[sapsz28]

If i swap all my parts from my rotating 350 assembly and put in a 383 rotating assembly with my same 041 heads.Will i change the compression drastically, again using the same cc volume pistons ,head gasket etc but for a 383,and instead of a XE268, put in a XS274s,or even a XS282S, current compression 10:1 in the 350.

[F-BIRD'88]

When using 64cc heads on a
383 use a dished piston to keep it pump gas friendly.

[ericnova72]

With all variables kept the same, just changing from 3.48" stroke to the 3.75" stroke will result in the 383 having .5-.6 more compression due to the larger swept volume(more cubic inches) being squeezed into the same size space at TDC. Your 10-1 will become 10.6-1.

Compression ratio calculator here at www.wallaceracing.com on the calculators page

[cobalt327]

Originally Posted by sapsz28

If i swap all my parts from my rotating 350 assembly and put in a 383 rotating assembly with my same 041 heads.Will i change the compression drastically, again using the same cc volume pistons ,head gasket etc but for a 383,and instead of a XE268, put in a XS274s,or even a XS282S, current compression 10:1 in the 350.

Besides the rise in CR, the pistons for a 3.48" stroke crank will have the wrong compression height.

So, since you have to change pistons or rods anyway, the best choice is to use a "D"-shaped cup piston w/the correct volume to keep the CR where you want it.

[sapsz28]

I was thinking a 3.75 scat 9000 crank, scat 6 inch pro comp rods floating pins, 7/16 cap screws, clearanced for strokers, but I have no clue as to the type of piston i neeed,the cam will be a Comp solid flat tappet grind # 12-677-4,or12-676-4.
Asfar as the pistons any recommendatrions the block is .060 397010 with 041 heads fully ported 2.02-1.60 254cfm@.600 lift flow bench tested,before last rebuild,due I go forged ,hypereutectic,?, I will not be adding any power adders,but I do intend on using the cams full potential any suggestions D shape ,2 valve releifs ,4valve releifs I'm not very good in this dept. I dont want the compression higher than 10.50-1 --11.00-1 we have 94 octane here plus the availabability of additives makes getting 100 octane no problem to put in the tank. Any help would give me peace of mind fellas.Thanks everyone

[ericnova72]

A zero decked block and a 2 valve relief piston(4cc) will get you 11.1-1 if you truly have a 64cc head.

Your 041's probably were bigger than 64cc when new, likely 66cc, and it is hard to say how big they are now if the port work was done right, relieving the chamber around the intake valve would make them bigger yet, then some milling might have taken some volume back off. You really have no idea what they are now.

Best thing you can do is get a 30-50cc syringe from the pharmacy or a veterenarian and along with an old CD check the chamber volume so you know what you are working with.

Block the head up level on the bench seal the valves lightly with a little grease, install a spark plug, and seal the CD to the deck surface with some grease(or Vaseline) to make a pocket that will hold liquid. Add some food coloring to some water or rubbing alcohol and fill the chamber thru the CD center hole and record the volume needed to do it.

Then you will be able to make accurate decisions, anything less will just be a big guess.

I consider forged pistons the only choice, especially with the rpm capability of the solid cam. Keith Black/ICON forged or Probe are good low cost forgings.

[sapsz28]

Thanks alot you sure are an eye opener.

[cobalt327]

Do be sure to use a CD or piece of plexiglass, plastic, etc. w/a hole in it for adding water and allowing air to escape.

If you don't use a cover like that, the surface tension will allow you to add a LOT more water than the chamber's actual size. You wouldn't think it would be all that much, but it is.

[sapsz28]

Thanks a bunch Cobalt.