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Offset grinding a sbc crank........

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Offset grinding a sbc crank........

Postby 6sally6 » Sat Feb 13, 2010 11:33 pm

We are considering offset grinding the crank journals(2.10) on a 350 Chevy and using the 2.00 small journal(old 327) rods. Heres the question....IF we already have a zero deck height on the block...how far out of the hole will the pistons be? We are wanting to run a negative deck anyway to try and pick up some compression. See any problems with this plan?
thanks
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Re: Offset grinding a sbc crank........

Postby fastfiat » Sun Feb 14, 2010 12:12 am

I don't think thats the way you want to go. Even if you run the piston out of the hole ( witch i have never herd of ) you would have to run a thicker head gasket to keep the piston off the head deck defieting your higher c/r. You"ll need new pistons with the correct compression highth and the compression you want. We run a off set ground crank ( 3 9/16 ) in our blown alcohol moter and it.s a good combo but needs to be done right. Good luck.
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Re: Offset grinding a sbc crank........

Postby trmnatr » Sun Feb 14, 2010 1:53 am

6sally6 wrote:We are considering offset grinding the crank journals(2.10) on a 350 Chevy and using the 2.00 small journal(old 327) rods. Heres the question....IF we already have a zero deck height on the block...how far out of the hole will the pistons be? We are wanting to run a negative deck anyway to try and pick up some compression. See any problems with this plan?
thanks
6sally6


What are you going for? 3.26" stroke? 3.27" stroke?

It may work fine, how far do you want the piston out of the hole? Whats your rod length? Compression height?
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Re: Offset grinding a sbc crank........

Postby governor » Sun Feb 14, 2010 10:04 am

You can have the crank offset ground to keep the very same stroke as you now have. If you want to move the piston up out of the hole say .010, then that is how much stroke you need to have your crank grinder add.

Just grinding the crank undersize by .100 will not change the stroke as you would stay on the same center line. Stock large journal crank is 2.199-2.100, small journal is 1.999-2.000

You can add as much as .050 stroke as long as your crank is not already under size, or a little more if you go under size on the small journal grind. If you change the stroke more than a few thousands, you will need a different comp dist piston.

Not sure I would do this just to use a stock type 327 small journal rod, as the smaller bolt size could end up with a weaker rod. Now if you were using an after market small journal rod that had good bolts, you would be ok.

This is my 2 cents.

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Re: Offset grinding a sbc crank........

Postby levisnteeshirt » Sun Feb 14, 2010 10:09 am

i asked the tech at KB why they didn't make a piston for that ,, he told me i could take .040 off of the top of the 5.7 rod 350 piston and it would do fine , just no nitrous

if you use a 327 6.0 rod piston , with a 1.385 comp height , and a 5.85 rod , 3.562 stroke ,, it comes out to a .001 above deck at 9.015 ( .010 cut off of deck )

there is a crank on ebay right now that looks good for this , its a blem .010 under ,, but might be worth looking into ,, wouldn't need SJ rods

http://cgi.ebay.com/ebaymotors/ws/eBayI ... MEWAX%3AIT

i've looked at these rods if you use your crank ,, says its for a 4.6 ford , but it has the same width and diameter at the journal as a chevy , and can be ordered with a chevy pin diameter

http://cgi.ebay.com/ebaymotors/FORD-4-6 ... 27aee4f130

or maybe these rods
http://cgi.ebay.com/ebaymotors/Eagle-H- ... 27af1cc3ba

I wonder why Scat doesn't make an economical I beam in a 5.850 length , 2.0 journal ,,, eh ,, prolly sell too many :lol:
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Re: Offset grinding a sbc crank........

Postby SKeown » Sun Feb 14, 2010 11:52 am

You can actually change the stroke .100" on a perfect crank going from a 2.100 to a 2.00" pin size, that's .050 additional up and .050" down. Back in the day, I used to have Reath Automotive alter a 3.5" stroke to a 3.625" stroke by chroming to the 2.00" size. EPA frowns on that process today.

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Re: Offset grinding a sbc crank........

Postby 6sally6 » Sun Feb 14, 2010 4:44 pm

levisnteeshirt wrote:i asked the tech at KB why they didn't make a piston for that ,, he told me i could take .040 off of the top of the 5.7 rod 350 piston and it would do fine , just no nitrous

if you use a 327 6.0 rod piston , with a 1.385 comp height , and a 5.85 rod , 3.562 stroke ,, it comes out to a .001 above deck at 9.015 ( .010 cut off of deck )

there is a crank on ebay right now that looks good for this , its a blem .010 under ,, but might be worth looking into ,, wouldn't need SJ rods

http://cgi.ebay.com/ebaymotors/ws/eBayI ... MEWAX%3AIT

i've looked at these rods if you use your crank ,, says its for a 4.6 ford , but it has the same width and diameter at the journal as a chevy , and can be ordered with a chevy pin diameter

http://cgi.ebay.com/ebaymotors/FORD-4-6 ... 27aee4f130

or maybe these rods
http://cgi.ebay.com/ebaymotors/Eagle-H- ... 27af1cc3ba

I wonder why Scat doesn't make an economical I beam in a 5.850 length , 2.0 journal ,,, eh ,, prolly sell too many :lol:



I really LIKE the idea of running FoMoCo rods in a Chevy!If we went this route....5.850" rods, pistons with a 1.3585 comp. height, and offset grond crank by .050 the pistons would be out the hole by .001? How far out could I run them and not have problems with piston rocking and ring pack issues? How about piston to valve problems? Using open chamber 3947040..64 cc heads. 1.94/1.50 valves.
Thanx
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Re: Offset grinding a sbc crank........

Postby levisnteeshirt » Mon Feb 15, 2010 1:00 pm

those are aftermarket H beam rods ,, i'm guessing RPM rods ,, the other rods are just 5.850 small journal Eagle rods ,, bout 60 bux more expensive

P-V would be determined by your cam ,,, and valve reliefs in your pistons ,,,
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Re: Offset grinding a sbc crank........

Postby 6sally6 » Mon Feb 15, 2010 2:52 pm

levisnteeshirt wrote:those are aftermarket H beam rods ,, i'm guessing RPM rods ,, the other rods are just 5.850 small journal Eagle rods ,, bout 60 bux more expensive

P-V would be determined by your cam ,,, and valve reliefs in your pistons ,,,


If I do the math right....IF the pistons stick out ....say 020 and I have a head gasket 025 that should leave a quench area (or P/V clearence) of 005. The piston will actually pretrude into the head by this amount, right? I suppose I need to make sure the valve releifs are deep enough for the extended time the cam hold the valve open, right? I could also "fiddle" with the camshaft timing to close earlier to maybe "grab" a litle more compression. Still looking for max CR since race fuel will be used/
Thanks,
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Re: Offset grinding a sbc crank........

Postby levisnteeshirt » Mon Feb 15, 2010 4:36 pm

go to here to enter your stroke, , deck and rod length figures to see what you can come up with
http://www.eaglerod.com/

you'll have to decide how how piston to head clearence you want though
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