piston help

[mignum]

how do i find the right piston for a 3.25 stroke 6.125 rod in a 350 block with spacer bearings ?

[istock11m]

Deck height -Rod length - 1/2 of stroke= comp height. 9.025-6.125-1.625=1.275 comp height. That is on the basis of the deck being stock height.

[perfconn]

Right way to do it Buddy would be to deck the block down to 8.800 and save some weighr and use a 1.062 compression height piston.Better still get rid of the 6.125 rods and use a 5.850 rod but still cut the deck to lose weight.

[istock11m]

Or buy a 3.5 stoke 6 in rod piston and save the time and expense of cutting the block that far.

[perfconn]

Cutting the block will cost a lot less than a new crank and rods and you still wouldn't get the weight savings.

[hucktyson]

Cutting the block will cost a lot less than a new crank and rods and you still wouldn't get the weight savings.

Is there a bigger chance of the block cracking after you cut almost a 1/4" inch off the deck ?

[perfconn]

Not cracked one yet

[istock11m]

My bad. I thought the OP had the block, crank, rods, and just wanted to know what pistons he could use. If you cut that much off the deck you will need the intake machined, and different pushrods, etc etc.

[SLM98]

What the weight savings in pounds? Need to shave some weight off a bowtie block.

[perfconn]

If its a 9.025 block you can save 25-30 pounds just by decking down to 8.800 even more if you get the grinder out and do a lot of deburring on the block

[SLM98]

Guess I better make sure my CBN cutters are sharp and I'm stocked up on grinder wheels! Thanks

[mignum]

Thanks terry i didnt have a clue about doing any of that cutting the deck down, so i see that i can get a really light piston in there. why do you say even better is the 5.580 rod here.

[perfconn]

Buddy,
Its all about rod/stroke ratio.With a 5.850 rod and a 3.25 stroke you will be able to run a bigger cam and make more total hp.Most of my 3.270-3.280 stroke motors I use a 6 inch rod but a 5.850 rod will run better.The 5.850 rods are harder to find but run better.

[500BOMBER]

The question was...........

how do i find the right piston for a 3.25 stroke 6.125 rod in a 350 block with spacer bearings ?

I would call Ross Pistons and ask if they had a set for that combo on the shelf.

[stilhead]

weight

Don't think you can lose 25 0r 30 pounds by cutting .225 off a sbc block head surface. That surface is roughly 19.250" by 5.688" . Cast iron weighs .2609 lbs. per cu.in. 19.250 X 5.688 X .225=24.6 cu.in. X .2609 =6.42 lbs. And there are four 4.125 holes X .225 that will remove three more lbs from this number=3.42 lbs And don't forget about the water jacket and head bolt holes. So about 3 lbs per side, maybe 6 lbs total off the block. And how thick will your intake gasket need to be if you do this? Just get the right piston and rod combo and save yourself a lot of time and money.