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Thread: Use 400 rods or 350 rods in 383?
          
   
   

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  1. #1
    larry0071's Avatar
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    Use 400 rods or 350 rods in 383?

     



    My machine shop recomends not going with the Eagle SIR 5.7" rods because of the clearancing that will be required to clear the cam, he says go with a shorter stock 400 rod and it clears with no modifications.

    The Eagle rods are most likely better material, but after you grind a big chunk out of the cap/bolt is it still better?

    Also what is the length of the 400 rod vs the 5.7" 350 rod?

    Is thrust side loading an issue with the more sever rod inclination angle or are things still decent with the 400 style rod?
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  2. #2
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    A stock 400 had a 5.565" connecting rod length. All other SBC's used a 5.7" Rod length. This was done to keep the piston from smacking the cylinder head.
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  3. #3
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    This is how I figure it! :
    The 400 Chev would wear out the bores alot quicker than the other standard production motors because of the short rod length. I will try to explain three different options to build a 383 :

    The stock 400 small block chev crank turned down to 350 chevy main bearing size, you have the stock counterweight and you will have to use the stock chevy short rod because the crankshaft is counterweighted for the short rod.

    Eagle crankshafts: For the 383 you can buy either cast steel or forged steel. The crankshaft will drop straight into the 350 block also they have the larger counterweights so that yuou can run the standard 5.7in rod or the better eagle 5.7in steel rod which are claimed to handle up to 600hp. For the camshaft clearancing problems you can use the 12point connecting rod nuts and a little bit of clearancing on the side shoulder of the rod, this does not weaken the rod in any way. As far as I am aware this setup is externally balanced.

    Scat crankshafts: There is a big choice with these crankshafts. They have bigger counterweights to use the 5.7in stock length rod as explained above and externally balanced in one option. Another option they offer is aninternally balanced setup were you use the standard torsional vibration damper and flywheel. These cranks have massive central counterweights. These also come with the option of cast or forged steel.

    The advantage of using the last two cranks is they are brand new and not wornout and they have nicely radiused bearing journals and oil holes.

  4. #4
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    The shop I am using deals with Eagle cranks/rods. The pistons will be forged.

    One thing I am confused about is the compression ratio thing, in BB Fords you can safely use a 9:1 to a 9.5:1 and not really need anything but regular unleaded so long as the quench is tight at about .038" to .042".

    He is saying that even with a zero deck block and .040" gasket that 8.75:1 is going to cause problems in a 1 ton truck that hauls 12,000 lb loads.

    He wants to go with a deeper dish and get 8.2:1 to stay clear of detonation.

    I did polish the chambers and plan to run a zero deck and dished piston, but I felt that 8.75 to 8.85:1 would be plenty safe. Do you all have any experiance on where the SBC CR seems to cause problemsunder heavy loads and regualr (87 octane) unleaded fuel?

    His reason for going with the 400 rod is the fact that the ring package can be a standard stock style vs going with the pistons that fit the 5.7" rod use a smaller ring package do to pin height. He feels the stock/street ring package is more durable. Is this a true concerne?
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  5. #5
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    Well as for your compression ratios, what a lot of people overlook is the dynamic compression ratios. To cut a long explanation short, dynamic compression ratio is governed to a major extent as to the time when the intake valve closes. So realy the selection of your pistons profile (eg dished' domed or flat ) is closely tied in with your camshaft duration.

    Some of the other senior members should be along soon, to add a few pointers.
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  6. #6
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    I already have the Crane 2040 in my house(#114132, Powermax 2040)compucam for non-roller application, its a computer friendly grind. In your experiance will this cam grind allow for the 8.75:1 or maybe even 8.9:1with 87 octane without any issues?

