Calculation for inlet temperature

[PhilT]

If a power run in done on a rolling road, the inlet temperature is circa 80C, and the bhp figure comes out at 400...

Does anyone know the calculation to adjust the bhp figure?

[s2driver]

Adjust to what? An inlet temperature of, say, 45 deg C?

I don't think that you can produce a simple formula for accurate results. You could probably get a ROM (rough order of magnitude) figure by calculating the change in air density and hence air mass flow rate. This is simple.
Providing you know that with a higher mass flowrate of air that you still remain with the same mixture ratio you could calculate the theoretical increase in energy liberated from the fuel/air mix. Don't know how much the engine's efficiency would change due to the change in temperatures within the system but it is probably better to get empirical data (if possible). Ask a tuner if he has data from near-identical cars with different inlet temperatures to give an estimate. Using multiple data points with minimised variables allows you to make a more educated 'guess'. Keep the rolling road, car spec, operator the same and just compare the effect of the temperature change. One flaw to this one is that I know some tuners who have seen anything from 230 bhp to 265 bhp from standard S2s running identical specification under comparable rolling road conditions: why the hell is that?!?!?

Delivering more air-mass to an engine through cooler charge at a given boost pressure may take you out of the limits of your ECU or other installed components. You may not get any more power if the injectors can't keep up (shouldn't run them at higher than 80% duty cycle anyway in my opinion). The ECU might back off the boost pressure in the presence of a cooler charge to maintain stoichometric or slightly rich depending on where your foot is on the throttle. Keeping it lean is easy with a denser charge but very bad since your combustion temperatures can go through the roof. This was a relatively common problem on Micky Mouse Escort RS Turbo conversions. ECUs are quite smart to avoid this in our cars but not sure how well you can utilise more air-mass effectively.

Thinking about water injection [img]images/graemlins/wink.gif[/img] or better charge cooling through water spray on to the intercoolers [img]images/graemlins/1syellow1.gif[/img] or, even, bigger intercoolers [img]images/graemlins/laugh.gif[/img] ?

80 degrees is a bit on the high side! Who's rolling road was it? Were they supplying a high enough airflow to the intercoolers? Probably easiest just to get a second opinion at another rolling road. What charge temperature is expected on this particular engine on an average day?

Lee

[Doug_RS2]

I got 319bhp at that same place - Well Lane Turbo Centre - about 10 minutes after Phil. The blower was aimed above the intercooler on our cars!

I have plots from Star Performance for 322bhp and the AMD plots of 335bhp. I was happyish with the 319 but thinking back I'm using Optimax and Octane booster now so it should have been more. My torque curve was sh1te though. If I use Phils theory of him thinking he should be at 430 instead of 400 then I can normalize my results to 340bhp!

Q: Does the S2 compensate for temperature - slighlty more boost on a warm day - so misting the ic is pointless??

[s2driver]

Q: Does the S2 compensate for temperature - slighlty more boost on a warm day - so misting the ic is pointless??

I am not sure how our ECUs exactly compensate for varying ambient temperatures. Hopefully it concentrates on the charge temperature.

I presently run a standard S2 intercooler which is fine at the moment. Compressing air leads to the production of heat. Passing hot air through an intercooler trasfers some of the heat from the charge to the intercooler. The heat is then convected away from the intercooler by the air going through your grill. Increasing the size of an intercooler to say that of an RS2 item does 3 things. Firstly, It allows a large surface area to transfer more heat to the intercooler from the hot charge. Secondly, there is more mass of aluminium in the intercooler allowing it to absorb more heat energy for a given temperature rise. Thirdly, a large intercooler has a large surface area to transfer heat to the air outside the car. The ECU dials back the boost pressure as the charge temperature increases. Reducing temperature differentials between the intercooler ad the charge reduces your heat transfer significantly. Additionally a hot day affects the heat transfer from the intercooler. Charge temperature increases in the manifold over time only arise because you are putting more energy in than you can remove.

Whilst using a standard intercooler seems illogical for the power hike I am targeting. Water injection allows me to speed up the heat transfer from the intercooler and hence from the charge. My stage 2 mods should use a much larger intercooler than the RS2 item to allow muuch faster heat transfers but addmiteadly I may be limiting how long I can generate high boost for before the ECU intervenes with the standard one installed. Implementing this large intercooler will come with significant body mods. I also intend to reduce the amount of intercooler hose by around 6 feet with a cutom inlet manifold with the throttle body at the front of the engine instead of the back. This will also be a custom intercooler to my specification and CAD drawings. I know a certain company that is developing intercooler units for performance cars based on industrial heat exchanger type cores which are better designs anyway.

