more power

[mfortune0]

Originally Posted by Shifted

There are no ITB or bored single throttle body kits available for the 928. However, a few people have installed ITB's with very good results.

Given that the diameter of the stock throttle body inlet is 3.75", I don't see there being much to gain by increasing that diameter. The potential gains for the intake could be in things like intake side tank spacers, lower restriction air filter setup, or a custom intake manifold.

The stock manifold has the resonance flap that the ECU moves at about 3.5k RPM to extend the torque curve. It works very well.

The spacers are a "thing" and I think that 928 Motorsports has/had them for sale.

928 Motorsports also offered a replacement flywheel, but I can't speak to whether or not it is lighter. Maybe worth investigating.

Pelican resells some of the 928 Motorsports products, for what it's worth.

Regardless of what changes you make, you're going to want to retune the ECU's. The SharkTuner lets you tune the stock ECU's after swapping in some programmable chips. However, if you're going to be buying the SharkTuner itself, I would recommend you instead switch to a modern ECU like MegaSquirt Evo Pro, or one of the MAXX or Thunder ECU's.

Obviously, if you go the ITB route, you'll be doing Alpha-N speed density. It seems like others are happy with that for their ITB 928's, but I have no personal experience with that combination.

The stock fuel injectors at stock pressure levels are plenty to handle much more power than stock. They are batch fired, and switch to double the firing frequency at higher RPM's. Effectively doubling how much fuel they can deliver, and how much power that they can support.

I wouldn't recommend changing the fuel injectors unless you're going to be pushing the power output above 400hp at the wheels.

Another option to consider is forced induction. Supercharger kits are still available, or you can roll your own. There aren't any turbocharger kits available, but they can also be built from scratch.

I have a turbo system on my 928, and it is very doable and completely worth it. However, it will require a deep dive on several systems and disciplines if you're doing it yourself.

If you want the "Easy" button, get a porken chip. It's got a routine in there that advances the ignition timing until knock is detected, then backs off a little. Since our engines are knock limited, that means you end up with the absolutely maximum power that your specific car can support. Safely.

If you decide to program the ECU yourself, you can play with the tip-in and acceleration enrichment to improve throttle response.

Thanks for the information

[Mitsu]

Thanks a million for sharing your very detailed experience and knowledge on 928 ! I am very interested in your turbocharger set up. How do you manage the boost/fuel/ignition control ? Are you using a Motec/Haltec ECU ? Is there a turbocharger kit that I can base on ? Such a kit saves me a lot of time figuring out for the piping, brackets etc. I've checked your video clips. Your car is very quick. BTW, your steering wheel is very cool ! In the past, I have built many cars including 911RSR, Jaguar V12 XJR-S TRW with Tremec 5 speed (I have 2 other XJSs) , TVR Cerbera that I still race with A7075 connecting rods, Motec controlled, AP twin plates etc. Porsche 928 GTS 5 speed was a car that I have dreamed of owning. After waiting for many years, I finally came across a kind of barn-found 928 GTS. I really want to update the car because I think Porsche 928 is such a car that has an outstanding drive-train concept and it still outstands among new GT/sports cars of today.

[Shifted]

My turbo system is not based on a kit, unfortunately. It's all from scratch.

On my system, I used the SharkTuner programmer to reprogram the Porsche factory ignition and fuel ECU's (also called the EZK and LH , respectively):

SharkTuner – A complete tuning system for the Porsche 928

To use it, you open up the two factory ECU's and replace stock chips with programmable chips that will let you program the ECU's using the SharkTuner box and software. Standard fuel/ignition map stuff. Again, I don't recommend it and I wish that I had known then what I know now. Any significant development stopped on the SharkTuner a long time ago, and it's antiquated compared to modern systems. You can't even review and edit tunes offline. You have to be plugged into the car and the car turned on to even look at a tune. That's a major hassle. You've got to have a laptop plugged in at all times if you want to do any logging at all. And despite using a MAF, you cannot set calculated AFR targets, all you can do is set the amount of fuel to inject. Fine for the 80's, but way behind the rest of the world today. Even the program's interface looks like something developed in the 90's.

I plan to replace the SharkTuner on my car with MegaSquirt (MS3Pro EVO):

https://www.diyautotune.com/product/ms3pro-evo-standalone-engine-management-system/

If you're comfortable with Motec/Haltec, I'm sure that it will work well. I don't think that they support MAF, so you'll have to go pure speed density. And probably add additional lines to go full sequential instead of batch fire. The '87+ 928's have a hall sensor on the passenger cam shaft, so full sequential is possible, as is per-cylinder knock control.

For the boost pressure, I am using a Tial wastegate with an 11.6 psi spring in it. I don't use a boost controller. Yet.

Your car collection and experience sound awesome! You'll have no trouble with modifying the 928. Do you do a lot of time attack racing? Any other racing as well?

A few shots of my system:












I won't bore you with the details

[Mitsu]

Wow, very clean installation ! impressive ! power is also impressive ! 540wHP, that is nearly 635Hp ! Air/Fuel ratio is also very well controlled. 11.6@peak horse power, meaning piston cooling by fuel. plus a water cooled inter-cooler. Motec does not support MAF system. Motec supports TPS/Engine RPM map(PGM) or MAP/Engine RPM(D-Jetro). the boost control and the actuator control are also available. the good thing about motec/haltec is that the software is easy to use and auto tuning function using a wide band O2 sensor works quite well. Anyhow i really thank you so much for sharing great amount of precious experiences on Porsche 928 mods and spending your time for me.

