Why so little??

[Kev]

Had my car serviced and dyno'd the other day at coach house garage services in Aberdeen, well recomended

The plot from the dyno gave me a bit of a shock as I've had a few mods done to the car, so was expecting a little be more than I did Here's the plots:
http://farm4.static.flickr.com/3290/298 ... ffb0_b.jpg and http://farm4.static.flickr.com/3194/298 ... 8b84_b.jpg

List of mods: ported head with std valves, piper 633 cams, piper vernier pulleys, piper 4-2-1 manifold, pipercross viper induction, larini club sport exhaust. I'm still running the std ECU and CAT. I've got Ricky Gauld on the case, to see why its making less than I was expecting. I'm getting him to check the cam timing next week and he reckons the cat will be strangling it a bit as well.

Anybody got any ideas

[philthy]

I dont think its a million miles away esp with the CAT in place.
Is the timing set up properly? Any changes to the mapping at all?

[robin]

Torque curve is all wrong.

With most porting work you can lose a bit of torque <3,000 RPM, but I would expect better than 100 lbft from 2,500 RPM to the red line, so you've lost a lot.

Even if the low numbers are down to differences in rolling roads, (i.e. we could scale them all up by 10% for some reason) I would expect a different shape curve with those cams fitted.

With standard cams/valves/exhaust manifold, you would expect to see peak torque around 5,000 RPM and then a fairly sharp tail off to the red line (you lose about 20 or so lbft in the last 2,000 RPM).

With these cams I would expect peak torque to come at a higher engine speed, probably to around 6,000 RPM and then a shallow tail off to the red line. The difference between the slopes of the tail off means that in a standard engine, peak power comes before the red line, whilst in ANY tuned version of the 1.8K peak power will be at the 7K red line. If you think about it, a sport 135 head dropped onto standard ECU and manifolds produces 135BHP - it has standard valves, cams with a bit of porting ... yours is deffo wrong.

My guesses:

(1) If you have a wide-bore 4-2-1 fitted, you need to replace it with either a de-clagged standard manifold or the narrow bore 4-2-1 or 4-1, preferably the one without the flexi, if you don't mind the fact that the exhaust is then under some stress unless you uprate the engine mounts too. The wide bore manifold causes low exhaust gas speed and this means much less scavenging. If you have lagged the pipe it can cause similar problems (though to a much lesser extent - very unlikely to be the issue here I think - the scavenging effect happens because of gas cooling in the pipe - if you lag it, you reduce the cooling or shunt the point of cooling further down the pipe - this in turn increases the RPM at which the scavenging effect will be most pronounced). The standard manifold when de-clagged is good for 160BHP (and perhaps more) - i.e. the region you are aiming for with current mods.

(2) Check the lift on overlap at TDC very carefully and compare to Piper's recommendations for those cams. I'll bet you don't have enough overlap, perhaps not even as much as standard cams should have. With no overlap, the exhaust manifold has no chance of scavenging at higher RPM. It's possible you have much too much overlap, and the low RPM torque figures would back that up, but then I would expect to see a rise in torque at higher RPM, not a drop ... unless, of course, the issue is that it's running much too lean also.

(3) Get a run done on another rolling road, just to give a cross reference, and this time make sure they have a wide-band O2 sensor stuffed up the tail pipe with the results plotted on the graph!

Cheers,
Robin

[Mikie711]

Kev,
your engine and mine are very similar in spec, have a look at my plot I posted after the rolling road session we had, the difference is probably down to the emerald running adaptive mapping and the way mine has been set up. The figures are very similar. As you can see mine is running very lean on the top end. Ricky has a wide band probe and he probably has the plot with it saved on the machine just didn't give you a copy, pop in and ask him to print on off.

Mike

[robin]

If you look at Mike's torque curve you can see it's also falling away, but the clue is in the AFR posted on the other picture (you have to combine the two pictures in your mind to see torque vs afr ... btw, that's always what you want to see when trying to work out whether your engine is working as well as it could). Where Mike's torque curve tails off from 5,000 gently (power still rising, not falling), the AFR is heading into lean territory. To me this implies that it's possible it could hold torque for longer/generate more power further up the rev range.

The reason for this is simple - it may be lean at this rev range because the engine is flowing more air at this point (due to cam duration and overlap) and the ECU isn't putting in enough fuel to compensate for the extra air. If this is combined with incorrect/overly advanced ignition timing (lean mixtures burn faster) the peak cylinder pressure is reached too soon in the engine cycle and it doesn't develop as much torque. To understand this, imagine trying to pedal away your bicycle from standing start with the pedals exactly vertical - you just compress the crank rather than turn it (in fact you would never ever move if it weren't for the fact that there is always a way of persuading the crank to turn a bit by shifting your body position using some other muscles); once it's turned a bit, you start generating forwards motion; peak acceleration is when the pedal is horizontal, then tails off again as the pedals return to the vertical. The engine works the same way, except it isn't using a constant force (you are - it's your body weight, unless you have fancy clip ons) - it's force starts out as nothing, then builds as the mixture burns/expands, then tails off again as it cools/exhaust port opens. So we need to time that peak force to be at as good an angle as we can get it ... unfortunately, but the time the angle is 90 degrees, the chamber volume is so large that pressure has tailed off loads - this is one of the fundamental inefficiencies of the 4-stroke engine - but it turns out that peak pressure at something like 20 degrees ATDC is the best compromise). Two things effect when peak pressure is reached - ignition time and burn speed; for perfectly filled/mixed cylinder, burn time is more or less constant - so ignition advance must be increased as RPM increases to try and keep hitting that 20 ATDC point. Leaner mixtures burn quicker, so you need less advance (though first off you need more fuel to return the mixture to a safer level; this may slow down burn enough that ignition advance is OK).

