snorkel (DF), headers, decat & exhaust. Running standard air filter and 95 RON fuel.

[NoelWatson]

I agree. From what I’ve read, adding 15% to the rwhp figures of an NSX is probably a more accurate way of estimating the crank bhp than adding 19%.

In any case, your car seems to be running very well and it produced peak power at an air/fuel ratio of 12.9:1. The air/fuel ratio curve of your car looks quite different than, for example, Ewan’s. Is your engine management system stock?

I have a feeling that the lower number is the unadjusted for atmospheric

[NoelWatson]

What air/fuel ratio did you have from 6000-7500 rpm?




>13. Looking at my 321bhp, ratio was <12. Furthermore, the curves were very similar low down, producing about 270bhp @6000rpm.

[greenberet]

I have a feeling that the lower number is the unadjusted for atmosphericLooking at the footnotes of the dyno charts, practically no dyno correction factor should have been applied. With a barometric pressure (BP) of 98.0 kPa, a relative humidity (RH) of 65%, and an intake air temperature (IT) of 13°C, the dyno correction factor should have been 1.002 or 0.990 depending on which standard SRR corrected to. Basically, the test conditions were already equivalent to standard temperature and pressure so no adjustment was necessary.

Looking at the footnotes further, it might actually not be so easy to compare the maximum horsepower figures of all the cars. In all of the dyno charts, the overall gearing (TN = total numerical ratio) was assumed to be the same. However, since the five speed transmission’s gearing varies based on model year and the six speed transmission’s gearing is different yet again, that may have impacted the results. Dynos measure torque and calculate horsepower based on that and rpm. If the rpm weren’t determined by measuring the engine’s ignition signal in the engine bay but were calculated based on the overall gearing, assuming incorrect gearing might have impacted some of the results.


the curves were very similar low down If your horsepower curves were very similar low down across your dyno runs but varied at high rpm, that’s the opposite of NSX 2000’s chart, strangely enough. The horsepower of his LEV 3.2 varied a great deal low down but above 6000 rpm, the horsepower curves were almost identical.

The mystery continues but I wish you good luck and hope you solve it!