Engine blocks and strokers
 

Where (if anywhere) can I find detailed technical data on our 928's? I have the shop manuals and have read through them repeatedly but cant really find the detail I am looking for.

What are the differences/changes in the engine blocks over the years? Are some superior to others? How much over bore can these blocks handle? Can some be bored further than others? Were there changes in cooling or oiling? What is the best block to use when building a major bored and stroked 928?

I have been digging through the posts and would love to hear further details and experiences, dos-donts, what worked, what didn't, opinions on parts and suppliers from others here who have built or are building bored/stroked high performance 928 motors. Im looking to build very high horse street/track motors for my 928's where reliability driveability and maintainability are not sacrificed. I would rather overbuild than break something.

By far the best source is the set of 928 tech info CDs prepared by Jim Morehouse. Jim's email is jim928ATptd.net Change the AT to @ - just trying to stave off the address-gathering robots.

We have no financial or commercial relationship with Jim...

General rule of thumb is that 95mm and 97mm bore blocks can be bored to 100mm but not much more, 100mm can take 104mm pistons with some luck. There are largish variations between similar block types on how wide towers they have. None of this is documented in any factory docs that I know of. More data here.

Vilhuer wrote:
>>>>General rule of thumb is that 95mm and 97mm bore blocks can be bored to 100mm but not much more, 100mm can take 104mm pistons with some luck.

While Vilhuer is correct regarding the general rule of thumb, I think more specifically speaking Reynolds states that the minimum tolerance for wall thickness is .250", although there are overbored motors out there running in the .220" range without issues. My motor has some walls that will be even thinner, so I guess we'll know the true limits whenever it finally gets assembled.

With all of the recent developments in forced induction systems for the 928, I think you will find easier paths to 928 horsepower by going with a supercharger or one of the up and coming turbo kits.

There are a few of us out there that still believe that there is no replacement for cubic inches, and are building the big motors just for the love of engine building, but dollar for dollar, were are getting much less bang for our buck.

The best block for overboring is the one with the thickest walls, but there hasn't been any real trends in finding thicker wall blocks. I've seen a pretty thick walled U.S. Spec '85-'86 block, and I think others have as well, but I don't know if I'd rely on those model year blocks to be consistently thicker than an S4 block. You will need to sonic check the block to be sure of what you're getting.

The early '87 S4 blocks had "crank sprayers" designed into them, which at above 4 bar open and spray oil onto the cylinder walls under the pistons. The 928 is known for having windage issues at high rpms, so this may not be a blessing, and most likely contributed to Porsche discontinuing the design in the middle of the MY run.

Stroker cranks are hard to come by, but most out there were built by Scat, although Muldex has made some as well. The strokers run Chevy rod journals, so you can use Chevy rods (small end needs to be resized if you run Porsche pins), and the Oliver rods I am using don't appear to have any clearance issues. If you go with another rod, you may have some clearancing to do in the block.

It appears that the stock radiator can handle cooling the big motors, but I think just about everyone goes with an after market oil cooler.

Stroker builidng is pretty much a learn-as-you-go process, because you are basically building a full custom motor. You've got parts that weren't engineered together, and you are now forcing them to work together in a stressful environment and there isn't a lot of collective experience out there (yet) to say what will or won't work. Not exactly like building a 383 small block chevy, although there are a lot of strokers that should be completed in the next couple years.

Good luck EB338 if you choose the path to strokerdom, there are many of us on the path right now, just haven't reached the end yet.

Eb338 few stroker engines actually exist .... very few and a basic 6 liter stroker dynoed 318 hp at the rear wheels and 384 ft lbs torque circa 1999 , the big 6.5 with head and exhaust mods hit 407 hp and 460 fts . Current " race " engines are around 500 hp of which 4 - 5 exist . Building a 928 race engine is definitely swimming up stream nothing about it is easy....nothing ! Scatt has made the most 928 cranks but I do not think anyone has ordered any more in the last few years (they previously required a 10 unit minimum order) Moldex in Michigan has made several including some of the very early ones and will do them one at a time it just always takes a LOOOOONNNNGGG time no matter what the initial estimate. The camshafts quickly become a limiting factor GT cams are much in demand. Starting a project with anything less than an S-4 1987 or newer makes the task doubly difficult. Brenden C. is our Poster Child for how long the process can take at THREE YEARS and counting since his S-4 was last a running driving car.

