I don't believe you can "differentiate the differences" by claiming "Getting to XXX HP via stroking and/or more RPM is much harder on an engine than achieving the same HP through forced induction". That's simply not the case and might give someone reading the thread a false sense of security. I've seen blown stock block engine blocks split in two and the owner is adamant that it never went over the stock rpm. I've also pesonally suffered breakages on various turboed engines that I kept at low rpms and with stock crank throws. Sure a high rpm motor with a longer stroke is stressed more and a forced induction engine is also stressed more too even at lower rpms and with a shorter stroke. I really don't want this discussion to turn into a childish 'my method is better than your method' pissing match like has been seen in past turbo vs blower threads.

 

Mike, I too do not want this to turn into a pissing match. Theres no such thing as "my way". You are making vague statements that are simply untrue when taken at face value. I feel they need to be cleared up. You can do it, or you can let someone else do it. Personaly I don't care who does it because I have no dog in this fight.

You stated that "I think it's safe to consider a 928 block as inherently weak and in need of reinforcement for high HP use". Your only qualifier was high HP. I think that your statement is misleading. You can achieve XXX HP by:

A: Increasing the stroke.
B: Increasing the bore diameter.
C: Increasing the RPM.
D: Increasing the amount of air and fuel in the charge.

I started to list what I feel are the problems inherent with each method, but I have decided that I will let you do it. Have fun.

 

Where can it be strengthened if the larger bore is required for the task at hand? The large steel sleeves are being registered to the case as well as is possible (Top and bottom) as described by Mike for his project and in Todd's pics for 90S4's engine. Maybe more locator pins (shuffle) for the bottom cradle, but what else is there?

We need the sleeves for either high boost or large piston usage, as the original towers balloon and crack and move and scratch. The piston choice is limited unless you wish to subscribe to the idea that Lindsay racing has come to, which is that Swain tech coating on the skirts of Forged aluminum pistons will work with the Alusil bore.

If that idea is refused you have wet sleeves or the original bore towers coated with Nikasil. No boost over 15 or so though with the stock bores.

I now have a 8cw Stroker crank from Scat. I want a huge 928 engine, and I don't want it to crack anything but the pavement under the tires. And I want boost with that. I'll replace the transmission when it blows up (We'll burn that bridge when we get to it as my grand dad always said).

How far are we to go before we are no longer modifying the 928 engine but simply sticking something in the car we love? I'd of thought we could go quite far before that happened.

 

Fabio, sorry but I don't like your tone and don't believe anything positive can come from any further interaction with you so please understand if I ignore you from here on, nothing personal, just trying to avoid conflict.

 

Brendan, it's a dilema to come up with a practical way to strengthen the block, nothing obvious stands out. Hammer's shuffle pinning may be the most practical way of improving things without darn near machining a new block from a huge billet. I did similar shuffle pinning on mine and included dowel sleeves along the outer row of 8mm bolts, 10 additional dowels. Another relatively easy job may be adding a plate to the lower cradle much like the common 'girdles' you see sold for American v8s. I don't know how much that will help, it could be a 50% or a .00001% improvement, I don't know but it would surely help. Heck, you could wad up some paper mache in plaster the outside of the block and it would help, just not very much . Just for kicks here's what I consider a snake oil attemp at block strengthening:
http://cgi.ebay.com/ebaymotors/ws/eB...3564464&rd=1,1
It may be stronger to take 200 dollar bills and tape them to the block.
I'm mulling over ideas that involve intricate machined steel braces in the main web area but nothing I can think of is easy to implement. SwayBar had a very good point when he mentioned tuning as important. Detonation is the one ever present condition that can cause harsh damage and always seems to occur eventually somehow, maybe prudent Hammer like mods along with careful tuning is all it takes to have a strong healthy engine?
BTW, about the sleeve register, mine just rests on the bottom surface because that's where the studs are anchored, down low. I'm glad it's that way and not shallow head stud threads at the top of the block, it helps 'tie' in the cylinder area. I'm sure Todd's is that way too. There are alot of characteristics of a 928 block that are very positive and it's a nicer canvas to start with than a typical American stock block v8, it just has it's own considerations to address just like any modified stock block engine. You don't see anyone drooling over an exploded view of a small block Chevy

 

Controling it should be easier in NA engine than in force fed even though displacement is increased. What removing cylinder towers does to way knock sensors see things is other matter. I think I'll cast new block from different aluminum with 120+ mm towers and insert dry steel sleeves in. Problem solved.

 

It is for sure that the high silicon material used for the block is very brittle and in the end this is the limiting factor. Porsche used special casting techniques to improve quality, but the fundamental problem still exists.

As far as knock sensing goes, the theory suggests that the shock wave generated by detonation is more a function of cylinder bore than anything else. Resonances in the block or cylinder itself are secondary.

Porsche used a nice wideband knock sensor in the 928. This should make iot easier to modify the filtering in the EZK for larger bore engines. Although I haven't fully investigated the filtering circuits yet, they appear to be analog filters which can be modified to suit larger bore diameters.

 

That sounds like a great idea Who's up for this job?

 

Well, failure analysis is always the best way right? What broke, and where did it start... We start there.

Did we ever receive pictures of failed blocks from anyone that has seen them?

Larger studs for the main girdle?
What about a steel lower girdle? Different properties, but it could be an alloy instead of what it is, which is aluminum, but a lower Si then the tower part of the block.

 

From what Greg described in breakages starting at the mains and going up the cylinder, here's what I envision being a likely fracture line and force direction, this is where the cylinder meets the main web. On mine it comes to the same depth but is a larger diameter for the sleeve.
Brendan, I too thought about larger studs but the strength of the threads in the block might be a concern.
Sterling, I know that 'billet' blocks have been used in drag cars. Just being made from a higher quality material than cast aluminum is enough to make the strength equal to iron. I can't imagine what it would take to obtain a chunk that big let alone machine it, (shudder).

 

Doesn't look to hard.

http://www.youtube.com/watch?v=QsmiIeAkE-o

 

Nice. Very very nice.

 

Brendan an others check out this Topgear clip about too much power and not enough weight reduction I hope you can see from this, the folly of persueing such huge power in a chassis that wont be able to handle it.

For my thinking the guys who have the strokers at 570 to 600 rwhp, that is going to be more than adequate for the job, with that type of power and the right rear end ratio you will have the ability to hit 220 mph! As for worrying about breaking gearboxes when it happens, add driveshafts, torque tubes, clutches etc. When it fact the car that is well sorted and lighter will be a quicker track car. Much quicker infact, I mean that Brabus can't even put it power down with super wide rubber and the most advanced traction control systems and they went down in power!

I think put your efforts into the right areas as I don't think there is many people on this board who can afford to spend big dollars on things that wont work.

Greg

 

Group buy.

 

Point well taken Greg. I think its still all very fun, and we should all do it before its illegal.