So in Mike's case I would expect a healthy dose of extra fuel plus some fine tuning of ignition to hold torque further up the rev range.

In Kev's case, we don't have the AFR data, but I do know that the MEMS doesn't do tooo badly running mods up to about 155BHP, though it will lean out at the top end. AFAIK it adopts a safe-rich mixture on wide open throttle and uses the least amount of ignition advance that they could get away with to make the power; so when you add extra gas flow, you start to move the mixture towards the lean side, but it's still OK; the effective ignition advance is increased (leaner mixture burns faster) but as the original ignition timing was conservative, you get away with it within this range of tuning.

Cheers,
Robin

[Edit: so in short, I still think you need to check the cam timing].

[Kev]

And the numpty of the week award goes to ..........................................ME, for posting the same link twice

I've changed the second link to the AFR plot. And the CAA gave me a license to work on aircraft

Thanks for the help guys, especially for your explanation Robin, as always, very informative

I've got the car booked in on Wednesday so Ricky can look at the cam timing, it's the only thing I can think of, that would have such an effect. He was hoping to do it yesterday for me, but he didn't have his verniers. I'm sure I've got the narrow-bore 4-2-1 manifold, can't think of any reason why Dan would've fitted the wide-bore.

Thanks again

[robin]

AFR doesn't reveal it going mega-lean - in fact, when the torque is falling off quickly the AFR is actually returning towards the rich.

To me that implies that the engine isn't breathing at higher RPM as it should with these mods. Realistically the only things that can cause that are cam timing or blocked intake/exhaust - check that the air filter isn't clogged, then check cam timing (well, lift on overlap at TDC - this more accurate way of checking cam timing); if that reveals nothing check that the cat hasn't collapsed.

Cheers,
Robin

P.S. if it holds torque as it should for another 1,000 RPM then a more gentle tail off and I would expect somewhere around the 150BHP mark.

[campbell]

Fascinating stuff. Not least Robin's Walking Talking Textbook insight

Perhaps an interesting lesson in how a mod at a time makes it easier to see positive (or cancelling / worsening) effects.

[robin]

Campbell - I'm just regurgitating the digested contents of internet engine folklore ... I had no more idea about how to tune an engine than anyone else 10 years ago and even today my knowledge is 99% theoretical

Cheers,
Robin

[tuscan_thunder]

check that the cat hasn't collapsed.

this was my first thought.

[mwmackenzie]

Bloody hell Robin your a walking talking Guru!!!! Great knowledge and a great read... loving your work chief!

[tut]

Kev

I have arranged everything with Ricky, and he now has the complete T/B kit, ECU, and C/R gearbox, and I am also sending down a CAT replacement pipe which you can have as a present to see if the CAT is stangulating.

Of course you do not have to have Ricky do the actual fitting, I will leave that upto you, but thought that as he is already working on your car that is the way you would want to go.

I would have thought that if he gets everything working together, that should make a good 160-170 hp, and the C/R gearbox will also make the upgrade come into its own.

When are you back home?

tut

[Kev]

I cleaned my airfilter about 500 miles ago, so unless I've got birds nesting in there, that should be ok. I'll see what Ricky finds tomorrow, before I go shopping for a new cat, prefect time for a sports one I think.

[Kev]

Kev

I have arranged everything with Ricky, and he now has the complete T/B kit, ECU, and C/R gearbox, and I am also sending down a CAT replacement pipe which you can have as a present to see if the CAT is stangulating.

Of course you do not have to have Ricky do the actual fitting, I will leave that upto you, but thought that as he is already working on your car that is the way you would want to go.

I would have thought that if he gets everything working together, that should make a good 160-170 hp, and the C/R gearbox will also make the upgrade come into its own.

When are you back home?

tut

I'm always home

Thanks for the offer Tut, but I'm assuming your CRP is for the S1 and its different to the S2. I've already got a C/R gearbox as they came std on the basic S2. My aim was to hit the 155-160hp mark, just need to get everything working together, but I have the best man on the case. The missus would kill me if she found out how much I spent on the car, especially since we're suppose to be saving for the wedding. Ho Hum, I know what I'd rather spend my money on

[tut]

Sorry Kev, ignore everything that I have posted. They really should put me out to grass. It was meant for Kev from Aboyne, Abz-Elise who is in India at present, and has an Inferno S1.

I am setting him up with Jenveys, ECU and C/R box for his car.

You must have wondered what the hell I was talking about, but good for the rest of the Forum to have a laugh and think that the fall affected the silly old buggers brain as well.

tut