When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
For a given peak power and peak power rpm requirements, an appropriately designed four valve head will make more torque at low rpm than an appropriately designed two valve head.
That‘s true but if you Drive my S3 and than the S2 you will say the 2 valver is more fun because the engine likes to rev and the 4 Valve Engine has the characteritic like a tractor.
Over all the S3 has more torque and HP but the emotions make the S2 with the Engine Sound and the Party from 4.000 rpm to 6.500.
For a given peak power and peak power rpm requirements, an appropriately designed four valve head will make more torque at low rpm than an appropriately designed two valve head.
No debate/no doubt about that.
However, that's not the point, here.
I've got clients who insist on having 2 valve engines in their 2 valve vehicles, but also want them to be more modern and more practical.
Because of all the pieces I've developed over the years, I'm in a unique position to built that vehicle.
That‘s true but if you Drive my S3 and than the S2 you will say the 2 valver is more fun because the engine likes to rev and the 4 Valve Engine has the characteritic like a tractor.
Over all the S3 has more torque and HP but the emotions make the S2 with the Engine Sound and the Party from 4.000 rpm to 6.500.
Karsten, I fully agree with you. I have never driven a S3 but my impression is that the S4 camshafts are too mild.
Furthermore, the gear ratio of the accelerator pedal is so great that you have to step on it very deep before anything happens.
My wife's BMW Alpina 4.6L V8 has a much nicer and more agile engine. This engine also has an intake manifold of modern design (pictured), similar to the one of Porsche Panamera V8 or the custom manifold made by Mr. Brown, which makes the engine rev up much easier. The camshafts in the Alpina engine are a lot sportier than in a 928 S4 (pictures).
Åke
This is what John Gill recently said about his new engine: Greg knows this I haven’t posted my results yet on the new engine , its makes much more power over the previous unit . Wednesday had a chance to have a run at the track day , I ended up being the entertainment , as I managed to stick the car into the fence , damage sustained to the frontal area , mostly cosmetic but ended the day .On a positive note the car had ridiculous acceleration so different from previous , will be very easy to get into some serious speed trouble on the longer tracks with higher speed potential.
Åke
I take the liberty of posting the latest dyno curve from John Gill. 393.5 kW @ 6900 rpm at the rear wheels is very impressive. That is 535 wheel HP which is well over 600 HP at the crank.
This is John Gill's comment on the updated engine:
The car is scarily fast I am a lot more conservative than I use to be, lucky I upgraded the brakes which are up to the task, but I believe that car would be at least capable of redline in top gear which I up towards 300 kph in short squirt. This is where a serious off could occur, I have already had a couple near moments, it is now nothing like the previous characteristics of the car previous to drive.
Åke
Quite simply, I've got quite a bit of demand for high output 2 valve engines for the early cars. I've got several clients anxious for these engines, making the investment in time and effort simply an investment in our shop's future.
Worth noting, I never go hunting for the maximum amount of airflow I can possibly make. Making huge intake ports with higher than necessary airflow isn't my goal.
I carefully match my airflow requirements to my needs, in order to retain velocity at the lower rpm and mid rpm ranges. This increases drivability by making additional torque and horsepower in the entire rpm range. (5.8 liters doesn't hurt, BTW.)
As I mentioned above, Euro S2 engines are very "soggy" below 4,000 rpms, due to terrible volumetric efficiency in the lower rpm ranges.
While tolerable, due to the lighter weight of the 2 valve cars, certainly not optimal.
Once volumetric efficiency reaches ~110%, increased airflow does absolutely nothing, unless the rpm limits are greatly increased. (At 7,000 or even 7500 rpms, there is a limit to the amount of airflow required. More airflow is only useful if the rpm limits are greatly increased.)
Making 500 hp at 9,000 rpms, with huge camshafts and poor intake velocity (which results in an engine that is terrible below 5,000 rpms) is completely useless to me.
None of my clients have any desire for this engine or the desire to brag about how much horsepower they have at 9000 rpms. They desire smooth drivability through the entire rpm range, with great performance, very efficient fuel use, while easily passing any emission test, if required.
Higher torque through the entire rpm range, with excellent usable horsepower and fantastic driveabilty at reasonable rpms is my goal. This is what I do, and what I've always done.
However, this engine is only a tiny part of our equation:
Combine an engine, like this, with all the ancillary pieces I make...butter smooth clutches, greatly improved suspension components, extremely durable torque tubes, greatly improved limited slips, extremely durable transmissions, improved braking with extremely "high end" ABS, greatly increased A/C performance (I can go on and on, but you get the idea) and we can create a really fantastic "modern" 45 year old car!
Mr Brown, I have a 1985 928S (LH Jetronic injection) which you over there call the S2 Euro. I can not say it is sloggy below 4000 rpm but it feels more alert over 4K than the S4. The S2 camshafts are not as conservative as for the S4 engine (picture).
I have been porting cylinder heads since the midle of the 60's so I think I know what I am doing. Huge intake ports with low airflow velocity do not work well with hot long-duration camshafts but can work well with mild standard camshafts.
The S2 engine has 40 mm intake ports which are too large for the intake valves (45 mm) used. If you increase the size of the intake valve to 48 - 50mm, you get a much better ratio. The secret of getting good airflow and thus a higher degree of cylinder filling is not large ports but in many cases oversize intake valves.
The S2 engine standard intake port flow very well and is difficult to improve on.
Although the oscillating parts of the S2 engine are heavy, they can be made lighter in order to spin the engine a little higher. Larger displacement is always good to get a more elastic engine with improved torque.
Åke
I think Porsche know the 928 could make far more Power but the top sportscar was the 911 Turbo.
Imagine the engine from the first Cayenne Turbo in the 928.
