[wildcat]

I've posted comments on this previously with mixed response, and after my "opinion" about chips and those I've potentially alienated as a result... (no offense intended)

I'll illicit a response on this topic again. (You may conclude it is just pure ignorance on my part but having spoken to several mechanics as well as the realization that optimization for say track racing does make sense, I have concluded that Porsche has in its own interest programmed the performance of the 968 to be as enhanced as possible for a multitude of applications. Modifying the engine with a super/turbo charger does require a remapping and of course that makes sense as well.) I realize too that a Tip is not a manual and the impact of such a modification might be negligible (implying I may have a bias as a result, I don't but..)

 

On to the topic...  

 

I've attributed this "lag" to throttle response (mechanically) as in the butterfly valve (but which really includes the time it takes for the air to enter, the sensors to sense the change, the computer to respond) and to the MAF as a specific element in the chain.

 

I've also wondered about the Tiptronic and concluded it is not the transmission; while not a manual which is probably a little more robust, I don't think its been retarded for the high torque of the engine.

 

The most obvious reason for throttle lag has eluded me. The Vario-Cam.  

 

That is when I notice the lag disappears, when the Vario-Cam kicks in. By comparison it is most definitely a lag.

 

So having determined that this is the major difference in throttle response, which for some reason has not be mentioned as a possibility, I inquire as to whether anyone has attempted to modify the signal which enables the Vario-Cam. This is presumably a function of the ECU and may even be programmable through the chip...

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[Kim]

You ought to check, simply because it takes 0.2 seconds and costs nothing, that the throttle cable that passes over the puley is tight.  If it is loose and there is slack there would be some sort of delay. If it is not that, I have reached the limit of my knowledge on this matter and will retire to something else.

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[MCL968]

I would also check the cam timing, as small changes can move the torque curve around the RPM range. Perhaps, for a Tiptronic equipped car, the factory cam settings are less than optimal and a degree or two of advance might yield more power in the range where it is most needed.

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[flash]

the variocam is most likely not the culprit.  it kicks on at 1500rpm, and kicks out at a bit over 5k.  it is also easy to test.  it is not adjustable.

 

the tiptronic computer definitely retards timing at certain points.  it does it a LOT at abrupt kick down, so as to protect the engine from detonation when the rpms jump like that.  this was one of the hardest things to tune around when i was doing the SC kit for the tip.

 

the real issue is the spin up of the torque converter, and the taller gears.  there just isn't enough torque in the engine to spin the taller gears any faster.  the transmission is much heavier too.  all of that sucks up your torque.  once you get it spinning, it can perform nicely, but off the line it is a dog.  similarly, unless you get the rpms up over 4200, it will seem like a lot of lag.

 

keep in mind that the best the ECU can do is .25 second response, and that is only in the high mids and high rpms.  below 2k it is .5 seconds.  this is to smooth out what would otherwise be an even lumpier running condition.  the large pistons create uneven running, and porsche found it to be better not to make a lot of adjustments there.

 

the cam timing can be adjusted, but what it does is a trade-off.  you can swing it one way and gain low end torque, but at the sacrifice of upper end horsepower.  you can also swing it the other way, and gain upper end horsepower, but at the sacrifice of low end torque.  no free lunch here.

 

if you are experiencing real lag, i would guess it is due largely to a worn engine.  i would do a leakdown test to ascertain the real condition.  even a compression test would give you some indication, though you have to factor in carbon build up to what could be "inflated" readings, as it can easily raise the readings by 10.  if your pistons are clean, and you are down at 180 or so, it's likely time for a valve job.  if you have say 100k on the motor, and your pistons look carboned, and you get a reading of 190, then you really likely only have about 180 or less. remember, a loss in compression is directly connected to power loss. a 10% loss in compression would be about a 10% loss in power.  going from 200 to 180 would be that 10% loss.  that's 25hp, but more importanly, this would be experienced most at lower rpms, where the chambers have less ability to seal up and generate power.