[husker boxster]

I'm about to tap out of this thread. I'm finding it harder to enjoy it. But before I bid adieu, I'd like to make a suggestion:

You've come across a batch of rare 928s. You haven't said if you're in the states or in Europe, but your 92 GTS is very rare in the US and quite rare ROW.

https://www.928oc.org/the-porsche-928/model-info/production-volumes/928-production-numbers

Worldwide there were less than 1000 GTSs produced in '92. How many are still on the road or road worthy 30 yrs later? Taking one of those remaining GTSs and turning it into a race car is such a shame. Even if yours was in sad shape (you haven't provided pics), there are guys over on RL that could have it back into shape in months. Its a car that should be kept as it came from the factory, not cobbled into a garden variety track car. Your other cars are similar - the shark community would love to have them as is.

I would suggest selling your stash of rare sharks and find an 87 or 88 S4 auto that drives nice but has a roached out int. Modify the engine all you want, bolt a 6spd Corvette transaxle on, and go to town racing that mother. With the money you'd make from the sale of your 3 sharks, you could easily find a race car candidate and afford the mods to make it go fast.

Once you get the cutting torch out and start making a rare car into a race car, the value drops like Biden's poll #s. And what's the plan WHEN (not if) you blow a rod out the side of the block? There aren't a lot of those GTS engines floating around. There are plenty of 5L engines to be had. Blow one of them up, not a rare 5.4L.

Feel free to call me a prude. They're your cars and you can do what you want to with them. But please consider what you're about to do and think it through. If this car doesn't mean much to you, sell it to someone who will appreciate it for what it is and do your thing on one that's not so special.

Thanks for your consideration.

[Mitsu]

I fully understand that 92 Porsche 928 is a rare one and feel kind of responsible to keep it the way it originally was. At the same time, I would like to enjoy the car by extracting the potential without making a non-reversal modifications. I happen to have a spare 5.4 GTS engine which can be left completely normal. The entire car will be completely restored with the best paint job etc. All the interior will remain and restored or may be improved by leather upholstery etc. The will simply look fully restored 928 GTS but with modern performance. This is the direction I am heading. If so desired, every component can be replaced back to the original. I attached some photos of my cars to let you see my direction. they are all still under my possession.






I hope some of you can understand my direction !

[Shifted]

Very nice collection.

I have the same perspective on the 928. I can reverse the turbo installation and leave no sign that anything was ever done. No fender holes or anything like that. In the mean time, I get to enjoy modern performance.

Do whatever makes you happy. It's your car!

[Mitsu]

i am glad to find that Shifted has the same perspective !

[Mitsu]

Hi all, I am still thinking about how I can boost the performance of my GTS. I thought of going for centrifugal supercharger but it seems difficult to purchase it these days. If someone knows where I can get it, please inform me on this. Also Shocki suggested to install GT cams but obviously, it is quite difficult to find them. After a bit of study, it seems that S4 cams are a bit more performance oriented than GTS cams? Does any one can comment on this topic ? I know that there was a big discussion on the cam-profile topic. Suppose S4 cams have duration of 220deg@1.0mm lift, then the valve timing set at I.O@5deg btdc I.C.@35deg abdc, E.O@35deg bbdc, E.C.@5deg atdc would be a quite ideal valve timing I can set. any comments are highly appreciated.

[Mitsu]

Shocki, I forgot to ask you how much power are you getting with the mods you have made. I found a company in Germany called "Dblias dynamics" who can regrind the cams to 928GT profile. I happen to find a set of S4 cams and ask them to regrind them. You have a recommendation on the valve timing set up? Thanks for your kind attention and time !

[Alfa145V6]

Hi guys, I dip into this thread rarely as I sold my ‘95 GTS a year before the values in the UK went crazy!
There used to be threads about a twin turbo set up by a member in here. John K***?
I was tempted at the time but never did it. Also supercharging was available. 10 years or so ago.
Might be worth a forum search?
I can see why the OP wants to get more power. A car is to be enjoyable and to hell with the value.
The GTS is quick and making sure it’s in tip top condition will make sure the horsepower is still there.
So many new German cars are frightening fast these days. Too fast for me to be honest. Also the fast Nissan. There will be less gnashing of teeth, frustration, loss of sleep, etc by getting one of those! Having said that, I’m mad keen on the project and wish you good luck. You certainly sound knowledgeable and capable on the systems.

[Mitsu]

Hi Alfa145V6, I know what you mean. I used to own a 928 S4 auto some years ago. The car is designed right and kept wishing to find a GTS 5 speed and I found it(them). The normal state of the car is by no means "SLOW". But I don't want people to think 928s are classic in terms of performance. With proper tuning either NA, Supercharge or Turbocharge, the car can still exhibit its great potential without sacrificing its elegant characteristic. Many in this forum gave me a lot of knowledge and experiences, which I really appreciate. Understanding what is available on the market and my specific desire, I think I am going for NA tuning. I have bought a set of S4 cams to be reground to GT duration or may be a bit wider around 270deg duration. Free exhaust including headers and X-pipe etc. ported intake and throttle body up to 2.5mm. Light weight flywheel and pressure plate. 355mm Brembo in front and 343mm in the rear. Specially build height adjustable shocks. Yes, the LH tuning chip will be incorporated at the start. I will wait if I will use ITB at the moment. There is an ITB set up for Corvett which might be a starting point to fabricate one. I will think about it. Light mods should bring the power up above 400hp, hopefully !