The 928 was to expensive to build, to good to earn money, a dinosaur.
Mr Brown, I have a 1985 928S (LH Jetronic injection) which you over there call the S2 Euro. I can not say it is sloggy below 4000 rpm but it feels more alert over 4K than the S4. The S2 camshafts are not as conservative as for the S4 engine (picture).
I have been porting cylinder heads since the midle of the 60's so I think I know what I am doing. Huge intake ports with low airflow velocity do not work well with hot long-duration camshafts but can work well with mild standard camshafts.
The S2 engine has 40 mm intake ports which are too large for the intake valves (45 mm) used. If you increase the size of the intake valve to 48 - 50mm, you get a much better ratio. The secret of getting good airflow and thus a higher degree of cylinder filling is not large ports but in many cases oversize intake valves.
The S2 engine standard intake port flow very well and is difficult to improve on.
Although the oscillating parts of the S2 engine are heavy, they can be made lighter in order to spin the engine a little higher. Larger displacement is always good to get a more elastic engine with improved torque.
Åke
I bought (and still use, although modified) my first flowbench when I was 19 years old....a Superflow 110. That was in the very early 1970's.
I, also was modifying heads before this, in the late '60's.
I strongly believe that testing intake ports at vacuum levels not found inside an internal combustion engine at WOT is a huge mistake (not realistic), so I'm conservative on the amount of "intake suction" I test with.
I agree/use bigger intake valves in my 5.8 liter 2 valve engines.
The larger displacement allows improved velocity through the larger intake valve/port, allowing the use of the larger valves.
As you are certainly aware (also being one that concentrates on airflow) there is much more to making a good cylinder head than just stuffing in a large valve.
I'm guessing that you and I, in the same workshop, could create some amazing engines.
And an update to my race car project
, thanks Ake for posting the graphs , aside from this I found something else to break shown here , interesting thoughts from the racers , I have spare one of these but if this is the fuse , than will I move the problem somewhere else , i.e. GB has better quality units of these (alloy) .
And an update to my race car project
, thanks Ake for posting the graphs , aside from this I found something else to break shown here , interesting thoughts from the racers , I have spare one of these but if this is the fuse , than will I move the problem somewhere else , i.e. GB has better quality units of these (alloy) .
Nice work on your engine, John!
I'm amazed that any version of a 928 clutch, regardless of how it is modified will "hold down" your engine...this was always the weak link, for us.
I do make 300M clutch shafts...and 300M torque tube shafts.
However, there appears to be some external damage of your clutch shaft, where it is broken. If that shaft hits inside of the T/O bearing collar, it will quickly turn red hot and fail...regardless of the material it is made from.
A couple of suggestions:
1. Make sure that you insert the clutch shaft as far forward as possible in th pilot bearing, when you assemble the clutch. Then pull it to the rear 2-3mm's, before tightening the bolts.
If you insert a clutch shaft into a pilot bearing held in your hand, you will see the issue. There is very little support for the shaft when inserted all the way forward. (Porsche fails to mention this, in the Workshop Manual.)
2. Make sure the front torque tube bearing has not lost (or has damage to) the plastic bushing, which takes up the dimension between the shaft and the actual bearing. Also make sure this bearing has not migrated to the rear. Any slop/migration will result in "whipping" of the torque tube shaft and allow the clutch shaft to contact the inside of the collar.
For bigger horsepower engines, I would strongly recommend Constantine's bearings, which are way more "robust" than the stock pieces and fit both the torque tube and the torque tube shaft far tighter.
I also move this front bearing forward 4 inches, to better support the torque tube shaft, in high horsepower applications.
If either of you have done this, would it be possible to stick the 48mm intake valve from the 1989 944 NA 2.7 into a 928 head?
I know Porsche increased the bore of those engines to 104mm, but the valves are also spaced wider apart in a 944 head which is why they did that.
I think that could improve flow through the 2 valve head by a noticeable amount. It certainly was noticeable in the amount of torque that a 2.7 made VS the 2.5 with only a 15 hp increase otherwise.
If either of you have done this, would it be possible to stick the 48mm intake valve from the 1989 944 NA 2.7 into a 928 head?
I know Porsche increased the bore of those engines to 104mm, but the valves are also spaced wider apart in a 944 head which is why they did that.
I think that could improve flow through the 2 valve head by a noticeable amount. It certainly was noticeable in the amount of torque that a 2.7 made VS the 2.5 with only a 15 hp increase otherwise.
Yes. They work great.
At over $400 each retail, they are expensive.
However, because I'm always very concerned about reliability in my engines, the legendary Porsche quality is a definite attraction.
Moving the valves outward, because of the increase in bore size, also has some attraction, especially if one has the desire to greatly enlarge the intake port (which I do not, as mentioned above.)
However, the ability to unshroud the valve in the combustion chamber, greatly improving the combustion efficiency, likely trumps this.
The sleeve which fits around the shaft shows small rub circle internally , it looks as though as the shaft failed it grew in area and rubbed the sleeve , you see if you blow up the photo that the shaft has a peak at each side of the fracture point , my observation suggests that it started to twist before failing , the pedal started to engage long just before failure , I thought this strange now I know why .
The clutch is not stock , Jim Berry from race clutch here (Stanthorpe) removed all the self adjusters , (he has been a Sachs agent for 40 years) and modified the plates for 4 fingers and increased the clamp pressure .
The clutch is magic to use with no semblance of slipping , and very uniform and light , it is converted to use Tilton pedal box in the cockpit with a quick release connector.
I am seeing him tomorrow for a backup set .As he is getting older and as these knowledgeable people disappear the knowledge goes with them , young peaople are not interested in this line , I will post a photo of his plates later on.
07-24-2021, 04:16 AM
Race car update