 

there are a lot of little things you can do to help with power.  for starters, use a good synthetic 10-30 or 10-40 oil.  this will reduce stiction off idle.  use ngk iridium spark plugs.  this will help with carbonization at low rpms, and provide faster ignition.  make sure your cap and rotor are free of corrosion or wear.  this maximizes the inputs from the ECU and gives you the best chance at ignition.

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[wildcat]

No, I'm not experiencing "real" lag just a delay relative to how it comes on above 1500 rpm. Its not much... I notice it when running the engine up from idle in neutral. And from a standing start when the Tip in D kicks down to 1, you can feel the rush as it revs up to transfer to 2 again. That little gap between 2 and 1. In manual mode there's a slight delay from 1 and then its on... seems to be related to 1500 and the Vario-Cam coming on.  I agree I don't think its a Vario-Cam problem.  What I was inquiring was if the Vario-Cam could come on at say 1000 instead of 1500. You say its a trade-off, and I guess that makes sense, if the range of the timing is fixed then you can only shift the bandwidth up or down the rpm range. I think you've answered it, it was not designed for "off the line"... its a sports touring coup... It really comes on above 1500 no question. So I am satisfied that the rest of the system is functioning as it is supposed to. But when you notice things like that I  want to delve into it. I had a Seca 750 back when, and it had downdraft carbs. It was a really fast bike for a shaft drive (11 seconds in the quarter)  but there was a slight delay at start off.  And it was designed to be an off-the-line bike. But the plungers in the carbs where pulled up by vacuum, no direct link to the throttle cable. (And there were after market carbs that responded instantly to throttle twist making the bike a second or so faster. But they weren't street legal.)  I realize this is a totally different system of fueling the engine but the similarity is reminiscent.  Thanks and those additional tips are useful in general.   

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[flash]

a lot is due to the nature of it being a large bore 4 cylinder, with a LOT of balance mass (very heavy flywheel or in the case of the tip, a torque converter).  it takes a bit to get that mass moving.  a 3 liter 6 cylinder would rev much faster.  it's really hard to get a nearly 3500lb automatic transmission car off the line with only 225 peak lb/ft, and much less than that down low.  if you look at the curve, it's really below 200 most of the way.

 

the variocam is operated by an hydraulic valve, very similar to an automatic transmission valve.  i suppose you could play with that.  not sure it would be worth it though.  it only changes cam timing.  that's only going to get you so much.

 

as said, this is not an off the line car.  that being said, i'm well down into the 4s 0-60 now, so, not too bad.  could never get there in a tip though.  the flex damper couldn't handle that much power.

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[wildcat]

I'm not sure that the problem lies in the mass of the car or the Tip. Once the car is rolling and you kick it down to first, it takes off like one would expect a Porsche to do, which is why I find this anomaly so curious. Revving the engine out of gear, I notice it, and it may well be as you say the balance mass.  That's as plausible an explanation for the phenomenon as is reasonable at this point. 

 

As always appreciate your insight.

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[wildcat]

You ought to check, simply because it takes 0.2 seconds and costs nothing, that the throttle cable that passes over the puley is tight.  If it is loose and there is slack there would be some sort of delay. If it is not that, I have reached the limit of my knowledge on this matter and will retire to something else.

The throttle cable was tight... you could rev the engine without slack... but the butterfly valve was delayed in lifting when the throttle was applied.  I tightened it so that at the merest pressure the butterfly valve (the little bar with an adjustable stop) would rise. That has improved the response considerably.

 

I was at a stop and I took off as usual and I heard the winding up of an engine, a white VW GTi was gunning for it, I stepped on it but I was already in second gear, I heard him shift 2 more times before I got out of second... I laughed, he gained on me and I was going for third and he pulled off... silly Rabbit...

