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Old 03-24-2006, 07:46 PM
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clearance issues on my 400 small block

I was wondering I'm building a 400 small block.It has a 4.185 bore 6" rods,and a 11.1 standard flat top piston.The block has zero deck height,and the heads are made by Jegs Hi performance.there aluminum with 197 runners,and 64cc chambers,The cam I am running has a 600"lift Intake,and a 600" Exhaust.What I was wondering,is the valve going to hit the piston?Should I run a dish to keep this from happening?Is the only way this I can tell is to build the engine.The cam doesn't have a small base circle is it going to hit the rods?Will I have to grind the rods for clearance?How much power should a engine like this make?It has a open plenum with a 750 double pumper(victor junior intake) Holley carb.Here is the specs on the cam.Any info on what engine power should be,and recommendations on engine combo would be greatly appreciated

http://www.compcams.com/Technical/Se...UMBER=12-470-8


For some reason the web site want pull up the specs,but you can click on it and put the 12-470-8,and then go to ick her,and it will pull up the specs.Once you click on the web site go to search,and then in the upper right hand of the page put in the part number.If you need them thanks for looking

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Old 03-24-2006, 07:56 PM
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Will I have to grind the rods for clearance?

Don't even think of it, you may have to clearance the BLOCK.

As far as the piston to valve clearance, does the piston have valve reliefs? Without taking the time to do the calculations you should be ok, but using some putty to check is always a good idea (after rod to block clearance checking).
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Old 03-24-2006, 07:59 PM
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Quote:
Originally Posted by Lonestar
Will I have to grind the rods for clearance?

Don't even think of it, you may have to clearance the BLOCK.

As far as the piston to valve clearance, does the piston have valve reliefs? Without taking the time to do the calculations you should be ok, but using some putty to check is always a good idea (after rod to block clearance checking).
I was told without running a small base circle cam I would have to grind on the lower part of the rod for clearance to keep the 6" rods from hitting the cam
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Old 03-24-2006, 08:01 PM
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They have a 2 valve release,and the valve sizes are 2.05,and 1.60
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Old 03-24-2006, 08:05 PM
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Are you still putting the engine together, or is it completely assembled? You need to check all of those clearances as you put the engine together. Nobody will be able to give you a definite answer. Measuring is part of the engine building process. If you dont do it, you're setting yourself for a world of hurt (in the pocketbook)

If you measure the piston to valve clearance and determine you have inadequate clearance then you're going to have to run a cam with less lift of get some pistons with bigger valve reliefs in them.

I've never had an issue with rods coming anywhere close to contacting the cam lobes on anything I've built so I couldnt tell you much there...
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Old 03-24-2006, 08:10 PM
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It has been a very long time since I put 6" rods in a 400 block, but if memory serves correct then we had to clearance the bottom of the cylinder sleeves as the longer rod either made contact with or came too close for comfort to them.

Grinding on the rods is a no no...

As far as the piston to valve clearance, use some modeling clay and get a clearance.
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Old 03-24-2006, 08:37 PM
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The engine isn't together yet.I have been researching parts and trying to make as much streetable power out of this 400 as possible,and I've never ran a cam with 600" lift.I could consider running a slight dish.I'm probably going to have valve to piston issues,but while I am building the engine I will check everything.I've bought everything execpt pistons.The block was decked.line honed,and bored.If I use clay will I have to bolt the head down on the block,or how would I go about checking that.I'm not sure about small base circle cam.I know you should run them in stroker engines,but is it the rod that comes in contact with the cam or what,What does everyone mean when clearance the rods.I don't have a small base circle cam,and was told not to use one.This build has kept me up a night,with some people saying this and that it's frustrating,but the help from everyone on this site really helps alot.I am an A.S.E. tech,and have been working on cars all my life.There is alot I don't know and do not mind admitting that,but I am 24 and I'm young ,and everyday I learn something new.oh yea the rods are h beam rods,
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Old 03-25-2006, 03:06 AM
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i know several people who have run larger cams than that with similar 406 motors. you should have enough piston to valve clearance. as far as the rods go, most I beam rods should have enough clearance. H beam rods usually have the clearance problem. you really need to build the motor and check all clearances.
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Old 03-25-2006, 03:06 AM
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i know several people who have run larger cams than that with similar 406 motors. you should have enough piston to valve clearance. as far as the rods go, most I beam rods should have enough clearance. H beam rods usually have the clearance problem. you really need to build the motor and check all clearances.
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Old 03-25-2006, 05:37 AM
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I had to get a small-base circle in my 408 sbc with 6" i-beam rods. If remember right, the machine shop still had to clearance 2 rod bolts for clearance. This was with around .550" lift on a Comp 282XR with 1.6 rockers.
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Old 03-25-2006, 10:10 AM
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Use 5.7" rods, if ya haven't already bought the super duper 6" rods and pistons to match.


