What's wrong with running stock 400 sbc rods? [Archive] - Chevelle Tech

: What's wrong with running stock 400 sbc rods?


Junkyard Dawg
Sep 23rd, 06, 3:49 AM
I have a 400 sbc sitting in my garage that I want to build. When I got it, it was a complete long block.

Everyone says the stock 5.650 rods are junk and to run 5.7 rods.

My question is what is wrong with the stock 400 rods? Are they weak? Are they not good for a high performance application?

If it helps any I was planning on making the engine into a nice street engine that can hold it's own. I was planning on running a nice roller cam but not build it radical. I just want something that would be close (if not more) to the power of an LS1 but not be tempermental and still have good street manners.

Also what about reusing the stock pistons? I don't plan to spray this engine. I will however ditch the 882's and run a set of Vortecs unless there's a better head to go with.

greg_moreira
Sep 23rd, 06, 4:31 AM
Couple reasons really. Number one.....It dont matter how long the rod is.....most any small block chevy STOCK rod(5.7 inches, 24 inches.....9 feet....whatever) they aint all that great for performance apps. They arent the safest pieces you can use. You can work on em and get em prepped to take a bit of a beating, I wont doubt that. But for the money invested in refurbishing stockers to do a good job.....your most of the way to a descent forged(like a scat for example...good stuff at a good price)......so..........might as well step up since your almost there! Same with heads for example. Spend 600 bucks on doing the best you can with stock smoggers....or spend 200 more on the vortecs your looking at that will end up much better in the end.

Another thing....longer rods tend to reduce the load on the bores a hair. So the longer you go(rod lenght), the better chance you have on releiving stress and taking away load from the bores.

Also, longer rods are said to be LESS sensitive to detonation. Longer rods dwell longer at top dead center and less at bottom dead center. The longer dwell time at TDC is said to ease up on the pinging factor(good thing))....but some of these things are kinda hard to test. Im not building two identical motors with different rod lengths and running them just as hard and just as long just to see which one wears the bores less or pings less. Fortunately, the load thing can be graphed out, and although the difference is very minimal, there is a difference so you can see it. The pinging thing....you just have to try it, but its said to work by many and Im sure someone out there smarter with more time and cash than me has tested it in order for this theory to have developed.


Lastly....longer rods(especially aftermarket with better profiling) often allow for an easier(and cheaper) internal balance job. This is also proven in a lot of situations.

In the end.....buy GOOD rods. Thats the most important thing. You will hardly notice some of the other things I mentiond...but you will know right away if you break a rod.

dreis454
Sep 23rd, 06, 6:56 AM
That is all good advise BUT. You can run the short rods in a 400 that will be kept under 6500. I ran my 400sb for 10 years in a 69 Nova bracket car that ran 11.50's @ 117,I shifted @ 5800 1 to 2 & 63 2 to 3. car had 4.56 gears in it.
After running it like that for 10 years (well over 500 1/4 passes & never blew up) I finally pulled it apart & put in the 5.7 eagles. Then I shifted @ 7200 & when 11.00 & 10.20 on a 150 N.OS. hit in 2 & 3. Don't be too afraid of the short rods but do put good bolts (arp) in them.

bracketchev1221
Sep 23rd, 06, 8:08 AM
I believe that the 400 rod is 5.565 in length. So the difference in in length is greater.

forcd ind
Sep 23rd, 06, 8:55 AM
usually you can go to a longer rod if your changing pistons, helps side loading, but the stock rods would be fine for what your doing

383Malibu
Sep 23rd, 06, 9:46 AM
...My question is what is wrong with the stock 400 rods? Are they weak? Are they not good for a high performance application?...
Also what about reusing the stock pistons? I don't plan to spray this engine. I will however ditch the 882's and run a set of Vortecs unless there's a better head to go with.There is nothing wrong with the stock 400 (5.565") rods for a mild (say 400 hp) build, although they still need re-conditioned and good rod bolts. And, as Greg mentioned, at this point you're getting close to the price of aftermarket rods.

