Re: 383vs400 crankshaft
[Re: Performance Only]
#1410705
03/29/13 02:52 PM
03/29/13 02:52 PM
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Joined: Dec 2005
Posts: 1,495 Shelby mi.
JAKE68
pro stock
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pro stock
Joined: Dec 2005
Posts: 1,495
Shelby mi.
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depends on what hp level you are going to build. street motor keep 400 crank it is fine.
JAKES AUTOMOTIVE
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Re: 383vs400 crankshaft
[Re: jeff500]
#1410706
03/29/13 03:09 PM
03/29/13 03:09 PM
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Joined: Jan 2003
Posts: 25,988 Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,988
Rio Linda, CA
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The 915 heads with the original 400 pistons won't get you anywhere near 10-1 compression.
You probably wouldn't need to rebalance the assembly with a forged 383 crank because the piston weight isn't that much different. While the 400 piston is larger in diameter, the pin height is lower.
The INTERNET, the MISinformation superhighway
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Re: 383vs400 crankshaft
[Re: John_Kunkel]
#1410708
03/29/13 03:39 PM
03/29/13 03:39 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Quote:
The 915 heads with the original 400 pistons won't get you anywhere near 10-1 compression.
I calculate that if the OP can get the heads down to 72 cc's (and they'll need to be milled for that), run steel shim head gaskets, then assuming the pistons are .100 in the hole at TDC (which is about what the stockers run), the compression ratio would only be 9 to one.
At 78 cc's, the CR would only be 8.6 to one.
At 90 cc's, you're looking at 7.8 to one.
Put some thick Fel-Pro 1009 head gaskets on it instead of steel shims, and knock another 2-3 tenths off any of the above figures.
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Re: 383vs400 crankshaft
[Re: dogdays]
#1410710
03/29/13 04:41 PM
03/29/13 04:41 PM
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Joined: Jul 2010
Posts: 2,091 Delray beach, Florida
Performance Only
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Joined: Jul 2010
Posts: 2,091
Delray beach, Florida
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Quote:
Balance factors: 383 steel crank vs. 400 cast crank. They both use the same rod. They both use a piston that's the same or very close weight. 383 cast cranks used exactly the same factory imbalance as the 383 or 400 cast cranks. And they were somewhat interchangeable on the assembly line, between cast and forged 383s.
My opinion is if you remove the 400 cast crank and swap in a 383 forged crank with the 383 harmonic damper and flywheel/torque converter, you will have a typical Mopar factory balance job on the result. The Mopar balance jobs aren't known for their precision, but we didn't hear about any problems back in the day. Now that everyone is balancing to a gram or less, ANY Mopar factory balance job can be improved. But don't expect a noticeable difference. So swap away!
And, if you're hoping for 10:1 compression without changing pistons, dream on...you'll never get there.
R.
We'll just have to agree to disagree on that. I've balanced a lot of mopar engines and what your saying is not what i've seen in actual practice.
machine shop owner and engine builder
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Re: 383vs400 crankshaft
[Re: ProStock1320]
#1410714
03/30/13 03:59 AM
03/30/13 03:59 AM
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Joined: Jan 2005
Posts: 4,862 the frozen wastes...
Pale_Roader
Swears too much
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Swears too much
Joined: Jan 2005
Posts: 4,862
the frozen wastes...
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Quote:
Please excuse my lack of knowledge but what does the OP need to get 10-1 in his engine? Closed chambered heads, mill them, deck the block a bit, thin head gaskets, yes? How much more would he need?
Would turning down the rod journals to 010 undersized but doing it like 440 rod journals are offset ground to BBC size do anything to help or is that wasted effort?
You could spend yourself poor at the machinist to reinvent the whole thing, or you could spend a few hundred on pistons. I've driven myself bats with the math on this puzzle... just buy the damn pistons!
That said... i have a No-buck zero-deck 400 ready for the rebuild in my shop. Found a standard bore re-cond. 400 at the junkyard, free in trade. Had some .030" over 440 pistons (stock low comp, perfect comp ht. for lowdeck) kicking around. Enough rods to build a V700, and a couple steel 383 cranks. Bore the 400 to just 4.35", flycut the pistons, balance it all and pow! Zero-deck/steel crank/balanced 400 to go with some nice 516 heads and .040" quench. Total cost? $125 + machining/balancing. Kinda hokey... but i bet it screams.
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Re: 383vs400 crankshaft
[Re: John_Kunkel]
#1410716
03/30/13 09:37 PM
03/30/13 09:37 PM
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Joined: Jul 2010
Posts: 2,091 Delray beach, Florida
Performance Only
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Delray beach, Florida
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Quote:
Quote:
We'll just have to agree to disagree on that. I've balanced a lot of mopar engines and what your saying is not what i've seen in actual practice.
