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That is interesting because both of my GT-cammed engines with their timing slightly retarded, were right at 185 psi.
So that would imply Colin's cams, in this instance at least, are way more retarded than GT cams. In other words, the intake valves are being held open much longer on the compression stroke versus GT cams, bleeding off compression psi lowering its dynamic compression ratio.
I would love to see a dyno-sheet of these cams in action to see how much they shifted the power upward in the RPM band.
Just for fun, I'd be tempted to advance the cam-timing (..intake valves close sooner) so that a compression test would then register 180 psi at the cylinders.
The comparatively low compression pressure test readings are symptomatic of a reduced LSA and thus more overlap and that is generally speaking an undesirable characteristic in a street motor and more so for an automatic I suspect. If overdone the other downside might be reduced vacuum that could impact the effectiveness of the stock servo.
I suspect that Colin managed to design a cam balance that is superior to what Porsche designed. Never heard anyone complain about them so proof of the pudding is in the eating as it were. Presumably they have a nice rasp to them soundwise and whereas the S4 cams are progressive I suspect Colin's design has a more noticeable punch at around 4k rpm or so as the thing comes on cam.
Perhaps Marti can describe the cam sensation from a drivers perspective- rather nice I suspect.
You are pretty accurate regards the power band, they start coming on cam around 4 - 4.5k with the power continuing to build right up to the red line. For the auto (89 MY) it will typically kick down into the power band. Torque is not destroyed lower down and feels not unlike the standard S4 until it starts singing above 4K. Once above 4.5k then it really feels very strong.
I have high hopes for my new manifold that it can add power below 4.5 and everywhere above, that would be the cherry on top for me.
That is interesting because both of my GT-cammed engines with their timing slightly retarded, were right at 185 psi.
So that would imply Colin's cams, in this instance at least, are way more retarded than GT cams. In other words, the intake valves are being held open much longer on the compression stroke versus GT cams, bleeding off compression psi lowering its dynamic compression ratio.
I would love to see a dyno-sheet of these cams in action to see how much they shifted the power upward in the RPM band.
Just for fun, I'd be tempted to advance the cam-timing (..intake valves close sooner) so that a compression test would then register 180 psi at the cylinders.
I seem to recall Colin saying that these are sometimes run slightly advanced, maybe he can chime in if he reads this and the affect it has.
I would have loved to have increased the CR at the time of the rebuild but sometimes you can only do so much. I am not sure I will get round to it now as I am more likely to experiment with a wet liner project after completing the manifold project.
The camshafts have a wider LSA (114deg).
But the lift and duration numbers are substantially larger than GT camshafts.
I typically find that power really starts to come in around 3k rpm with the cams and a properly functioning flappy.
On the dyno putting these straight up (not advanced or retarded) they do not lose any power over factory cams. In fact, right off the idle, they have more power.
With a functioning flappy valve around 3300 rpm on the dyno they showed a massive improvement over factory. 329 vs 260 ish was the before/after (did also get MSDS headers and exhaust on this one at the same time as cams).
I never read much into compression numbers as I've seen gauges have over a 50psi difference on the same engine back to back. What matters about compression gauges is consistency between cylinders. If all the cylinders showed 120 psi with no variance I would not worry. To better check the health of the engine you should do a leakdown test.
But the lift and duration numbers are substantially larger than GT camshafts.
I typically find that power really starts to come in around 3k rpm with the cams and a properly functioning flappy.
On the dyno putting these straight up (not advanced or retarded) they do not lose any power over factory cams. In fact, right off the idle, they have more power.
With a functioning flappy valve around 3300 rpm on the dyno they showed a massive improvement over factory. 329 vs 260 ish was the before/after (did also get MSDS headers and exhaust on this one at the same time as cams).
Okay, a 5-speed with GT cams and an exhaust will do 320 - 330 rwhp.
Your numbers tell me that your cams would be a good alternative if no GT cams are available, so good job creating them.
You numbers are 30 - 40 psi lower than what I've consistently seen on stock S4 engines.
Could just be the gauge. Were you there years ago when we were running compression tests on a couple 928's in Murphy's garage? We had three different gauges and the spread was more than 30psi difference between them.
When doing a compression test, consistency between cylinders is what's important. If a problem is suspected, then you do a leak-down for more accurate readings.
Could just be the gauge. Were you there years ago when we were running compression tests on a couple 928's in Murphy's garage? We had three different gauges and the spread was more than 30psi difference between them.
I'd like to know, why can't we ALL have tools like this?
Could just be the gauge. Were you there years ago when we were running compression tests on a couple 928's in Murphy's garage? We had three different gauges and the spread was more than 30psi difference between them.
