[~JM~]

I've been slowly collecting parts to build a 406.

So far I have a block (that still needs to be machined), a Scat cast steel 6" rod internal balance crank, a set of 6" rods, set of aluminum Pro Topline 200cc angle plug heads, rocker arms & a few other small pieces.

Last night I ran across a good deal on a Scat cast steel 6" rod internal balance crank for a 383. It's one of the lightened cranks.

So now I'm trying to decide wether to build a 406 with a factory 2 bolt main block & all the potential problems that may or may not occur with a factory block. Or play it safe & build a 383 with a 4 bolt main & what is probably a more stable block.

I'm a big believer in the more displacement theory but I don't want to put the time & money into what may be a short lived block.

Intended usage, is a fun street car that must be well mannered & run on pump gas. Low maintenance is a high priority.

Now here's a curve ball... Lately I've been thinking about turbo's.

So... What do you guys think? I would really like to hear from someone who has built, thrashed & possibly destroyed both.

Thanks.
~JM~

 

[wiskeesour]

406 and splay the mains. Its cheap enuff.

 

[XLexusTech]

383 if you thinking power adder for sure.

 

[Camaros-n-Chevelles]

406, Splay the mains as Harley says above, H Beam Rods, Forged Pistons, and Forged Steel Crankshaft.
Tory

 

[XLexusTech]

well if you decide to go 406 would you consider passing the 383 deal on to me?

 

[Larger Dave]

The SBC 400 two bolt main block is structurally stronger than the previously available four bolt main blocks. Reason being when they went from a four bolt main to a two bolt main they increased the thickness of the main webs in the bottom of the block, and added 10% more nickel to the mix when they cast the new two bolt main blocks making the block tougher.

Additionally 406 is bigger than 383, bigger is better when you are comparing the same length stroke. Just be sure to bore steam holes in the heads you bolt on top of the 406 block because they are needed for street driving.


Larger Dave

 

[zdld17]

When someone mentions a 400 block, I think of the topic of cracks in the surface of the deck, around the head bolt holes. I dont know how a person get around them but its been mentioned here. After all machine work was done, these cracks started appearing. Just a thought.

 

[Larger Dave]

When someone mentions a 400 block, I think of the topic of cracks in the surface of the deck, around the head bolt holes. I dont know how a person get around them but its been mentioned here. After all machine work was done, these cracks started appearing. Just a thought.

It is not limited to the SBC 400 it is common to all small blocks. That is why most engine builders use and recommend head studs. Because the decks are so thin on all small block Chevys, and get thinner when you square the block to get zero deck height.

Larger Dave

 

[wiskeesour]

The SBC 400 two bolt main block is structurally stronger than the previously available four bolt main blocks. Reason being when they went from a four bolt main to a two bolt main they increased the thickness of the main webs in the bottom of the block, and added 10% more nickel to the mix when they cast the new two bolt main blocks making the block tougher.

Additionally 406 is bigger than 383, bigger is better when you are comparing the same length stroke. Just be sure to bore steam holes in the heads you bolt on top of the 406 block because they are needed for street driving.


Larger Dave

Dave I agree with you and prob always will, 100%. that said My opinion would be to splay the mains due to future probable use with a huffer. The added nickel does make the block stronger than earlier castings....however, the constant 7-? boost will be hard on the bottom end....wouldnt you agree also? I say this so I may learn. I have never played with a huffer.

 

[Larger Dave]

Dave I agree with you and prob always will, 100%. that said My opinion would be to splay the mains due to future probable use with a huffer. The added nickel does make the block stronger than earlier castings....however, the constant 7-? boost will be hard on the bottom end....wouldnt you agree also? I say this so I may learn. I have never played with a huffer.

He is thinking of using a hair drier instead of a huffer. They do not hit as hard, or as fast as a Roots, so you can get away with a lot more boost with them than a big 8-71 or screw type that starts stuffing at the hit of the throttle. Buick was using hair dryers with even fire V-6 cranks that has half of the crank the throw going one way, the other half of the throw is either 36° or 53° degrees, (I can not remember this late at night) behind it.

Should do just find if he stays happy with even a normally aspirated 406 can do and then keep his boost within reason.


Larger Dave

 

[wiskeesour]

Ok, thanks for the input. I dont know much about boost. I had thought 'boost' was just that-'boost' I didnt realize there was a difference between the different types.
Thanks Dave.

 

[Larger Dave]

Ok, thanks for the input. I dont know much about boost. I had thought 'boost' was just that-'boost' I didnt realize there was a difference between the different types.
Thanks Dave.

You are right in that regard; 8 PSI of boost from a turbo is equivalent to 8 PSI boost from a Roots (sort of: there is a marked difference in the thermal efficiency between the two that results in a less dense charge from the Roots). Aside from the fact that the Roots blower heats the incoming charge more than a turbo (or centripetal supercharger for that matter), by the time a turbo has built to it's maximum level of boost the motor is spinning near peak horse power. With a Roots the blower builds boost instantly (it is coupled with the crankshaft) which will put much more stress on the crank than the Turbo will as it waits to spool up. Additionally all of that horsepower to drive that blower is hanging off the nose of the crank (unsupported) which puts a strain of the crank that the turbo driven motor never sees.

