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Old 08-06-2010, 05:58 AM
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327 Build with 6.125" rods. Who's done it?

I ran across a thread where a guy said he built a small journal 327 with 6.125" rods and pistons from a 350 with a 6" rod. and made some great horse power. I'm wondering if this is a somewhat common build? the math works out perfectly and since I plan on taking the hi comp pistons out of a 327 I have, maybe I should go this route? Would this have much advantage over a stock 327 SJ?

The user was 1970SSNOVA. Here is the thread. All the way at the bottom.
Chevy 327

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Old 08-06-2010, 06:27 AM
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Rod length will help if you have restrictive heads or are chasing high RPM, it also helps a little with bore wear. Its not a bad idea to run 6.125" rods but don't expect a huge gain.

Your rod/stroke ratio will move from 1.75 to 1.88.

I would also be questioning the claimed power from the engine you're modeling after, 1.43 ftlb/ci is some serious stuff... His build looks to be a race engine not a streetable engine at all.

Last edited by turbolover; 08-06-2010 at 06:36 AM.
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Old 08-06-2010, 07:30 AM
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Quote:
Originally Posted by turbolover
Rod length will help if you have restrictive heads or are chasing high RPM, it also helps a little with bore wear. Its not a bad idea to run 6.125" rods but don't expect a huge gain.

Your rod/stroke ratio will move from 1.75 to 1.88.

I would also be questioning the claimed power from the engine you're modeling after, 1.43 ftlb/ci is some serious stuff... His build looks to be a race engine not a streetable engine at all.
Agree^^^Don't think that this plan will be some "silver bullet" secret to building stupendous power, the 6.125" rod just helps the piston be lighter. It would help throttle response on a light race car but don't expect miracles because of it, it won't instantly be a Big Block slayer due to a rod length change. The build you are referencing will require a decent amount of regular maintenance to keep track of the valvetrain, and scheduled valvespring replacement.

Nothing wrong with the 6.125" rod plan though, every little bit helps, and no reason not to do it with the easy availability of the pistons - something that wasn't there in the 1960's thru the early 1990's.

You could also do it with a 6.125" rod 350 piston and use 6.250" rods in your 327, but the really short piston will make this a short term competition engine only, aimed at very high rpm like a Competition Eliminator engine... a $20,000+ engine that gets rebuilt every 50-100 passes.
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Old 08-06-2010, 07:34 AM
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A popular stock car engine is the 4.125bore/3.25stroke/6.125rod combination. The bigger bore unshrouds the valves some, the short stroke like the 8500RPM, and it make's a legal cubic inch engine at 348ci. Many short tracks are easier to drive, especially longer races on only 4 tires, with a engine thats a little down on low speed torque but still make a big horsepwer number.
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Old 08-06-2010, 08:36 AM
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"Would this have much advantage over a stock 327 SJ?"

talk to the cam company, the longer rod will hold the piston at the top longer, like raising the CR, may call for a cam change.

Should rev like all get out.
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Old 08-06-2010, 09:12 AM
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The one thing I wish I could have accomplished with my 327 is to get some lighter pistons. Stock 327 pistons tend to be WAY too heavy IMO. That would be an excellent way to accomplish that and a longer rod will give it more time @ the top of the cylinder. I see no downside to going with the longer rod/lighter piston approach save the cost of the rods..

I say go for it!!
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Old 08-06-2010, 10:52 AM
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Quote:
Originally Posted by 65smallblock
The one thing I wish I could have accomplished with my 327 is to get some lighter pistons. Stock 327 pistons tend to be WAY too heavy IMO. That would be an excellent way to accomplish that and a longer rod will give it more time @ the top of the cylinder. I see no downside to going with the longer rod/lighter piston approach save the cost of the rods..

I say go for it!!
That's the exact reason I'm looking at doing this. I have to swap out the domed pistons anyway since I want to lower the CR to run on pump gas and leave the option open for a centrifugal supercharger. Also stock forged flat top 327 pistons are heavy slugs. Since I'll need new pistons and forged 327 flat tops are about the same price as forged 350 6" rod pistons, it should really just be the extra cost of the rods which I might be able to recoup some of it by selling the domed stock pistons and brand new GM 327/350HP cam that's in the engine now.
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