I have a very nice 350 4bolt sitting around.

I have a 400 crank turned down and I have 400 rods already resized.

I thought I had the pistons but they are 30 over and the block is std bore. The pistons are hypers.

So do I bore the block and go with what I have

Or go 383 crank and 5.7 or 6.0 rods

Or do I go with the above forged crank, pistons and HD rods?

I'm probably going to sell this so I want to see how many people go the street/strip cast way and how many want more. It may find it's way into my 76 truck or 65 El Camino though.

I have appropriate heads either way both iron.

if the block has no wear i wound not bore it,the cheapest way to go is to buy new pistons std. bore.there is nothing wrong with using 400 rods in my book but i would use good bolts.if you have to bore block then you will have the pistons.i have had two 383s both built with the 400 rods with no problems .the last ran a best 7.40 in the 1/8 mile in my chevelle ,sold the moter to a friend with a camaro he has ran a some 7 teens with it.nothing special about the motor ,and that is running 186 cast heads with cast flat top pistons.i also have 400 motors with same set ups one with 400 rods and one with 5.7 rods and there is no time difference in the car at all.just my thoughts

good stuff. I think there are trends to overbuild out there. I haven't decided which way to go but I didn't look at the rods until today. Guy said they were 400 rods.

Nope they were 6 inch forged and had been machined to work with a 3.75 crank.

So I've got some figuring to do.

Thanks for the great advice and I'll let you know what happens.

jobberone the 6 inch rod would be over kill for sure in a every day engine in my book, anyways they would be great in a race motor because of the lighter pistons.if you are going to have to get new rods and pistons you might as well get the 5.7 rods and pistons to match.there is no difference in the money over the 5.56 rods and 350 pistons nowadays as you probably know

Why would 6" rods be overkill in a street motor? I'm pretty positive there are guys here that run 6" rods in their street/strip motors. From what I know, I don't believe their overkill. What would be overkill is if someone were to put some huge cam just because it's big on a daily driven motor running 87 octane and 8:1 C/R....or...running extremely high compression in a street motor and trying to use 91 octane....you get my drift? Not trying to knock on you Junk yard dog, but I don't see how 3 tenths more on a connecting rod could be overkill in a street motor. I'm no expert here, so I can obviously be wrong here and/or have misunderstood the differences between 5.7" and 6" rods.

Originally posted by jobberone:
I have a very nice 350 4bolt sitting around.

I have a 400 crank turned down and I have 400 rods already resized.

I thought I had the pistons but they are 30 over and the block is std bore. The pistons are hypers.

So do I bore the block and go with what I have

Or go 383 crank and 5.7 or 6.0 rods

Or do I go with the above forged crank, pistons and HD rods?How much has that 400 crank been ground down? If it's near or at .030" under, it's toast!

Like Junkyard dog said, there's no problem in using a 400 crank with a std bore 350 block. Sure it'll be a 377ci, but other then you, who else is gonna know? It's a 383ci for all they know ;) :D

If the block does need to be bored out, then you'll be able to use your .030" over pistons.

What do you mean by "HD" rods?

HD was my shorthand for heavy duty rods. Regular rods have a beam of .500" and less pad under the bolt. The HD rod has a beam width of .575 and more material under the bolt or a thicker pad.

The 400 rod is just a shorter version of the 5.7 with different bolts to clear the cam and a different bolt pad interface for clearance.

I'm not talking about aftermarket or "pink" rods.

The 6' rod requires a piston pin height obviously different from the 5.7 assuming a normal deck height. In a 350 block it's pretty high. The 6" rod just stays at TDC and BDC longer helping breathing and it's a longer lever which should give more torque. But you don't get more stroke since with any of the three rods pin height changes with all three to allow piston valve clearance.

You can use "normal" 350 pistons with 400 rods and a 400 crank with turned down mains. If you go to 5.7 rods you need 4" or usually 4.030" pistons with the proper pin height instead of normal 350 pistons. Same with 6" rods with the pin placement even higher on the piston.

So my regular 350 pistons will not work with 6" or 5.7" rods using a 350 block and 3.75 crank stroke.

If I use the forged 6" rods I don't have to but probably should go to at least forged pistons and probably even a forged crank.

What the heck it's only money right.

Alex, that grinding down the crank more than .030" is a myth. Do you know how the first 383 strokers came about? 400 crank with the main journals 0.200" that's more than 6 times the "limit".

