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Old 06-18-2003, 02:07 PM
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6"rods in 400 chevy small block

I am considering using Scat H-beam 6” rods and a Scat 400 crank in my 406 Chevy small block, my question is what clearance problems will I have with the Cam and Block when using the 6”rod???? And what can I do to resolve the problems???

Any help o these issues would be greatly appreciated.

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Old 06-18-2003, 04:15 PM
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Are you worried about the clearance with them being h-beam or 6" or both. If you switch to a 6" rod from a 5.7" you should have a little more clearance becuause of the longer rod does not swing as far as a shorter rod causing less bind on the crank, but i'm not sure on the h-beam. I went from a 5.7 I-beam to a Scat 6.125 h-beam rods in my 327 and had no problems with clearance on mine. just be sure to change to a 1.125 compression height piston.
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Old 06-18-2003, 05:29 PM
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Thanks for input cc69

I am worried about both the H-beam and 6” length.

The logic of going to a longer rod and lessen the rod angle to give more clearance makes sense to me, however I do know that when you swap the stock 5.565” 400 rods with stock 5.7” 350 rods in a 400 small block the cap bolts will hit the cam shaft and possible the bottom of the block so you need to grind some of the bolts off about .050”, so the logic of improving the rod length does not work with the 5.7 rod and leave me confused and worried about the 6” rod.

I would think if go to a 5.7” causes a problem, then a 6” rod would cause even more of a problem????…I’m confused!
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Old 06-18-2003, 05:40 PM
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Arrow

The reason cc69 didn't have problems was the difference in stroke between the 327 and the 400. I don't know if you'll have clearance problems, but from what you said it sounds like it, I do know they make smaller base circle cams for clearance problems in some engines. From what you describe it's actually the big end that causes the clearance problem.Scat should be able to tell you what interference you'll run into.
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Old 06-18-2003, 05:44 PM
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The clearance problem in 400's with rod change is due to rod profile, not the added length. All the length does is change the pin hieght. OE 400 rods are profiled a bit differently to clear everthing. I just finished a 6 inch Pro Mod I beam buildup. I had to remove about .100 inch in the bottom of the cylinders to clear the cap screws, and about .050 on the top of the crank end of the rod to clear the cam. It actually cleared the cam, but a clay check showed only about .010 to .020 clearance. I am running a .525 lift and .253 @ .050 lift cam, and a smaller one would probably have enough clearance.

Something to keep in mind is that every rod manufacturor will have a little bit different profile and may require more or less clearancing in different places.

Chris
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Old 06-18-2003, 06:21 PM
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I will take look at the small base circle cams, I think I read somewhere that they are made for the chevy 400sb. Thanks woodz428


TurboS10 that sounds scary grinding down the bottom of the cylinders I wonder if I will have that problem with H beam rods.
Did you need to disassemble your rotating assemble after grinding down the the rods to have it balanced?????
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Old 06-18-2003, 09:23 PM
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Quote:
Originally posted by 406chevelle
I will take look at the small base circle cams, I think I read somewhere that they are made for the chevy 400sb. Thanks woodz428


TurboS10 that sounds scary grinding down the bottom of the cylinders I wonder if I will have that problem with H beam rods.
Did you need to disassemble your rotating assemble after grinding down the the rods to have it balanced?????

Yep, it really sucks grinding in a block you think you are ready to assemble. I set up towels to keep the filings out of everything, and then washed and blew it out again. The factory 400 block is already clearanced a little bit, I just removed a bit more material. It is in the very bottom of the cylinder, and the water is not real close. My block is tall grouted, so I was not worried about that anyway.

I removed less than a gram of material fromt he rods. It was just one high spot where the cap screws went through. The balance was not effected enough to matter.

What really pissed me off is I told my machinist to check all that out before assembling the block(cam bearings, plugs etc.) Since he did not, I had to figure out how to keep filings out of little holes. I had to be really careful.

Chris
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Old 06-18-2003, 10:50 PM
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hey i have put 6" rod s in a 400 before when we did the engine bined so we ground down the place the rod was hitting and it run fine .
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Old 06-19-2003, 10:29 AM
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Is this engine for street use or race only?I wouldn't recommend using 6.00" rods in a 400ci. on the street under any sircumstances.For extended street use the piston instability of using the long rod will reduce engine life(that's why GM used shorter rods in the first place).6" rods on a 400 crank moves the piston pin up very near the oil ring and this increases piston rocking in the bore,which inturn causes increased piston and ring wear,and can cause increased ring flutter at higher RPM's.For racing these are miner concerns, cause the engine is rebuilt regularly anyway, but on the street it makes for an unreliable engine combo.In a 327 or a 350 it is less of a problem and can be lived with easier.
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Old 06-19-2003, 03:33 PM
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What you are saying makes sense supperrodder, its not worth the improvement in the rod angle, I am going with the 5.7? rods.

Thanks for input supperrodder!!!
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Old 06-19-2003, 06:20 PM
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Chevelle,
Sorry for the interlude, but how can you tell if you have a small block 400 or big block. I mean besides the codes. I was having this conversation with "fat man" at the race shop no more than 1 1/2 hours ago
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Old 06-19-2003, 07:10 PM
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Stinky don't quote me on this but I believe the 400 big block (really a 402) is about 175lbs heavier, and about 4" taller and wider.
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Old 06-19-2003, 08:59 PM
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Quote:
Originally posted by 406chevelle
Stinky don't quote me on this but I believe the 400 big block (really a 402) is about 175lbs heavier, and about 4" taller and wider.
And the valve covers are TWICE as big,and twice as many bolts holding them on
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Old 06-19-2003, 09:02 PM
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Quote:
Originally posted by superrodder
And the valve covers are TWICE as big,and twice as many bolts holding them on
Unless it's a pontiac 400ci.,then they have a loop on them so you can tie a rope on them to use as an boat anchor:p
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Old 06-19-2003, 10:13 PM
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you are talkin about a pretty big boat superrodder!!! LOL
I don't know much about pontiac motors but when I was 17 a not very smart friend left his buildup very quick 6.6liter 78 trans am with me for the summer, WOW it was a LOT of fun, also use to help my dad work on his 67 GTO 400BB 4speed that was the car I learned how to drive in, seemed pretty fast at 15 years old.
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