1990 Carrera 4 Dyno Runs
02-22-2013, 03:45 PM
#17
I know that I don't post around here, but an engine is an engine, and I tune / tuned cars myself from carbs, stock ECU, and a few stand alones myself for years.
There is no way a properly tuned car (timing, AFR, Cam timing in some cases) won't perform better than a non optimal one.
Therefore a properly tuned car will run safely, responsive, and make more power.
Different engines like to run with different AFRs, but from my experience 11.s and low 12s on a NA car is just plain rich, you're burning gas and loosing power.
There is no way a properly tuned car (timing, AFR, Cam timing in some cases) won't perform better than a non optimal one.
Therefore a properly tuned car will run safely, responsive, and make more power.
Different engines like to run with different AFRs, but from my experience 11.s and low 12s on a NA car is just plain rich, you're burning gas and loosing power.
02-23-2013, 11:33 AM
#18
Rennlist Member
Join Date: Jun 2010
Location: Detroit (Rock City); 1990 C4
Posts: 1,710
Likes: 0
Received 4 Likes
on
4 Posts
Something to consider is that the typically provided dyno plots are all about power at WOT. They say *nothing* about drivability (unless you're looking at plots from some car with a too-huge turbo that has a power delta of 250hp in the 500 rpm span where the boost comes in; I can predict with 100% success that'll be a little twitchy...).
What do people say when they're gushing about their SW chips? Often they talk about how much more tractable and drivable the car is. My point is that you're not going to see evidence of that on a WOT pull plot.
What do people say when they're gushing about their SW chips? Often they talk about how much more tractable and drivable the car is. My point is that you're not going to see evidence of that on a WOT pull plot.
02-23-2013, 12:34 PM
#19
Advanced
Join Date: Oct 2012
Posts: 61
Likes: 0
Received 0 Likes
on
0 Posts
Ok, I will give my two pennies worth...
Best performance From fuelling is at approx lambda 0.91, meaning you are running nine percent richer than stoich. Most of the time gasoline engines run rich at full load from 3000rpm onwards. This is done to cool the cats and/or the exhaust ports. Typical max temp for a cat is 950deg C, measured with a thermocouple one inch from the front face of the brick and centre brick deep.
If you change cams, you increase the air charge, meaning more heat. Therefore you need to increase the fueling(injection pulse width) to compensate. Manufacterers therefore measure the exhaust port temp, cat temp and cylinder head temp during the engine management system (EMS) optimisation.
The lambda controller only runs opto the point where the engine needs its component protection fueling, after this it runs open loop, where it increases the lambda based on internal models. By changing the cams, the actual air charge is higher than the modelled air charge for the open loop fueling model, causing the engine to run too lean. also it needs to run even richer due to extra power. How much richer depends on the temperatures you are measuring with the new cams.
The lambda sensor in the 964 is a two point sensor (Bosch type LSF), new models run wide band sensors (LSU), the wide band can say how much or how lean, where the two point can tell just rich or lean. Because of this the ems on he 964 cannot compensate beyond the calibrated close loop open loop setting, where a more modern system can.
Also the air flow meter is a volume meter, not a mass flow meter on the 964. That means that modifiying cams has another issue, that the air charge correlation of the flow meter is no longer as expected by the ems. This is another reason for the fuelling to be off.
Another issue is, is that the pistons also have a max temperature, as well as the valves. These are measured by special temp plug pistons and valves. On the 964 there should be enough headroomwhere this is not an issue if you just change the cams.
Changing the air charge means you need to optimize the ignition settings. Your current ignition angle is too early, causing knock that than will be compensated for by the knock system. The knock system is only allowed to pull out somewhere between 9 to 12 degrees of ignition. If you need even later ignition it would knock. Late ignition has a disadvantage though, the exhaust gases get hotter, meaning you need even more fuel -> even richer (see above).
We only do this optimization on an engine dyno, to make sure we can keep all other variables constant (temperatures, air flows, engine speed, engine load) while we do the measurements. For most people this would be unrealisticly expensive, as a dyno with all required equipment will be $85k a month. You would need about 2 weeks on a 964 to do a good job. The alternative using a chassis dyno would be able to give a safe calibration, but not a optimum one.
I know the more modern 997s wich are pretty much on their limit, making any mods without optimizing the rest causes terminal engine damage. The 964 being much older hasnt been pushed to its limits as far, at least from its internal components point of view. I dont have any knowledge on the 964 cooling, but I assume the heads will get critical at some points due to its air cooling. Perhaps you could compare the turbo cooling, that should be able to cope with the additional power.
