400s are a shorter rod than a 350. Most 383s use a 5.7 or 6” rod
https://www.google.com/search?q=400+sbc+rod+length&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari
CK5
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Vortec Heads on a sb400
- Thread starter patnick
- Start date
https://www.google.com/search?q=400+sbc+rod+length&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari
I understand that.,...
beags86
Eastbound and Down
Well if your trying to build a budget build. It's fine. But if your going to up grade the crank or if you need to machine the crank there really isn't a cost difference.
My crank was shot, they were going to to need to turn it. Plus I wanted to get a forged crank. When you decide to buy there is zero price difference.
In my opinion if your going to spin the sucker you don't want the weight hanging off the ends.
T
tenderfoot
Guest
beags86
Eastbound and Down
Since rod ratio was brought up, and @tenderfoot has been trying to figure out which direction his 400 build is going.
There are a few things to consider with rods.
1. A longer rod will decrease side loading of the piston. That decreases blow by.
2. A longer rod gives you more dwell time at tdc. Seen point 4.
3. A longer rod "effectively" makes the Piston lighter and less prone to breakage
4. A longer rod Allows for more burn time and a more efficient burn. Remember effcient engines build power, not that "if she's lean she's mean" hogwash, that stuff is for amateurs.
5. You really want the rod ratio to be over 1.5
The factory 400 is a 1.48.
(I used 5.7 rods to bring mine to 1.52)
There is also a school of thought that the factory 400 rods are not at strong as a 5.7 or 6.0. but I personally can't speak to this, as I have never blown up a 400..
I did a longer rod for the performance reasons.
Follow up to point 4. Check the volumetric efficiency on my dnyo sheet. Check the numbers at the peak tq..... 92.5
Pretty forkin good for a bunch of budget parts put together by a redneck like me.
Anyways that's a very rough and quick overview of some of the connecting rod stuff to think about.
There are a few things to consider with rods.
1. A longer rod will decrease side loading of the piston. That decreases blow by.
2. A longer rod gives you more dwell time at tdc. Seen point 4.
3. A longer rod "effectively" makes the Piston lighter and less prone to breakage
4. A longer rod Allows for more burn time and a more efficient burn. Remember effcient engines build power, not that "if she's lean she's mean" hogwash, that stuff is for amateurs.
5. You really want the rod ratio to be over 1.5
The factory 400 is a 1.48.
(I used 5.7 rods to bring mine to 1.52)
There is also a school of thought that the factory 400 rods are not at strong as a 5.7 or 6.0. but I personally can't speak to this, as I have never blown up a 400..
I did a longer rod for the performance reasons.
Follow up to point 4. Check the volumetric efficiency on my dnyo sheet. Check the numbers at the peak tq..... 92.5
Pretty forkin good for a bunch of budget parts put together by a redneck like me.
Anyways that's a very rough and quick overview of some of the connecting rod stuff to think about.
Last edited:
bassackwards
1/2 ton status
beags86
Eastbound and Down
So you want me to spend 1200 bucks to gain 11 ft lbs of torque?
And I would lose horsepower.
bassackwards
1/2 ton status
LOL! $1200 for Vortec heads? Why not just buy the new ones from S-D for $750 or so. But no, I'm recommending you replace your heads, just recommending to those that have not yet spent a bundle on heads to properly size them
Well that is the point here. Needs to match cam, compression, power expectations
End of the day, the engine you want may not be the one I want. So choose wisely
beags86
Eastbound and Down
I was referring to the AFR heads here.
I don't know how much AFR heads are without looking for I was guessing.
I don't need to change my heads at all. They are properly sized for my engine. Which is a completely built 406. With a big cam, 10.1 compression and 475 horsepower. That runs off pump gas. I actually might change to different intake for a different fuel injection setup. Which would probably put me over 500hp.
If i put vortec heads on my engine and I would be stepping back into 1996. My engine would suffer immensely.
Yes, I agree you need to size your heads to your engine. And the basic run of the mill small block, 170s,180, are fine. But if your going to make real power you need bigger heads. It's plain and simple. Why does everyone love the LS engines? Because they come factory with heads that flow way more then any small block could dream of. A factory LS3 head flows 260....
