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Discussion Starter · #1 ·
Hi, I picked up a forged crank and rods for basically a steal off a guy a while back when i was planning on building a blwer motor. Because of money i had to postpone that project but instead of just letting the parts sit, when i pull the motot for a little overhaul I decided i would put the crank and rods in. The crank is standard 350 specs so that will go right in but the rods are 6in instead of the standard 5.7in. My question is, can i put the 6in rods in without a problem or do would i need to do any modifications for them to work? Also would i feel any difference in the motor with this swap?
 

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You will need pistons with pin location for the 6inch rods.
Compression height of 1.260 is what is needed. w a 3.48 stroke crank.

I would absolutely use the 6 inch rods. :yes:


SRP makes some awesome light weight, skirt coated, forged piston kit for that application.
Part # 271056 for flat top .030 over flat top they have dome and dish also.

http://www.jepistons.com/Catalogs/SRPPRO/Chevy_SB/350_flat-pro.aspx

Al



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Hi, I picked up a forged crank and rods for basically a steal off a guy a while back when i was planning on building a blwer motor. Because of money i had to postpone that project but instead of just letting the parts sit, when i pull the motot for a little overhaul I decided i would put the crank and rods in. The crank is standard 350 specs so that will go right in but the rods are 6in instead of the standard 5.7in. My question is, can i put the 6in rods in without a problem or do would i need to do any modifications for them to work? Also would i feel any difference in the motor with this swap?
You would need the pistons for the crank stroke and also for the rod length. Pistons will have a higher wrist pin bore so as not to come out of the deck. On my last 400 I ran a 6" Eagle rod and I had to notch each cylinder for the rods and 3 places on the oil pan rail. On my current 383 I had to just do 4 cylinders on one side and that is with stroking it to a 383 and with Scat Procomp I beam rods.

Different brand of rods will have to be checked for clearance. You can just put one piston on the crank(no rings needed) and run it thru one side of the block, then turn it around and run it thru the other side. You can clearance with a carbide cutter on a drill or die grinder as needed. Each one I clearance I take my shop vac and clean out all the shavings I can, do the next until finished and then pull the crank out, clean all my main bearings, crank, block, the one rod and bearing, blow out the block with compressed air and reassemble.
 

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As the others offered, you will need he proper pistons, and check of fit, and I would look a proper balance as well.

About would you feel a difference? If the new rods are heavier than what you replace and all else stays the same, I would expect some decrease in performance, even if its slight.


In my opinion heavy rotating/reciprocating engine components cost performance when compared to lighter parts of equal performance capability.
 

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As the others offered, you will need he proper pistons, and check of fit, and I would look a proper balance as well.

About would you feel a difference? If the new rods are heavier than what you replace and all else stays the same, I would expect some decrease in performance, even if its slight.


In my opinion heavy rotating/reciprocating engine components cost performance when compared to lighter parts of equal performance capability.
yea this may see correct, but your talking about +/- grams.. with the forged pistons, and less material (maybe) with the pin being heigher in the piston, you wont notice A BIG DIFFERENCE.. if you wana save weight.. buy a 2k crank and it will weigh 35 +/- a few lbs, then your talkin..

but now for real improvement with the 6'' rod.. your going to notice how the motor is going to rev in the higher RMP's A LOT smoother, thus letting you rev higher and for longer without damaging bearings.. a lot of people can chime in that do have the 6"inchers, and tell you they might, they might not, but there really is a difference.. theres even some with 6.125:devil::devil: those man-oh-man.. if i could:rolleyes::rolleyes: its supposed to giv you more dwell time, but i dont wana get into all that..

but YOU MUST BALANNCE the rotating assembly:yes: dont skimp it out.. it makes a big difference.. not just on performance, but in Longevity of your motor.
 

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Well 6" rods are supposed to give you more dwell time, not that you would know it or feel it I don't think. I have ran the 6" rod, but never took the exact same engine and combo and tried it with a 5.7 so I couldn't tell you if there is any difference or not. Some say for spraying NOS use this or that, but every combo is different and others have just as good of luck with shorter rods.

