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Old 01-15-2005, 11:27 PM
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5.7 or 6.0 in a 383

which rod is a better choice for a 383.. i know a 6.0 rod will put less stress on the engine because it will produce less side thrust.. but is there more of a chance of the rod hitting the cam with a longer rod? what other problems would there be with the longer rod? or would my best bet be the 5.7?

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Old 01-16-2005, 12:26 AM
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5.7 vs 6.0

The 5.7 rod is the cheapest to purchase and dwells longer than the 5.65. The 6.0 is more expensive and the power gain vs dollars just doesn't make cents. The problem that exists is with the connecting rod bolt length. It may hit the cam. I opt for scat cap screw rods. They are desined to clear. I am told but have not tried it; to use ARP bolts on the stock 5.7s. The bolt is supposed to be angled enough to clear the cam.

The reason a longer rod has less side thrust is because the wrist pin sits higher in the piston lessening the rod angle. If it didn't sit higher the length of the rod would push the piston into the head.

When purchasing the piston you must specify rod length to make sure the wrist pin hole is in the correct place.

Last edited by bracketeer; 01-16-2005 at 05:20 AM.
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Old 01-16-2005, 09:08 AM
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Doo ya no, rod length don;t have a big affect on side thrust unless chambers ignite wrong
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Old 01-16-2005, 09:28 AM
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ya i no

were talking 5/100ths of an inch
but the difference in price is much bigger

Last edited by bracketeer; 01-16-2005 at 09:35 AM.
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Old 01-16-2005, 11:31 AM
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I don't know about you guys but the price diff. is hardly there. Check out HERE


1,135 for flat top 5.7 rod
1,199 for flat top 6.0 rod
$64 really is not that BIG of a price diff. however for the gain you make going from 5.7 to 6 I would save the 64 for something more important.

Chris
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Old 01-16-2005, 12:33 PM
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Torque 6inch vs rpm 5.7
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Old 01-16-2005, 12:47 PM
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well i found some scat rods on ebay for 245.. forged.. with arp cap screws.. and the 5.7 are only about 20 bucks cheaper than the 6.0... so what about something like this .. where the price is that close.. tax time is growing closer and i need to know what to buy! lol.
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Old 01-16-2005, 12:55 PM
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I have destroyed two sets of the scat i beam rods they are only rated to 6500 rpm!!the big end will oval if you rpm these rods!
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Old 01-16-2005, 03:43 PM
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hmmm.. glad you informed me.... i might have to look at some other kind now.... would hate to put it together and have to tear it all down within a few months.... thanks for the heads up.
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Old 01-16-2005, 04:02 PM
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most of the pistons designed for the 6" rods have the wrist pins located in the ring grooves which can lead to oil consumption. i used 5.7" for my proj.
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Old 01-16-2005, 06:40 PM
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Cost

Go spend the extra $65 on rods. Let me know how cheap the rest of the trick parts were to make it work.
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Old 01-16-2005, 09:42 PM
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It really going to depend on your intentions with this motor. By that I mean you have to ask if you are going to spray it or blow it, or are you going to run N/A now and in the future. Also, what is a reasonable RPM limit for you? Do you wanna spin it up to say 7500, or are you going to hang down around 6500 max?

The reason for all these questions all boils down to weight of the rotating assembly and strength of the piston crown. The more abuse you plan to throw at it, the stronger it needs to be.

We've had debates on this back and forth for years on another board I frequent as the strength differences between I-beam and H-beam rods, and I've never seen any good evidence either way. A Scat H-beam is a good solid affordable rod that will hold a ton of power, but the Lunati pro-mod I-beam is just about as strong as your going to find (unless you step up to an Oliver or other high dollar rod). Eagle, Scat, Lunati; All good choices for strength. H-beam is easier to clearence for generally, and always get high quality fasteners, be they cap screws or bolts. ARP is hard to beat..

Now down to the brass tacks of your question..

