Audi v8 down on power??

[Donick1980]

Hi there, my name is nick, I’ve owned my s5 for about 9-10 months now and I’ve genuinely had trouble free time with the car so no need to pic anyones brains lol

so to my problem... I’ve just had car dyno’d basically to see where car was at After a carbon clean (proper one).
Car seems to be about 50 bhp down from the last time it was dynod 5 years ago.
I have a graph from MRC from 2016 when car made 372ps and 480 nm of torque, I think this was achieved after a carbon clean and map tweak.

so tonight it has made 318 bhp and 440 nm @ power station in Tewkesbury.

I know there different dynos but 50 ish bhp difference seems excessive and to be honest the car has never really felt (to me) like it had 370 bhp...

First thing I’m gonna do is get it back to MRC for health check where I believe it will be dynod again.
i’m just wondering if anyone had any ideas what could possibly be the cause for loss of power?

only probs I’ve had with the car is one time last august car completely lost power while driving on motorway, pull on to hard shoulder then tried to restart.... would just turn but not fire. Until 10 mins later sprung back into life then drove perfect again for 5 or so miles then did it again. Did this another 3 times before I got off at services and brimmed it with fuel (already had half a tank). Had diagnostics done when I got home and not a single fault??? Until today it hasn’t done it again, but when operator of dyno pulled it on to the rollers it cut out ...EXACTLY the same as before, would not fire after numerous attempts ?

so guy plugged diagnostics tool in while it was sat there, surprise surprise no faults...
So we left car for 5 or so mins then tried again and fired up no probs.

only Other thing I’ve noticed with car is it seems to take quite a few cranks to start and this is the same whether hot or cold.

which is leading me to think fuelling prob somewhere? Car seems to run perfect though with no misfires and no codes ever popping up??

any input will be greatly appreciated 👍

nick

[Donick1980]

Hi guys to confirm it has just been carbon cleaned, it was previously carbon cleaned at MRC and that was when it dyno’d approx 370...
I have a feeling it has been down on power since I’ve had it, the carbon clean made it a little livelier but it’s never felt quick... had a remapped 335i previously and that would’ve destroyed the s5 in a straight line.
Strange thing is the s5 feels quicker than my old s4 v8 ??
I could do all this digging around, looking at/for possible fuelling issues that may not be there and it could just be I had some st fuel in it🤯

I’ve got my mechanic to check fuel pressures this tues and also change fuel filter (which is in tank so may well have been neglected by not changing it) and give it general service.... prob get him the also check coil packs while he’s there...

I’ve also got it booked in at MRC on the 29th for a health check on their dyno, the one where it originally was mapped.
Should know what’s going on a bit more then?

Some pics of carbon clean before and after:

[Donick1980]

samoht said:

Crank position sensor could be on its way out?

You’re not first person to suggest this.... eerrrmmm??

[Donick1980]

[Donick1980]

Yeah know these dyno numbers shouldn’t really be compared, it just 50 bhp seems a great deal to be out? There’s a small part of me hoping it is 50 horses down coz if I can find them, then the car will be all I’ll ever need ...

I remember when I just added a straight through from turbo 2.75” exhaust to my fiat coupe 16v turbo back in the day and it added 50 bhp and the difference I felt was phenomenal. 😍

[Donick1980]

Yeah was gonna try this, so measuring say 60-100 ? Torque stats quotes stock car at 6.5 sec 60-100... I actually think mine is quicker than that.... Dry toMoz aswell

[Donick1980]

Let me know what you find .... if you remember lol..

[Donick1980]

ghost83 said:

Any chance the mrc dyno was bhp and this one is wheel horse power?

Transmission losses would see around 50bhp

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?🤯

[Donick1980]

Sounds like a plan👍👍

[Donick1980]

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?

[Donick1980]

[Donick1980]

[Donick1980]

I don’t unfortunately...

MRC was ran in 5th
Power station ran in both 4th and 5th
Power of as 318 and 314 respectively...

[Donick1980]

stevesingo said:

Manual?

Yes manual

[Donick1980]

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...

Lol

Nice find .... I’ll try and do some comparisons then ... Thankyou

[Donick1980]

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...

[Donick1980]

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

[Donick1980]

[Donick1980]

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 ?

[Donick1980]