GMKF

Hello 928 crowd !

So sorting trough my Porsche-"documentation" drawer last couple of months I found an old DeVek catalogue my dad must have fetched up during his visit to DeVek with my Grand Dad (who still owns a 928S4) in the late 1990's to 2000. I also still occasionally wear a DeVek T-shirt...After reading trough the catalogue I wonderd if DeVek's offered a 6,5L engine pack with 432hp and 472 torques to the rear wheels was the max displacementwise...
They said a 6.5L with 100hp per liter is in the works. I dont know how that tourned out...
But how far can you push the 928's engine displacement wise ?
Thanks !
Max

FredR

Some of our specialists are pushing 7 litres but whether such proves reliable remains to be seen. The proven engines generally displace 6.5 litres. I do not think 100 bhp per litre has been achieved n/a but not too far from it has. Something close to 600 bhp from a 6.5 litre motor has been achieved but I am sure you will get some firmer numbers from others.

Catorce

My 6.54L motor made 602 HP NA on an engine dyno. There are more powerful cars out there, I am told.

ptuomov

Mike Simard did 640 rwhp with 7L engine, so weven with 10% driveline loss that's 711hp or 101.5hp/l.

FredR

I knew he made some big numbers - figured that the additional capacity might reduce the output to capacity ratio slightly but clearly not the case. It would be interesting to know how well it holds up long term given the huge capacity and the specific output.

GMKF

Im assuming you cant order a crank "off the shelf" for this type of build
Someday I would like to rebuild a sad 928S4 to "If Kremer had raced 'em" spec

FredR

I suspect the crank is the relatively easy bit assuming it is one of the "available versions" but then Mr Simard is quite an artist. Getting the cylinders to that spec is something else not to mention the individual throttle bodies, cams etc etc.

Bigfoot928

the 6.5 liter and 7 liters had the same cranks. Bore size was different. From what we have seen there are less than 5 Devek stroker engines running out there, and more failures than running ones. Devek never really got near the 100hp per liter.

worf928

Catorce

^As you know, the only ones out there building big 928 motors commercially TODAY (i.e. not as a hobbyist) are Greg Brown and Carl Fausett. I am not sure anyone else is doing this, but I could be wrong.

GregBBRD

The only way to get to 7 liters is by machining the original cylinders away, completely, and cutting away large amounts of block material for new steel cylinders to sit on. What block structure remains is very minimal and since the Alusil material is extremely brittle, it may crack and fail very quickly...only time will tell.

Our 6.5 liter version has proven to be extremely reliable, while making very similar horsepower that the 7.0 liters make. We built an ITB version about 6 years ago that now has almost 30,000 miles on it. It made over 600hp on a DTS CERTIFIED dyno.

I just performed a 60,000 mile service (actually 62,500 mile service) on a 6.5 liter version. The really interesting thing about this engine was that it still had the same spark plugs we installed 62,500 miles ago....the owner never had a reason to change them! Other than deteriorating can gears (they actually had 110,000 miles on them) and a scary aluminum oil pump gear, with multiple cracks (never use an aluminum gear....Porsche superceded these to steel for a good reason) the sevice was completely normal. No debris in the oil filter, perfect compression. New belt, water pump, all 4 cam belt gears, rebuilding of the stock tensioner, and routine service parts....back on the road.

Suffice it to say that the terrible reliability that the Devek engines were renouned for has been solved in our facility.

I, personally, do not believe the 7.0 engines will last for any significant time....probably in the "sub" 100 hour range. There simply isn't enough crackcase left to support the cylinders.

hacker-pschorr

The 7 liters Mike Simard and Twin Turbo Todd built, the cylinders were cut out with new steel cylinders installed.

Details on Simards engine:
https://rennlist.com/forums/928-foru...-your-car.html

Photos of Todd's build:
https://rennlist.com/forums/928-foru...the-works.html

Todd scrapped the idea of a 7.4 liter, and strokers in general in favor of boost. If he ever builds himself a total custom engine again, we've been talking about a de-stroked engine with lower displacement. With his current engine surviving all these year past 8,000rpm and over 1,000hp, not sure he'll ever see the need. As he continues to lighten up his car, he's talking about turning the power down.

His twin turbo is using a stock (drilled) crank & rod bearings. Custom lighter piston & connecting rods.

The 7 liter Todd built does not have an off the shelf 6.5 liter crank. In his opinion the rod / stroke ratio is wrong on most strokers, he corrected this with the 7 liter and the 6.4 in Kibort's car (they have the same Moldex crank).

7 Liter:
110mm bore
3.700" stroke
6" rod

Kibort's engine:
4.085" bore
3.700" stroke
6" rod
This is a bored out block, not pressed in cylinders. Build photos here:
http://www.erik27.com/rennlistmotor/

Build notes from Todd here:
https://rennlist.com/forums/928-foru...l#post13342314

After these projects, Todd has also scrapped the idea of ever using the narrower and larger diameter Chevy rod bearing. In his opinion going narrower / larger diameter is the wrong direction & the 928 bearing dimensions are superior.

The motor in Kiborts car has a twin that I doubt the current owner will ever complete. Outside of that I think you are correct. The only known source for a 100% new stroker engine are Greg Brown & 928 Motorsports.

I suppose someone could twist Todd's arm to build one, but I honestly don't think he's interested in such a project.

Knowing their history, I'm sure such a build would involve boost over displacement. Side note, friend of mine has Mario Andretti's Kramer 935. Pretty sweet ride.

GMKF

Thanks for the awsome information I'll go on reading those specific threads...

If I remember correctly Kremer wanted to stuff a 928 engine with twin turbos into a 962 chassis to compete later on in group-c... But turbo-ing a 928 engine in that cramped space for endurance racing ? not really optimal in my opinion...

GMKF

That's good enough reliability in my book... Thanks for your info Just asking how much is a complete engine from you ?

GregBBRD

That question is impossible to answer....completely depends on what power level is desired and what options are chosen.

I've built engines that made 400hp and ones that make over 600hp...and everything in between. Engines that cost 30K and engines that cost 70K.....and every price in between.