5.565 or 5.7 Connecting Rods in 383 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 01-13-2005, 07:40 PM
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5.565 or 5.7 Connecting Rods in 383

Hi there,

Went down to talk to my mechanic today about building a 383. I told him i wanted to use my existing PM 5.7 Vortec connecting rods and he didnt like the idea of having to grind on every rod to make them fit correctly. Instead he wanted to use a 5.565 rod out of a 400 because he said they wont have clearance issues and I will gain more power by doing this. Is this true? I really dont want to buy new connecting rods if I dont have to. Is it that big of a deal to grind on the 5.7's to make them fit? Any advice would be greatly appreciated.

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Old 01-13-2005, 07:47 PM
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rods

Here's the deal. The 5.7 rods have longer connecting rod bolts than the 5.65. The top of the bolt (depending on cam size) may come up and clip the cam lobe. The 5.65 rod was developed at the factory for this not to happen.

Paying a machinist to grind your rods is expensive. It has to be assembled, tested, ground if necessary, taken apart, and balanced.

The 5.7 rod well dwell longer and increase hp and torque. He lied. Get a new mechanic!!!

You can buy cap scew 5.7 forged rods for about 400 bucks. They don't have the clearance problem. They are worth the money. I'd rather spend money on good rods than give it to a machinist. I wouldn't give your mechanic a dime.
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Old 01-13-2005, 07:57 PM
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I would stick with the 5.7 rods and upgrade them with ARP rod bolts. These bolts usually have a shallow cap with a small angle on the outside edge to help with clearance, plus they are much stronger than stock. 5.565 rods are no good in my opinion, they don't dwell as much plus they put a lot of side loading on the cylinder wall.

Are you rod journals on the crank you have the same as a 350? If so then stock 5.7 rods should fit without any grinding.
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Old 01-13-2005, 09:02 PM
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Scat 4340 forged steel rods with ARP 8740 capscrews and doweled caps are around $250 from just about everyone. Scat rods will have to clearanced for use in a 383/406 to clear the camshaft.

GM has a set of rods used in the HT383 crate engine PN-12497870 $350 from most of the dealerships. These rods will clear the camshaft without any grinding.

I can't think of any reason to put used rods in a high performance engine.


Larry

Last edited by coldknock; 01-13-2005 at 09:15 PM.
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Old 01-13-2005, 09:10 PM
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If you are using an aftermkt crank, the short rods usually will not work. The counterweights will hit the piston skirt.
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Old 01-13-2005, 10:23 PM
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I have eagle Sir 5.7 rods in my 383 clear with no problem. Well under 200.00 on E bay. I really don't see what the rod length has to do with hitting the cam! The crank is what moves the rod would still have the same clearance wit ha 6 " rod I think .....Am I wrong on this
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Old 01-13-2005, 10:27 PM
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Quote:
Originally posted by 67 Deuce 4 Me
I have eagle Sir 5.7 rods in my 383 clear with no problem. Well under 200.00 on E bay. I really don't see what the rod length has to do with hitting the cam! The crank is what moves the rod would still have the same clearance wit ha 6 " rod I think .....Am I wrong on this
It's not the rod length. The rod bolts are longer and sit up higher on the big end of the rod. That's why GM made the 400 rods with short bolts.

Larry
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Old 01-13-2005, 10:57 PM
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Definitely stay with the 5.7 rods. Or even Better, go with a six inch rod. When u increase the stroke without also increasing your rod length u lose your rod to stroke ratio. In doing so u will lose your dwell time ( the amount of time the piston sits at the top of its stroke, the longer the dwell, the more time there is for your combustion pressure to build on the top of the piston before it starts the power stroke) but u also increase your piston speed. Your piston speed, more so then your RPM is going to be your governing factor as far as when your engine reaches its threshold for staying together.

You will also essentually be losing the pistons leverage to turn the crankshaft. You'd rather use 24" breaker bar then an 18" wouldn't you.

Stock 350
3.48" bore x 5.7" rod = rod/stroke ratio of 1.638

383
3.75" x 5.565" = 1.484
3.75" x 5.7" = 1.52
3.75" x 6" = 1.6


It still isn't as good as a stock 350's ratio but it is the best you can get. It is possible with slight clearancing of the rod bolts, small portions of the block, and with a piston that has an extremely low compression height, which will also mean it weighs less, an added bonus.

The 6 would be best, the 5.7 will work fine, but please, please don't use the 5.565"
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Old 01-14-2005, 12:36 AM
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So it sounds like I should stay away from the 5.565. Thanx for the heads up. Well then, here are my options. Use my existing PM rods, add new ARP bolts and grind them till they fit or buy new rods that will work with a 383 crank where no grinding is required? Does Eagle or Scat make these kind of rods for clearancing issues like mine? I think "bracketeer" made a good statement, "I'd rather spend money on good rods than give it to a machinist." The one thing I dont understand however, is that some people seem get away with no grinding at all and others have to grind to make them fit. How can this be possible? Is one motor that different from another without taking into consideration the lift of the cam?
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Old 01-14-2005, 12:48 AM
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Unless you are using a 6.0" rod there should be no interference problems with the cam unless you are using an extreme amount of lift+duration. The older 2-piece seal blocks and the newer 1-piece seal blocks have slightly different amounts of material in the oil pan area. ( where grinding may be needed) It really depends on the rods you use and the bolts. I would recommend ARP bolts. They already have a bit of a wedge shape to them that aids in clearance. Some rods have more material than others around the crankshaft end. If you were to purchase a 383 rotating assembly you would probably only have to do a slight amount of clearancing on the block. This really is an extremely simple process. Any competent engine shop or home builder should be mor than capable. of performing this.




Also, the rod length has a lot to do with the clearance needed. If you draw it out and think about it, a longer rod, when at top dead center will be possitioned at less of an angle from the engine centerline, meaning it is closer to the camshaft than a shorter rod.
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Old 01-14-2005, 01:01 PM
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I too am building a 383 and was looking at some rotating asemblies. The rods in a rotating assembly should clear everything except maybe parts of the block?
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Old 01-14-2005, 01:27 PM
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rods

First let me start off by stating that rod/stroke ratio making more hp or torque is a non issue...This subject has been brought up many times on this site as well as others, and the numbers if they exist are very small and only come into play in all out racing engines.

I will ask hotrod20s as i have ever time this issue is talked about, What are your dyno findings when testing the theorys of rod stroke ratio???? What did you find in actuall real world numbers say between a 3.48" stroke with a 5.7" rod and say a 6.0" rod????

Chevy21 your engine will run the exact same weather you run a 5.565", 5.7" or 6.0" rod in it................

BOBCRMAN, hit the nail on the head, you really need to be careful with the shorter rod because they will sometimes cause the skirts to hit the counterweights. But to answer you question there are no issues with grinding the top of the rods and bolts for clearance. I have done it many times with no drama. I would use the 5.7" rods but not because they are going to make any more power/torque but because of the issue with the pistons hitting the crank.

Keith
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Old 01-14-2005, 04:04 PM
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The angle on the rod bolt needs to be ground to .375" from the ID of the big end.
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Old 07-11-2008, 10:16 PM
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400 rod bolts in 350 rods will help clear cam, Dema Elgin taught a class where a 383 was built with both rods same camshaft very little diffewrence. Pro stock Engine builders have built engines with all different rod lengths no difference.Nascar says say long rods help on a restrictor plate motor.
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Old 07-11-2008, 10:33 PM
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