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Old 09-13-2008, 09:55 PM
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400 Chevy with Short Rods

I'm building a 400 chevy targeting just over 300HP. Will using the 5.56" rods ruin this engine?

If I run the 5.7 rods I'd need to machine the pistons (stock 24cc dish) & I worry about the top ring & lack of ring land material.

I'd also have to clearance the rod bolts to clear the block & possibly the cam.

This all seems like a majior pain in the rectum & too time consuming for a stock rebuild.
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Old 09-13-2008, 09:59 PM
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Stock 400 rods can't take much abuse, and when they let go they ruin
everything. Do yourself a favor and fit the 5.7 rods in there, you will
be glad you did.
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Old 09-13-2008, 11:11 PM
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I personally think they would do just fine for something as mild as a 300hp 400 sbc. One would not have to spin it very high to obtain that kind of power
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Old 09-13-2008, 11:46 PM
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Quote:
Originally Posted by automotive breath
Stock 400 rods can't take much abuse, and when they let go they ruin
everything. Do yourself a favor and fit the 5.7 rods in there, you will
be glad you did.
Is there any particular reason that you can explain to me why they wont take much abuse & how they'd ruin everything?
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Old 09-13-2008, 11:54 PM
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Quote:
Originally Posted by HalfOunce
I personally think they would do just fine for something as mild as a 300hp 400 sbc. One would not have to spin it very high to obtain that kind of power
I also felt they'd be ok for my application.
I'll be shifting under 5000 rpm & not doing any drag strip racing.
I know it'll wear the bores out before it hits 80,000 miles.

I'll be starting out with fresh (torque plate honed) bores, new 24cc dish pistons, & cast rings.

I am going to have the crank turned & polished .010 .010

I have over 50 rods to choose from so I should be able to pick a set that matches weight, strong I-beams, & hopefully doesn't need the big end resized.

If the rods do need any resizing work, I'll definately spend the money.
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Old 09-14-2008, 12:46 AM
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The 400 rods are very week at the big end. Maybe not a problem
for what you want to do.
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Old 09-14-2008, 04:38 AM
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What will ruin the engine are shortcuts and/or cheap crappy parts. When you know something going in and do it anyway, well, I guess you know what to expect.
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Old 09-14-2008, 03:07 PM
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I read thru the contribution to your question. My take is this; the 400 short rod is indeed less than ideal strength wise, a lot of compromises were made on the big end to fit it into the crankcase. In a mild engine this isn't a big problem, but it's there. These rods also accelerate wear on the piston and cylinder wall because they make some pretty sharp angles that would rather push the piston out the side than up the bore. Again in a mild engine that doesn't see more than 4500-5000 RPM this has proven to work. But in a high power high RPM engine the situation soon causes problems with ring seal and accelerated wear. Pushed far and hard enough you could get a catastrophic failure.

If you run a 5.7 inch rod, you will have to build this like the popular expansion of the 350 to 383. You will need a piston that re-positions the pin to keep the crown at or below the deck. This is not done by milling the piston crown as that would compromise too much strength in this highly loaded, very hot section of the piston. You will also experience rod and cam lobe interference. The choices here are grinding on the side of the offending rod in and about the area of the bolt head -- or -- using a small core cam to get the necessary clearance. The rod grinding approach is the most common, either done at home or some manufacturers sell a clearanced kit.

Be careful with a clearanced kit. When setting these up, sometimes they still have space problems with the cam and you're driven to do a bit of grinding. I recommend that you don't by a clearanced kit that is also balanced for this reason. Its less expensive to check out the parts of a clearanced kit and make clearance adjustments if necessary then send the assembly to the balance shop. There have been problems with pre-balanced assemblies which then result in the expense of rebalancing after you have to remove material from the rods to clearance it, so just do it and pay for it once.

Where and when you have to grind on rods and rod bolt heads, I much prefer to use the cap screw rod where the bolt threads into the shank end rather than the bolt and nut design. If you have to clearance the cap screw style rod, you're at least not grinding on the highly loaded bolt head and rod bolt seat.

Bogie

Last edited by oldbogie; 09-14-2008 at 05:54 PM.
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Old 09-14-2008, 05:39 PM
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For what it's worth, I'm running the stock 5.565" rods and the stock crank in the 400 I built and put in my car this summer. I made sure to use ARP hardware throughout the bottom end. I have run this motor to 6000 rpm after break in already and though I cannot predict the life span of this, it was what I did after much research on building my 400. Have the rods reconditioned and use good hardware and you shouldn't have a problem with your build, it is mild enough to handle what you are building. I'm pushing 450/500 hp/tq with mine.
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Old 09-14-2008, 06:32 PM
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side loading is what short rods do
they will wear the inside of bank 1
and the outside of bank 2
your rings will not like it
question is how fast will it happen in a performance engine
i used 5.7 rods myself and ofcourse i believe i should have used the 6 inch rod now
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Old 09-14-2008, 06:54 PM
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6 inch rods are best but put the oil ring over the wrist pin.
Generally speaking, only 2 rods will probably have to be ground to clear cam lobes. ARP makes bolts with tapered heads to reduce grinding.
Balancing and then grinding 2 rod bolts.... or even 8...... doesn't affect the balance enough to worry about. Think about "overbalance". That is about 20 grams on EACH bob weight. So IMO a little grinding/ 5 grams off each of 2 rods is irrelavent.
The X-treme pistons are an advantage, but expensive.
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