Like stated on here before it can help with piston scuff in different stroke to rod ratios.

I wouldn't lose any sleep over using either one myself and right now I have the 5.7 in my 383.
 

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Discussion Starter · #7 ·
Ok. Thanks everyone but it looks as I will probably just hold off on the rods for right now because the blower motor is still in the making so I hate to buy the pistons and then in a year or 2 buying pistons again for the blower motor. By thanks everyone for the info.
 

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On the SBC blower engines I have built I use the longest rod I can fit in and the 6.300 works very well fo what I build.

Comparing a 383 with a 5.7 rod is not apples to apples here. On 383 with 5.7 rods there is a lot more piston hanging out of the bore at BDC. Low rod ratio, heavier piston, more side loading. Most 5.7 rod 383 cranks are externally balanced.

A 6.000 rod in a 383 is a much happier engine when you weigh everything out
 

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On the SBC blower engines I have built I use the longest rod I can fit in and the 6.300 works very well fo what I build.

Comparing a 383 with a 5.7 rod is not apples to apples here. On 383 with 5.7 rods there is a lot more piston hanging out of the bore at BDC. Low rod ratio, heavier piston, more side loading. Most 5.7 rod 383 cranks are externally balanced.

A 6.000 rod in a 383 is a much happier engine when you weigh everything out

I agree 100%. Any performance 383 should get 6" rods period. Better rod ratio, lighter pistons, less side loading on the skirts and bores, better dwell time etc etc. My 13:1 383 with 6" crower rods zips to 7200+ at the snap of a finger.
 

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I like to be different--5.85" rod with a 3.80" stroke.
I have used 5.7" rods in a few 3.832" stroke combos that ran very well, but they were hard on cylinder walls. Still went 7500+. One was a LOW-buck Chinese crank, small journal Chevy rod, KB hypereutectic piston deal that ran 10.25/131 in a 72 Nova.
 

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I like to be different--5.85" rod with a 3.80" stroke.
I have used 5.7" rods in a few 3.832" stroke combos that ran very well, but they were hard on cylinder walls. Still went 7500+. One was a LOW-buck Chinese crank, small journal Chevy rod, KB hypereutectic piston deal that ran 10.25/131 in a 72 Nova.
Some times to internally balance a short rod stroker can cost alot of money here is a pic of a 3.750 callies I balanced for a blower application and I warned him that balancing maybe an issue and I recommended to 6.000 rods but it was his call.

After installing 4 slugs of heavy metal and the 650.00 balance job he was a little mad at himself to say the least. But he was warned LOL

 

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WITH A 383 I PERSONALLY WOULD USE 6 IN. RODS, THIS IS JUS' ME AND WHAT I PREFER, NO KNOCK ON 5.7's :no: YOU GET A BETTER ROD RATIO, BETTER DWELL, I DON'T KNOW THE DIFFERENCE YOU'D NOTICE 5.7's AND THE 6IN. WOULD YIELD LESS SIDE LOADING ALONG THE BORES AND SKIRTS.
TRIAL AND ERROR I TELL YA! BUT THAT COSTS, SO YOU MAY WANNA GET IT RIGHT THE FIRST TIME.
JUS' SAYIN' :yes:
 

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Some times to internally balance a short rod stroker can cost alot of money here is a pic of a 3.750 callies I balanced for a blower application and I warned him that balancing maybe an issue and I recommended to 6.000 rods but it was his call.

After installing 4 slugs of heavy metal and the 650.00 balance job he was a little mad at himself to say the least. But he was warned LOL



I think it cost me like $350 to balance my 383 with callies crank and 6" rods about 12 years ago. I think mine took 2 slugs of mallory and some drilling to get balanced.
 

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After installing 4 slugs of heavy metal
I have a cast 400 crank with 7 slugs of Mallory if I remember correctly--it was a 5.7" rod deal.

This would be a perfect subject for Horsepower TV, Car Craft or Chevy HiPo to do side by side tests.
It's been done before; very little change in power.
 
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