[torqhead]

Wondering what the stock 400 rods will support as far as RPM limit. The rotating assembly has been balanced.

[dataway]

I turned my bone stock (crank and rods), 68 YS 400, with 100K miles on it 6,300 rpm once .... made a little smoke and bent a push rod. Drove it another 30K miles after that, touching 5,000 quite often. But then I'd guess that next one that came off the assembly line could have blown all to pieces.

Answer probably has to come from someone that has raced a stock crank/rod engine many times.

[tom s]

Stroke and rod bolts will play a role on what would be considered safe.Tom

[Skip Fix]

I know John Schloe with his RAIV 400 stocker when they had to run stock rods used to buzz his close to 7000. But they were meticulously prepped.

[455TA]

My 455, stock crank, stock rods with arp bolts, and TRW pistons is set to a 5700 rpm rev limit and it has hit it more times than I can count while playing on the street, with no issues. I'm debating on setting the limiter to 6000 so I can keep from hitting the limiter on the track if I don't quite shift fast enough.

[STEELCITYFIREBIRD]

I would think it varies with the weight of the piston too (inertia).

[hurryinhoosier62]

The rule of thumb preached by H-O Racing and Nunzi Romano was 5,700 rpm for a STOCK 400 with factory cast rods. If you’re utilizing a build that has been rebalanced with lighter pistons and pins along with rods that have been properly inspected, resized with GOOD rods bolts, I wouldn’t see why a 6,000 rpm red line would be a problem.

[Will]

The factory rods aren't really the problem. They are good, solid units. What leads to failure of stock rods in most cases is the bolts. The factory bolts aren't very strong.

Having said that, the biggest problem with factory rods is you probably don't know their history. How many millions of cycles do they have on them? Have they been over-revved before? They could be fatigued and you wouldn't know it 'til it's too late.

With that out of the way and assuming the rods aren't on the verge of failure from age and duty cycles, I wouldn't hesitate to rev a 400 to 6500 RPM with stock rods *IF* you are running lighter pistons/pins, the rods have been properly prepped, and you're running good ARP bolts. As the stroke increases that RPM limit comes down significantly. I'd be leery of running a 455 to 6000 with the same rods.

I have a set of stock rods that should be up to the task. They are the original rods from my Formula, so lived their life in a 400 that was treated gently for the first 80,000 miles of its life. They had 130K on them when I took the engine apart. Even that second 50K that they experienced under my ownership wasn't that bad. I learned early on that revving the snot out of the engine was pointless. The car didn't have a tach back then but I learned to feel where the best shift points were and they were well before the engine was done revving.

I had those rods magnafluxed, weight matched, fitted with ARP bolts/resized, beam polished and shot-peened. I wouldn't hesitate to use them in a low-buck 400 build at this point.

[4zpeed]

Originally Posted by hurryinhoosier62

The rule of thumb preached by H-O Racing and Nunzi Romano was 5,700 rpm for a STOCK 400 with factory cast rods. If you’re utilizing a build that has been rebalanced with lighter pistons and pins along with rods that have been properly inspected, resized with GOOD rods bolts, I wouldn’t see why a 6,000 rpm red line would be a problem.

Agreed:

In addition, you will likely find any weak points in the valve train before having a rod issue.


Frank

[torqhead]

Originally Posted by 4zpeed

Agreed:

In addition, you will likely find any weak points in the valve train before having a rod issue.


Frank

The whole top end is new, all roller. The short block had been rebuilt previously and had minimal run time on it when I opened it up, but noticed it had been balanced. Don't know what kind of pistons are in it, although they're new since it was punched .030 and don't know if the rod bolts were changed. Needless to say cam/valve and everything else defines how a motor will perform and where its shift point from a performance perspective should be but I was just curious what the gang here on the forum views on the rods.

[Skip Fix]

My first 455 I had RAIV heads on had good bolts and polished beams on stock rods and I buzzed it to 6000-6100 all the time. Rods are in the stock 400 in the 81 now, the RAIV heads got billet Crowers in the next shortblock for insurance though-not many choices back then.

