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Here's a fun little engine. Stock GT that's a 5.8 liter.
I've been building a bunch of these "little" strokers, for various reasons.
This engine was from a really beautiful GT and "died" a terrible death from "intake debris" let over from cleaning, before paint. The damage to the cylinder bores was so extensive that they would not "clean up" at the first (and only) Porsche oversize of 100.5mm. This greatly "limits" the choices of repair, especially if the original engine serial number needs to be retained. In this case, we used factory 104mm pistons and just for giggles, tossed in one of our custom GTS stroke crankshafts. This combination enables us to use a connecting rod greater than 6" in length! The lighter forged piston, with the long connecting rod, and the lightweight custom crankshaft makes these engines "change rpms" (rev) very quickly.
The result is a "mini stroker" of 5.8 liter displacement. In this engine, every single piece was stock GT (down to the 100,000 mile catalytic converter), except for the crankshaft, the connecting rods, the rod bearings, the pistons, and the head gaskets. (I'm building another version of this engine, right now, with more aggressive camshafts (thanks to Colin) and my custom header/exhaust system....I'll post that, when it is done.)
This engine totally transformed this car. So smooth and so easy to drive. It starts from any street corner in 2nd gear, without issue (I found this out by "sleeping" at a light and starting out in 3rd gear, which it also does easily.) Note that it makes over 300 ft. lbs of rear wheel torque all the way from 2200 rpms to 5900 rpms, which is extremely nice. The 341 horsepower at the rear wheels converts to 380 flywheel horsepower, using a very conservative 12.5% correction factor....easily surpassing a stock GTS.
One of the really important things we have spent hours perfecting, is making all our engines extremely driveable. Hours and hours of "Sharktuning" has given us a fantastic ability to make these engines silky smooth. They run smoother than any stock engine and "transform" into a screamer, when the throttle is applied. That "almost perfectly flat" full throttle fuel curve is what most tuners dream of.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Looks like the torque peak comes in the early "hump" like the S4 cams....does this engine still have the GT cams? Does the change in bore and stroke negate the effect of the GT cams?
Looks like the torque peak comes in the early "hump" like the S4 cams....does this engine still have the GT cams? Does the change in bore and stroke negate the effect of the GT cams?
Yes. Stock GT cams.
Universally, in the internal combustion engine, increased displacement reduces the effect of a given csmshaft....the increased displacement increases the velocity through the intake port, at any given valve opening.
There's a classic example of this, in the Porsche world. Porsche made a "906" race engine with now world famous "906" camshafts. 2 liter displacement. The engines "came on" at about 6500 rpms. Install those cams in a 3.5 liter 911 engine....completely tame.
Universally, in the internal combustion engine, increased displacement reduces the effect of a given csmshaft....the increased displacement increases the velocity through the intake port, at any given valve opening.
There's a classic example of this, in the Porsche world. Porsche made a "906" race engine with now world famous "906" camshafts. 2 liter displacement. The engines "came on" at about 6500 rpms. Install those cams in a 3.5 liter 911 engine....completely tame.
VERY cool! People like you are the reason why I love older cars more than newer ones!
I'm new the 928 stroker engine options. I notice many references to not using the original crankshaft. Which CS is used? Aftermarket? Are there several "stroker" crank options?
VERY cool! People like you are the reason why I love older cars more than newer ones!
I'm new the 928 stroker engine options. I notice many references to not using the original crankshaft. Which CS is used? Aftermarket? Are there several "stroker" crank options?
For years, the "standard" 928 "stroker" crankshaft has been 95.25mm, which allowed one to build a 6.5 liter (and bigger) 928 engine. Stock 4.5 to 5.0 engines had a stroke of 78.9mm. When Porsche built the 5.4 liter GTS engines, they increased the stroke to 85.9mm.
I've had custom cranks built to my own specifications, for years. I first used Moldex crankshafts (old school fantastic crankshaft maker.) However, in order to more closely "watch", control the process, and build a more modern design crankshaft, I now have my cranks built closer to me, by a very famous crankshaft specialty shop.
Since I have these lightweight, stiffer, modern oil passage, modern design "GTS" crankshafts built for replacements in GTS engines, it was easy to grab one of these, have some custom length rods made, in order to build these 5.8 liter engines.
This has quickly become one of my favorite engines to build. Very responsive....and much easier on the transmissions than the 6.5 liter version, with a minimal loss of horsepower. These engines are very quick reving engines, that really shine in our lightweight 928's.
Additionally, the reduced stroke radically reduces the piston speed, which fits nicely into my future development plans.
which fits nicely into my future development plans.
Development plans???
Custom headers???
Would this 5.8 litter engine be well served by the Devek level 2 header & X-pipe system I have for my (unopened from factory and great running) outlaw GT?
I hate to open that one up, but at 29 years, it has to be coming up on head gaskets... While I'm in there, why not do a build?
You know how it is... Mo Powah = Mo Fun!
Someone else asked about the $$$'s involved? While this can be extremely variable given the state of the engine you receive, what is the cost for a solid GT core?
Great work Greg! I am happy that there are those in this community that make it their mission and life's work to not only keep these wonderful cars alive, but improve them incrementally in ways the factory would have done had they continued the model
Would this 5.8 litter engine be well served by the Devek level 2 header & X-pipe system I have for my (unopened from factory and great running) outlaw GT?
I hate to open that one up, but at 29 years, it has to be coming up on head gaskets... While I'm in there, why not do a build?
You know how it is... Mo Powah = Mo Fun!
Someone else asked about the $$$'s involved? While this can be extremely variable given the state of the engine you receive, what is the cost for a solid GT core?
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The Devek Level 2 headers are adequate parts and are a close second to my own header system. I would expect good results when used in combination with this engine configuration.
In a few weeks, we will have another 5.8 running, with headers and camshafts, which will be a good comparision, for you.
The 5.8 conversion adds about 10K to the cost of a stock rebuild that needs new pistons.
As a side note, stock GT (and GTS) engines are generally more costly to rebuild, because of the camshaft wear issues associated with those engines.
05-01-2019, 11:12 PM
Here's a fun little engine. Stock GT that's a 5.8 liter.
