audipwr1

Yeah swapping maps and turbos completly changes the behavior of the engine.
I was just curious what the goals were and in what context the motor would be used. Seems like an interesting project. After building a few pretty specialized engine packages I always like to see stuff like this

Red rooster

Jean,
I am afraid I dont share your confidence in the plastic dump valves. In applications where they have to operate frequently , VAG 1.8T etc, I have replaced valves before the proud owner took delivery of a new car!!

VAG have gone through numerous iterations on the part number and even ran out of warranty replacements totally , in Europe, for a while !!

On older turbo models with little part load boost , Audi RS2 , 944T, the plastic valves have a much more acceptable life , so maybe this is your situation ?


All the best

Geoff

IrocMan

Congrats, sounds good.
Kevin, it's a very lovely work you make here.
I'm working on a similar project, even a bit different.
I will create a thread not to dirt yours.

I really agree with you when you figure about RPM. I have 8000 rpm for target with a 3 liter and 24 valve engine. People always say I don't need so much RPM and my answer is always : how many rpm did 935, 936, 956 or even 962 take ?

We build racing cars, not turbo-diesel Audis

Red9

Kevin is that intake a 964/993 N/A intake. The 180 degree elbow comes from where? Or is available?What is the EVO plennum?

Kevin

Yes, 993.. The 180 degree elbow is a Porsche Motorsports item along with the center plenum with throttle-body.

Rob S

Nice work, Kevin.

Regarding twin vs. single plug, I know a very experienced head machinist in California (who does nothing but racing heads for Porsches) who believes that the greatest power (and detonation protection) can be achieved with a single plug. He claims the indentation for the second plug gets in the way of some combustion chamber shaping that he does and it disrupts the intended flow and swirl that more than make up for the lack of a second ignition point. I don't know more detail than that -- and I don't know how extensively he modifies the combustion chamber and piston crown to achieve this goal. I have never seen his product or any results to verify his claim, but he has an excellent reputation in the world of Porsche race engines.

I thought I'd throw that out there for you to think about. Perhaps whoever built this engine has come to the same conclusion?

Rob

Kevin

Rob, he might have some data on his feelings/findings but I think that he is in the minority. However, the Sportec engine ran race fuel. We need to have twin-plugs to add a security blanket against poor fuel. Why did Porsche go to twin plug on the 935's 964 and 993's? His claim of higher power needs to be proved.. I would still add the second plug..

Rob S

Kevin,

I tend to agree; as you know, I'm using twin plugs now and I wouldn't be wild about trying to go without. I'd definitely want to see proof -- in a big way -- before experimenting with a high-dollar single plug setup. And this guy definitely endorses the use of race fuel -- his heads are not meant for street engines, and not for race engines on street fuel. But I wouldn't judge twin plugs to be the only game in town based on what Porsche did with their 935s in 1978. And it's interesting that Porsche never put twin plugs on their 964 or 993 turbo cars. But I think that's for a different reason. Bottom line: there are some specialists, in the minority perhaps, who strongly believe that a single plug setup, with very well-designed combustion chambers, is superior to the standard twin-plug arrangement. I find that interesting...

JJayB

Porsche 911 GT2 1998 race cars built for customers were twin plug.
I guess the factory race engineers didn't know about the machinist in Ca.

Geoffrey

The issue of twin plugs is not high octane vs low octane, but one of flame propagation. The 102mm cylinder is large and the hemi style head Porsche uses is inefficient for proper combustion. Peak power will come with peak cylinder pressures occuring somewhere between 12-14 degrees ATDC depending on any given engine. After the piston has reached 12-14 degrees ATDC, it is accelerating at a higher rate, expanding the volume of the cylinder more than the pressure from combustion and pressure begins to fall off. To acheive that, you need to start the combustion process early since the flame propagates at a rate of 35-50 cm/sec whch creates about 20-30psi per degree of crankshaft rotation. These are the constraints you are bound by and why more ignition timing is required at higher RPM. In an inefficient design like the hemi head large cylinder with no squish area, you'll likely not be able to burn all of the air/fuel mixture by 12-14 degrees ATDC because you cannot start the flame kernel early enough to reach peak cylinder pressure. Higher octane fuel or said another way, slower burning fuel will allow for a little more ignition timing, however, it burns slower and you are increasing your pumping losses by putting additional pressure on the pistion as it is moving towards TDC thus reducing the power.

So, if you want to acheive peak cylinder pressure at 14 degrees ATDC and you have a fuel that will resist detonation up to 1200psi, and you have a dynamic compression of 160psi, and you start the ignition timing at 20 degrees BTDC, then you will have approximately 1180psi by the time the engine reaches 14 degrees ATDC, or very near the detonation limit for the given fuel, and that is best case math.

