20bhp off std on the rollers - need ideas

[pablo_vr6 0]

right was on the rollers today and got 171bhp (fly) 152 (wheels)

 

thats 20 down on std so plan to get back and source the problem.

 

I recently replaced the oil/plugs/plug leads and fitted a hks filter. the filter may be the prob but any other thoughts?

 

fuel filter?

cat?

afm?

 

any other things a I can check/replace?

 

thanks

-pablo

[vr6storm 0]

right was on the rollers today and got 171bhp (fly) 152 (wheels)

 

thats 20 down on std so plan to get back and source the problem.

 

I recently replaced the oil/plugs/plug leads and fitted a hks filter. the filter may be the prob but any other thoughts?

 

fuel filter?

cat?

 

any other things a I can check/replace?

 

thanks

-pablo

 

 

something not quite right there.............only 19bhp transmission/drag losses :? :? :? :? :? ...........152bhp @ the wheels is pretty decent for most VR6's

[dinkus 10]

You could be chasing a ghost. 152 at the wheels doesn't sound too bad (presumably for a VR?)

 

The actual number they get at the crank is all a big bodge anyway. You need to compare your wheel figure with someone else's known good VR to see how it holds up. Then if it's way out you can start playing with stuff.

[pablo_vr6 0]

really?

 

funny a mate who was there said his dads got 149 at the wheels.

 

the road he uses measures losses rather than going by fixed figures

[dinkus 10]

It's impossible to measure the actual losses in your transmission without whipping the engine out, measuring the crank and then comparing it with the wheels reading.

 

I'd say your VR is fine, don't worry about it.

[daves16v 1]

How do they measure hp at the flywheel?

[dinkus 10]

The only way of measuring the hp at the flywheel is by putting the engine on a bench and hooking it directly up to a dyno.

 

When you get a rolling road print out they actually measure the torque at the wheels, then take a guess at what the losses are from your transmission to arrive at a crank/flywheel figure. So when you get your engine chipped and miraculously have 30hp more than you did before...take a close look at the numbers and compare the wheel torque readings.

[Joe M 0]

All the rolling roads ive seen measure the drag by ppressing the clutch in when the car hits the rev limit and measuring the deceleration as the wheels slow to a halt. cant see any reason why that woul be classed as a big bodge.

 

Personally, I would try another rolling road as it sounds like the one above is a bit sh*t tbh.

 

If it is accurate and the cars down that much power then the most likely thing would probably be the cam position sensor, as there known to cause a 20-30bhp power loss.

[vr6storm 0]

really?

 

funny a mate who was there said his dads got 149 at the wheels.

 

the road he uses measures losses rather than going by fixed figures

 

by the looks of it if yer VR is giving 152bhp @ the wheels then i can't see it only having 170-ish at the flywheel

[Kevin Bacon 5]

Your cam position sensor is out I reckon.

 

Mine delivered 171 bhp too when I first got it, but £30 later and another run, 200bhp with 193lb/ft.

 

A failed CPS is very common on the VR. They don't last long and the ECU loads the limp mode automatically, so unless you know VRs very well, you'd be none the wiser.

 

K

[Kevin Bacon 5]

CPS or in VW speak "Impulse sender" p/n is - 021 907 601A

 

£30+VAT

 

Try that and you might regain your lost horses.

[vr6storm 0]

Your cam position sensor is out I reckon.

 

Mine delivered 171 bhp too when I first got it, but £30 later and another run, 200bhp with 193lb/ft.

 

A failed CPS is very common on the VR. They don't last long and the ECU loads the limp mode automatically, so unless you know VRs very well, you'd be none the wiser.

 

K

 

thing tho kev.....if it was out then why is he getting pretty decent at the wheel figures????????

[Kevin Bacon 5]

Yeah that didn't compute to be honest...... I was just going by the fly figure as that's exactly what mine gave with a dead sensor.

 

152 at wheels is pretty good and as all Rolling roads measure HP against a brake, hence the term Brake HP, that is the figure to believe. I reckon he fecked up the fly calculations.

[PhatVR6 0]

when mine was running flat it was the rear knock sensor.

 

get it on vag-com before you buy any parts.

[Andy Brookes 0]

here are the figures for my standard VR on the rolling road at Stealth this weekend just gone

 

Power at the wheels 156.4bhp

Power at the flywheel 196.5 bhp

[dr_mat 0]

Yeah - there ya go. Wheel figures, wheel figures, wheel figures, wheel figures. Need I say it again? :)

 

The best at the wheel figure I've come across for a completely standard C VR6 was about 162-165bhp, but it's much more common to see 150-160bhp at the wheels. Ignore the flywheel figure unless you've had the engine out the car and on an engine dyno.