Lee

[s2driver]

There is also a system described on the Autospeed website. You need to be a member to read it though but is a simple circuit based around a pic. Instead of wasting loads of water by misting the intecooler all of the time it learns the frequency of when you car is generating high boost pressures and hence lots of intercooler heat. By learning it anticipates high boost and starts misting to reduce the chargecooler temperature. When you have backed off a bit or come to traffic the system recognises the lower use of high boost and reduces the amount of water on the intercooler. In addition to being able use water more intelligently (albeit, rather simplistically: is than oxymoron?) the system kind of anticipates boost and starts to cool the intercooler during high loading. As I said previously, increasing temperature differentials increases the heat transfer. I am going to look into getting one of these made to suit my stage 1 mods.

Lee

[PhilT]

So how does this sound....

Air density decreases as temp rises. You have to use temp in degrees kelvin, so degrees C +273. So you take power measured at actual average inlet temp (70C) 403 and divide it by 303 (273 + 30C), asuming you see 30C on the road, and multiply by 273+70.

In other words 403*(273+70)/(273+30)= 456 ish hp

I'd guess that your inlet temps ran between 45 and 86 on sunday, so an average of 70.

[Crafty]

As S2_Driver says I don't think there is a reliable formula as there are other variables ( air density etc ) that also have a bearing. I played with a power/torque calculator program but couldn't come up with consistent results.

I've seen a website where a US guy is using one of these intelligent misters, url is http://public.fotki.com/ttschwing/. He hangs out on the tt forum now and again.

It doesn't look a bad system really, but ideally a mister or water injection setup wants to be controlled by the ECU itself to ensure that you have maximum control over *all* engine operations. Of course the stock ECU can't do this, which means you need to go mappable, using outputs to drive WI, IC spray, even nitrous - allowing you to manipulate the map to gain full advantage.

[Dippy]

I read somewhere that the ECU on the S2 reduces boost when the intake is cold, and increases it when warm, so that the engine performance is constant no matter what the ambient temperature.

As I say, I read that somewhere so I don't know if it's true or not. However I could believe it. On my S4 I have a boost guage and it doesn't seem to vary with temperature.

[jeffw]

If your measuring pressure in Bar then this will change depending on the ambient pressure which will be effected by external temperature.

[Simon]

I did think it was a useful visit to well lane (especially as it pinpointed my problem) but I did come away with a couple of thoughts.

The fan they had was sorely inadequate - not such a problem for me, but for the higher BHP cars I would have been concerned.

They didn't seem to be taking any other measurements, which I find strange, boost level, rpm etc

Last year I visited G-Force in aylesbury for a Skyline RR day, they took readings for boost and RPM, and had a HUUUGE fan that was difficult to stand in front of while running. All in all it was an impressive venue and the facilities seemed good - although on the other hand it did cost £50 a run!

Might be worth a visit for you big power guys [img]images/graemlins/smile.gif[/img]

Simon

[sitas3]

my car was also at well lane on that day and it didn't produce good results at all IMHO. I'd like to think it was down to the fan size/position they were using. However, the problem i have with this is that an MTM tuned S3 managed to produce respectable results (circa 265 bhp and 260lb torque). OK the torque figures were down but i'd expect with the settings I was running to at least match those of the MTM. Is it possible the Revo tuning does not behave well with higher temperatures compared to MTM for example?

[Greg_S]

I read somewhere that the ECU on the S2 reduces boost when the intake is cold, and increases it when warm, so that the engine performance is constant no matter what the ambient temperature.

I have heard the same also. Would expect it to be similar on the other S cars if they use the same kind of boost control and ECU Family?

[AL_B]

Sorry some of you are a little unhappy with the rolling road results. SiTaS3's results are strange, compared to the MTM'd S3. But there were also standard cars there, like mine, which produced expected (or better) results.

Perhaps the tuned cars do need better cooling, but it still doesn't explain why the MTM S3 produced what was expected.

Anyway, I enjoyed the meeting, and thanks again to everyone who turned up. Results are here...

Northern Rolling Road Meet (1) - Well Lane Turbo Centre

Cheers

AL