Audi v8 down on power??
Discussion
Donick1980 said:
318 was deffo power station’s quoted flywheel power, there dyno (Maha) gives massively low wheel hp reading apparently due to there being 2 contact points for the each tyre .... it’s twin roller front and back.
Wheel power was actually 218.5, this is due to claimed drag loss of 105bhp using there coast down method???
What engine exactly?Wheel power was actually 218.5, this is due to claimed drag loss of 105bhp using there coast down method???
Does the peak power occur at similar rpm for both dyno runs?
Donick1980 said:
Audi 4.2 v8 (s5)
Both dyno sheets are at start of thread bud...
but peak power was at 7000 ish (370bhp)at MRC
Then the other day peak power was at 6280 (318bhp)
I believe? I’m assuming power had stopped climbing at that point and that’s why he stopped at that revs?
370/7000*5252= 277lbft.Both dyno sheets are at start of thread bud...
but peak power was at 7000 ish (370bhp)at MRC
Then the other day peak power was at 6280 (318bhp)
I believe? I’m assuming power had stopped climbing at that point and that’s why he stopped at that revs?
318/6280*5252= 266lbft.
It could be the case the rpm scaling on the MAHA dyno was not right.
The rolling road measures torque at the wheels. To get power, we need a speed reference. That could be road wheel speed (the dyno measures this), which would give wheel power at a given road speed. But what we want is power referenced against engine rpm. There are two ways of getting this. Take a feed from the engine direct, through CANBUS or pick up on a coil or injector, or the operator tells the dyno that at a given road speed the engine rpm is X.
Get this wrong and the wheel torque does not change as this is measured, but that torque will be referenced against an incorrect engine rpm and the calculated power figure will be off.
Given that, and assuming the peak power engine speed has not changed, this may explain a lot as you have a 11lbft difference.
For some reason I can't see any images of the graphs. Is the shape of the toque curve the same?
If you know the speeds per 1000rpm in each gear, you can check this easily enough.
Donick1980 said:
Let me know what you find .... if you remember lol.. 
Well it’s the afternoon, but you’re paying peanuts, so expect monkeys.Open the link. It’s an Auto Motor und Sport test of a b8 S5... towards the bottom of the page there is a load of in gear acceleration results. Maybe upload a performance measuring app to your phone to record the in gear times...or record a few accelerations on video and analyse them later.
https://www.auto-motor-und-sport.de/test/audi-s5-s...
Kawasicki said:
Donick1980 said:
Let me know what you find .... if you remember lol..
Well it’s the afternoon, but you’re paying peanuts, so expect monkeys.Open the link. It’s an Auto Motor und Sport test of a b8 S5... towards the bottom of the page there is a load of in gear acceleration results. Maybe upload a performance measuring app to your phone to record the in gear times...or record a few accelerations on video and analyse them later.
https://www.auto-motor-und-sport.de/test/audi-s5-s...
Nice find .... I’ll try and do some comparisons then ... Thankyou
My theory is the following: either the crank or a camshaft angle sensor is giving a duff reading. This causes the occasional engine cut-outs; it also means that the variable valve timing isn't working, which is why the power curve peaks at a lower power and at a lower RPMs than it should, since the timing isn't being optimised for high-rev power. Anyway as said it sounds like the car's going to the right people to get to the bottom of it and sort it out.
samoht said:
My theory is the following: either the crank or a camshaft angle sensor is giving a duff reading. This causes the occasional engine cut-outs; it also means that the variable valve timing isn't working, which is why the power curve peaks at a lower power and at a lower RPMs than it should, since the timing isn't being optimised for high-rev power. Anyway as said it sounds like the car's going to the right people to get to the bottom of it and sort it out.
That would %100 make sense as you can clearly see where the variable valve timing kicks in on MRC graph as it dips for a split second , where as there is NO dip on latest graph and also its seems out of puff at 6200, but power was still climbing up until 7000 when originally tuned... Just found something interesting on you tube... it’s a dyno printout for a tuned s5 with miltek exhaust, pretty much like mine....
Interesting to notice we make pretty much exactly same power at 5000 revs and near identical peak torque...
but his gets a 2nd wind after slight dip (vvt kicking in) then carries on upto 365bhp and makes power all the way to 7000 revs...
Mines in toMoz for service, fuel pressure check and new crank sensor.... fingers crossed
Interesting to notice we make pretty much exactly same power at 5000 revs and near identical peak torque...
but his gets a 2nd wind after slight dip (vvt kicking in) then carries on upto 365bhp and makes power all the way to 7000 revs...
Mines in toMoz for service, fuel pressure check and new crank sensor.... fingers crossed
So took car to MRC and it was discovered that the inlet manifold “flap module thingy” (part that changes length of runners at 4700 revs) was properly knackered ...
So basically the runners were permanently stuck at the length which gives best “torque” low down.
So power would stop climbing around 5000 revs as the inlet was not changing from torque to power setting... this is part....
Car will now do 60 in around 4.75 secs and 100 in about 11.8 ..... gonna get it back on dyno tomoz so can compare with original graph... I reckon about 360-370 bhp ?
So basically the runners were permanently stuck at the length which gives best “torque” low down.
So power would stop climbing around 5000 revs as the inlet was not changing from torque to power setting... this is part....
Car will now do 60 in around 4.75 secs and 100 in about 11.8 ..... gonna get it back on dyno tomoz so can compare with original graph... I reckon about 360-370 bhp ?
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