I resemble that comment Jim.

October 2002. Trans on the 81 died (for the second time) and the 89 LH and EZK took a crap at the same time (I now suspect foul play from a previous mechanic resolder job on the EZK)

The engine I built *in my avatar* and have now sold was built in about 8 months.

The cylinder wall issue, which is on the original poster's mind, is a big one. How thin can we go with boost if we put a deck plate on? Can we wet sleeve like the 944 guys? That would give us 106mm or more. Kevin Vogel on the 944 boards has even larger bores. I hope he learns even more and can share with the community at large.

Imagine a stroker or GTS cranked motor with 106mm bores.

What can we do with 800hp? 900hp? I have no idea, but I know its going to be fun for some to fin out what breaks next.

B , Note how I cleverly misspelled your first name to disguise your identity :) ...So you sold the engine now the 89 engine goes into ? and the GTS crank into ? I would not obsess on getting the maximum bore ....two guys been out drinking nearly all night on the shortcut home from the bar as they cross a bridge over a small stream both felt the call of nature .As they stood there in the dark one mentioned to his friend "Boy that water is cold" Friend answered "Yea and it is deep too !" the morals of the story , first liar does not stand a chance and the last few inches really do make little difference.

as of jan 05, scat will do 1 crank at at time now, but it's still 6-8 weeks and moldex does take forever but does an awesome unit.... IIRC, mark kiobort proved we can use 85 cams and get great performance at a fraction of the cost/hassle of finding GT stuff... if you do nicom coated bores and use aftermarket pistons, you can save even more... carrillo and pauter rods can be had cheap w/cheby specs too...

just dont' convert a pre-87 and you'll do it for about the same cost as an OH w/factory parts and be way ahead of the game... unless you are a genius like brendan, be ready to open up the wallet to have someone experienced do it right the 1st time....

ah the block - right.... rumor has it that the 85/86 blocks are a bit thicker on the cyls, so the 104.5mm or 104mm is easier/safer to do, although IIRC there have been some good results w/later blocks too...

dont' forget to open up the valves and heads for the extra displacement WYiT.... have fun!!

Heh, I did notice that Jim. I do need a witness protection program...

78 engine is sold to a gentleman who will use it the same way I was planning. The 89 engine and heads will go into the 78 body (which is painted and almost ready for interior) with megasquirt as the EFI and ignition. Pistons are coated for boost, crank will go to Whittier on Friday, and heads may get the valves Mark A has suggested. I'm teetering on rebuilding the heads a bit. I'd Really rather drive the damn things finally, but I do want to do it right the first time. 75k miles wasn't as wear free on the 89 motor as some may suggest. Play in the valve guised COULD be normal, but I need to put a gauge on them. Valves were very sooty, as were the chambers. Rod bearings wouldn't have liked more then a few track days at the point I pulled them out.
A crank scraper and the crank drilling will need to be the end of it. No dry sump on the 78. 7k redline with boost at about 11psi with cometic gaskets.

Where is that middle line where its not so much fun anymore as neccesity? Many guys here still need to find it. I found it over 2 years ago and have passed it by a wide margin.

This is still a great interest. The rod size AND the side measurements must be changed. I also understand that you would still pay over 1000 for really good rods. Custom rods are already 1200-2k. I'm not sure if we should be relying on the 500 dollar rod idea, when even the chevy guys, when pressed, will tell you to buy carillo and the like. NOt the 400 dollar eagle stuff.

I had SOME experience over my shoulder, though I must say that it was more of an opprtunity to do it right the first time becuase I had all the right tools at that shop for the changes I made to the springs on the 2V. This second time around, I should be more efficient, and I won't have to ask as many questions - but I will still be learning.
To a machine shop, rods and cranks and pistons are just that - rods cranks and pistons. The blocks need special people and machines, (sonnen(sic) hone), and the heads can't be thrown around by monkeys either. I'm no Genius, and you don't need to be. Just read avidly, here, and on the internet, and in real books by people like A. Graham Bell, and of course Smokey, though I would like some more updated info. We will have to wait for some guru to retire again though.

