Chevy Nova Forum banner

1 - 20 of 22 Posts

·
Premium Member
Joined
·
13,309 Posts
there are a couple of 383's mopar 383b block, mercury 383 fe block, a .030" 350 block with a 3.75 stroke crank from a 400sbc...

hence a bored and stroked 350 (4.030 bore and a 3.75 stroke)=383
 

·
Premium Member
Joined
·
8,405 Posts
You can also destroke a 400 to get 383 cubic inches.
 

·
Registered
Joined
·
438 Posts
350 block + 400 crank = 383
400 block + 350 crank = 377
.030 overbore add approximately 5 cubic inches
i.e. .030 over 383 = 388,
.030 over 377 = 382/383

If you do it be sure your rod bolts clear the block. I believe you are supposed to have at least .060 clearance because the crank will stretch at high rpms.
 

·
Registered
Joined
·
771 Posts
Yup the kit comes with a 400 crank and you put it in the 350 block and pistons for a 383...But you can also get 2 different rods, 5.7 inches long or 6 inches long......
 

·
Premium Member
Joined
·
13,309 Posts
and 5.565 rods which was the first 383 chevy, till piston manufactures started making the 5.7 and 6.0 rod compression heights
 

·
Registered
Joined
·
1,658 Posts
and 5.565 rods which was the first 383 chevy, till piston manufactures started making the 5.7 and 6.0 rod compression heights
What is the benefit of running a 5.7 to a 6.0 rod? I know they move the location of the wrist pin up on the piston for the 6'' rod but do you get more torque with a 6'' vs a 5.7"?
 

·
Registered
Joined
·
3,895 Posts
What is the benefit of running a 5.7 to a 6.0 rod? I know they move the location of the wrist pin up on the piston for the 6'' rod but do you get more torque with a 6'' vs a 5.7"?
Ummmm, well.........:no:

But you'll hear everything in the world about less cylinder side loading because the longer rods have less angularity :rolleyes: to the theories of higher piston speeds and different dwell times....:rolleyes:

The BEST way I've ever heard it explained is:

Get the BEST piston with the BEST ring package for YOUR application and the BEST rod length is the one that will connect YOUR piston pins to the crankshaft correctly.:yes:

Anything else is unfounded conjecture.:yes: It may sound good and look good in print but it has never been proven on any dyno or track that I've seen.:no:
And I've seen plenty.......

Hint: There's more power to be found in the ring packs and cylinder bore finish than with ANY rod-stroke ratio crap!!!:yes:
 

·
Premium Member
Joined
·
13,309 Posts
that is hotly contested....other say yes still other say no.... IMO use what you like....

IMO again the real benefit is moving the piston away from the crank to allow for larger counter weights.. there for providing internal balancing.....

there is a bunch of math revolving around piston speeds in the three various rods lengths....
so other say the .300 long rod reduces side wall loading.. when you draw this out and add .300 to the length of a 5.7 rod you see the rod angularity shift is minimal... .. it is far greater from the 5.565 to the 6.0 rod and still farther from the 5.565 to the 6.125 still the angularity shift is minimal.. the difference being .56 or about 18/32" of an inch over all length difference..


If you draw that out in a straight line from a 3.75 rotational pivot the difference in piston pin to rod angularity is not that great....


I like to reference a very famous engine builder named Earl Wade(chief engine builder and crew chief for Dyno Don Nicholson 1964 to 1972) when asked about the controversy of different length rods.. Earl said: "as long as the piston dont hit the crank and dont poke out the top of the block... thats the right rod!"

to me the lightest combination is the best combination what ever the rod length is..
 

·
Premium Member
Joined
·
13,309 Posts
EDIT:

I will say this about rod length.. the Mopar LA engine has used a 6.125 rod since inception and 14 degree valve angles starting in ..1964. The New GM gen3 engine uses a 6.125 rod, the Olds 455 uses a almost 7.0 inch rod... to that

the ford 302/289 uses a 5.09 length rod, the 351W uses a 5.956 rod....



Here is Mark O'Neil the owner of Probe pistons commenting on a rod length issue with a 351 windsor build up.

Mark O'Neil

Rod length is, basically, irrelevant.

As far as the CHP kits...the reason I did that (originally) was because the only 5.956 rod that was available was stock. Using the 6.200 allowed a decent piston and a lot of options for upgrading the rod.

Probably the best reason for using it now is the comparative weights of the 1.350 C/H piston and the 1.600 C/H piston.

If you already have the crank and rods....changing the piston is probably the way to go if you wish to save money.

