I am really tired of hearing discussions in the form of "how much hp can (name your part) take?" Especially in the context of cylinder blocks. While I am far from any kind of expert in failure analysis, I know that most automotive component failures are not due to a single, sudden stress that exceeds the ultimate strength of the intact, new, undamaged component. These parts fail due to fatigue, whic is caused by repeated loading and unloading of a stress on the part. Microscopic cracks develop due to metal fatigue. There is progressive damage due to fluctuating stresses and strains on the material. Cracks initiate and propagate in regions where the strain is most severe in three stages.

1. initial microscopic crack forms
2. crack progessively enlarges across the part
3. there is a sudden final fracture of the remaining cross section.

In materials testing, parts are subjected to different stress levels to produce an "S-N curve". The Y-axis is stress and the X-axis is number of cycles to failure. That S-N curve allows designers to make a direct estimate of the expected life of the part in terms of stress — a basic design parameter. By locating on the graph the number of cycles similar to that expected during use of the part, designers can identify the appropriate design stress. The "fatigue strength" of a part is refers to the number of cycles a part can endure at a given stress level. Ferrous metals also have a property called the "endurance limit". Below this level of stress, an "infinite" number of cycles can be withstood.

Most of the areas of the block are probably below the endurance limit and will "never" fail absent corrosion or other accidental damage. About the only "block failures" I have seen were on forced induction or nitrous motors that had been bored out. In that situation, cylinder walls will split. Crankshft failures may be related to block design. If the main bores are are not sufficiently rigid, there may be flexing in the main cap area leading to main bearing failure and eventual crank failure/damage. There may be failures related to improper assembly. I have seen cracking through the head bolt area into the water jacket due to overtightening of head bolts/lack of material in this area. And so on. But block failure per se is exceedingly rare.

Rich

 

What Rich said above. Well put.

 

Well, I just had a block that was good to 700 HP. At 701 it went *POOF!*
So THERE!

 

Very informative

As a consumer, do we ever get to look at/compare these "S and N graphs"?

 

figured i would put it here for him!!

seems like every post i read from fred has something to do with baxter...just picking on ya man!

 

There you go again! Everyone knows those blocks are good to at least 702hp

Rich

 

is that SAE corrected?

 

Rich

 

I hope your thread was not directed at me at all. The main point in my asking was specifically at what point would a move up to a Bowtie be benificial in terms of dollars spent. Im just thinking long term. I know you cannot put a number on how much a block can take, I was more looking for a roundabout figure with proper block prep. As you can see from my last post in my thread I got 2 completly different answers from 2 different builders, people with over 30 years in the buisness,in other words more experience than most here. Im just trying to cover all bases. Its just the most logical thing to do when spending your money.Anyway my block is not a LT1 casting , I dont know how it differs if any in strength from the 86-92 castings. I checked the search and could not find enough info to answer my question, so i posted my thread.

 

Go to http://www.key-to-steel.com that will tell you a lot about how steel and cast iron break.

 

Nothing personal at all, that why I started a separate thread. Please accept my apology if you took any personal offense. It's just that the concept of a block being good to some specific hp number doesn't make any sense.

Rich

 

No problem Rich, I do agree you cant put any number on how much a block can take since many have shown #s of how much they have put through them. I was more looking for the information of how they got the block to withstand x amount of hp and tq. It seems to be the running consensus that to be able to survive 600+ hp is to run block fill and studs, something I didnt even consider(aka block fill). Just so much misinformation out there its tought to shift through it. Thing I found funny was the one builder I talked too completly disregarded block fill as not nessary and to forgo it for splayed caps. Correct me if Im wrong but I think you,Rich, as many others running where I will be putting my block all run block fill. Anyhow, no offense taken. Its benificial to talk with many here to actually see what they run and what they did to get there.Good day

 

Thanks for graciously accepting my apology.

I am a big believer in partial block fill for stock blocks subjected to very high stress. I doubt if it helps the block per se, but I think it helps the main caps from moving around which can lead to bearing and failure and a messed up engine! Again, as has been said before, limiting overbore will help the block survive and will help it make power by promoting good ring seal. At least for forced induction, I'd give up the added hp from the bigger bore for less bore distortion. NA I'd go for the bigger bore though.

Rich

 

Rich, could you tell me who put your motor together for you and where they are located. Im in the market for a builder, and want to get started asap

 

You may want to talk to Bret Bauer who can be reached at
bret@bauer-racing.com He is very knowledgble.

My machine work was done by Proformance in Rochester, NY and assembled by myself and my friend Bob. You can reach Matt at:
Proformance Specialties
(585) 288-1499
1115 Main St E
Rochester, NY

Rich