Some actual numbers would bolster your argument. As you know, machine shop balance and factory assembly line balance are way different.
The forged crank for the 1972 400 has the same part number (2268114) as the 383 from 1962-1971 which tells us there is no difference in the cranks.
John, 71 was the last year for the 383 and as you know, 72 was the first year for the 400. It stands to reason they wanted to deplete the old 383 cranks. I think we all know they'll physically interchange dimensionally. That does not mean that the component weights were the same. At the factory all they had to do was drill the counterweights differently. The pistons are not close enough in weight to just swap cranks from a 383 to a 400 and not rebalance it. At some point you'd have to decide what is close enough, right? So in your opinion, what would be close enough? 30, 40, 60, 100 grams? typically anything more than 1 Oz.-inch will cause problems. (28 grams)
machine shop owner and engine builder
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Re: 383vs400 crankshaft
[Re: Performance Only]
#1410717
03/30/13 09:56 PM
03/30/13 09:56 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
Quote:
Quote:
We'll just have to agree to disagree on that. I've balanced a lot of mopar engines and what your saying is not what i've seen in actual practice.
Some actual numbers would bolster your argument. As you know, machine shop balance and factory assembly line balance are way different.
The forged crank for the 1972 400 has the same part number (2268114) as the 383 from 1962-1971 which tells us there is no difference in the cranks.
John, 71 was the last year for the 383 and as you know, 72 was the first year for the 400. It stands to reason they wanted to deplete the old 383 cranks. I think we all know they'll physically interchange dimensionally. That does not mean that the component weights were the same. At the factory all they had to do was drill the counterweights differently. The pistons are not close enough in weight to just swap cranks from a 383 to a 400 and not rebalance it. At some point you'd have to decide what is close enough, right? So in your opinion, what would be close enough? 30, 40, 60, 100 grams? typically anything more than 1 Oz.-inch will cause problems. (28 grams)
The factory tried to maintain 14 grams or less.. but I know that varied somewhat
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Re: 383vs400 crankshaft
[Re: Performance Only]
#1410718
03/31/13 11:07 AM
03/31/13 11:07 AM
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Joined: Nov 2009
Posts: 2,275 Desert Tracker
HYPER8oSoNic
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Joined: Nov 2009
Posts: 2,275
Desert Tracker
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Quote:
Quote:
Quote:
We'll just have to agree to disagree on that. I've balanced a lot of mopar engines and what your saying is not what i've seen in actual practice.
Some actual numbers would bolster your argument. As you know, machine shop balance and factory assembly line balance are way different.
The forged crank for the 1972 400 has the same part number (2268114) as the 383 from 1962-1971 which tells us there is no difference in the cranks.
John, 71 was the last year for the 383 and as you know, 72 was the first year for the 400. It stands to reason they wanted to deplete the old 383 cranks. I think we all know they'll physically interchange dimensionally. That does not mean that the component weights were the same. At the factory all they had to do was drill the counterweights differently. The pistons are not close enough in weight to just swap cranks from a 383 to a 400 and not rebalance it. At some point you'd have to decide what is close enough, right? So in your opinion, what would be close enough? 30, 40, 60, 100 grams? typically anything more than 1 Oz.-inch will cause problems. (28 grams)
The big issue is whether or not the crank balance is internal (no added weight to flywheel/converter) due to being forged instead of cast. Weight balance is way differemt due to offset balancers and weight pads (flywheel/converter) on the cast crank assemblies. CANNOT mix parts between the two, otherwise you will eventually have a bad vibration and a very short engine life! ( BOOM, BOOM, POW!! ) Either type of rotating assembly, I would DEFINITELY spend the extra cash re-balancing it!! Free horsepower, way smoother operation and extended engine life.
"Stupidity is Ignorance on Steroids" "Yeah, it's hopped to over 160" (quote by Kowalski in the movie Vanishing Point 1970 - Cupid Productions)
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Re: 383vs400 crankshaft
[Re: John_Kunkel]
#1410721
03/31/13 03:58 PM
03/31/13 03:58 PM
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Joined: Jan 2003
Posts: 10,019 Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
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Posts: 10,019
Frostbitefalls MN (Rocky&Bullw...
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If it were mine I would check the bearings, (replace only if needed) check the bores for total wear, and if at all possible run it as is and put a good timing chain on a small hydraulic like the old 268H Comp cam, and have fun. You can cut the heads maybe .060 and use a steel shim .020 gasket, which should get compression up to the mid 8 range, which is why the short cam will work the best IMHO. With a cam that small, bowl work is all that is needed, along with a good competition valve job to make use of what you have to work with.
Last edited by gregsdart; 03/31/13 04:02 PM.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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