It's what I'd do. You can always build a different short block for the future, especially since the heads will outperform the combination.

Marks second Answerer the Rod ratio legend...

Quote:
Originally Posted by CHANMADD
The ratio between the crank stroke and the rod length is ,my friend, very important.
If the angle of the rod is to acute the rod will go through the cylinder wall at great speed and leave you on the side of the road!!!...

Mark O'Neil
Oh horse poop, my friend.
you carry any argument to the ridiculous extreme you can prove anything.

This, I think, is a reality based board. No one in the industry has a piston forging long enough to allow that scenario.....so I won't sweat it.

Rod ratio is not a consideration when designing a combination unless there is a serious mismatch between the engine and cylinder head sizes.

351C and BB Chevy have short rods....big head, little motor. BB Chrysler has a long rod.......big motor, little head.

I doesn't really matter even then but the rest of the time, pick a rod, it's all good.

Rod ratio is the least important piece of folklore to consider when building an engine.

this is the link
http://www.clubcobra.com/forums/showthread.php?t=95849
 

·
Registered
Joined
·
3,895 Posts
Here's a quotes from Darin Morgan of Reher-Morrison found in the August issue of Chevy Hi Perf.

"Most people tend to overgeneralize this issue. It would be more accurate to compare different rod-to-stroke ratios, and from a mathematical stand-point, a couple thousandths of an inch of rod doesn't really change things a lot in an engine. We've conducted tests for GM on NASCAR engines where we varied rod ratio from 1.48- to 1.85:1. In the test, mean piston speeds were in the 4,500-4,800 feet-per-second range, and we took painstaking measures to minimize variables. The result was zero difference in average power and a zero difference in the shape of the horsepower curves. However, I'm not going to say there's absolutely nothing to rod ratio, and there are some pitfalls going above and below a certain point. At anything below a 1.55:1 ratio, rod angularity is such that it will increase the side loading of the piston, increase piston rock, and increase skirt load. So while you can cave in skirts on a high-end engine and shorten its life, it won't change the actual power it makes. Above 1.80- or 1.85:1, you can run into an induction lag situation where there's so little piston movement at TDC that you have to advance the cam or decrease the cross-sectional area of your induction package to increase velocity. Where people get into trouble is when they get a magical rod ratio in their head and screw up the entire engine design trying to achieve it. The rod ratio is pretty simple. Take whatever stroke you have, then put the wrist pin as high as you can on the piston without getting into the oil ring. Whatever connects the two is your rod length."
 

·
Premium Member
Joined
·
13,309 Posts
here is a concise table regarding piston speed and rod length

here is the Quote in relation to the rods lentghs and the values used

I think this is another one of those issues that have only a tiny, tiny impact on performance. People refer to “piston acceleration” when they really mean “piston speed”. It’s the moving piston that pulls in the intake charge and regardless of rod length, piston speed is zero at TDC.

I plotted piston speed versus crank angle at 7,000 RPM for 6.500”, 7.000”, 7.500””, and 8.000” long rods, keeping everything else constant.

Notice that at TDC or zero degrees all the lines converge. There's no difference. At maximum speed, which is at around 75 degrees, there's a slight difference in speed, but I can't believe it's going to have much impact on the incoming charge.

The idea that the piston is going to accelerate away from the advancing flame front is preposterous.




the link

http://www.460ford.com/forum/showpost.php?p=778469&postcount=13

I forgot the Best Quote from Mark O'Neil on Rod Ratio.. here it is!:D

The correct rod to crank ratio is 8:1. Eight rods....one crank.

Unless there is an rather severe imbalance between cubic inches and cylinder head size rod ratio is irrelevant.
 

·
Premium Member
Joined
·
15,966 Posts
Of coarce in the famous words of "Paul Wright"
we have been down this road many times.

In talking with my buddies at the Nascar Engine shops.

The #1 reason to use the longer rod is to reduce the stress (more Durability) at the piston pin and reduces rotating energy.

This allows the engine more durable at HIGH RPM.
 

·
Premium Member
Joined
·
11,072 Posts
350 block + 400 crank = 383
400 block + 350 crank = 377
.030 overbore add approximately 5 cubic inches
i.e. .030 over 383 = 388,
.030 over 377 = 382/383
You better go back and re-do your math.....a 383 is a .030" over 350 block, a 388 is .060" over........
A standard bore 400 w/350 crank is 372; +.030" is 377; + .060" is 383....
 
1 - 20 of 22 Posts
Top