383 or 406 sbc

Old 08-21-2012, 04:14 PM
  #11  
DRTRCR22
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Default Re: 383 or 406 sbc

Originally Posted by cs89chevy
a guy around my way has two blocks that have been through the necessary machining and reassembled what im asking is what would most of you racers go with the 383 is a fresh 30 over 350 block with a 400 cast crank external balanced with 400 rods forged flat top pistons
and the 406 2 bolt block cast crank 10-10 5,7 rods cast flat top pistons decked .10 both for around the same price would really love to have some help with this guys
Wow, thee are still too many variables and too many questions to be answered before making a call on either one...
1st: When you say a 400 crank in a 350 block, with external balance, I am assuming it is a good after market stroker crank and not a cut down stock 400 crank...?
2nd: I have never heard of 400 (5.565") rods in any 383 combo...? I don't think you could find the correct compression height pistons for that...? Most assemblies have either 5.7" rods or 6.00" rods.
3rd: if that is true, and you have a 4.030" bore, with 3.75" stroke, and 5.565" rods, the short rod/tall compression height "forged" pistons would be incredibly heavy... a scary excessive balance risk...?
4th: If the 400 block is a true "406" (4.155" bore x 3.75" stroke), with 5.7 rods, that combo would be much lighter piston weight and easier on the rotating assembly.

The only real difference between a 383 and a 406 is the bore size, 4.030 vs. 4.155. Either 5.7" rod/piston or 6.00" rod/piston rotating assembly combination should be pretty much equal parameters between both blocks. Howerver, what 400 block number is it, that may be a critical factor? You can scan these forum threads for many arguments over different 400 blocks...

I have heard many arguments that a stock GM 2 bolt main frame with cast crank is more flexible and less prone to 'snap' under hard load/unload...?
You really need to tell us the application and intended usage before anyone can make an educated recommendation... JMHO...
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Old 08-21-2012, 04:17 PM
  #12  
Scooterz
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Originally Posted by fast75vega
Originally Posted by Rigsby
I love both stories (wazup & fastvega) about the budget motors & cast bottom ends (and stock 305 rods) in motors running in the 10's & spinning 7K to 8300... that is awesome!! Gives us hope & courage to build on a budget with results!! Of coarse- like wazup says within reason & balanced well.
my motor was balanced and no noticeable vibration at all and 100 pounds of oil pressure going do the track... 45 pounds at idle :wink: i was told by a few old racer/motor builders including the man that builds my motors ... that for every 10 pounds of oil pressure...you can spin a motor 1000 rpm's.... i like to leave a buffer zone and never fully tested their theory..... lol they say the crank/rods fail when the oil barrier between the two fails and you get metal on metal.... it made sense to me and they been racing long before they had all these aftermarket parts now days
I have heard this theory too; but I assume you would need to be more concerned about valve float & failing top end before the bottom would fail?? Wazup's motor shifted at 8300 & you shifted at 7K... could you really see that much more gain out of the power curve w/ 1300RPMS more above 7K? I assume this must have been a bigger difference in cam specs & head flow? I could build a motor similar pretty cheap & maybe reduce the comp some & run pump gas for street w/ 4spd.... it would be fun & cheap... sorry for the hi-jack on this thread.
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Old 08-21-2012, 04:52 PM
  #13  
wazup
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Rigsby, here is the best part when i took it apart the rods were ground on the cam side to clear the cam lobes (630 roller). I was amazed how long this engine ran. I bought the car turnkey and the man that owned it was in his 70s and had won with this car all over the place. The car was called the "Dirty Bird" out of savannah Ga. All i can say is i know i put around 300 plus passes on it all 1/4 mile, hell i ran every weekend all over the place,Fa.,Ga.,Sc., so i might have put more than that on it and dont know how many was on it when i bought it. I sure know i had alot of fun.
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Old 08-21-2012, 05:28 PM
  #14  
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OK, its been hijacked sorry.

The engine was a 406 with 2 bolt block 4.155 bore, stock cast crank,5.7 305 rods, trw 12.5 pistons, bowtie heads 205and1.6 valves fully ported, (junk porting) 630-630 roller setup, eldbrock tunnel ram with two 660s and 5000 stall w/gluide. Rear end 12bolt w/5.13. The only thing i did to it was intake and carbs oh ya nitrous only used a few times with this engine.

I didnt shift at 8300 but 7000, 8300 is what it went thru the traps at
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Old 08-21-2012, 07:50 PM
  #15  
zipper06
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I've been watching this thread from the beginning and was reluntent to weigh in on it but, but now it's time. First of all the cast steel crank is junk, and all of the MFG'er reconagise this, they say don't turn it over 6500 RPM and with good reason it runs around like a jump rope (flex's) and will eventually beat out the main bearings.
Secondly the stock 400 crack is a Nodular iron crank and is much less flexable and stronger. If you have a large C'clamp around you can tighten it until is distorts/bending ugly but it won't break they are also made of nodular iron. A couple yrs. ago i built a cheap 388" motor for a guy (649.00 rotating assm) cast steel crank, SIR rods, Hyperutectic pistons) on alcohol. It ran 6.29@112 in a 3,000 LB Camero, he was spinning it 7600 RPM with 5.86 gears. At about 50 passes it broke a valve head off. When the engine was pulled apart, it had also beatout the front 2 main bearings and broke the 2nd main web all the way up to the lifter bores. All this due to excessive RPM's O'h he had fun, but it was not repairable.
I guess i'm saying it's flip of the coin, the cranks will work within reason, but i would rather have a stock GM 400 crank anyday of the week than the cast steel crank from China.

JMO

Zip.
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Old 08-22-2012, 05:20 AM
  #16  
SuperComp1R
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wow, never heard of a cast iron crank turning 10,000 rpm. but hey who knows......
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Old 08-22-2012, 07:40 AM
  #17  
fast75vega
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Default Re: 383

Originally Posted by badfordfreak
wow, never heard of a cast iron crank turning 10,000 rpm. but hey who knows......
my gut say the same thing
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Old 08-23-2012, 04:50 AM
  #18  
DRTRCR22
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Also on the 383 combo, check to see how much clearancing was done on from EACH rod-to-block ....?

If they used stock rod bolt type rods and had to grind a bunch off the caps to clear the cam, or had to clearance a lot at the bottom of certain cylinders because of a bad 'centerline offset' from a bad mold pour, skip the 383 and go for the 406...

Just my honest opinion...
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Old 08-23-2012, 05:54 AM
  #19  
outlaw256
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well brother there are a few things i dont do and lying is one of them, and why lie to a bunch of guys that have been there and done that on this board.these guys can catch a bs story quicker than hell!
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Old 08-23-2012, 09:25 AM
  #20  
SuperComp1R
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well, as you see i said i never heard of a cast iron crank that would hold 10,000 rpm, and i also said who knows........ but i have to say that i do not think a cast crank not to even go to the required valve train parts that could hold 10 grand, these are just my thoughts, if its true, way to go, you dodged a nuke.
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