There are 4-valve heads having much larger valves and flowing up to 600 CFM available for the Chevy BB.
http://www.araoengineering.com/chevybb.htm
http://www.valleyhead.com/thunder.html

Why a 4-valve head is so much better than a 2-valve.
http://www.billzilla.org/2v4vpage2.htm

Ake

 

I haven't explored the limits of the 16v heads - we've done the small porting improvements and such, but never a *****-to-the-wall setup - (big valves + porting + seats and springs) and I'd like to do so.
Especially because we have some fairly wild cam grinds for the 16v motors (more than I list on our website).

But the right project hasn't shown itself yet to make this investment worthwhile.

 

Block fresh out of the oven (in the background) where it was warmed up evenly and then the cylinders pressed in.

Was it Goldilocks who said: "My! What big bores you have!"

After it cools, it will receive one thin deck cut to make the cylinders exactly the same height as the block (the cylinders are installed a little high just for this reason).

 

Look at the pictures above ^

Look at the distance left between any two cylinders... and you have an idea how much more bore we can get on these motors.... any larger and there would be no coolant flow between the cylinders at all. I could make the cylinder walls thinner, but am reluctant to do so unless it proves necessary.

 

Carl
Interesting point about coolant flow between cylinder sleeves..... I wonder how much hotter the "touching" parts of the cylinder bores would get vs the rest......continuing with that.....what effect would this have on the engine?

 

968 block has cylinder walls touching each other without any problems. Using different material as liner might cause some heat expansion issues but there shouldn't be any problems from blocking water movement in between cylinder towers.

 

968 cylinders are touching as well as have a shorter water jacket and don't have cooling issues. One of the 928 guys years ago used block cement to strengthen the block & didn't have cooling issues.

 

Siamesed cylinder walls are very common - especially in all the aftermarket blocks where, like us, they are punching out small blocks to carry the biggest bores they can.

Visit Dart's site here: http://www.dartheads.com/products/en...d-small-blocks
and note virtually every block on that page - SB Chevy, SB Ford, Race, etc - have siamesed cylinders.
Also a fair number of stock cast engine are siamesed, where manufacturers are trying to put more bore into smaller blocks for packaging purposes.

On the 928, were we to expand our cylinder walls yet bigger, so much that they would touch... this is what I would do...

We would start by re-profiling the outer cylinder wall inward a bit, give it a "waist" if you will, so that they touch at the top for gasketing, and they touch again at the bottom where they enter the block, but remove some of the outer cylinder wall in the center. Then you would have coolant flow again. (looking at our cylinder wall thickness in the photos above, you can see we left them straight and there is plenty of material thickness for this).

In addition, the head and head gasket would be drilled for a steam vent near the point where the two cylinders meet. Note the holes for steam venting/cooling in the dart blocks right at the siamese, and think of matching holes in the head and head gasket so coolant can flow and steam (if any) can escape.

 

With 7 liters displacement, does the motor rev up noticeably slower than a 5.4L and what do you set the rev limit at?

 

Revs FASTER due to the vastly increased horsepower or was that torque ??

 

no, I think it is due to gearing....

 

Depends on materials and construction, but back of envelope calculation is that torque depends on the sq in of the top of the piston, but piston mass is all three dimensions of the piston so mass would scale as a cube function vs torque as a square function. A piston twice as big has 4 times the torque, but 8 times the mass. Revs slower, lower redline.

Maybe this is a dumb question, but how small of a bore do you intend to make sleeves for?

Something like a 6.0L that used a stock crank and "semi" standard lower cost set of rods, pistons, and rings might have its own market for budget power.

 

Stock bore is 100mm. These are 4.25"/108mm. 108mm bore and stock 78.9mm stroke make 352ci/5.77L. You need to use a stroker crank to get up to even a 6L.

 

5.77L would not be bad at all, if that meant reuse of the stock crank and rods with only the added cost of the sleeving and custom pistons. Add to that a set of Euro S heads, maybe hotter 16v cams (with new springs and lifters) and get into what I see as the sweet spot go/$ of 350 to 400 rwhp cheaper than other routes.

 

What an interesting development, quite honestly when I think about it, why did it take so long to come to it ?
Going to a cast iron wet sleeve of 4.250 makes pistons so easy to come by, no messing around with coatings.
An engine with this style of sleeve and some boost will crack 1000 hp