Also, I think Tom Parsons (DZAUTO) turned down his 400 crank's rod journals 0.100" or so to use small journal rods and increase the crank's stroke to 3.85 making his 400 into something like a 420ci stroker motor.

As far as 400 vs 350 vs 6.0" rods, I don't think the rod length has much effect in a street engine at all. EXCEPT, that you might be able to balance a 6" rod assembly internally as opposed to the traditional method of balancing strokers externally w/ a dampner/flexplate designed for a 400. I see the advantage in the fact that there are thousands of non-400 dampners/flexplates anywhere you go, so if you happen to lose one on the road, chances are there's one nearby.

Just my opinion.

Originally posted by Slowpoke70:
Alex, that grinding down the crank more than .030" is a myth. Do you know how the first 383 strokers came about? 400 crank with the main journals 0.200" that's more than 6 times the "limit".Correct me if I'm wrong here, but, aren't the journals for a 350 smaller then a 400's journals? If so, what I was referring to was, after the crank is ground down to fit the 350's journals, then if it's ground down more then .030" under, that would make the crank to weak to be reliable.....that's from what I remember learning in "Auto Tech" in college and from what one of the guys told me at the parts shop I go to. I know that 400 blocks can be "stroked" to 420ci, but again, I was refering to a 350 block, sorry if there was any confusion.

Oooo, now I get you, sorry bout that.

No, I wouldnt say it would be too weak. The 400 crank has a 2.65 main. The mains in a 350 are 2.45. Originally, there werent off the shelf 383 stroker cranks out there to buy. The reason we readily available stroker kits now is because so many people backyard built these motors years ago. Many a 400 crank was ground down .200 to make it fit in the 350 block and it worked out well enough. If it wasnt done so frequently, the aftermarket would not have jumped onto the scene and started producing these kits. Im sure there are limitations, but for a street motor that might be run hard from time to time, I wouldnt worry about it too much. Most likely something else will break before the crank does(Assuming the bottom end is beat hard enough to break something). As far as the 6 inch rod deal, the pistons need to have the wristpin located higher to make it work, and the piston rocks in the bore more. For a motor that is gonna see sime driving time(like a street motor), this isnt always the best bet cause it can take its toll on the cylinder walls. Also, theres less meat on the piston, so depending on the piston you would go with, it can very easily be weaker than a piston meant for a 5.7 rod. Once again, I doubt that issue will arise if the motor isnt really beat on and/or if you go with a real quality piston to begin with, but these are the issues with longer rod motors.

Couple of things that I feel need to be addressed here :D

First one is the complete myth that a .030 crank is "history".
In my opinion this is complete crap.
If it is ground properly with a real good radius it will actually be stronger than a standard one without a good radius.
Years ago a very popular combo was the 350 built to a 364 with a 9/16 stroke & early 2" journal rods.
This is the worst case of grinding a crank as the rods are ground .100" & almost all of the grinding is on the inner side which lowers the crank overlap & this is the weakest point in a crank.
I drove a small block blown alcohol dragster a number of years ago & the first engines were built using a stock block & a stock GM forged crank ground this way.
It would last two or three races in this configuration before the crank was replaced & was making a bit more than 4 or 500HP. :D
Built a number of these stroker engines for the street & strip & never broke a crank & again, this is with almost .100" off the INSIDE OF THE ROD JOURNAL.

Second deal is the piston does not dwell longer at TDC & BDC with a long rod.
It dwells longer at top & LESS AT BDC.
The opposite is true of a shorter rod.

Third, why is a 6" rod piston weaker than a 5.7 rod piston & why does a higher piston pin location cause more rock or cylinder loading??
If you have less distance between the top of the piston & the centerline of the pin you have a shorter "lever" with less side loading as I see it.
If you have a shorter skirt it may cause slightly more piston rock due to less length below the pin but it ain't gonna be much.
Which engine is inherently nosier in regards to piston noise a 400 or a 350?? The answer is the 400,,, shorter rod, slightly more side loading,,, again SLIGHTLY IS THE OPERATIVE WORD HERE.

Here is my general take on rods lengths that I have posted on another forum a while back in response to losing power in a 400 small block from using a "short" rod:

"Short answer, Basically you are not losing anything.

My preference is a 6" rod simply because it makes internal balancing much easier with reasonably priced parts which is my preference but power wise don't expect any "magical" gains with a longer rod.

