997 tt/rs

Gentlemen, when you install a stronger spring in Westgate increasing the boost, how does the 964 turbo know how to manage the ignition and fuel injection if there is no engine management computer?
The same for the 964 turbo with a modified turbocharger.

thanks a lot
K

Megatron-UK

Simple answer; it doesn't.

There is a very basic lambda control, but it's only active for part throttle ('cruise'). Most of the engine control systems are discrete systems; there is no central ecu and the injection system is electro-mechanical (the injectors are not like the electronically controlled items on anything from the last 30 years - the K-Jetronic system was obsolete when it was fitted to the 964 turbo).

That's why the advice when changing any performance characteristics of the car to check out the fuelling/air fuel ratio and alter the fuel head to compensate (changing the base fuelling also changes it right across the rev range - you're effectively adding/subtracting a % of fuel). That's about all you can do without replacing any of the original parts (e.g an adjustable fuel head instead of the standard part, a programmable ignition controller instead of the distributor with it's hard coded advance profile, adding/changing injectors... and ultimately, swapping to efi instead of the factory system). There are some people who have expertise in optimising the fuelling settings on these cars, but they're hard to find - the K-Jetronic system sits in a middle ground between carbs and fully electronic injection; both of which are catered for very well. Interestingly the K-Jetronic system is found in a lot of other late 80's european cars (Audi, Ford, etc), but most of those had gone over to the coil packs and more advanced efi systems by 1990. The Japanese, of course, were way ahead.

I suspect if a more modern ignition and fuel control system was fitted from the factory, we would have seen significant improvements to the power and economy figures of these cars. Pretty much everyone else in the industry had moved on to wasted spark and multi-point electronic fuel injection when the stop-gap 3.3 turbo came out, but the 3.6 even shares pretty much the same system, despite moving to the single plug version of the 964 3.6 motor. It seems there was very little investment in the technology which was basically from the early 80's by that point.

That's not to say it doesn't work well... just it could have been so much better.

997 tt/rs

Thank you very much for your comprehensive answer.

And what controls the fuel pressure? Is there a regulator?

I think that any serious tuning does not make sense because it is associated with the replacement of the pins of the heads, I read that they get up around 1 bar, which is a lot of time-consuming and expensive work.

I already have the real tuning behind me, in 2004 I had a 996 GT2 which had 900 European horses and in 2010 I had a 997 turbo which had 850 real European horses so I know what it's all about.

Going back to the 964 turbo, I came to the conclusion that the modification of the turbocharger should be cosmetic, i.e. a light new design 9 blades turbine in original sizes and a compressor wheel which has 7 blades in the original size but has a more efficient map than the original compressor.

Do you think the original fuel system will work?

Megatron-UK

I'm not an expert on the fuelling system, but anything that changes the level of boost, or the air/fuel needs of the engine anywhere in the rev range probably needs to have the base fuelling looked at. The problem is that you really can't do much without impacting fuel delivery right across the rev range. I don't think you can just change the turbo on these and have it work optimally.

The fuel head and the WUR (warm-up regulator; but it is used outside of starting procedures also) work together to control fuel pressure delivery to the injectors. According to Brian Leask (https://930wur.com/), part of the problem in the overly rich part-throttle fuel delivery of these cars is that the additional fuel added to the engine is based on just the boost signal - which is why these cars tend to get really rich in the mid-range when the boost begins to build; look at any AFR readout for these cars and they all seem to bog down horribly in the middle.

There are some methods of getting around it, such as Brians own adjustable regulator which can alter where the extra fuel comes in, but whichever way you look at it, they're never going to be as efficient as something where you can add/remove fuel anywhere in the 3D map by setting a few bytes in the ecu rom.

Metal Guru

Turbo engines present the chance to raise hp relatively economically when compared to a normally aspirated engine but there are limits to what you can achieve around the stock CIS fuel injection.
The warm-up regulator is the analog device controlling fuel delivery. It reacts to vacuum and pressure signals.
Under normal cruise it sees vacuum and fuels to that. Under boost it sees pressure and fuels to that.
If you do ANYTHING to increase mass flow, you have to add fuel. If you retain CIS, you will need an adjustable WUR and have the wherewithal to carefully tune the car. If you add air by increasing boost, you have to add fuel or you will break piston rings, pistons, ect.
Also, the K27-7200 is at it's choke point as shipped from the factory. Raising the boost above .9 bar pumps a lot of superheated air into the engine so you will risk a $20k rebuild and you will not feel any increase in HP. Unless you replace the K27 with something that is more efficient, you won't get what you want.
You should perform a leakdown on your engine to see if it's healthy enough.
So, in summary, if you want more power while retaining CIS, you will need:
(1) Headers and free flowing muffler
(2) better turbo (K27/K29 hybrid or Garrett GT 35)
(3) Leask adjustable warm-up regulator
(4) Tools: Innovate AFR LM-2 hand held gauge, CIS pressure gages, Mityvac pressure/vacuum pump

997 tt/rs

thank you very much for the explanation guys !