When doing a compression test, consistency between cylinders is what's important. If a problem is suspected, then you do a leak-down for more accurate readings.
I was quite pleased with the outcome of the CR test as the cylinders were all very close to each other.
I would have still loved to have raised the static CR as I know this would have have given a few more ponies.
I've got 2 compression gauges and when I want to play a joke on someone who wants to borrow one, I give them the low reading one. Oddly enough, the Northern Tool one reads more accurate than my snap-on.
I seem to have a fault with the WB02 sensor which I am hoping someone can identify.
It has started to read maximum lean after a short time from start up without changing the map.
Literally the A/F mixture on the ST will look a little subdued around the stoic number, then start fluctuating between rich and stoic before just shooting straight to full lean 18.99.
I observed yesterday that it did this for the first few minutes until the engine had warmed up and then seemed to work fine but today it just registers full lean even after the engine is warmed up. If I stop the engine and restart I get it registering 9 while the engine if off and then with the engine started I get a small fluctuation for a few seconds around stoic before shooting to full lean
Does anyone know what this is?
I observed that when the sensor was being heated during the first few seconds of running the sensor worked, the second the heating cycle finished the sensor reads full lean. If I rev the car to introduce more heat the sensor will start working properly again. My conclusion is that the sensor has been damaged in some way by running slightly cooler in the cross over of the x pipe. It does say on the website for techedge that sensors can wear out quicker if run cooler.
I am going to replace the sensor with a new one and wrap the x pipe in an attempt to keep the temperature up in that section of the exhaust.
I observed that when the sensor was being heated during the first few seconds of running the sensor worked, the second the heating cycle finished the sensor reads full lean. If I rev the car to introduce more heat the sensor will start working properly again. My conclusion is that the sensor has been damaged in some way by running slightly cooler in the cross over of the x pipe. It does say on the website for techedge that sensors can wear out quicker if run cooler.
I am going to replace the sensor with a new one and wrap the x pipe in an attempt to keep the temperature up in that section of the exhaust.
Hope to be back Shark Tuning next week
Unfortunately, the Wideband gauge I put in my '79 does the same thing sometimes, usually on a long trip. Works fine most of the time but then starts reading leaner and leaner until it's maxed out at 18, but the car continues to run and drive fine. I've also had it go all the way the other direction where it's at like 8, where if it really was I'd be spitting out a black smokescreen but it just seems to be the gauge freaking out. Interested to know if your replacing the sensor resolves your issue as I may need to do the same.
I changed the sensor and applied some wrap to the exhaust to try and retain heat at the sensor. I also did the recalibration of the new sensor in free air as per the techedge instructions.
That has fixed the issue and I am now back in business with an accurate AFT reading.
Now that I have a reliable AFR again I have started to experiment again.
I have been working on start up fuelling using the Warm up map, cruise map and cranking map.
Bear in mind that my injectors are 30lb items it might not be surprising where I have ended up. I am assuming that when the injector size is changed within the ST software there is no alteration to the fuel map values. So the map is injecting the same values for any injector size. That means a 30lb injector is injecting a hell of a lot more fuel than the standard 19lb injector.
I first of all adjusted the area on the cruise map which is used at idle when the engine is warmed up. This generally ended up at -58.
I then worked on the warmup map which adds fuel when the engine is cold. This generally needed taken right back from the S4 values to between 20-0, I will continue to tune this over winter so I can get colder start ups.
Then I worked on the cranking map at all temperature ranges and also generally wound them right back.
My aim was to get the engine to start right off the key without throttle being applied.
I recognised at start up it was taking far too long to kick into life and was probably suffering from a overly rich mixture. Thinking through my assumption led me to start experimenting based on this and the evidence of longer than expected cranking.
No real surprise that everything needed wound back usinlg the 30lb injectors compared to the 19lb injectors.
I achieved my aim and the car kicks into life almost instantly now setting down to a nice balanced idle from cold. That’s a huge improvement on where it started.
Next I am experimenting with the acceleration enriching map which I believe is also pumping to much fuel in as this would be set up for the 19lb injectors. From my initial experiments reducing the values is giving a much sharper response although this really needs on the move ST to see how this works with the cruise map.
I may well be off base here but when one does as you have done and [presumably?] set the injector size value to 30 instead of 19 in the software, it is my understanding that the software adjusts whatever it needs to to arrive at the same equivalent settings as one had previously- i.e. plug and play type of thing. This is what I did when I fitted my 30lb design 2 four hole injectors and they seem to work well. The only info I did not have was the injector opening time and I left that as per the stock setting and figured that tuning would take care of the rest.
If by any chance I have this wrong hopefully I can take some learning from your experience.
09-29-2018, 12:36 PM
