Supercharging a 928
Discussion
V8mate said:
Just after general info really.
Supply and fit of kits seems popular in the States, but does anyone know of any supercharger kit suppliers here in the UK? (The kits seem more complex than many others)
Has anyone here done it? Any advice, pitfalls, things you'd do differently etc.?
Are early 928's CIS and later ones EFI?Supply and fit of kits seems popular in the States, but does anyone know of any supercharger kit suppliers here in the UK? (The kits seem more complex than many others)
Has anyone here done it? Any advice, pitfalls, things you'd do differently etc.?
Not quite right. All 928s had fuel injection from day 1.
In the UK, the 4.5 models and the S had mechanical CIS / K Jetronic injection systems. The S2 had L-Jetronic electronic fuel injection which improved economy and gives more tuning possibilities. The S4/GT/GTS had a more advanced LH system with eletronic ignition as well.
If supercharging an S2/S4+ will be easier to set up thanks to the SharkTuner product available from www.jdsporsche.com . Earlier CIS systems can be a right b
h to set up. You will probably need bigger injectors too if you're going for more than 400bhp.
Joel
In the UK, the 4.5 models and the S had mechanical CIS / K Jetronic injection systems. The S2 had L-Jetronic electronic fuel injection which improved economy and gives more tuning possibilities. The S4/GT/GTS had a more advanced LH system with eletronic ignition as well.
If supercharging an S2/S4+ will be easier to set up thanks to the SharkTuner product available from www.jdsporsche.com . Earlier CIS systems can be a right b
h to set up. You will probably need bigger injectors too if you're going for more than 400bhp.Joel
The Wookie said:
You might want to look a little closer into model years, I believe there was a particular sweet spot (might be 87/88 S4?) that had piston oil squirters which are ideal for forced induction. Some theorise Porsche were going to go F/I with the GTS.
Thanks. This is the kind of tip I'm looking for. The last thing I want is to throw five grand at upgrading a car only to find out that a modela month later had a stronger X part or better designed Y part.No problem at all!
I'm sure you've been on the Rennlist 928 forum, there's load of info on there and there are also actually a couple of UK based supercharged 928 owners on there, although I believe they're all Centrifugal type upgrades. Personally if I was going to do it, I'd spend the extra cash and go for a twin-screw!
Good luck with the conversion, I'd probably go for it if I didn't have a GTS, but aside from wanting to keep it relatively original, the 5.4 engine has a higher compression ratio and isn't really well suited!
I'm sure you've been on the Rennlist 928 forum, there's load of info on there and there are also actually a couple of UK based supercharged 928 owners on there, although I believe they're all Centrifugal type upgrades. Personally if I was going to do it, I'd spend the extra cash and go for a twin-screw!
Good luck with the conversion, I'd probably go for it if I didn't have a GTS, but aside from wanting to keep it relatively original, the 5.4 engine has a higher compression ratio and isn't really well suited!
I've always wanted a 928 and now seems as good as time as any.
I would always tend to buy the best I could afford so, naturally, was looking at GTS models.
But the price premium - a decent GTS being more than twice the price of a decent late S4 - didn't equate sufficintly (in my mind) to only 30 more bhp (I appreciate there were several other significant mechanical improvements on the GTS, but hey!)
Further digging seemed to suggest that £5k (plus or minus a bit) could offer as much as 150 additional bhp. Hence this thread.
Off-topic: A friend of mine had a 928 - a 4.7 - many years ago. My enduring recollection was that not only were the seats leather (black, with red stitching/ or possibly piping) but the entire dash and central console were also covered with the same stitched/piped leather. (Possibly the headlining too - though that may be a mis-recollection)
I've never seen another 928 trimmed like that. Has anyone else?
I would always tend to buy the best I could afford so, naturally, was looking at GTS models.
But the price premium - a decent GTS being more than twice the price of a decent late S4 - didn't equate sufficintly (in my mind) to only 30 more bhp (I appreciate there were several other significant mechanical improvements on the GTS, but hey!)
Further digging seemed to suggest that £5k (plus or minus a bit) could offer as much as 150 additional bhp. Hence this thread.
Off-topic: A friend of mine had a 928 - a 4.7 - many years ago. My enduring recollection was that not only were the seats leather (black, with red stitching/ or possibly piping) but the entire dash and central console were also covered with the same stitched/piped leather. (Possibly the headlining too - though that may be a mis-recollection)
I've never seen another 928 trimmed like that. Has anyone else?
V8mate said:
I've always wanted a 928 and now seems as good as time as any.
