more power
 

Hi, I am new to this forum. I have just bought 3 928s. 92 GTS 5 speed, 90 S4 5 speed and 90 S4 auto. I would like to have a bit more power. and good response. First, I am wondering if someone offers a big throttle option for S4 ? Is there enough thickness to bore the original TB to make it larger ? Does any one offer a light weight flywheel for S4? I really appreciate if you pass me you knowledge on 928s. Thanks a lot in advance. SmileWavy

There are all sorts of posts on improving the performance. I am of the opinion to keep them stock and enjoy as is. If you want the biggest bang for the buck, go buy a C8 Vette. Enjoy the 928 for what it is.

Thanks for your opinion. i really enjoy pulling potential performance of the car. I think Porsche928 model has been, in a way, under-rated and 911s have been always the center of attention. Supercharging can be an good option in terms of cost/performance ratio, but the high revving naturally aspirated engine sound is also extremely attractive to me. I have modified many cars including Porsche 911s, Ferrari308, Jaguar XJR-S, TVR Cerbera. Now I want to work on Porsche 928 GTS. The target power should be 400 rhp. It would be great to learn your experiences with 928s. thanks again for passing on your knowledge,

2 of your 3 sharks are rare and valuable and will be worth more money in stock form than modified. If you're insisting on modifiying the engine for more hp, I would suggest working on the '90 auto.

Others might disagree because of originality and rareness but the GTS engine is very responsive to modifications. It was (sadly enough) de-tuned by the factory. Although the 5-speed is a good match, the stock motor is missing the urge to rev beyond 4000 RPM. You always feel like your driving into a cushion.

To extract more power, there are a couple of things to consider:
1. If the LH-ECU is still original get the hybrid chip inside replaced by a new unit.
2. If the MAF has never been serviced, it's time to do so. (for 1. und 2. talk to Roger he can set you up with JDS units)

3. Replace the original GTS cams with GT units. The bad news is: they are rare and not easy to find. Re-grinding the originals might be an option.
4. Sharktune the LH and replace the original 19 lbs injectors with new 24 lbs units.
5. Get a self tuning EZK-S chip from Ken at liftbars.com. This way you'll also know if all sensors are present and working. Many cars lose power because the knock sensors or the hall sensor is not present. Without them the motor runs just fine but you're missing up to 50 BHP.
4. Get an X-Pipe from Roger with high flow metallic cats.
5. Remove the air pump extra weight and nobody really needs it.
6. Make súre that your ignition system is in top working order, replace wires, rotors, distributor caps and so on...
7. Time to replace the fuel pressure regulator and the damper with new aftermarket units from Roger too.
8. Fuel pump and especially the intank pump should be in good condition and working (especially the intank pump).

I have done all the above mentioned mods to my GTS with Rogerbox and it's my daily driver. No issues and very quick now due to the experience of others. Not as easy as supercharger bolt on power but worth it.

husker boxster, thanks for your suggestion. I undestand that 928s with manual transmission are rather rare especially GTS. Knowing that I still want to work on GTS without ruining its taste, like a wolf with sheep skin concept.(well not exactly). I hope to show you once it is done.

To Shocki, Thank you so much for your detailed information. It helps me a lot when I need to locate the uprated components. I am thinking to use Motec M84 for fuel and ignition management because I am quite familiar with it. Where can I find the X-pipe ? Should I fabricate it ? I think GT cams have something like 230deg duration. Maybe I could go up to 285deg. How do you think ? What about the light weight flywheels ? Anyone offers it ? Thanks again for your great help !

Call Roger at 928sRus he'll set you up with the X-Pipe.
The GT cams have more lift too. You can go more aggressive in terms of duration but driveability will go down.

Flywheel? Sorry, no idea.

Thanks a million Schocki! Your info. is very helpful.

Did anyone out there try to bore out the throttle body for later 32valve 928?

please inform me the part number for 928 GT cams. Does 9281052720 part number represent GT cams ? Thanks for advising in advance!

In 1-4: 928 105 271 01
Ex 1-4: 928 105 273 01
In 5-8: 928 105 272 01
Ex 5-8: 928 105 274 01

If you're going to custom ignition and fueling then you may as well investigate individual throttle bodies and custom headers to go with the cams and other upgrades.. if cost is not an issue.

Thanks Shocki ! i will try to find them. Otherwise, I will ask for regrinds.

Thanks Pagno ! I've got a set of headers already. Does anybody offers ITBs for 928 ? if so, I am highly interested. Let me know. I've found this. He bored out the original Throttle body by 2mm.https://dynotuning.net.au/dyno-tunin...dified-engine/

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 Shifed, Your information is very helpful. I am still wondering which direction to go; Supercharging or classical NA tuning. I know with NA tune, you have to spend a lot to get a small gain. Also tractability, Idle quality will be lost. Supercharging by means of mechanical or turbocharger do offer simple and assured power increase. Currently, i am thinking to go with mechanical supercharging using centrifugal supercharger. The power I am looking for is about 400whp. I've found the aluminum flywheel in the Pelican parts and ordered it immediately. I am really a fan of 928 drive-train concept and still want to prove that the system works excellent by beating Porsche 911 GT3s etc. I am not planning to build a complete race car but a GT car which is still competitive at the tracks. I really appreciate all your advises that I can get to make it happen !

