Is it possible? 1

[vagman2]

Hello all,
In a local automotive forum there is huge discussion about a chassis dyno graph, which states that an 2.0L 16V (C20LET)Opel Astra car is about 388 hp@wheels. That power is reached at 6250 rpm and 1.6bar intercooled boost. Most of the internet calculators didn't prove that number(usually 30-40hp less).
Please, I need your formulas and way of doing your math about a proper approx hp estimation. Any good hp estimation links are highly appreciated too.
Thanks in advance!

 

[BrianPetersen]

Back-of-notepad plausibility check.

Means it's making 326 lb.ft of torque at that RPM.

A good normally-aspirated 4-stroke spark-ignition engines running on gasoline will make 70 - 80 lb.ft of torque per litre of displacement and 90 lb.ft per litre is difficult but possible (and that's at peak torque, not peak power), so a 2 litre would probably do 150-ish lb.ft but 180 is plausible. For rough numbers you can assume that the power/torque are proportional to the absolute manifold pressure if the intercooling is really good. And that begs the question ...

Are we talking 1.6 bar boost pressure above atmospheric (i.e. 2.6 bar absolute intake manifold pressure), or 1.6 pressure ratio across the compressor (1.6 bar absolute intake manifold pressure)?

If it's 1.6 pressure ratio then the quoted power is way high. If it's 2.6 pressure ratio then it's quite plausible.

 

[LionelHutz]

So, are you trying to prove your numbers are true or that someone else's number is high?

Chassis dyno's are a good tool for parts/combo testing and engine tuning.

Their less useful roll is to print out a curve for bragging rights (assuming a happy operator).

 

[dgallup]

It's well known that some brands of chassis dyno's throw in approximately 15% bonus factor so the numbers come out big. Keeps the customers happy.

 

[BrianGar]

@ Vagman, thats very possible, the Audi A4 BTCC / STW engine made 305hp , 2.0l 16v, N/A.
Its currently being trashed about as to how it was reached on a well know VW Internet site.

 

[vagman2]

Hi,
We are talking about 1,6 bar above atmospheric.
@ LionelHutz, it is not my car neither a person I know. The dispute is between the tuning shop owner and a forum member. The main point of the member is that there is not enough air going through the engine at these rpm and boost(assuming AFR about 11-11,5:1) for that power level. The FMIC is big enough. The dyno fan is industrial centrifugal type. I would assume there is good cooling during the test. What would your calcs show?
Thanks for all inputs.

 

[Junior37c]

388hp on an 86mm squared 4 cylinder at 6250 rpm comes out to be right around 28 bar of BMEP. More than reasonable for an absolute pressure of 2.6 bar in my opinion. To put it in perspective that'd be just over 10bar at atmospheric pressure, which is actually relativly mild tune. Ofcourse you lose some in pushing the turbo and heating of the charge but I consider it plausible. My question is why is he only running 18m/s of piston speed on what's clearly a performance oriented motor?

All that said, the dyno operator could still be fudging the numbers, god knows a lot of them do. Last time I played with winpep software the default temperature if the sensor was unplugged was 31c, that'd should be listed on the printout and would be a quick and dirty way of double checking him. Also checking the listed atmospheric pressure against an elevation table. If the printout lists neither of these things it aughta list a dyno correction factor, which you can manually verify, even a loose idea of what the conditions were on the test day at that location should get you a ballpark figure and you'll know if he's been playing with the correction factor.

There's other ways to make a dyno lie but generally this is the one "shady" dyno operators will use.

 

[vagman2]

There's no corr. factor provided on the dyno sheet. I know that dyno is located at sea level. My question is about your approx hp estimation based on formulas though.

 

[LionelHutz]

Wow, someone who actually wants their RWHP number to be lower than the dyno measured.

Personally, I find the arguements about the "RWHP" numbers from a dyno completely useless.

Recently, I saw someone post that changing their wheels lowered the "RWHP" by 12hp and that he could really feel the 12hp loss on the street. The sad part is that he had no clue that the "RWHP" due to inertia will change depending on the acceleration rate of the vehicle. The even sadder part was that when I wrote an explanation of how the HP required to accelerate the inertia of the wheels depends on the acceleration rate I got told that I'm just "reading from a textbook and have no clue about the real world" = idiot who doesn't know and doesn't want to learn.

In the above case, the wheel dyno results should have been used to show that the new wheels will have a negative impact on the performance of the vehicle, not that the new wheels caused a "loss of 12hp".

Similar in this case, he should be more concerned that the engine was stable on boost and that the AFR and timing was tweaked to reach the maximum HP. If it was a brake dyno then part throttle situations could have been simulated as well and some tuning done there too...

 

[vagman2]

Hi,
It is load type Dynocom dyno with 24' roller but that doesn't matter now. If we assume about 15% tranny and tyre losses, that makes 445hp at the crank! How about that number at 6250rpm and 1,6 bar gauge boost? I just need some math here, is that power level possible "on paper" at least?
Regards!

 

[BrianPetersen]

1.6 bar gauge boost = 2.6 bar absolute manifold pressure near sea level. That amount of power is plausible from that size of engine with that much boost.

Detonation control at such high boost pressure and with a compression ratio in a normal range is, of course, quite another matter, even with very good intercooling, but that's not the question that was asked.

 

[patprimmer]

Back to back testing on the same dyno can be very accurate re the difference from changes, however for absolute values dynos are not a precise instrument. Wheel dynos are even less precise.

Dyno operators learn to tell people what they want to hear and many will exaggerate a reading to satisfy the unrealistic aspirations or bragging rights of the customer.

In my opinion you are on a pointless exercise.


Regards
Pat
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[izzmus]

How large are the fuel injectors?

 

[vagman2]

@ izzmus I'm sorry but have no idea.