Drive train losses on older cars are approx 12% on a 2wd, I assuem about 18-22% on a 964 4wd.
I would see if I could find someone who has a bosch 964 strategy description as well as the required files and knows what he/she is talking about to do an optimization. I know for sure I will not update my engine, if I need more power I will buy another car.
Not many answers, just some info.
Rob
Best performance From fuelling is at approx lambda 0.91, meaning you are running nine percent richer than stoich. Most of the time gasoline engines run rich at full load from 3000rpm onwards. This is done to cool the cats and/or the exhaust ports. Typical max temp for a cat is 950deg C, measured with a thermocouple one inch from the front face of the brick and centre brick deep.
If you change cams, you increase the air charge, meaning more heat. Therefore you need to increase the fueling(injection pulse width) to compensate. Manufacterers therefore measure the exhaust port temp, cat temp and cylinder head temp during the engine management system (EMS) optimisation.
The lambda controller only runs opto the point where the engine needs its component protection fueling, after this it runs open loop, where it increases the lambda based on internal models. By changing the cams, the actual air charge is higher than the modelled air charge for the open loop fueling model, causing the engine to run too lean. also it needs to run even richer due to extra power. How much richer depends on the temperatures you are measuring with the new cams.
The lambda sensor in the 964 is a two point sensor (Bosch type LSF), new models run wide band sensors (LSU), the wide band can say how much or how lean, where the two point can tell just rich or lean. Because of this the ems on he 964 cannot compensate beyond the calibrated close loop open loop setting, where a more modern system can.
Also the air flow meter is a volume meter, not a mass flow meter on the 964. That means that modifiying cams has another issue, that the air charge correlation of the flow meter is no longer as expected by the ems. This is another reason for the fuelling to be off.
Another issue is, is that the pistons also have a max temperature, as well as the valves. These are measured by special temp plug pistons and valves. On the 964 there should be enough headroomwhere this is not an issue if you just change the cams.
Changing the air charge means you need to optimize the ignition settings. Your current ignition angle is too early, causing knock that than will be compensated for by the knock system. The knock system is only allowed to pull out somewhere between 9 to 12 degrees of ignition. If you need even later ignition it would knock. Late ignition has a disadvantage though, the exhaust gases get hotter, meaning you need even more fuel -> even richer (see above).
We only do this optimization on an engine dyno, to make sure we can keep all other variables constant (temperatures, air flows, engine speed, engine load) while we do the measurements. For most people this would be unrealisticly expensive, as a dyno with all required equipment will be $85k a month. You would need about 2 weeks on a 964 to do a good job. The alternative using a chassis dyno would be able to give a safe calibration, but not a optimum one.
I know the more modern 997s wich are pretty much on their limit, making any mods without optimizing the rest causes terminal engine damage. The 964 being much older hasnt been pushed to its limits as far, at least from its internal components point of view. I dont have any knowledge on the 964 cooling, but I assume the heads will get critical at some points due to its air cooling. Perhaps you could compare the turbo cooling, that should be able to cope with the additional power.
Drive train losses on older cars are approx 12% on a 2wd, I assuem about 18-22% on a 964 4wd.
I would see if I could find someone who has a bosch 964 strategy description as well as the required files and knows what he/she is talking about to do an optimization. I know for sure I will not update my engine, if I need more power I will buy another car.
Not many answers, just some info.
Rob
02-23-2013, 05:21 PM
#20
Rennlist Member
Thread Starter
Hey Robbie,
Thanks for your words, love all the techy talk. I myself was wondering about the air charge because I'd gone to a sportier cam and the Euro RS valves (51.5mm intake, 43.5 mm exhaust) and thought that the car would be running leaner. The AFR's came back on the rich side, so not sure where my logic failed.
My knowledge of ignition timing is midieval at best but I do have faith in Steve Wong's ability to address these concerns. He does seem to have a loyal following and a good reputation in these matters.
I expect to have a new chip sometime next week and will post impressions and hopefully will redyno on same dyno to see what improvements have been made.
Thanks for your words, love all the techy talk. I myself was wondering about the air charge because I'd gone to a sportier cam and the Euro RS valves (51.5mm intake, 43.5 mm exhaust) and thought that the car would be running leaner. The AFR's came back on the rich side, so not sure where my logic failed.
My knowledge of ignition timing is midieval at best but I do have faith in Steve Wong's ability to address these concerns. He does seem to have a loyal following and a good reputation in these matters.
I expect to have a new chip sometime next week and will post impressions and hopefully will redyno on same dyno to see what improvements have been made.