It would probably be best to use a stand-alone ecu before starting any tuning. It may turn out that a good ECU tuning will greatly improve the feeling of a stock car....

Can you tell me how is it that the FVD company claiming to be a company with 30 years of experience in the porsche brand offers such power kits and there is no word on ignition or fuel control?

https://www.fvd.net/de-en/FVD9651000...93-octane.html

Megatron-UK

The assumption is if you fit their sport cams and 1bar wastegate spring, you will get the fuelling adjusted to raise it across the range to cope with the increase airflow. Any reputable Porsche garage familiar with the air cooled cars would do that as part of fitting the parts. I recall seeing a figure of 3% CO at idle being an indicator of the fuel level being raised sufficiently to accommodate those modifications, but you would only know for sure with a rolling road session with an AFR sensor.

Lots of people fit 1bar springs, and lots of people fit sport/SC cams, and most of them do it using the original engine electronics and fuelling - it seems that most of them accomodate it by simply raising the base fuelling on the fuel head, but some people go further by fitting something like Brian Leasks adjustable WUR, or the old-and-crude-and-dangerous mounting of a 7th injector into the inlet manifold. All of them are non-optimal. I've seen a few people over the years able to modify the fuel head and WUR to optimise things to a greater degree, but there's not many people out there with the knowledge or skill who do this (I know of potentially 1 in the UK, for example).

In all likelihood, your 1bar spring and sport cams will be probably be fine on the original fuelling system (assuming it's all working correctly), as long as you get it checked out.

Metal Guru

The 3% CO is the value for idle. It does get the plunger in the fuel head in the proper position so you run 14.7% at constant load and 11.5 - 12.6% under boost with a stock engine.
The limit in all this is CIS itself. CIS cannot keep up with the fuel needed under boost. It's pretty typical to have to have an initial afr of 11.0 or 11.5 % at boost onset in order to be safe at 12.5% at 6000 rpm because it will drift to there (fun fact: the EPA refers to a 12.5% afr under acceleration as the "maximum lean torque AFR"). A stock engine with the wur values set to factory spec running .9 bar boost achieves this. I know this because I've measured this countless times. Change anything that increases mass flow and you are out of the window.

Cams are one of those things that will add mass flow and blow your stock fuel curve up (more duration means the valves are open longer = more mass flow). Bigger turbos have a even bigger effect. You won't be fine. You will be flirting with disaster every time you put your foot down.
I recognize I'm just a guy on the internet (although I have many years experience in fuel systems engineering at a domestic OEM whose name begins with an F), I encourage anyone to verify what I'm saying with Chris at TurboKraft. He's been tuning 930's and 965's for a long time and is a font of knowledge. The Pelicanparts 930 board has many knowledgeable guys who have tuned CIS and/or converted to EFI and are willing to impart their experience.
Buy Charles Pobst's book on CIS to gain a better understanding of the system. Also, a book on turbocharging engines will come in handy too.

Megatron-UK

I think we are saying the same thing, but from different angles. I think we are both saying CIS/K-Jetronic is archaic. I think we are both saying it is incapable of fuelling at the optimum amount at certain points in the engine speed/boost range. I didn't realise that a cam swap on the turbo engine made that much difference (my experience elsewhere is that it tended to move the area under the curve, but not necessarily increase it significantly). Sufficient extra boost from the turbo of course makes a massive difference, and by all accounts there's not much more to be had from the standard K27.

I think everyone agrees that you can't just fit add-ons that change the mass air flow any substantial amount without having the fuelling adjusted (or at least checked) on these older systems.

Metal Guru

Concur.
When a cam adds duration and lift (time that the valves are open and the height they open to) the engine is experiencing an increase in mass flow.
I think that anyone who wants more power and isn't interested in doing their own wrenching and tuning should just buy a new Turbo, is big HP is the priority.