 

These are OLD engines. Unless you've recently had the whole top end replaced and head gasket done, you're likely to be down compression on several if not all cylinders, you're likely to have gas leaks all over the place and you *can't* expect top figures, unless you're VERY lucky and the car has been grannied for it's whole life.

 

Obviously you *could* have a problem with one of the sensors on the engine that could be robbing you of a few HP, but I'd say read up on rolling roads before you cry into your beer.. ;)

 

From what I've read an absolutely peak condition VR, running to factory spec, should put out around 162bhp at the wheels. That would equate to 190bhp at the crank. Anyone who's getting around this should consider themselves lucky... Anyone reporting over 200bhp at the crank and less than 165bhp at the wheels is being fed an illusion to make them feel better! ;)

[Scott 0]

I got 159bhp at the wheels..... not bad for a 113k miler VR6 thats never been apart

 

But yeah I agree the wheel figure is the most important.... shame most people dont realise this and quote over inflated flywheel bhp figures....

[pablo_vr6 0]

i dont think the fly calculations are too bad. also up was a mate in a completely standard 1.8 zetec focus and it read 114.9bhp compared to specced 115bhp.

 

Surely these things are pretty good at measuring the transmission losses using the coast down method?

 

 

he also has vag-com so its going back to hook up to it and see if any of the sensors are duffed. Ive had a feeling the raddo wasnt at full potential since I got it and had estimated around the 170bhp mark. definately doesnt feel like a 190bhp car anyway.

[dr_mat 0]

You can't "feel" bhp by the way, you can only feel torque.

You can make the car have higher bhp figures just by producing the same torque at higher revs.

The "coast down" method is rubbish, a very vague approximation at best.

Based on some physics - more reliable calculations - I think 152bhp at the wheels equates to around 180bhp at the flywheel, so you're only 10bhp down anyway. Which is easily explained by low compression and/or heat soak and/or small engine sensor problems.

It's worth running it by VAG-COM, but if it doesn't show anything I bet you'll be chasing ghosts trying to regain your "lost 20bhp"..

[pablo_vr6 0]

isnt bhp a mathematical function of torque?

 

what are your calculations btw? Im interested to know where the 180bhp came from.

 

If this is normal then cool but if i was going to mod it then Id like to start from the best point as possible rather than bolt sh!t on and hope for the best :)

[Kevin Bacon 5]

Yeah Horsepower is derived from a calculation based on the torque figure. Henny knows the exact equation.

[dinkus 10]

bolt sh!t on and hope for the best :)

 

Yeah I definitely wouldn't bolt shit on. Slows it down and makes it rather smelly. But then you could be going for that agricultural look I suppose :lol:

[dr_mat 0]

There was a long discussion on power/torque a short while back and someone pointed us to the pumaracing.co.uk site (IIRC), which had some really good write-ups of this stuff. The short answer was: bhp(wheel) = (bhp(engine) - 10bhp) * 0.90. So work that backwards from the wheel figure to the engine one with:

 

bhp(engine) = (bhp(wheel)/0.90) + 10

 

and meanwhile:

 

power(bhp) = torque(lbft) * revs(rpm) / 5250

 

so if your engine produces 180lbft at 5250rpm it's producing 180bhp at 5250rpm.

[Storm Monkey 0]

Wont this vary depending on your gear box/transmission efficiency? Just about everything from design, condition, oil type, tyres etc will all have an effect.

 

HP is a function of power and speed. Its a little easier to work in metric for this.

 

power(W) = torque(Nm) X Angular velocity (2 X pi X rpm/60) as far as I can remember.

 

where 1KW = 1.341 HP (NB Audi and VW often use PS, which is around 1.03 HP)

and 1lb/ft = 1.3558 Nm.

 

E.g. for the same power, you can get high speed, low torque, or low speed, high torque.

[dr_mat 0]

Yeah, the above was an approximation, but it seems to have been based on some sound physics and a couple of assumptions about the "average car". If you've got dragging brakes or heavily sticky gearbox oil you might find your transmission culls more power than average, but there's no really good way of measuring it.

And as for metric, wossat then? ;)

 

Yeah compare and contrast diesels to petrol engines: most turbo diesels these days produce in excess of 200lbft torque, but rarely get above 130bhp, yet a 1.6 petrol engine can have 150bhp coaxed out of it (Honda!), even if torque is only about 90lbft.

 

But at the end of the day, the torque curve is the one you're interested in, power is secondary.