Fastest928

For those of you who have been following this effort, we have now crossed the 3000 mile mark, and to date, no noticable oil usage on the freshly rebuilt "all stock GTS parts" GTS engine!

This is using the stock oil breather system...the same that is used on all S4's and 6.5 strokers...all which have low to no oil consumption at 3000 miles.

It appears that Porsche's engineers are damn good.

So, in conclusion, oil consumption has nothing to do with the change in block breathing that is so unique to the GTS, nothing to do with the stroke, nothing to do with the air breather system...it is simply, piston oil retention!

BTW, the block, even after over 140,000 miles was within spec to the 5th diget, that is .0000x". This cannot be said for any S4 or earlier 928! The factory engineers accomplished what they set out to do..increase the longevity of a block!

Next effort...dyno the beast and determine the value of super blueprinting on a stock engine. On a 6.5, it is worth at least 30 - 60 rwhp!

Marc
DEVEK

Steve Cattaneo

How is that niccasil engine block fairing? , any negative reports?


Happy New year to all. <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />
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Randy V

That's good to hear.

If those Porsche engineers were so smart, why didn't they install this oil breather system on the GTS at the factory?

Fastest928

Randy,

The oil breather system is not the issue....just as it is not the issue on any strokers built up from either S3, S4 or GTS's.

Since there are no longer replacement blocks being cast, Porsches engineers identified ways to make the blocks last longer....and they did it at the cost of a qt of oil every 500-600 miles!

Regards,
Marc

Shark_gts

Problems that stem or are combined from multiple sources are harder to understand and diagnose. With the small amount of observation we've seen, we believe engine or crankcase pressure, induced by the intake/breather system, works in conjunction with the piston design to cause oil consumption.

Sure changing the pistons is a solution, but that simply costs too much hassle and $ for your average stock GTS owner. So are there alternatives? Owners should continue to investigate breathing modifications simply for the ease and cost reasons.

Randy V

On the surface, your explanation sounds plausible Marc, but I just can't see it as being the primary reason.

The original 928 engine, with its silicon etched aluminum cylinders, was ahead of its time for longevity and strength.

I find it kinda hard to believe that Porsche made these changes to the GTS engine soley to increase the life of an engine that was already good for half a million miles with routine maintenance.

Steve Cattaneo

I think it’s a design flaw. A thin film of oil is left on the cylinder walls when the piston moves down. The oil rings wipe some of that oil off the wall. Not all of it since some is used to lubricate pistons, rings, cylinders and valves. I think because of a design flaw in the oil control rings (too wide a gap, wrong composition) there is too much oil being left on the cylinder walls allowing it to be burned upon combustion.


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Fastest928

The oil on the wall is the issue, and the factory know/knew it. We had a conversation on this topic when they visited us....pistons in hand!

Here are some facts:

FACT - stroker engines built with non modified GTS pistons burn oil at the rate of 1 qt every 500 or so miles

FACT - we have built 6.0 engine using those exact same non modified GTS pistons, and they have the exact same oil consumption as a GTS

FACT - we have built GTS engine with modified pistons and oil consumption is similar to a S4

FACT - we have built stroker engine with modified pistons and the oil consumption is similar to an S4

FACT - all our stroker engine use the factory breather systems and the ones using modified pistons use oil at the S4 rate or less

FACT - the issue is that the quantity of oil on the cylinder wall is not being scraped off and shedded at a rate suitable for low oil consumption.

FACT - ring design may be a factor, but their influence is not measurable

FACT - decrease the amount of oil spashed on the cylinder wall, and the oil consumption will decrease


This last fact should be of use to anyone wanting to minimize the effect of the GTS pistons inability to shed oil....keep as much oil off the crank as possible and your oil consumption will decrease.

I am not saying do not work the band aids, or everyone with GTS go out and rebuild your engins, just don't ignore the facts. They just might help you better understand the issues at hand and come up with a better band aid or solution!

My research and direction was to determine if the factory was "right"...and guess what: they are/were!

"With knowledge, there is the ability to change the outcome of any situation"

Believe it or not......

Regards,
Marc

srv

Marc...

Good informative post!

T_MaX

Marc, you must be doing something right. Max told me you rebuilt his 89 S4 to 5.3-5.4 specs and it hasn't used a drop of oil in almost 3.5k miles.

kudos to your corner

Shark_GTS, installing a dry sump the oil system could also be considered. The only draw back would be finding a place to put the oil tank

RH

Steve Cattaneo

Marc, <img border="0" alt="[king]" title="" src="graemlins/r.gif" />
With out revealing any trade secrets, are your 6.0 pistons chrome, iron, or other coated?

