Attached is a sonic test performed on a production, siamese bore, 1997 Gen VI block used exclusively for 16 years in a marine application. The engine has been run primarily in fresh water, with four seasons in brackish. The measurements were taken from a 4.560” bore configuration. It has since been bored to 4.600”.

On the x axis the cylinder wall thickness of ~ .273”-.278” is consistent with the 4.84” bore centers.

The major (Y) thrust axis walls vary from a min. of .255” to a max. of .389”.

The minor thrust area varies from a min of .260” to a max. of .365”.

There is evidence of core shift in this block.

The production block decks will run ~ high .3xx” to low .5xx” In a closed deck application the decks tie the cylinders together, a critical element in bore stability. Always remove minimal deck material (less than 5% total dependent upon base thickness) or the cylinder case will distort increasing blow by and compromise cylinder seal. Avoid all blocks that have been decked beyond what is necessary to straighten or clean for Ra.

This block would make a good mid performance NA engine and bear watching with the increased cylinder pressures of forced induction. I have witnessed many production blocks north of 850 that have compromised/cracked the main webbing.

Bob

bob,thanks for posting this information,what do you say is a max bore for a gen5 block,i know someone who went to 4.530 and it failed,it cracked at the main webs.it was in a race car and did not make many passes before the failure.

Think you need to check your number Mike. 4.530 would make a stock 4.250 block 280 over. I personally wouldn't go anymore then .060 over on a marine block.

I believe he is referring to a 502 block. Which a 4.530 bore is .060 over 502.

you are correct,i was talking about 502 block.

Mike,
I would hesitate to put a hard number on that max bore value due to the disparity between individual engine blocks, due to core shift, casting anomalies, porosity and prior usage. Our approach would be to sonic test anything over a preset value (IE 4.500”), keeping the data with the block for future reference. You would then have the opportunity to base the future intended usage of the block on that data. If you have a block that tests well, there is the opportunity to invest in good parts for the build. If the block is marginal, it’s probably a good idea to keep the budget and scale in check for a more pedestrian build. With the understanding that everyone has some form of budgetary limitation I would add that sonic checking of your block is a very cost effective, inexpensive, measure.

For example, based on the testing data I posted, I would be confident using the above block in a NA application to ~775 HP. Some will make the point they may have exceed that number, however, it is still near the end of the road as per design limitations. While I won’t say it can’t be done, I will go on record that you need to proceed with caution. Start playing with power adders, crossing the 800 mark on a production (non Bowtie/Dart) block and you’ll find yourself tip toeing past the graveyard. At 1000 Hp it’s not a question of if, but when. As Billy Godbold says, “BYOM”.

Bob

so in other words mike the engines you built for joe b are grenade motors..ticking time bome and he wants to put 2171's on them lol..

bob,good info as usual,thanks for the reply.

im not sure what you mean but joe b has dart big m block.

As you probably know; Bob, is a friend of mine well over 6 yrs. I am proud to say; since then Bob, has supplied me with cams. He proved to me he could make a broader and higher power range than I was getting before. Even though the numbers from the prior supplier were good at higher rpms, he proved to me with the data collected the power was actually lacking where I needed it. Since then; we have always hit or exceeded those expectations.
As you can see from his post; his information is based on DATA. From having data, you can determine any issues that can or will arrive from this information. This is something that is in our conversations, from the start to the end.
So as expected from Bob, his post; to this thread is always based from data, and is not just from an opinion. Being said; this is a technical section. We should all try not to argue with each other. Sure we all have experience, we have successful builds and some that give us headaches, there are people who have deep pockets to buy the best of everything and others that only have a certain budget. Truthfully; in this business in which I have been for 24 yrs, you have to make wise decisions on what you can do, to fit the customers build, in a realistic decision.
It would be nice to be able to post information, without wondering if someone is going to argue with you or say; your a jackass. When I see name calling going on; I avoid getting involved or posting information pertaining to the thread. I will make a statement as you know; if the statements are from someone else. Repeated, or questionable. Getting into name calling, just lowers yourself.
I would think, that all of us would like to be able to pick-up the phone and talk to one another if need be.

Thanks for you time, Lets all smoke a PEACE PIPE We need to set an example for; Wasington