At high RPM the motor is well on it's way to maximum volumetric efficiency (pumping air at it's maximum efficiency), this is when the turbo is moving the greatest volume of air, when the motor is ready for it. This combination of volumetric efficiency, thermal efficiency, and utilization of waste heat to power the turbo is why they are the ultimate power adder.

I also agree that a splayed billet steel four bolt conversion combined with main studs will provide for additional support that can add another 150 additional horsepower to the 450 horse capacity the block has now. Beyond 600 horse it is time to buy a Dart Little "M" and start over with all forged internals.

Larger Dave

 

[wiskeesour]

Learn somethin' new everyday.

 

[68rs406]

406, hands down. A 383 will be plenty stout, but look at it this way, when you get the bug for more power, how hard and expensive will it be to get 20-30 more horse/torque from an add on, you can have it now buy building the 406, all else equal.
A buddy of ours runs a pretty mild 406 (honestly) with I believe an 80mm turbo on his chevy II, it's totally streetable, and he's run 7.90 with it, on drag radials. The same motor he's been running for quite a few years reliably.
The 400 done correctly is just as reliable as any other smallblock, the siamesed cylinders are not as good as non siamesed for staying perfectly round after heat cycling, but it's really far from an issue especially on a street motor. Two bolts with studs are prefered, and splayed 4 bolt caps are best. The ultimate is a little M block.
I have a 406 in my Camaro thats been in there for going on 6 years, I drive it all over the place, race it (11.40 in 100% street trim) and have never had an issue with cracking or overheating. And oh yeah, no steam holes drilled in my heads, but don't get me started on that subject.....

 

[~JM~]

Thank you all for the replies.

To add some more info... The block that I have is a 509 block. I also have a a stud kit from ARP. The block was a rusty thing that was in the corner of a garden shed for several years. I've had it baked, shot peened & magged. So far the only trouble area located was the outer starter mount. It is cracked like the starter came loose or was allowed to hang off the one bolt. I need to look into having that repaired.

I have not had the cylinders sonic checked yet. I recently moved to another state & haven't developed a feel for the area yet & which machine shop I should use, etc.

Sean, I may know the car you are talking about. Turbo Terry?

I used to live a bit south of you. Now I'm just on the other side of the big river.:yes:

Thanks
~JM~

 

[~JM~]

well if you decide to go 406 would you consider passing the 383 deal on to me?

Sorry I didn't get back to you sooner.

Most likely I will keep the 383 crank even if I decide not to build a 383 right now. Save it for later.

 

[68rs406]

Sean, I may know the car you are talking about. Turbo Terry?

I used to live a bit south of you. Now I'm just on the other side of the big river.:yes:

Thanks
~JM~

Cool, Portland?
His name is Brian Macy, he's quite the turbo guy and definately knows how to make them work, he won drag radial last year at the SCSN in Vegas, ran a 7.90 in qualifying.
He owns Horsepower connection in Olympia. We are actually changing the car we race over to a twin turbo setup, Brian will likely be helping us out a bit with the initial set up, and it looks like I'll be learning more about turbos real soon....:yes:
Here's a pic of Brian's car...

 

[~JM~]

That's the car I was thinking of. I have yet to actually meet owner.

I know the guy that owns the Malibu they built for PINKS.

 

[CNC BLOCKS N/E]

We have seen far more problems with 400 blocks then the 350 blocks as the 400 have a big main line making for a weaker webbing over the 350 block and now with the bigger cylinders makes for a thinner webbing over the 350 blocks and with the bigger cylinders it makes for a weaker decks which is very common to see cranks in the decks over the 350 blocks.

With the weaker decks there is much more cylinder distortion over the 350 blocks causing poor ring seal over the 350 blocks

Here is a link to go over
http://www.maliburacing.com/forum/viewtopic.php?t=52010

 

[68rs406]

We have seen far more problems with 400 blocks then the 350 blocks as the 400 have a big main line making for a weaker webbing over the 350 block and now with the bigger cylinders makes for a thinner webbing over the 350 blocks and with the bigger cylinders it makes for a weaker decks which is very common to see cranks in the decks over the 350 blocks.

With the weaker decks there is much more cylinder distortion over the 350 blocks causing poor ring seal over the 350 blocks

Here is a link to go over
http://www.maliburacing.com/forum/viewtopic.php?t=52010

I would assume you've seen this primarily in bigger power levels? Thats the reason I feel above about 500 horse by much the little M is the way to go.
But talking about a street strip motor in the 500 horse or so range, I have seen very few issues with a properly prepped stock block, i.e. studs on two bolt mains or splayed caps, among guys we race with, and from talking to the guys that do a lot of the machining for us. Obviously you've seen quite a few more than me no doubt, but considering I have really only ever seen an issue with a factory four bolt block I can't imagine its that common at those power levels?