Likewise, for a mild build with no nitrous, there is nothing wrong with the stock pistons. Of course, if you go to a longer rod, you will have to change the pistons also and then it makes more sense to go with an aftermarket forged piston.

bigjimzlll
Sep 23rd, 06, 10:06 AM
The longer the rod...the lighter the piston

pdq67
Sep 23rd, 06, 12:33 PM
My 406 has stock rods in it and has done fine shifting up around 6,000..

I didn't like to go much higher b/c the big motor just kinda felt/sounded like it was straining up there..

Not like the little bitty junk301 I've ran before that would go up until my points bounced fine and that was like 7,500 rpm or so back then.. The little sucker was made outta junk parts and was unbalanced to boot!!

pdq67

Junkyard Dawg
Sep 23rd, 06, 12:44 PM
Thanx.....and yes my plans are to not spin this engine past 6000 rpm.

As mentioned I wanted to run a roller cam, probably a hydraulic unless it's better to run a mechanical.

Seems like most people build 400's to be tempermental 500 hp engines. My goal was to build mine with at the most a fairly lumpy idle....nothing radical...yet can give the LS1 boys a run for their money.

As mentioned I don't plan on spraying this engine. It may see some track time but it will spend 80% of it's life on the street.

Ditto on the ARP hardware. I guess for my application it's a hit or miss sort of deal.

Also I'm curious as to how much power I'd be making on what I'm wanting to do? You think 450 hp is out of reach? Or do I need to run some sort of wild cam/head combo for that?

dreis454
Sep 23rd, 06, 12:53 PM
450hp is not out of reach but you are talking about a good size roller & decent set of heads. On mine I had a ft solid & dart sportsman 2's with 11 to 1 comp. The key for the cam is big duration in a 400sb. I was running 266 & 269 @ .050 on a 108 LC

Junkyard Dawg
Sep 23rd, 06, 12:57 PM
Would I need to run AFR's to achieve this goal? Or could I get away with Vortecs?

And would running the duration I need to get to make 450 hp cause the engine to be tempermental?

JUNK YARD DOG
Sep 23rd, 06, 1:05 PM
i have no problem with 400 rods at all with good bolts.i have run two engins identical in heads and cams and they both ran the same times the 400 rod motor did show a little bit better 60ft times but that has to do alot with track conditions.as mentioned i dont recomend turning them up over 6500 if you wont them to live.myself i would not spend the money on the roller for the street ,i think i would take that money and put in in a set of much better heads than the vortecs.you will be spending alot of money on those heads just to get them ready to run a roller cam.i also changed to a roller from a solid cam and did not pick up any better times at the track it did lighten my bill fold some though.for the street the vortecs and a good solid cam will be alot of fun to drive though.and remember its your money so spend it wisely

Junkyard Dawg
Sep 23rd, 06, 1:34 PM
i think i would take that money and put in in a set of much better heads than the vortecs.you will be spending alot of money on those heads just to get them ready to run a roller cam.

What kinds of mods must be done to make a roller cam work with the heads?

Also did you mean to say you went from a solid hydraulic to a solid roller and dind't see any improvement?

So are you recommending a solid flat tappet for the street?

pdq67
Sep 23rd, 06, 4:17 PM
Here you go from over at SGCOG!!

They have a big-time "sticky" on Vortec's!!

http://www.nastyz28.com/forum/showthread.php?t=56505

pdq67

Alwhite00
Sep 23rd, 06, 5:11 PM
I'm running stock rods in my .030 over 400 SBC. Runs great and pulls awesome. This is by far the best engine I have ever owned as far as power. Nothing radical. Performer cam, Weiand stealth intake, 650 CFM Edelbrock carb, Headers, Performance HEI, Ect. I shift around 5,000 right now as it's still pretty fresh. I probabally will not spin it past 5,500 as it has everything stock on the bottom end as far as fasterners and such.
I have not experienced a 400 with the long rods so I can not attest to the difference. I'm sure they are better for the above mentioned reasons but I am very happy with mine. I built it 10 years ago and it sat on a engine stand till this spring. Not even sure the long rod was the "in" thing back in 96 or if it even existed.

LK

pdq67
Sep 23rd, 06, 6:46 PM
I put my 406 PAW rotating assembly kit together back in '85 in the dining room.