By "track", do you mean Drivers Education events? Or, do you mean competitive racing? Or do you mean...it COULD be competitive at the track, but you don't intend to actually take it to the track?

There are a lot of areas that you could address. Brakes, alignment, suspension, tires, LSD, weight, etc.

400 rear wheel horsepower with the GTS 5.4L should be achievable with ITB's and a proper ECU. Maybe with the 5.0L motor? Not sure. I don't know a lot about ITB's on 928's beyond what I've read that others have done.

If you're considering forced induction, consider a mid-mount turbo. The turbo can be mounted right in front of the manual transmission (it won't fit there with an automatic transmission). A turbo has a much broader torque curve than a supercharger, and comes on gentler than a supercharger, so it's easier on the driveline. It also leaves room in the engine bay to do maintenance.

If you're up for modifying the motor, you could always stroke your motor to get more displacement and power.

Of course, swapping in an LS is also a possibility.

Whichever way you go, it will be rewarding :)

Shifted, Thanks a lot for your comment. The tracks I meant like time attack event at the race tracks.
How is the turbo-lag with a mid mount turbo ? Due to the distance to the turbo and from the turbo, the lag may be an issue ? I agree that LS is a nice motor but i want to leave the porsche motor inmy 928 GTS. i7ve ordered the aluminum flywheel already but I recognize that the pressure plate is really heavy. Any possibility to use Tilton or AP multi-plates clutch set up ? Thanks for sharing your knowledge !

I am by no means an expert, but I'll share what I know...

Since you're talking about serious track racing, you absolutely must address the oil consumption and starvation issues that the 928 has. I'm going to assume that you're familiar with those issues, though.

You are probably already very familiar with car setup in general for tracking a car. The 928 has a lot of overlap in general. Additionally, there are rear brake caliper/rotor upgrades available, better brake pads, wider wheels, brake proportioning valve options, and of course you can adjust the alignment to suit your needs.

For the clutch, I can't speak to Tilton and AP specifically. As you probably know, you can make just about anything work if you're willing to do the Planning/engineering/fabrication. If Tilton or AP say that they've got pieces that fit, or their specs seem similar...worth a shot? Since you want it to remain a Porsche driveline, this next part may not interest you, but several people have swapped in a Corvette transaxle. It's stronger, smoother and a 6 speed.

Personally, I upgraded to a Spec Stage 2 clutch. I didn't weigh it when I installed it, though. However, I think that I still have the stock pieces. If so, I could weigh them if you want something to go off for your research. I'm very happy with the clutch and would absolutely install it again. Even though my max torque exceeds the rating by a little bit, I haven't had any slipping. It doesn't shudder and has been problem free. As you probably know, you shouldn't pick the clutch just based on max rating, but rather on puck/disc type vis-à-vis your intended use. If you're going to be driving your car on the street, I absolutely would stay away from puck and metallic disc style clutches. That might not help you much, since you're looking for light weight. But, I love my Spec clutch.

If what you're looking for is responsiveness, the tip-in tuning can make a big difference in that area.

On the turbo...this is what I've noticed:
-Max boost (11.6psi) by 2,700 RPM
-Boost threshold below 1,500 RPM (I don't know how far below, because I don't want to lug the motor)
-Boost lag: When going from full coast under 2k RPM to suddenly WOT, it is about two tenths of a second before boost. When cruising under light power at or above 2k RPM, it's already right at the boost threshold so boost is practically instant. When using anything beyond quarter throttle, it's under boost already. When downshifting, boost is instant, no lag.

My turbo is mounted right in front of the transmission. I had the exhaust manifolds and all pipes up to the turbo and wastegate ceramic coated. I then wrapped them in high quality exhaust wrap and put a turbo blanket on the turbo. The wrap and blanket did make a noticeable difference. The turbo itself is a CompTurbo CTR 6767 Oil-Less. There is a break in period for that particular turbo during which the power and threshold is the same in 5th gear, but the lag is greater. After it breaks in, it's noticeably less lag.

The important thing with the turbo is not so much length of pipe, but heat and velocity of the exhaust gases. With the right engineering, a mid mount can perform extremely well. It also has the benefit of cooler charge temperatures before it even gets to the intercooler.

When autocrossing it, I don't notice any issues with lag. The extra power is there all the time. And since I'm typically keeping the RPMs above 3k when racing, it's always at max torque. Unlike a supercharger that peaks at max RPM, the max torque is readily available with a turbo in any situation that you care to use it. If I wanted to get fancy, I could have the boost pressure adjust based on RPM to make sure that the torque curve is absolutely flat all the way to redline. But, I like the simplicity and reliability of a regular wastegate :) Maybe when I install the new ECU, I'll play with boost management.

I can't properly put the experience into words. It's ridiculous. The power is ALWAYS available. I love it and there are absolutely no aspects of it that disappoint me.

Below is a link to some videos that I took of driving it last month. I had my "winter" tires on, so traction was somewhat limited and I had to modulate the throttle a good bit on the brisk accelerations.

https://rumble.com/user/ShiftedonTime

I think that your objective of being competitive with modern Porsches in Time Attack is achievable if you approach the car's setup holistically.

Feel free to drop me a private message if you would like to exchange contact information. I would love to see what you end up doing with your car.