Audi v8 down on power??

Audi v8 down on power??

Author
Discussion

Kawasicki

13,041 posts

234 months

Wednesday 17th February 2021
quotequote all
Donick1980 said:
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 ?
Glad you got it sorted and thanks for posting.

Ozone

3,039 posts

186 months

Wednesday 17th February 2021
quotequote all
I bought an S5 V8 a few weeks ago and didn't realise that on the fuel flap it recommends either 95 or 98 RON.
What are you using to get the figures you've shown?

Donick1980

Original Poster:

35 posts

38 months

Wednesday 17th February 2021
quotequote all
I believe car was mapped for ATLEAST 97 Ron when done at MRC..... I only ever put 99 in it though but theoretically 97 would prob achieve very similar figures?

Nick

Ozone

3,039 posts

186 months

Wednesday 17th February 2021
quotequote all
Useful to know, thanks thumbup

Glad you got the problem sorted.

Donick1980

Original Poster:

35 posts

38 months

Wednesday 17th February 2021
quotequote all
Thanks pal👍

samoht

5,633 posts

145 months

Wednesday 17th February 2021
quotequote all

Ah yeah I can see that the variable induction being stuck in the low-rpm position would cause similar symptoms. You were right that there was something wrong with it, glad you got it fixed & thanks for posting the resolution.

Did they have any opinion on whether the induction flap problem could have caused the occasional cut-outs? Or do you think that is a separate problem? Anyway glad the power's back :-)

Donick1980

Original Poster:

35 posts

38 months

Wednesday 17th February 2021
quotequote all
Separate problem MRC believe but as it happens so so rarely at mo they told me it’s not worth finding the fault because to find the fault will/could involve hours of removing virtually all electrical modules/ecu’s to find it... basically a needle in an EXPENSIVE hay stack if I got MRC do it!! It’s only happened twice in about 5-10000 miles...

Nick

Donick1980

Original Poster:

35 posts

38 months

Friday 19th February 2021
quotequote all
The saga continues....

This is message I sent to MRC today after after going back on local dyno....

“Hi Sarah, this is Nick Davies.... you guys had my Audi s5 4.2 in a few weeks ago for health check on dyno and found I had a broken manifold flap control actuator.
Could you give me a call ASAP please as I want you guys to have another look at it, I’ve had part fitted locally and all seemed fine till I put it back onto local dyno. I’ll email you the before and after graphs to see what you guys think but it now seems it is stuck in the “power” mode as it’s not making as much low down torque as before???
The new actuator is definitely moving as I watched it kick in when car was on dyno .
I’m just wondering if it’s been fitted incorrectly?? Car does feel quicker though🤯

I’ve added the before and after dyno print outs they’re are so differentfrown

BEFORE


AFTER


My brain is fried.... car feels faster, will do 60 in under 5 secs yet is down 20 bhp and 50 Nm of torque??


AJB88

12,263 posts

170 months

Friday 19th February 2021
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comparing figures between 2 dyno's isn't ideal.

I've known cars to make +30 or -30bhp between Dyno's.

My old Stage 2 Leon FR TDI made 238bhp on JBS dyno, made 205bhp on Awesome GTI dyno then made 207bhp on Shark Performance dyno.

Donick1980

Original Poster:

35 posts

38 months

Friday 19th February 2021
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That’s same dyno, about 4 weeks apart ... frown

vaud

50,289 posts

154 months

Friday 19th February 2021
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I'm not an expert, but the second graph looks ok?

Playing devils advocate - are you worrying too much about absolute numbers and not about real world performance and drivability/response from the car? i.e. if it is actually quick and drives well, then is the dyno relevant?

Donick1980

Original Poster:

35 posts

38 months

Friday 19th February 2021
quotequote all
I understand what your saying but knowing now what I know about the part that has been replaced and how the manifold flaps work, to my mind now it seems it has gone from one extreme to other by that I mean I was informed by MRC the car/flaps were stuck in “Torque” phase so that’s why I was getting stock peak torque at the correct rpm (approx 3500 revs) but the actuator wasn’t moving the the flaps at around 4800 revs (to put runners into power mode) making power tail off whey earlier than it should.

But now after fitting new flap actuator torque is really low but you can now see on the graph the “power phase” is kicking in yet power is lower??

I just feel something still isn’t right, the graphs are so different, I’m wondering if the intake was reasembled incorrectly after it was carbon cleaned?
The mechanic that fitted new actuator did say the car was still throwing a fault for the flap but because it felt more lively I thought nothing of it ??

Is it even possible for a 1650kg 4wd car with 300 bhp to do a sub 5 sec 0-60 ??


vaud

50,289 posts

154 months

Friday 19th February 2021
quotequote all
Donick1980 said:
Is it even possible for a 1650kg 4wd car with 300 bhp to do a sub 5 sec 0-60 ??
Gold R estate is 1600kg, 300hp and 5.1sec, unmodified.

stevieturbo

17,229 posts

246 months

Friday 19th February 2021
quotequote all
Donick1980 said:
Is it even possible for a 1650kg 4wd car with 300 bhp to do a sub 5 sec 0-60 ??
Who really cares ? It's such a pointless performance stat.

Donick1980

Original Poster:

35 posts

38 months

Friday 19th February 2021
quotequote all
I agree but my point is you would need X amount of bhp the achieve this.... the facts are after fitting new actuator car is down ANOTHER 20 horse yet car is over a second quicker to 60 (pointless I know) and 2 seconds quicker to 100...
the only reason I’m questioning it is because the graphs are SOOOO different and to me it now looks like car/flaps is stuck in power phase .... if the graphs were similar I’d prob just be happy that car felt quicker.... but to have peak torque at 5200 is just not right for this engine.

I’m deffo not chasing numbers, if I was I certainly picked the wrong platform.... hardly any gains to be had from this V8!! frown

PH_77

1,312 posts

92 months

Friday 19th February 2021
quotequote all
vaud said:
Donick1980 said:
Is it even possible for a 1650kg 4wd car with 300 bhp to do a sub 5 sec 0-60 ??
Gold R estate is 1600kg, 300hp and 5.1sec, unmodified.
The WLTP MK7 300hp Golf R estate claims a 0-60 time of 4.9s.

Donick1980

Original Poster:

35 posts

38 months

Friday 19th February 2021
quotequote all
Yeah but isn’t that 200 kg lighter? And 100mph is more like 14. Something seconds?
Stock s5 was meant to be 4.9 (manual) but that is with the claimed 354 bhp

Donick1980

Original Poster:

35 posts

38 months

Friday 19th February 2021
quotequote all
Sorry wrong car I think lol... but that car you mentioned WLTP thingy actually gained .2 of a second even though it lost 10 bhp!! How??

PH_77

1,312 posts

92 months

Friday 19th February 2021
quotequote all
Donick1980 said:
Sorry wrong car I think lol... but that car you mentioned WLTP thingy actually gained .2 of a second even though it lost 10 bhp!! How??
lol

First R estate has 300hp, 4.9 to 60, apparently
Second R estate (7.5) has 310hp, 4.6 to 60
WLTP R estate has 300hp, 4.7 to 60, stock car mapped for more torque.

Because everyone launches all the time.... So it's all pretty meaningless.

Donick1980

Original Poster:

35 posts

38 months

Friday 19th February 2021
quotequote all
The only reason I’m quoting 0-60 is coz it would give an idea maybe of bhp when comparing it to stock figures ....
would 0-100 give better idea or 60-100??