I am going to put together a 302, i am gonna take an LT1 and put a 3" stroke crank, and add some 6 inch rods to make up the difference in the compression, that is my question...i punched in the numbers on a calculator and found that with regular 350 pistons, a comp height of 1.561" the deck clearance will be -.026 (with a standard chevy deck, 9.025") and i did the same pistons with a 6 inch rod and a 3 inch stroke and the comp height came out to be +.036, i understand that the +/- must be reversed to calculate compression, i got a higher compression with the long rod/short stroke, than the long stroke/short rod (10.696 opposed to 10.3***), all my calculations were done with a stock LT1 combustion chamber, 58cc as well...I am just trying to clarify if this is all correct and that i will end up with the compression as i found it to be with the 302 set up, and will there be a problem with using a piston meant for a 5.7" rod with a 6" rod?
Please dont ask why i am doing this, or please dont say "just to stay at 350ci or stroke it!", i have my reasons. Thanks for the info!!

 

With a 350 piston on a 6" rod with a 3" stroke crank will it have the proper wrist pin height? Personally I don't think you'll get proper clearances trying to use a stock piston.

You're moving the piston up into the cylinder .300" by using a 6" rod instead of a 5.7" rod. You're then decreasing the stroke from 3.48 to 3" so technically you're dropping the piston .180 down into the cylinder.

I really don't think the piston skirt will clear the crank when the piston is at BDC.

 

so i should just get 302 pistons? where can i get them for a 6 inch rod?
Thanks

 

get 302 pistons,also check at summitracing.com they might have them.just checked all they show are domed top pistons.

 

i checked there, but they do not specify wether it is for a 6 inch or 5.7 inch rod...or does it matter?

 

go to kb-silvolite.com they only offer two pistons they are both for a 5.7 rod.it really matters wat rod it is there specifically designed to use that rod with that piston.

 

You must use a 302 piston for a 302. Make sure the crank is a large journal crank for a 350 block as most 302's where small journal cranks. Replacement 302 pistons will be for a 5.7 rod. To go with a 6" rod you will need custom made pistons. This may be better for your application as I don't think a replacement 302 piston will produce a low enough compression ratio for a good street engine on pump gas

 

It is an LT series engine, so i would like to keep compression to around 10.5-11.5... so right around normal for these engines, and i have seen them up to 13:1 on 91 octane gas as well... any ideas as to how much a custom set will cost? just curious to know...

 

heard they cost up wards of 800 dollars.

 

Even JE pistons in their SRP line doesn't make a 302 piston for a 6" rod. I think because of the short stroke, the 6" rod will put the wrist pin up into the compression rings. Normally a longer rod piston just moves the wrist pin into the oil control ring.

If you want to build a 302, you'll have to use 5.7" rods. Longer rods are designed for longer strokes, not shorter ones.

A good forged piston is around $100 each. Cast and hypereutectic pistons are a little bit cheaper but not much.

 

If I remember correctly, you can use the 5.94" PM rods from the 4.3L 'baby LT1' engine and a stock-spec LT1 piston to build a 302. From what I remember, the 4.3L and 5.7L Gen II engines both had the same pin height in the pistons, just a different diameter for the differing bore size. Thats why the 4.3L got the longer rods than the 5.7L. Use those rods and 5.7L pistons and you should be good. Those PM rods are actually very strong too.

Do some research to verify this though... I'm 99% sure what I said is true, but 99 is not 100 lol.

 

"If you want to build a 302, you'll have to use 5.7" rods. Longer rods are designed for longer strokes, not shorter ones."

The opposite is true. That is why a 400 has a short rod, and it is necessary to clearance the bottom end for a 383 stroker with the 5.7/6 rod.

http://www.ariaspistons.com/custompistons.html This is a link for an order form. Arias will build almost anything you want, and do it well. If you haft to know how much it will cost, then it is probably more than you want to spend.
In short, I would stay with a 5.7 rod just for dollar since. The expense of custom pistons will out way the benefits of a longer rod in my opinion.

 

I was planning on using those rods...or the six inch... sincethe 4.3L uses the EXACT same pistons as the 305 vortec, which are used with a 3.48 stroke with 5.7 rods...so i figured a 3 inch crank and 6 inch rods...and like i said before the numbers said i would have a little higher compression with the 6 inch rods and short stroke, but i do not know if that is true...if anything i will just buy a 302 crank and use 5.7" rods...as stated...it will be much cheaper, and easier to just do it that way...

 

rod length has absolutely NOTHING to do with static compression... nope length still doesnt affect compression

 

well i figured it would...bucause like i was thinking about doing...keep the 350 pistons and shorten the stroke...the piston will be put down .48 inches deeper into the cylinder, and the piston not reaching all the way to the top, so i figured use a longer rod to make up for the drop in stroke (i did not know about the differences in the pin height, piston skirt, etc, etc...) and put it back up .3 inches, with a 6 inch rod...neverthe less, the piston is Still not where it would normally be with the 3.48 stroke...so i would figure that would affect compression because there is more space between the piston and the top of the Combustion chamber, so the air would be less compressed due to the larger amount of space...
but i dont know, that is what i figured with some basic math and common sense...but like i said i dont really know...i was just curious...

 

If you have a difference of 1/4" in stroke, then you need a difference of 1/8" in rod length.

Example= 400 crank + 5.625 rods + 350 pistons = cheap 383 (in a .030 block)

So, if you have a 3' stroke instead of a 3.480 you would need a rod 5.940,
a 6.' rod would push the piston out of the hole .060.

 

You learn something new everyday...
Thanks for that info! I did not know that...
but would pushing the piston out be bad? would it hit the head or something?

 

It will hit the head.

 

I built the same combination it brought piston 1/16 out of hole I used 52/1000 head gaskets and motor hits 9500 chip with no problem

 

I'm running DSS forged 350 flat top pistons