Did you modify the pistons shirt?

Did you decrease the factory piston to bore clearance?

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Fastest928

Steve,
The 6.0 pistons are mahles. Although we have used custom blanks with our developed coating. Out of three engine using this coating, we had one failure due to fuel washdown. We will only sell coated pistons to folks willing to take the risks, but offer no gaurantees.

We modify almost all the pistons we put into engines, as do most engine builders.

Piston to bore dims are crucial....especially if using german pistons which call for a .0008 piston to wall clearence.

Regards,
Marc

Shark_gts

&gt;My research and direction was to determine if &gt;the factory was "right"...and guess what: they &gt;are/were!

The factory was right to produce a few thousand cars that drink oil like beer at Oktoberfest? (relatively speaking). If that is being right, well you know the results. And they pissed off many GTS owners along the way and had to replace engines under warranty too. So that is no success. I am sure if you cruise into Porsche with your low-miles GTS and mention it drinks oil they might hold up a crucifix.

I have come to the conclusion that "superior" engineering doesn't always produce a better final product. The entire process of engineering is just as important. A guess is that with a limited budget Porsche may have forgone complete and exhaustive engine testing, as say during a complete new design introduction, since they were only changing a few components. The result was this oil consumption "feature" or attribute managed to slip through.

slate blue

HI this post is to Marc, Randall and any other interested parties, can I first say I don't disagree with anything you have stated Marc. I just want to add something and get some feedback or an opinion.

From my personal knowledge of the GTS engine, those pistons are forged and are chrome plated. The pistons in all other 928 engines are iron coated and cast. From what engineers tell me and my understanding the iron coating works well with the cast piston probably because it has a little porosity and the molecules are not so tightly packed and as such the iron has the ability to adhere quite well.

When things are forged and you drop a 90 tonne weight on them, their properties change, the ability to stick some coating on to this is much more difficult. I have seen GTS engines with slight score marks from what I believe is the chrome coating comming away or wearing given that it is so thin. Remember the factory has had extensive experience with forgings but with nicasil blocks not alusil. The GTS was the first and these pistons were KS if I'm right and then came the 944s2 and 968 Mahle pistons. From my knowledge they solved the problem, but look at the price!

I would be interested to know who AMG Mercedes use for their pistons as they also use alusil if I'm not mistaken.

Next topic, but it is related, drysumping, I believe the best way to solve the 928s achcilles heal oil comsumption and bearing failures, is to apply the BMW quasi dry sump system. Store the oil in the sump. But in a sealed container. Use the existing pump to suppy the oil to the bearings. The sucker pump would replace the airpump and you could probably develop some crankcase vacuum too. While I was there I would add a windage tray and crank scraper. <img src="http://www.momentoffame.com/snapshots/MomentOfFame/l28196.jpg" alt=" - " />

While I've got you Marc, the S4 intake manifold, I always thought it was pretty good, but according to others who have subscribed to 928 Forum magazine, it is quite restrictive. Can the runners be enlarged or inproved? Seems a pity to throw it in the bin. From my obsevations of the latest and greatest intake manifolds, they all have two throttle bodies with two air mass meters, can the s4 be reworked? I know I would be a big job but it may be the best to keep the resonances charges happy.

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Fastest928

Greg,
We build all our stroker engine with forged pistons...some are actual GTS pistons and the oil consumption is similar to the S4 which uses cast pistons. So I would debate the argument about forged components and metalurgy. And as such, , keep that argument with the chevy folks who use cast iron blocks and the oil consumption is due to piston to bore clearance...cast is tighter than forged.....that is another topic.

The factory's goal was to increase the lifespan of the block...and after measuring a GTS block with over 140K miles, and to the .oooo5th digit, there is almost unmeasurable wear....so, if that was the goal, then they acheived the goal.

The stock intake will support at least 430 rwhp. We have extrude honed and hand ported S4 intakes and on stock engine, no difference! Even on S4 engine with mods, no change.

Recently, testing was completed by another company demonstrating that a trick manifold produced the same results as a stock one.....I am waiting for the published results of the high tech manifolds as my modeling has shown that there will be minimal gains over stock.

We have been working on a manifold for over a year, built two prototypes that did not work, and currently, we are finishing the building of two pre-production intakes using our very unique runner system. They will be tested shortly on the white car engine (we have a perfect baseline) with no changes other the intake and the fuel/ign system. all other parts are exactly the same!

Regards,
Marc