[Tom Vaught]

Originally Posted by hurryinhoosier62

The rule of thumb preached by H-O Racing and Nunzi Romano was 5,700 rpm for a STOCK 400 with factory cast rods. If you’re utilizing a build that has been rebalanced with lighter pistons and pins along with rods that have been properly inspected, resized with GOOD rods bolts, I wouldn’t see why a 6,000 rpm red line would be a problem.

X2, I ran my 389 + .060" (same as 400) WITH 143 GRAM MOPAR PINS AND A SET OF GOOD ARP ROD BOLTS, to 6500 rpm many many times over 15 years. Only thing I hurt was the camshaft and one lifter in that time period. I always thought that the lighter reciprocating mass and the crank balance job helped a lot. I also had a very good rev limiter in the car. Saved me a couple of times when the rear axle pieces broke.

But I did have the rods I used x-rayed and magnafluxed before I used them. Factory Cast
1967 New Rods right from GM.

Tom V.

[PurelyGTO68]

Agree with the others also...
I used to do a lot of street and strip racing back in the late 80s. Mostly 400 cubic inch engines....stock rods, bolts and pistons would normally be good to 5500 rpm or so. When we built an engine, we spent quite a bit of time prepping the rods (stress relieve, hardness test, weight match, resize big end, lighter pins, Mopar bolts etc). Those engines would usually be good for 6500 rpm if the cam grind was supportive.

The major thing we learned is bolt torque method is critical. We liked the torque to stretch method since that seemed to have more consistent results for our builds. Good quality rod bolts are a must in my opinion...

Sent from my XT1585 using Tapatalk

[PunchT37]

I have a 455 here with stock rods, bolts, trw's and heavy pins. Been together since the 80's. Been past 6000 a few times and 5600 to 5700 a LOT. Still alive today. Runs fine today. Good oil pressure, no knocks, etc. Has ported 6x's and a 246/253 cam. So, it wants to rev. Lucky, I guess.

A 400 with a 3.75 stroke should be able to out do that.

[PunchT37]

Course, I wouldn't run em in any new engine I built. But, as others have said, I don't think they're as weak as most believe.

[Speargun]

I use to turn my daily driver 400 with +.030 TRW slugs and stock rods, crank, & bolts to 7200 on a regular basis. It was a 557 block and finally spun the #3 main bearing after 3 years and 25k+ miles.

[PunchT37]

Originally Posted by Speargun

I use to turn my daily driver 400 with +.030 TRW slugs and stock rods, crank, & bolts to 7200 on a regular basis. It was a 557 block and finally spun the #3 main bearing after 3 years and 25k+ miles.

We turned my buddy's 428 to 7200 to 7300 MANY times with the '58 to '62 rubber rods. Never lost one.

Sleeper car. '79 GP. Dark maroon with that motor. Out with the 301, in with the 428. What a blast.

[JLMounce]

455 with stock rods, stock crank, .030 Speed Pro's. The engine sees 5700 every time it's driven for the most part. I have a fuel and spark cut set at 6000 rpm. On a shorter stroke 400, with stock rods that have been prepped, I wouldn't worry about 6000 rpm.

[PurelyGTO68]

Originally Posted by PunchT37

Course, I wouldn't run em in any new engine I built. But, as others have said, I don't think they're as weak as most believe.

Agree. With the availability of forged rods at reasonable prices these days....it doesn't make sense to run stock rods unless it's a bone stock build.

Sent from my XT1585 using Tapatalk

[JLMounce]

Originally Posted by PurelyGTO68

Agree. With the availability of forged rods at reasonable prices these days....it doesn't make sense to run stock rods unless it's a bone stock build.

Sent from my XT1585 using Tapatalk

I believe Dave acquired the shortblock pre-assembled. If it's otherwise in good condition without the need for a full tear-down, I'd say run it unless it's a full race build.

I agree if you're doing the whole thing from the ground up, worth it to go with aftermarket rods, pistons, bolts etc.