There is not a single Porsche 911 air cooled engine that I would not run twin plug ignition on. Twin plug ignition starts a large flame kernel which increases the flame propogation rate. Just like an ice cube melts faster when cut into little pieces due to the increase in surface area, the larger flame kernel also has more surface area to burn the air fuel mixture.

The 993GT2 was a homologated racecar and depending on the rules of the sanctioning body bound by the street 911 GT single plug engine design. This is why the GT2 race car ran with single plug ignition in most series.

I'm in the process of installing MoTeC on a 996 GT2 engine which has a far better 4 valve pentroof head design. The head volume is approximately 60% the size of an air cooled engine. I am expecting either the engine to require less ignition timing or produce more power at the same ignition timing than an air cooled engine. The customer wants to retain the variable lift and duration on the camshafts although that is for emissions and economy, not performance. They are very simple in how they work and not infinately variable like the BMW VANOS or dual VANOS found on the M3 and M5 engines.

AVoyvoda

On an earlier post, Geoffrey, you had mentioned that Motronic and the standard ignition system are at their limit at around 6,500 rpm, due to "dwell time" and other details. Combined with your comments about the inefficiency of the Porsche head and the ignition timing requirements of single plugs, are you saying that anything over 6,500 is virtually un-obtainable? Or at the very least, so random in terms of combustion, that it might result in long term engine damage?

Geoffrey

No, I'm not suggesting that at all. The two issues you mention are separate. The factory ignition system found in the 964/993 N/A or Turbo is inductive and uses coils that require about 3ms to fully charge. Since this is a distributor environment, the coil is required to be charged 3 times in one crankshaft revolution. So, the coils are at 100% duty cycle when the engine is operating at an RPM where 1 crankshaft revolution is 9ms or 6666rpm. Ignoring the spark break time and ringing that occurs which also takes time between each spark event and assuming that you can run the coils 100% duty cycle without burning them out, at 6667rpm, the coils cease to be fully charged. This means that they will no longer be able to provide the full amount of energy and therefore a weaker spark will occur. Weaker spark means less ability to jump a given spark plug gap and the engine will misfire. Closing the gap on the plug makes reduces the required energy, but also resuces the flame kernel, and therefore the flame propogation, and therefore cylinder pressure, and therefore torque. The solution is to run more coils (waste spark or CPP) or find an ignition system that operates faster.

There are many engines that run past 6500rpm. In fact, my RSR engine with a distributor will run to 8000rpm, but I'm using a digital high quality CDI system (actually 2) which is about 3x faster than the factory inductive ignition and operates using different principles.

AVoyvoda

That's what I understood. But there is no mention of a CDI system in this thread. Motronic and presumably the standard ignition system will be retained. Therefore, following your logic, the spark may be so weak (or non existent) at 8,500 rpm that incomplete combustion may occur (or none at all) filling the cylinder with unburnt fuel mixture that could result in catastrophic failure. Is this correct?

Geoffrey

I think that there are a lot of considerations that go into an 8500rpm air cooled large displacement engine and the ignition system is only one of them. I'd be more concerned with the weight of the piston and short rod to stroke ratio than the ignition system which is easy to design properly. To answer your question, yes, I would agree with your logic, although I doubt it would result in catastrophic failure.

The Bosch Motronics ECU contains both the engine management system and the ignition system drivers. In other words, the ignition system is integrated into the engine management system. It is inductive and based on a single coil per distributor strategy. You can install a better analog CDI system like the Crane setups that have been discussed in other posts. This helps because it is much faster and the spark contains more energy.

The other factor that needs to be taken into consideration is the volumetric efficiency which is directly related to cylinder pressure, and as the engine begins to fall off, the ignition demands decrease. So, although you cannot fully charge a coil, it may contain enough energy to still light the spark plug. The engine may run, but not be optimized due to a weak ignition system.

AVoyvoda

What I am trying to get to is this:
Following your logic, even if you fit re-designed (stronger+lighter+balanced) engine components such as pistons, crank, rods etc and better heads, the limitations of the standard coil ingnition system would make performance very "ify" at 8,500 rpm. You need CDI type ingnition. That's a large part of what Motronic does, no longer needed. Therefore, you might as well throw away the Motronic and replace it with something better and easier to map, such as Motec.
Which is precicely what you did with your race car. GT3 crank, special pistons, rods, head, cams, Motec, CDI, the works.
In other words, to be able to achieve reliable power at 8,500 rpm you need to replace most of your engine (virtually all that's left from the original engine is the crankcase, and even that needs to be pinned), ignition and engine management system. As to cost, very large. On top, the new turbos and intercooler. Cost becomes larger still. It's also debatable, whether at that point it's still a Porsche engine. Every component, bar the case, differs from the original.
One needs to consider, whether the exercise, at such huge cost, is truly worthwhile.