Guys I'm trying to determine if I have 350 or 400 rods in my 383?? How do I tell??? The pistons mounted on them are trw 2256. and it has a scat crank in it...
I'm getting my block machined, machine shop said 400 rods local speed shop said 5.7 rods...What gives???

Thanks

Brian

You have 400 rods.

Brian,
That piston in a 383 requires 400 rods. If you used that piston with a 350 rod it would come out of the top of the block about 1/8" ! Have your machine shop show you a 350 rod. If you look at the top of the rod bolt, you will see the difference. The 400 rods have a round "cutout" where the bolt hits the top part of the rod.

OK so if I have 400 rods am I loosing a lot of power or what am I to gain or loose???

Brian

little to nothing IMO.

Originally posted by 64chevlle:
OK so if I have 400 rods am I loosing a lot of power or what am I to gain or loose???

Brian Basically you are not losing anything.

My preference is a 6" rod simply because it makes internal balancing much easier 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 is less sensitive to intake reversion given the same cam as the piston dwells longer around BDC.
It also moves away from TDC SLIGHTLY faster which tends to help crappy heads or restricted intake stuff.

Here is something I have posted before for a little more info :D


I'll probably catch all kinds of flack for this but here's my opinion.
First let me say I normally prefer a longer rod but,,,,,
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!

In a longer rod engine the piston dwells longer around TDC & less around BDC which can be argued both ways.
If it is moving away from TDC slower it isn't putting as much power into turning the crank but it gives the charge more time to build pressure.

Ok, if it's a "short" rod it is moving away from TDC faster it will put more power into turning the crank sooner. :confused:
My basic opinion of rod length is if you don't have a good reason to change that actually makes sense,,,, leave it alone.

This was summed up real good at the Superflow Advanced Engine Technology Conference this year 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 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 ;)
That was pretty much the consensus on the importance of rod length in overall engine design.

Cool, I have been wondering about this, because my 385 has rods from a 400. Thanks for the info!

I cannot sufficiently argue with any of the above enough to make a really good case one way or another. In the past 30+yrs, I've built 25-30 SB400s and only one of them got the shorter 400 rods. The rest got 350 (5.7) rods. Although, that one 400 has since been rebuilt again and now has 5.7 rods. I am basically an advocate of using a longer rod, but in a SB400 (or a 383) I DO NOT like to use a 6" rod for one specific reason. When using a 6"in rod in any SB400+ configuration, it requires the use of pistons which have the wrist pin hole at least partially into the oil ring groove. Is this detrimental to overall engine durability? Maybe, maybe not. I personally DO NOT like it though! Yes, to build any kind of SB400 into a longer stroke configuration will probably make a better engine with a 6" rod, but because of the various potential disadvantages which are, or may be, associated with such an engine (very high pin hole, real short piston, increased piston rocking, etc), I just purely do not like the 6" rod in the 383-400 engines.
Also, when you start getting into building REALLY healthy SB400s (or 383s), it becomes a matter of justifying the expense on a small block. If a person is not REAL careful, it becomes real easy, real quick, to put more money into a SB400 than what could be spent on a really nice 454!!!! Yes, I know, sometimes the only remedy for an engine requirement is to build a SB, such as a stock chassis 66-67 ChevyII (extensive mods are required to put a BB into one of these stock bodies) or a 62-earlier Vette. Otherwise, a BB will fit into almost anything else, plus, a 454 can be built for the same price (sometimes less) as a SB400----------------------and totally outperform the 400! So, when you start looking at the prices for engine parts plus machine work, take a close look at what it will cost to build a 500hp SB400 vs a 500hp 454.

Thus, I pretty much have to agree with Mike, in that what you will gain in comparrison to what you will spend between using a 5.565, 5.7 or 6" rod just may not provide a significant, if any, seat of the pants benefit (or noticeable increase on a dyno). Every street/performance SB400 that I have built over the years has used stock (but reconditioned/resized with new bolts) 350 rods----------------------AND NEVER A FAILURE. I pick up 350 rods wherever I can find them and let my machinest cull them. I've pulled rods out of numerous junk 350 engines (most for free) and mixed and matched them in other engines. Once they have been resized and balanced for a particular engine, they become equal.
Now I'm not talking about using these rods in a blown or serious NOS engine, but an aspirated healthy performance engine. This is not cutting corners, this is making the best use of what you have for your $$$$ investment.

Aren't 400 rods quite a bit weaker due to the cut out for the bolts? Or so this is what I have always been told.

Steve

Originally posted by wanarace:
Aren't 400 rods quite a bit weaker due to the cut out for the bolts? Or so this is what I have always been told.

Steve No, they will still take a lot more abuse then people give them credit for ;)

And I agree with most of what Tom says but my preference is a rod long enough to internally balance the engine which in most cases has been a 6" rod.
The ring support rail is in my opinion a non factor.
You are only supporting the ring for about a half inch over the pin & there is really no load on the oil ring anyway.
I have built a few stroker small blocks & rats over the years & have never had an issue with the support rail.
I have one 496 in a motor home on propane that has somewhere in the neighborhood of 150 thousand miles on it now with 6.385 rods & SRP pistons & the thing gets beat to death considering the weight & configuration of the "mobile house" going down the road.
This is just one example of an engine with a support rail, got lots of 383-400 type engines runnin around with a lot of miles & no problems.
Nothin against 5.7 rods, got lots of those too.
I just prefer the 6" for the ease of balancing.

Also, I agree with Tom as far as the stock 400 rod goes, I normally scrap them.

This does not mean they will be a problem.
I have a customer with a circle track 400 2 barrel deal that has been running the same stock rods & cast crank to about 5800-6000 for about 6 years now ;)