Larry
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Old 03-25-2006, 12:12 PM
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I know the Scat I beam 6" rods have enought room for cam cleanrace. they actually have more clearance than the 5.7" I beam rods. If it is a "stroker " rod there shoul be plenty of clearance. I would use the 6" rods because it makes the rotating assembly lighter and it will internal balance easier. What brand are the rods? by the way, your going to be over 11.1 compression. Most flat top pistons for a 400-408" motor with 64cc heads are listed at about 11.5:1 and since you zero decked your block your going to be close to 12.1 compression. If you do have a honest zero deck, run a .040" head gasket to get the right quench and to also lower the compression some. What is the specs of the cam?
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Old 03-25-2006, 01:31 PM
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If the pistons have two valve reliefs, the deck surface is level with the pistons and he uses a 0.040" gasket the compression will be 11.6-1 + or - a tenth.

With 314 degrees of duration on both lobes the engine does not need less compression, it needs more.

6" rods, of equal construction, do not weigh less than 5.7" rods, they weight more. It's a matter of mass.

There's no good reason for using 6" rods that put the wrist pin up behind the oil ring when a 5.7" rod will do the same job just as well.


Larry
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Old 03-25-2006, 01:41 PM
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Quote:
Originally Posted by coldknock
If the pistons have two valve reliefs, the deck surface is level with the pistons and he uses a 0.040" gasket the compression will be 11.6-1 + or - a tenth.

With 314 degrees of duration on both lobes the engine does not need less compression, it needs more.

6" rods, of equal construction, do not weigh less than 5.7" rods, they weight more. It's a matter of mass.

There's no good reason for using 6" rods that put the wrist pin up behind the oil ring when a 5.7" rod will do the same job just as well.


Larry
It depends on the cc of the valve reliefs. Different brands have different cc`s for the valve reliefs. The SRP pistons are listed as 11.6:1 but I don`t know what deck height they list that for. If you zero deck that it will be higher than 11.6:1.

I did`nt see anything saying the cam was 314 advertized but I`m not familyar with comp cams specs. The .050 duration has alot to do with the compression as well.

6" rods won`t be that much heavier if at all. The pistons will be lighter because there will be less material. Most engine builders I`ve talked to say if you want to internaly balance a 383 or 406, the 6" rods make it easier and the 5.7" rods will almost always never internaly balance. Also the 6" rods give the piston more dwel time at TDC.
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Old 03-25-2006, 03:16 PM
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3-5cc is the norm for 2 relief pistons. It doesn't really matter anyway, except where valve clearance is concerned. Like I said, it's not enough to begin with. 252 degrees at 0.050" and 314 total, 110 LSA on a hydraulic roller cam is BIG. 11.5-1 will do but it's not optimal. I'd use a smaller cam, maybe one space up from the bottom of the page.

You can recite everything you've ever read in magazine articles and Smokey's books about long connecting rods, light weight pistons, dwell time, and decreased loads on the thrust side of the cylinder wall. That's all good stuff if we're talking about 500+ cubic inches, a difference of at least an inch in length, and we're shooting for 800+ horsepower over 7000rpms. Even then the results of using a longer rod would be less than you think.

In a 450-500hp small block Chevy, 0.300" of extra rod length ain't gonna amount to hill o' beans.

Been there and done it already.


Larry
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