HELP NEEDED - V6 MK II Power Loss

[theslayyer]

Hi ...

Does anyone know anyone that can help with my little problem ?

I have a perfectly smooth running, well behaved Clio V6 MK II (255) - but on a reliable set of rollers with a good reputation for being accurate, it's only producing 196bhp on a standard map WITHOUT cats and a nice free flowing Janspeed exhaust + airbox.

I'm realistic, I don't expect Renaults figures of 255bhp, but I'd expect at least 230.

We've spent HOURS on the rolling road with about 3 sets of guys analysing and checking stuff, but we cannot get to the bottom of it.

It runs like a dream and is still really quick, but the power figures are a mystery.

We've tried alternative fuel maps, checked the VVT operation (this bizarerly cuts in before 2000rpm on this car) - it doesn't smoke or use oil, it's only done 12000 miles, uses high quality fuels and oils (all it's life), has been serviced every 3000 miles.

Someone has suggested the next thing to check is CAM timing in case it's been assembled one tooth out on the belt - which would account for this kind of power loss.

Anyone with any experience of this ???

Really need to get to the bottom of it!

Thanks in advance.

P.

 

[k1ano]

Does sound a bit like a mystery Paul ...

I am only summising as I don't know much about Vee engines specifically but the VVT sounds suspicious ... I was thinking it was around 5k RPM borne out by a change in characteristics in my car - perhaps also that of others. Cam timing could be a possibility aswell as the calibration of the electronic throttle - there is a guide in one of the online manuals on the site.

Short of a/f mixtures - which I would expect look good, there are only these ancillary things really - apart from ambient air temps affecting power output of course.

I guess arguably though - if it feels good on the road the numbers aren't so much of an issue ...

Martin

 

[v6Max]

How are you "feeding" the car air when it's on the rollers?

 

[theslayyer]

It's just snorting air through it's duct on the side - there's no fan on it or anything.

The results are VERY consitent. Temperature varients over the last few runs (spread over a couple of weeks) have made a difference of only 1 or 2bhp max.

We started this game cus the (Janspeed) cats collapsed and blocked the exhaust system - that's why I ditched them - wasn't going to have that happen again.

The fueling mixture is OK, a tad rich but only by a tiny margain.

I'd be interested in what the VVT is supposed to do in this engine - we tried switching it manually (by 12v feeding the switching solonoids that control the oil feed to the phase cam) - if it's not switched at low revs, there's a big power loss low-mid end.

There's no switching behaviour shown at the top end.

I agree there's a "step" in power output on all these engines - mine is around 5750rpm - but it's only a small step. It's nothing to do with valve timing, more mapping and ecu control elsewhere I think.

Trouble is, without a reference car on the same rollers, I can't get a comparison - the car might be perfectly normal ...

Anyone want to come and run on these rollers ? I'll pay for a power run!

P.

 

[theslayyer]

It's Cheltenham btw.

The rollers.



P.

 

[Brett]

The Ph1's 230bhp and the Ph2's 255 were probably taken from the flywheel. Given that they are definatly very optomistic anyway, I wouldn't be suprised if it is around 200 brake at the wheels.

 

[Duncan]

as per bretts thoughts, 196 at the fly or at the wheels is the key!

if its at the fly it might be worth looking into, but if its at the wheels then you dont really have any worries.

the most important thing is how it feels to drive though!

 

[theslayyer]

This is a calculated figure (with losses) at the crank.

Power at the wheels is 154 ish.

If they are all the same then I'm wasteing vast amounts of cash chasing a ghost, but as I've got no one elses car to compare to, I don't know if there's a problem or not!



P.

 

[Mike T]

the cars switchable cams are not a high rev performance issue - they switch at low rpm for decent slow running - not like Honda at all.

If theres no restriction on the air-in side of things and the compressions are ok and the fuel pressure is ok and the exhausts are ok and the timings ok and the cam timings ok then I haven't a clue but it should make about 250 at the crank.

I assume you are getting full throttle at the throttle body - it is electric and french after all?

MIke

 

[TRW1]

Compression check.....

 

[Rich]

Compression check.....

That's what I was going to suggest + check your plugs, though at 12k miles I'd be shocked if the rings are shot already, at least through normal use, unless it's gotten really hot which is what happened on an old car of mine basically due to a dodgy rad at some point in it's life.

 

[Jamesv6]

It does sound like your Vee isn't very well. From past reading most MK 2s are about 240 bhp

Would it be quicker to try some different rollers?
Has it been anywhere near GDI?

 

[Brett]

In your first post you say the car still feels quick....If you've calculated the car as having 150bhp at the wheels, the car would feel pretty sluggish and if you ask me, not at all quick. I personally think its either down to the rollers or a very small misscalculation.

 

[theslayyer]

Thanks for all the input guys. The car does indeed feel quick - my neighbour described it as MENTAL the other night. That's why it's all so confusing.

I know that most rollers read far too high - this one is known to be very close.

Compression tests AND leak tests are on the way - we've checked that the ECU is reading 100% throttle etc.

Cam belt positions for cam timings will be checked next week too.

Plugs are changed every 6k - I only changed them about 300 miles ago.

We'll RAM a 100mph air blast down the side of the car with the air intake on the next run I think!

I'll keep you informed.

Off to the Nurburgring tomorrow morning. It'll still put loads of cars to shame over there. :badgrin:

P.

 

[Peter255]

Def somethign wrong there mate!

Check my thread in special projects for what my car is putting out (not that far from your spec).

You should be getting 190 ATW not ATF! [smilie=icon_eek.gif]

Mk2's don't make 255 std, but they DO make 230+

Hope its nothing serious!

Peter

 

[Jamesv6]

How is the Vee going now Paul? Did your ring trips go well?