    Cam Style Hydraulic flat tappet
    Basic Operating RPM Range 2,000-5,000 RPM
    Intake Duration 050 inch Lift 210
    Exhaust Duration 050 inch Lift 216
    Advertised Intake Duration 270
    Advertised Exhaust Duration 276
    Intake Valve Lift with Factory Rocker Arm Ratio 0.440
    Exhaust Valve Lift with Factory Rocker Arm Ratio 0.454
    Lobe Separation (degrees) 114
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  7. #7
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    Oh, what of these "Small base circle" cams for 383 conversions, should I have been looking into this to elliminate clearance issues on the rods? Whats the give and take with these style cams over the one I now have?
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  8. #8
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    Thanks alot for the guidance guys. I'm still trying to learn this SBC thing. I'm an old 460 Ford guy, so this new electronics infested, swirl headed chevy stuff is a bit beyond my area of expertise. Last time I messed with a GM was my 71 Chevelle and that was when I yanked the engine, sent it away for a re-do and reinstalled the rebiult one. I cut my teeth really on BBF engines as far as getting inside, it seems that the BBF is a far cry more forgiving, as far as stroking. ANy ways, thanks for you guys being here to hold my hand while I swim thru this 383, I am actually trying hard to not look as "GM dumb" as I really am.

    Thanks guys.
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  9. #9
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    i havent been doing this long but my first motor was a trail and eror 383. first 383 had 5.7 rods ground for clearence for a cam with a lift of .510. this year i put 6.0 eagle stroker rods in it clearence is there for cam .558 lift and can go more but as for block clearence depends on the block. i had to grind oil pan rails and grind some out of the bottom of the bore (piston skirt doest even come close to this area). but what ever u do 5.565, 5.7, 6.0 have the whole rotating assemby balanced
    the longer the rod the broader the power curve correct me on this if i am wrong anyone but pretty sure

  10. #10
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    Well, I spoke to the machine shop today...yea, its been setting there for weeks untouched! The boss machinist has been sick with (new-moan-ya) ...lol...I cant spell that one... any way, after talking with him, I told him I am just not feeling good about that 400 rod, so I instructed him to get with my program and get the eagle crank and eagle SIR rods, and asked him to locate a piston that used a standard ring package. I will follow up with him tomorow to remind him that we need a zero deck height and I may ask him to fly cut the pistons a bit before its ballanced just in case I end up with this engine in 2 years and want to toss it into my Chevelle. I think I'll have him cut the pistons for about a .6 lift cam with a 108 lobe sep. just in case.....hey, you just dont know. Anyways, Im getting close, I hope this guy is feeling better and can get his shop running again. Maybe shortly after the new year I'll have a SBC in my garage on my stand to paint purple. Real men have purple engines, or at least real men that let thier 5 yr old girl pick the colors...lol.
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  11. #11
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    Originally posted by techinspector1
    the jury is still out on long versus short rods as far as horsepower is concerned. Here are 2 views on the subject. I don't know who wrote the Desert Performance piece, but the second piece was written by Ron Iskendarian, son of the famous "camfather" Ed Iskendarian.
    http://www.desertperformance.com/bulletins.htm
    http://www.iskycams.com/techtips.html#2005
    Both of those are interesting articles, BUT they do not show any concrete evidence of what they claim, like dyno sheets of the same engine with different rods (I remember seeing this somewhere, but I can't find the magazine to scan it)...So in other words, it's just their opinions as far as I'm concerned.

    When you consider that stock 400 rods are over 20 years old and are probably fatigued, and it would be smarter and probably cheaper to just by Eagle SIR rods, why wouldn't you buy the 5.7" rods? Isky even admited in his article that the longer rod will increase HP, but by a lower amount than what he claims to be "hype", so if youre changing the rods and pistons... why do it half-assed? Get the longer rods with the 5.7" pistons and make the extra few HP, whether it be 5-7hp or 30hp, youre changing the rods anyways and every last HP counts.

    Apparently rasing the rod/stroke ratio has an effect of moving the power band up a little...I don't know if this is entirely true as I have not seen any tests to prove this.

    And the clearance problem with 5.7" isn't that bad with the Eagle SIR rods, just take your time and use clay to measure the clearances....And like I said TAKE YOUR TIME, you can't replace metal if you've taken too much off.
    Last edited by BlueDSM; 12-18-2004 at 09:43 PM.

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