I'll lightly port match again, and the S4 intake needs those side plates to open up the trumpet intake areas. What mark K has found with webcam or elgin (I forgot) and those 85 32V cams is great. I may do that to lower the effective compression a bit on the 89 motor for more boost. I need lag to tell me how much it will account for.

elgins did the cam work for mark, IIRC under $500.00!! wish I'd had the mojo to try them out instead of just going w/the GT stuff - could've saved $1400.00.... glad somebody finally figured it out for the team though!!!

good point on using experts for each component... it only makes sense, although it does open the door for finger pointing a bit - so you do have to be on the ball enough/have the right players to keep everyone from turning it into a pissing contest or "doing it their way" ie full race vs street AT car, etc...

I just used carrlllo A series rods - $1100 or so, good to about 600/800chp (depending on revs/pistons/etc), used by bracket racers/sprint cars/etc... at 580gr they seemed plenty strong for my old gal w/418gr pistons and low revs (stock limits).... you might need the heavier stuff that mark A uses if you're going into the boost zone/higher revs w/heavier pistons.... pauter makes a really neat custom rod too (iirc around $1300)... TI rods seem to be the real bomb, but at well over $2.5k, way beyond my budget/needs... seems each engine builder has their own "mix" of favorite stuff too - which indicates theres more than 1 way to skin the old cat, within limits....

IMO, bell has some neat ideas - but our 4V heads seem to defy/or be beyond his dated wisdom - like for quench - so IMO dealing w/a 928 pro is really worth it.... course, what I did was not an experiment as much as just following along what's been working already for devek, mark A and others (w/a couple of my own hair brained ideas), but your project is decidedly rather innovative - so you have less to go on for reference there mr B....

interesting note on the trumpet intake areas - anybody ever really confim gains w/a stroker running the 968 stuff w/them??? heck, all I did was have the bowls blended for the larger valves, not much intake work so the manifold fit just fine... even my ported exhausts lined up nicely w/the devek headers, so I didn't even bother there either.... seems to dyno right where I'd hoped - but you never know for sure "what got missed" w/out taking it apart, re-building w/different stuff, re-dyno, etc - a ton of $$ and time just for a few more (or potentially less!!) HP on a street car that can't keep the tires from smoking already... in fact, I've gotta get an LSD before I mess w/any more power - guess you can add that to the list for any stroker or FI car too... :)

oh yeah, a block thread - gotta admit, a nice 502cu cheby block does seem to offer some benefits.... oops, did I open up that can of worms so soon??? sorry... hehehe....

Oh so true.......

The boost on this 5.0L block will only be about 10 or so, and I felt that the "forged" 928 rods from the early cars (damn, I gotta email H) would do in this "nearly stock" engine. Some outer margine polishing on the exhaust valves, and making sure there is nothing sticking to the intake valves will be as much as I will do on the heads (mentioned porting)

Just had an interesting convo with a 944 guy. Seems a 5k race 2V 944 head from Millege passes 300cfm, (not sure of port velocity if Greg Grey is watching), and low and behold, the STOCK, 300 dollar ebay S4 head this guy had tested did... 300cfm. Nice.

Dyno results on the intake plate spacers were from the guy in LA that disappeared after he sold his S4. Not sure, but I saw that when I took the intake off and immediatly emailed Z asking what was up. I suggested machining the reinforcement lines off the back of that plate, but obviously maybe the spacer is a better and easier idea. Maybe I will do both. :)

Brendan,

Still have set of early S4 rods hanging in my shop, looking for a good home. :)

Ah, thanks Adam. H has promised me his rods for many moons, and I have yet to pay him. I will honor my promise to pay him.
I appreciate your offer.

How is your engine going? And new news on pistons and bore tolerances? I will be there soon, but hopefully won't need to change anything. Which rings did you end up using?