Need help in understanding differences between 327 & 302 pistons

wally409

Well Known Member
I have the opportunity to build a 327 small journal block with a 283 crank but I don't believe I can use a regular 327 piston in this scenario. I'm not a machinest but I believe the 302 piston has a bit of a lower pin placement because of the shorter throw of the 283 crank to allow the tops of the pistons to get to the tops of the cylinder for decent combustion. Any info and specs would be greatly appreciated - and is there other ways of using the above combinations. I see that 302 pistons are roughly twice that of 327's. Thanks. Wally
 

Ishiftem

Well Known Member
Supporting Member 2
You do need the 302 pistons. If you used a 327 piston, the piston at TDC would wind up 1/4 inch below the deck. Now you could use a longer rod but unless you were buying aftermarket rods anyway, you are better off buying the right pistons. Even with a 6" rod you would need to mill .050 off the tops of the pistons to get a zero deck. That's my take on it.
 

Dan Hunt

Well Known Member
Supporting Member 5
the stroke on a 327 is 1/4" more than a 283.Thats 1/8'' up and 1/8'' down.I think a 12.5 327 piston on a 5.7 rod with a 3'' stroke would work.(piston would be down the hole .125)
 

Ishiftem

Well Known Member
Supporting Member 2
I wasn't thinking about the fact that it is only 1/8 in each direction. D'oh! :doh
 

Don Jacks

Well Seasoned Member
Supporting Member 3
A budget way to build a 302 would be to use a 5.92 in. rod,and a 350 piston.The 5.92 rod was used in the 94-96 4.3 8,but the crank pins were ,however the same size as the 68-up small blocks,as opposed to the smaller size journals used in the pre 68 engines.I dont know of any aftermarket rods that are the 5.92 size.:dunno
 

MRHP

 
Supporting Member 1
Using the above method, would you have the same engine characteristics as a 302?
 

models916

Well Known Member
Supporting Member 7
Shorter stroke on the 283 crank and the same SBC rods means the pins in the pistons have to be moved to locate the piston at the top of the bore.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Brian,I'm going to use Ronnies line here."At my age,and your making me think"!I think,if your using modern designed heads,pistons and rings,and camshaft,you can exceed the "old days"power numbers.I worked with an engine builder in 68-69,at that time,using stock chevrolet parts[a little head work was snuck in],cross-ram intake,headers with open exhaust,we were pulling 480-495@7200.:love
 

MRHP

 
Supporting Member 1
I keep threatning to build a 302. I have no use for one, but I want one. A friend of mine gave me a 302 that was a G.M. test mule dyno engine and has some kind of General Motors tag on the block. It's been mine for a year or two but I haven't seen it yet. Someday I will see it. Hopefully. Don, that must have been one hell of a motor. They sound fantastic at full song.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Yeah Brian,they do sound sweet at 7000-7500 rpm with open exhaust.Those engines we did were S.C.C.A. motors,nothing much below 4000,but once past 5000,hang on.We had to use parts with factory part numbers[optional Z-28 cams,cross ram,2 four barrel intakes and such].The "trams-am" series cars could make changes that we werent allowed to do,and were reportedly in the 525 range,but the stock "pink"rods werent too happy at :eek8000,even with that 3 in.stroke.That GM "mule"motor is probally bad a@s!!!!!!!!!!!!!:love:crazy
 

jr.W

Well Known Member
Something I have seen before.
302 has 3" stroke 350 has 3.48 stroke. Stroke difference is .48 half of that is .24
so if you use 350 pistons for a 6" rod then use 6.25 rods your only .010 up
the bore from stock.
 
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