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[wildcat]

The platinum wire came in, I got 5" worth because you need the length to manipulate the wire inside the "ramjet" tunnel. (Got a better way of describing it?) Got it soldered in and no more warming up idle concerns.  The thermal conductivity of platinum makes the difference.  I only needed 2" of the wire. So for 5" it was $20.00 plus shipping and tax. Got an extra 3" left. I didn't think of this but I probably could have super glued the 2" strand of platinum to another 3" or 4" strand of copper wire and I would have enough "wiggle" room to solder, wrap and solder the other end.  (Now I've got a back up strand anyway.)  How's it running? Better than before the wire broke.   B)

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[Waylander]

If your not handy with a soldering iron


0 280 213 012 Is a direct replacement we have two of these running over here now and they work perfectly and fit perfectly


Cheapest is a Chinese copy at £33 or about $50


Smooths out idle and really improves throttle response if yours is old and dirty

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[wildcat]

And there's a slight drawback - well for folks around here an intolerable drawback... the thermal efficiency of solder is less than platinum and a special alloyed solder is still less efficient than platinum which is why the platinum is clamped through the tiny little posts and not soldered.  In a pinch the copper works, the platinum much better but not perfect. It runs great at anything but idle and not all the time but enough to be annoying.  Well, I tried.   :angry2:   

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[MCL968]

Yes you did, and I know I learned a lot in the process, especially about the presence of an affordable alternative to the stock unit. I appreciate the schooling!

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[flash]

lol - welcome to the club.  sometimes stuff just doesn't work out.  that's how i managed to spend $150 on my car.  they say edison failed 1000 times too before he got the light bulb worked out.

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[wildcat]

I was amazed it worked at all... truly. In spite of my frustration it does work quite well but like most of the more mature around here, you want it to work and work right and are impatient with any less. And I learned a few things in the process... thanks for the support.

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[wildcat]

ICV gummed up, hence the idle problem. Carb cleaner fixed it. Replaced air filter. Re-initialized ECU and the machine is good to go... hadn't given up on the problem, just took it off-line. 

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[Waylander]

I had a massive air leak in my ICV, had to take it to bits as the O ring at the joint between the motor body and the valve was in 4-5 bits, 50 cents O ring some cleaner and a bit of sealer all fixed.

 

another of those simple but frustrating jobs as you need to be double jointed to get it off

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[wildcat]

Half the battle is discovering where the problem lies... I got all kinds of strange clues, including parked on a slope with the right side higher than the left, where it worked, and the right side lower where it stalled.  I thought it might be a fuel filter problem which I'd had changed 18 months or so ago. I was taking the MAF off and on and no doubt disrupted the ICV in some fashion. But I suspect its more than that, its also the reprogramming of the DME.  First I used copper, and then platinum and it had to adjust to each which outside literature says can take up to two days, and the memory should be cleared as well. If its a close match you probably wouldn't notice. So it was a combination of things or the ripple effect as I call it.  Anyway its a go...

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[wildcat]

Back on topic and to add closure to this saga...

 

Disconnected the ICV.  Set the idle manually with the set screw. Fired it up several times till I got the idle set where I wanted it. Engine stable.

 

NO THROTTLE LAG. Tach goes up and down smoothly with no dips.

 

A guy that races 944's said "dump it"... any reason I shouldn't?

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[flash]

the ICV provides a needed additional source of air for off-throttle.  if you remove it, the engine will likely start to stall when driving and letting off throttle.  this is due to the throttle plate position, when set correctly.  if not set correctly, the car won't pass emissions testing, let alone odd low rpm and cold running issues.

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[ds968]

Not sure if we're talking about the same thing, but I adjusted the idle set screw to increase the rpm at idle by about 400 above the set norm, although I did not disconnect the ICV . There is no adverse symptom whatsoever when letting off throttle or at any other time, and the car easily passed the somg test, clean as a whistle . But like I said, I did not disconnect the ICV, and the car is supercharged so that might offset the otherwise potential symptoms flash mentioned in the above post ..

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