GregBBRD

Since other engines can do this, there's really no reason why our engines can't.

Of course, the "trick" with the relatively tall gearing of the 928 is to not trade too much torque for horsepower.

Red Flash

So, it sounds like you have created a kind of "GT Plus," and I am sure it runs fantastically. I always "imagined" that a full stroker would shift the 928s character in the spectrum slightly towards "muscle car" character. To me, the 5.8 approach sounds like a much more appealing route, especially with a manual and especially given the ability to use more stock parts.

But the "stock" aspect is where I am having trouble understanding what you are actually doing. What exactly is stock on this approach and what is changed? I tired to do the math just to understand it for myself and not to pick nits about rounding errors:
Standard GT: stroke 78.9, bore 100, displacement 5
Standard GTS: stroke 85.9, bore 100, displacement 5.4
Build Mentioned in First Post: stroke 85.9 (?), bore 104, displacement 5.8
Build with GB CS: stroke 95.25, bore 100 (?), displacement 5.9

If I had a damaged motor, like the one described in the first post, the 104 bore would be the way to go. If I have a stock GT with a block still in great shape, I would be hesitant to change the bore to 104. So, is this 5.8 concept still possible? Or, do you need to use the 104mm bore? Whatever the case, congrats! Very seductive approach that harmonizes with the overall concept of the 928.

GregBBRD

Our options become somewhat limited around what pistons are available, from Porsche.

Currently, there are no oversize pistons available for the '85/'86 pistons or the GTS engines. (I'm building a GTS engine, right now, with first oversize pistons. I had to gather up pistons from a bunch of various sources....some very old stock, with different variations in rings, which I had to "fix".)

In some cases, like the engine in this discussion, there were very limited alternatives.

The good thing about using a 104mm bore is that should anything "go wrong", there is always a "repair" size of 104.5mm.

As far as a 95.25mm stroke by 100mm bore (with stock, available pistons) is concerned, the connecting rods would have to be very, very short. I'm dubious that this would be a viable combination.

In short, I see no downside to the 104mm bore.

Darklands

Very impressive engineering Greg! You build so nice things so far away!

Achtung Höchstleistung
Seien Sie vorsichtig bei der Verwendung vom Gaspedal

[img]blob:https://rennlist.com/774a75ef-222e-4b61-acd3-efc205ddc4bd[/img]

John Veninger

Very nice Greg!

merchauser

greg, a lot of enjoyment for me is doing as much as I can myself, and also saving labor costs. are you willing to sell a component kit for building a motor like this?
I would bet there are others that would be interested as well.

Thom

I know you are doing very well to improve many issues on the various 928 engines which are generally very compromised, but a mere ~66 crank hp per liter with 4V heads... seriously?

Kevin in Atlanta

Yeah, but stock exhaust and intake and heads - not sure what you complaining about. This is a great starting point for the owner to go farther later. YMMV

Red Flash

Yes, but you have to look at the overall driveability of it, and how it matches the character and strengths of the rest of the car.

It sounds to me like a winning a proposition in a number of scenarios.

GregBBRD

.....I can only do so much using the stock cams, stock intake, stock exhaust (with factory cats) and only doing a displacement change, like in this engine.

Given those parameters, I'm extremely pleased with the results.

And like I said, this is a "base" engine, from which we can see if other changes help or hurt the power output.

Stay tuned....we "running in" another version of this same engine, tomorrow, with cams and headers.

GregBBRD

I can (and do) supply any pieces someone desires to people to build their own engines. For instance, all Kevin wanted, for his engine, was some connecting rods. He had a crank and pistins.

I also am very generous of my time and advice...ask Kevin.

However, think of me as a master chef. I can supply the main ingredients to make a special meal, but there are many tricks to turning those pieces into a culinary delight. Plus, me supplying just the main ingredients leaves the "want to be cook" at home, free to supply all the ansulary ingredients...and he could easily pick out the wrong tomatoes or the incorrect brand of herbs and end up with a disaster.

And then, there's the obvious question: Can the person getting the main ingredients even boil water, much less combine the ingredients into a great meal?

Kevin in Atlanta

That is an understatement. Thanks, Greg.