Welcome to my world. 
Having wanted one since I was 7, I got a late S4 a couple of years back and thoroughly enjoy it.As the Wookiee says, the guys on rennlist in the US rate the earliest S4 engines as being the best for supercharging; for the first part of the 1987 model year (precisely how much is a sbject of some speculation) the engines had oil squirters which bathed the undersides of the piston crowns with nice, cool oil. A feature rapidly deleted, presumably for cost:benefit reasons. The tricky part is, you'll never know for sure whether the engine has squirters unless you open it up, since there seems to be little rhyme or reason to their distribution! The main thing about the earlier (87-88) S4s is that they had a lower compression ratio, which makes supercharging easier and safer for the head gasket.
The one thing I would say if/when you buy a 928 is that you should focus on getting it running properly as the first order of business. The cars have a complex vacuum system which, if leaky, causes all sorts of odd running and low-power behaviour. The S4s and later have hot-wire MAFs, which age and fall out of calibration leading to weak running and poor performance. The electrics are complex (though not Satanically so, as some would have you believe) and I know from experience that a dodgy £3 relay can cause all sorts of perplexing problems until you find it, and change it.
The good news is that there's a great source of information at www.928.org.uk, and a number of extremely knowledgeable bods in the UK who can help with any problems you encounter.
All the best
Quaint
ETA: "full leather" which covered the entire interior with the same leather as was on the seats - dash and all - was, I think, standard on the very early cars and an expensive and rarely-specced option thereafter. 8)
Edited by Quaint on Thursday 29th April 15:52
Quaint said:
As the Wookiee says, the guys on rennlist in the US rate the earliest S4 engines as being the best for supercharging; for the first part of the 1987 model year (precisely how much is a sbject of some speculation) the engines had oil squirters which bathed the undersides of the piston crowns with nice, cool oil. A feature rapidly deleted, presumably for cost:benefit reasons.
SpeedTalk Forum said:
There are instances where the added oil will push an engine into failure -- an unintended effect. Porsche tried adding squirters to the wetsump 928 engine but that motor was so close to the edge with aeration and associated windage issues that they had to be withdrawn.
Last post
Hi V8, I have a 1982 928s that I have supercharged. I looked at the kits from 928 Motorsport in the states and could jus not bring myself to part with the £5k that the kit cost. I also spoke to Paul Anderson, who was in the process of fitting one of these kits on a 928s2 and was not overly impressed with the service and support he recieved from them. In the end I decided to knuckle down and build my own.
The full story is published on our group website at :- http://www.lemaniacs.co.uk/forum/index.php?topic=6...
I have used a centrifugal supercharger, twin screws are for efficiant, however if drive is lost to the centrifugal type the car will still run. All in all it was not the most difficult project in the world and the basics of how to piece it all together are fairly simple.
The end result is a joy to drive, I am running it at very low presure (6-7 lbs) and am currently getting 375bhp out of a engine that is 28 years old - with no problems to date.
I wish you well with the project and would recomend it to anyone as the cars are not slow to start with, but the extra power tranforms the car and is a constant suprise to all who see it in action.
The full story is published on our group website at :- http://www.lemaniacs.co.uk/forum/index.php?topic=6...
I have used a centrifugal supercharger, twin screws are for efficiant, however if drive is lost to the centrifugal type the car will still run. All in all it was not the most difficult project in the world and the basics of how to piece it all together are fairly simple.
The end result is a joy to drive, I am running it at very low presure (6-7 lbs) and am currently getting 375bhp out of a engine that is 28 years old - with no problems to date.
I wish you well with the project and would recomend it to anyone as the cars are not slow to start with, but the extra power tranforms the car and is a constant suprise to all who see it in action.
V8mate said:
I know it's 'only on the internet', but I read on another forum...
Interesting, and entirely plausible. The 928 engine is certainly known for windage problems, many of the guys who track them in the US use crankshaft scrapers or dry-sump systems to solve the problem. The main issue seems to be aeration of the oil - the resulting foam gets sucked up the oil feed pipe and hits the 2/6 main bearing first - the bearing then fails due to oil starvation.SpeedTalk Forum said:
There are instances where the added oil will push an engine into failure -- an unintended effect. Porsche tried adding squirters to the wetsump 928 engine but that motor was so close to the edge with aeration and associated windage issues that they had to be withdrawn.
Last postI like the idea of a home-made blower kit. Though really, I want a twin-screw setup running stupid boost.
Gassing Station | Porsche General | Top of Page | What's New | My Stuff