XXO/BVGC '38 Chevy Coupe Build

[38flattie]

Well first off, congratulations on some pretty impressive numbers.  What is frightening is that you are doing it with only 3 mains.

Frightening? I prefer 'dangerously exciting', or 'tantalizingly nerve wracking'! Lol!

But I’d check to see if there is a problem first.-Chris, with the HP I'm trying to achieve, I have to assume everything is a problem at this point, and can change that stance once we are convinced it's not.

Yeah, I know, you asked for "experienced advice" - would you settle for an outside the box thought?.  Absolutely-Thanks!

I’d concentrate my efforts on the center – it’s the least supported.-I agree.

Can you machine a girdle with the center cap integrated - one piece - and splaying out parallel with the webs?  That is a definite consideration, along with most of the suggestions above.

Outside the box. Why not tie the main girdle to the heads outside the block. With gathering bolts of some type.
Richard

Richard, I'm going to discuss that idea with Dale!

Thanks!

[SPARKY]

is there a head bolt that lines up with your new main caps---you being a driller you may figure a way to DRILL down    and tie in!! 

[38flattie]

Sparky, the head bolts are on an angle to the main bolts.

I drill directional wells, but haven't yet tried directional bolts!

[Milwaukee Midget]

Outside the box. Why not tie the main girdle to the heads outside the block. With gathering bolts of some type.
Richard

 

Look up the K series Rover/MG engine.

http://en.wikipedia.org/wiki/Rover_K_engine

Maybe think of the girdle as the crankcase - the block as the cylinders sandwiched between the girdle and the heads.

[SPARKY]

we want them to be at an angle  if we can get to a main cap on an angle---would be very similar to "splayed" ---reverse angle--- just doesn't rely on original block main webbing for strength has the whole block to 'sandwich" for strength

[38flattie]

Duh-of course we do! I'll check out the spare block when I get home, but I don't think it will work.

I'm thinking a real heavy bedplate, cross bolted through the outside of the block, into the mains, with a center main splaying out parallel with the webs, like Chris mentioned.

The cross bolts could go through a 'plate' on the exterior of the engine, to help 'spread' out the load.

Anyone think of a reason this won't work?

Of course, I'm REALLY open to ideas here!

[maguromic]

Buddy, Another problem you will run into with high boost is keeping your bores round.  Think about posting your block and maybe adding a 1" square band around the block, we are going to be doing all this to the GMC.  I first saw the band on Pete Ardema's V4, its a turn buckle style and he just tightens each side to where he wants it. Tony

[38flattie]

Tony, that's a very intriguing idea!

Do you have any pics of this setup?

OK, I'm going to need 25-30psi boost. How do I figure cylinder pressures, based on that?

Is there a rule or calculation, to figure out if the cylinder should handle the pressure, cased on wall thickness?

[maguromic]

Buddy, its really easy to build out of 1" or 3/4" square on an inline engine like the V4 or in our case the GMC.  On a "V" style motor you would have to do some fitting but it can be done.

This is Pete's V4 motor, notice the band with the turnbuckle below the head.  Tony

[Tman]

Also a "block posting" link I think Tony showed me.

http://www.muller.net/sonny/crx/engine/posted.html

[hotrod]

This is the way the subaru performance community pins a block to stabilize the cylinders.




Image source= http://forums.nasioc.com/forums/showthread.php?t=2267859

They do a plunge cut with an end mill then push an aluminum dowel into the cut and then finish it to the surface of the block.
This way you are supporting a length of the cylinder wall not just a point and at the very top of the cylinder where your peak cylinder pressures occur.
Peak cylinder pressure occurs with the piston only about 11 -14 crank degrees past TDC, if you work that out geometrically the piston is only a fraction of an inch down from the top of its stroke when peak cylinder pressure occurs.

This method also does not breach the exterior of the block and create a possible coolant leak path.

[edit] the pins are only an inch or so long.[/edit]

Larry

[Tman]

That is very cool info Larry!

[RichFox]

Block pinning is good for die cast blocks. Don't know about old Cads.

[Jack Gifford]

... Peak cylinder pressure occurs with the piston only about 11 -14 crank degrees past TDC, if you work that out geometrically the piston is only a fraction of an inch down...

However, the force on the walls (pressure x area) is greatest with the piston (or more precisely, the top ring) a significant distance further down than that. And, the greatest bending moment on the walls is even further down yet.

[Jack Gifford]

... This method also does not... create a possible coolant leak path...

In a dry-deck engine it would however create a coolant leak potential that wouldn't otherwise exist.

The possibility of coolant steam pockets seems worrisome also, if used at 4 - 6 spots around each cylinder.

Looks to me like a "crutch" for insubstantial cylinder walls. Crutches have their place, such as during an event; but not in the design phase.