I made a little box-cradle for it that just fit the pan rails and I just rolled it around using three pieces of small dia. pipe.

I still have the box up on the shelf in the garage and it's now on my motor stand after being pulled for my 496.

pdq67

sschevellefan
Sep 23rd, 06, 8:05 PM
My buddy has a 406 with stock rods and crank, forged dished pistons, Dart pro 1 215cc cheads with 72cc chambers and a Isky 304 Mega cam and runs it up to 6500 with no problems. Been this way for almost 5 years. runs high 11`s. Another friend had a 383 with the 400 rods and was spinning it to 7000 and was running mid 11`s. no problems with that one either.

JUNK YARD DOG
Sep 23rd, 06, 8:38 PM
dawg i had a solid flat tappet 556 533 lift and 256 264 dur.at 50 and went to a solid roller 615 lift 256 dur at fifty with no gain in et.rollers take bigger springs and alot more spring pressure .you will need studs and the heads cut for the bigger springs and the guides will have to be cut to take more lift .by the time you do all that machine work on the heads plus the price of the heads if you are buying them you can put a little more with it and get much better heads that are already fixed for rollers or solid cams.im a firm believer in solid cams roller or flat tappet for street or track.with good rocker arms there is very little valve adjustment anymore.if its something you are driving everday then go for a hydralic .as for as performance goes hydralic rollers are way to heavy on the valve train and you are leaving horse power on the table.now there are many ways of doing things and this is only my way of thinking

pdq67
Sep 23rd, 06, 9:16 PM
Imho, the best of both worlds is a good solid lifter cam!!

Longevity even tho you will need to check lash periodically.....

And rpm capability!!

pdq67

Dave Birdwell
Sep 23rd, 06, 10:59 PM
BTW, ALL Chevy rods (except for the powdered metal ones) are Forged. Most engine builders will tell you, IMHO, that the rod itself is not the weakest link, it is the piston, or the rod bolts. One of our techs has a smallblock rod hanging on the shop wall that came out of a motor that hydraulic locked. It is bent 90 degrees, but it ain't broke...

pdq67
Sep 24th, 06, 1:57 AM
That's why I am NOT a fan of PM rods!!

In my dumb, old-fashioned, Mechanical Engineering, humble opinion, they JUST aren't tough enough after all is said and done!!

Do a long term "Charpy" notch test on them at say 100,000 miles running wide open in a Z-28 motor and then If the SOB's were 100 percent solid/compacted I'd use them, but I don't think they are so I figure therefore they have weak spots built into them when tested in THE REAL WORLD LONG TERM!!!

But everybody know's how I am about the "new and improved" stuff.

pdq67

Junkyard Dawg
Sep 24th, 06, 2:29 AM
dawg i had a solid flat tappet 556 533 lift and 256 264 dur.at 50 and went to a solid roller 615 lift 256 dur at fifty with no gain in et.rollers take bigger springs and alot more spring pressure .you will need studs and the heads cut for the bigger springs and the guides will have to be cut to take more lift .by the time you do all that machine work on the heads plus the price of the heads if you are buying them you can put a little more with it and get much better heads that are already fixed for rollers or solid cams.

My oval ports have the screw in studs and guideplates too, but for a roller there's actual mods needed done to the heads I see....cut guides and cut spring areas?

I may have to yank out the XE284 and go with a solid flat tappet....power is key, the car isn't a daily driver...I don't suppose I'd need to mod anything to make a solid flat tappet work would I? (other than a spring swap but I plan on that anyways)

Also I have oval ports and intend to keep them so I guess I can't go too crazy on the cam, just have to find what works right. :)

JUNK YARD DOG
Sep 25th, 06, 12:17 AM
hold on dawg i thought you were talking about small block vortec heads they do need alot of machine work .if your running big block heads you will have to ask some body besides me on them sorry for the confusion on my part

Junkyard Dawg
Sep 25th, 06, 3:51 AM
I was talking about Vortecs, then I got to thinking about my big block which is why I wandered off and posted that, sorry I went a little off in left field. :o

Now I feel like a dummy....