There are arguments for both short & long rods & in my opinion the best rod is the one that is long enough to connect the piston & crank together & leave you enough room for internal balancing.
Their is a minimal gain in regards to cylinder wall loading which gets way overblown in a longer rod,, but the shorter rod will move away from TDC SLIGHTLY faster which should tend to help crappy heads or restricted intake stuff.

I feel Rod length is one of the most over rated, over discussed parts of engine building.
I favor a rod long enough in strokers to be able to clear the needed counter weight as it normally makes balancing easier. If the rod is too short you can't get enough counterweight on the crank to balance it.
If you were to take the crank angles differences between say a 5.7 & 6" rod & overlaid them on a graph you probably wouldn't be able to differentiate between the two lines on the graph!

This subject was brought up & was summed up pretty good at the Advanced Engine Technology Conference a year or two ago in a round table discussion with some of the very best in the business of engine design in NASCAR.

This ain't a direct quote but I believe it went something like this:
You decide on a stroke, design a piston to fit your needs, measure the deck height of the block & then make something to hook them together ;)
As I recall, that was pretty much the consensus on the importance of rod length in overall engine design."

I am leaving for the AETC conference & won't be back until next week so you guys have fun pickin this apart but I won't be able to respond graemlins/beers.gif

I would go ahead and go .30 over to freshen up the cylinder walls, and it gives somewhat of a more variety to tame a bigger cam if you want more hp. I have 6" Eagle Hbeams in my driving on the street mostly 383.

I think the 6" rod in this combo does cause more problems but I agree it's slight and unless you're placing extreme loads on that engine over long periods of time it won't make a difference.

The pistons for a 6" rod on a 3.75 crank in a 350 are high enough up to create a lot more unequal loads on the piston skirt. This is going to create more side loads and more wear. That's why piston pins are generally put in the middle of the mass for production cars so they will be more reliable and make less noise.

I said I don't race anymore but an old way to get around that was to shorten piston skirt length. That doesn't fix that problem completely though.

But again that is for extreme loads and you're not going to know the difference in a street motor. It's just going to need to be rebuilt some day the same with all engines. Maybe a little sooner or not but it'll be far enough down the road you won't know it's from pin placement.

I do disagree about the TDC and BDC thing. If a reciprocating assembly is true then the piston will dwell the same time at BDC as TDC. It has to. It's only a matter of thousands of a second anyway so you're not going to notice the difference on the street between those rods. If you're racing to get every little bit of gain here and there they all add up. So then all the little things matter.

as soon as i wrote what i did i knew it would start ,but thats what makes this a good sight all the different appinions,anyways yall do it your way and ill do mine my way and injoy the reading

Originally posted by jobberone:
I think the 6" rod in this combo does cause more problems but I agree it's slight and unless you're placing extreme loads on that engine over long periods of time it won't make a difference.

The pistons for a 6" rod on a 3.75 crank in a 350 are high enough up to create a lot more unequal loads on the piston skirt. This is going to create more side loads and more wear. That's why piston pins are generally put in the middle of the mass for production cars so they will be more reliable and make less noise.

I said I don't race anymore but an old way to get around that was to shorten piston skirt length. That doesn't fix that problem completely though.

But again that is for extreme loads and you're not going to know the difference in a street motor. It's just going to need to be rebuilt some day the same with all engines. Maybe a little sooner or not but it'll be far enough down the road you won't know it's from pin placement.

I do disagree about the TDC and BDC thing. If a reciprocating assembly is true then the piston will dwell the same time at BDC as TDC. It has to. It's only a matter of thousands of a second anyway so you're not going to notice the difference on the street between those rods. If you're racing to get every little bit of gain here and there they all add up. So then all the little things matter. =

Well,,,
I gotta go catch a plane but a quick response to this,,,
First one is if the longer rod puts more pressure on the skirt, exactly how does it do this if you have less leverage between the pin & top of the piston & why are 400's noted for having more side loading on the walls??
Again, all else being equal a longer rod puts SLIGHTLY less load on the cylinder wall & the only thing that is putting this side load on the wall is the skirt ;)

Second, you are mistaken,, all else being equal if you lengthen the rod the piston dwells slightly longer at TDC & slightly less at BDC
Don't believe it,,, plot the piston position per degree & show me :D

Have a day,, gotta go get on the big bird to Colorado graemlins/waving.gif