As you increase the rod length, the pin is going to move up an equal amount in the piston, which will decrease the compression height of a given piston. This decreased compression height will give you less material on the piston crown, and make the piston lighter, but not as capable of withstanding the kind of pressures you would see on a blown or nitrous motor for the long term. The smaller piston would also place the pin about 20 thou into the oil ring land, and require a support ring (or rail) for the oil control rings. Not such a bad thing, but it's up to you. If your looking to run N/A all the time, and would like the lightest possible piston, then this is the way to go. Just don't spray 250 on it and expect it to live long.

The 5.70 inch rod will move the pin down enough to gain some valuable compression height (and strength) if you plan to spray it or go with a blower. Also, if your building it for a lower compression and need to use a dish , you'll gain some thickness in both the ring land area and the crown with a shorter rod, which makes for a happy forced induction piston but also makes for a little heavier piston/rod combo.

Personally I like a 5.850 rod, but they cost a little more. The give you more meat up to (like the 5.7 rod), but you can get VERY light pistons for them, and the pin doesn't protrude into the oil control ring land. I run 5.850 Scat forged H-beams in my 383, and regularly (read every day... lol) spin it to 7000 with no troubles (except for tires). I put around 430 to the wheels, and spray 200 on top of that, and I've never had a problem. The key to high RPm usage is to make sure the main caps don't "walk" and take out the bearings, and that is solved with good quality 4 bolt caps and good hardware.

Just decide on your budget and goals first, then buy accordingly.

Dave C.
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Old 05-03-2008, 09:46 PM
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Quote:
Originally Posted by 280zxWith305
which rod is a better choice for a 383.. i know a 6.0 rod will put less stress on the engine because it will produce less side thrust.. but is there more of a chance of the rod hitting the cam with a longer rod? what other problems would there be with the longer rod? or would my best bet be the 5.7?
Pistons can be lighter with a longer rod but they may rock in there bores a little more... We have to keep a eye on rod weight as to not cancel out the bob-weight savings...crank counter weights can be lightend at that point and with a light flywheel or small dia. converter faster than normal engine response can be anticipated...
6.125 or so is about it for a 3.75 crank in a stock deck block... I would go 6 inch as you are not using super-shorty pistons.."tend to rock,burn oil,Race only...
Keep rod weight as lite as possibe...
all in all long-rod combos work in theary but to take full advantage You will have to have a stout wallet
Without the lite crank , lite flywheel, and low gears and trick bob-weight style of balance job , the rewards of a trick long rod motor may not be met.....GO FOR 5.7 RODS.....
DR

Last edited by Haulin327; 05-03-2008 at 09:57 PM.
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Old 05-04-2008, 07:58 AM
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Any of the 383 engiens we have built for the street we have used 6 inch rods in all of them with zero problems and we have some with the SRP pistons and we used a spacer ring in those pistons.

Engineman302 the engine in this link http://www.chevelles.com/forums/show...highlight=DYNO has run for 3 years now with no oil consumption problems and when should I start seeing this problem??? and why would they make a piston and ring package that was going to use oil??? HMMM.

We have also used the Mahle pistons which use a metric ring package and use no spacer rings in the pistons and again no differance between an engine with SRP or Mahle piston as far as using oil.

We build a lot of circle track engines with 5.7 and 6.0 rods and we do see a differance on the dyno and going from a 5.7 to 6.250 rod there is even a bigger differance on the dyno.

When using a stock 400 rod or a 5.7 rod in most cases you are restricted to exteranlly balancing the crank which will run into more money when you have buy a weighted flywheel or pressure plate and balancer and its not hard to find a neutral balanced flywheel, flexplate and balancer.

I would have to say there is less friction in an 383 using a 6.0 rod over a shorter rod.
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Old 05-04-2008, 08:56 AM
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Zombie thread.
Hahahahaha

Neither Engineman302 or the OP have been here for 2 years and 11 months.



Later, mikey
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