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Topic Review (Newest First)
07-25-2013 02:16 PM
1986c10 I think why you got that low was because of your deck and compressed gasket thickness values. I used values of .02 and .02ish i think to achieve around a .040" quench. Giving a little over 9:1. I got this assembly in a trade and would much rather go with a 4.25 stroker kit and am leaning that way alot more with the little compression this engine has. I feel like i would have to run a smaller cam etc with that low of comp. And thats a good thought about the heads but I just had them rebuilt and have way to much $ into them to get rid of them haha.
07-25-2013 09:18 AM
66GMC
Quote:
Originally Posted by 1986c10 View Post
Oh wow, those cheap scat 9000 cranks are pretty solid. Im going to look into a kit with one if I can sell what I have. Will the 432 rotating assembly work for what I have though? All I have so far is the rotating assembly block and heads
It will go in a 2wd shortbed chevy street/strip
454 block .030" over
427 crank making 432"
781 heads 2.19/1.88 118cc chamber
Hydraulic roller cam im thinking something in the .600" lift range to take advantage of the head flow
Dual plane intake
th400 that will be built and whatever recommended stall converter
Rear gears will be decided at the same time
The main issue i see is very low compression, 9.07:1 with the 16.5cc pistons I have. I dont think that would make a good combo. I wanna make around 550hp for whatever thats worth
Using Summit's Compression calculator with your numbers...
4.280 bore (4.25 +.030)
3.76 stroke
118 cc heads
-16.5 cc domed pistons
assumed .020 piston-to-deck clearance
assumed Felpro gasket with 4.370 bore and .039 compressed thickness
I get 8.69:1 CR and 432.77 CID

Using Wheelspin's calculator
I get 8.65:1

I've just removed my 781 heads and replaced them with 063 versions (68/69 396 closed 101cc chambers) hoping to get around 9.0:1 with my flat-tops.

Your setup with 063 heads would be awfully close to 10:1 ... which is right where you probably want to be.

From what I have read in regards to quench, decking the block to 0.00 would give you good quench and an additional .4 (10.4:1) compression. I also think, again based on what I have read, that the "perfect" CR is 10.25:1

I would also point out that you're obviously giving up some cubes with that shorter stroke. Is there a reason that you want or need to do this?
07-24-2013 09:02 PM
cobalt327 I hope I'm wong too! The number can go either way, depending on what you want to see:



The parting line will be the easiest to see indicator:



Good luck!!
07-24-2013 08:47 PM
1986c10 aww man why do you have to ruin my fun. I'll check it out when im home friday. Good eye but im praying youre wrong
07-24-2013 08:44 PM
cobalt327 I'm purdy sure thats a 3904815. Makes it a 396,402...cast, nodular iron according to Mortec and others. Look closely at the other "8" and see the difference in the center of the digits. The "8" is straight across where the "9" is slightly slanted.

As far as 'ringing' a crank to tell if it's forged or cast, unless you have a hell of an ear for it- as in you handle cranks daily- you can't tell cast from forged. If you have two similar cranks, one forged and one cast, they'll sound different but unless you know which is which and ring them at the same time, all you'll know is they ring differently.
07-24-2013 08:35 PM
1986c10 Oh wow, those cheap scat 9000 cranks are pretty solid. Im going to look into a kit with one if I can sell what I have. Will the 432 rotating assembly work for what I have though? All I have so far is the rotating assembly block and heads
It will go in a 2wd shortbed chevy street/strip
454 block .030" over
427 crank making 432"
781 heads 2.19/1.88 118cc chamber
Hydraulic roller cam im thinking something in the .600" lift range to take advantage of the head flow
Dual plane intake
th400 that will be built and whatever recommended stall converter
Rear gears will be decided at the same time
The main issue i see is very low compression, 9.07:1 with the 16.5cc pistons I have. I dont think that would make a good combo. I wanna make around 550hp for whatever thats worth
07-23-2013 09:09 PM
66GMC FWIW ... I had a new Scat cast crank 910454 installed and balanced in my 2-bolt main 454.

My machinist "guarantold me" that I wouldn't have a problem running my engine up to 7,000 RPM, and I have read much the same on many internet forums.

David Vizard, author of How To Build Chevy Big Blocks on a Budget seems to have good things to say about them, too.

According to him ... (page 32)
A GM factory Forged Steel crank (like yours) has 120,000 PSI strength
A GM factory Cast Steel crank has 80,000 PSI strength
and a Scat 900 Cast Steel crank has a 110,000 PSI strength.
07-23-2013 07:39 PM
1986c10 Shoot, i think i meant to say it had a thin casting mark like a non forged. Now im just confusing myself. If that casting number comes back as forged like you said then it must be forged. Yippee! thanks man! Now to decide whether this short stroke higher rev combo will live in a studded 2 bolt or to try and sell it and get the 489 kit that I really want...
07-23-2013 07:07 PM
66GMC
Quote:
Originally Posted by 1986c10 View Post
Sorry its been awhile, it has a wide parting line like a cast but rings if i hit a counter weight with a hammer lightly like a forged...
Read it again ...

Quote:
Rule of thumb. If the parting line on the side of the crank throw is only a line, up to 1/16" wide it is a casting. If the line is 1/4" plus and looks like it has grind marks on it. It is forged.

Stand crank on end, on a shop towel. Rap a counter weight with a hammer. If it goes "thunk" it is cast. If it rings clearly, like a bell, it is a forging.
WIDE parting line = forged

Rings like a bell = forged

3804815 = forged

366T/396/402/427/427T 3.76" stroke.
07-23-2013 04:50 PM
1986c10 Sorry its been awhile, it has a wide parting line like a cast but rings if i hit a counter weight with a hammer lightly like a forged...
10-08-2012 03:56 PM
1986c10 okay, thanks 1932 batman. I will check it out next time im home but i believe it to be a cast 396 crank not sure why nothing matches the casting numbers though... Its all balanced and im trying to sell the whole assembly to get a 489 kit.
10-08-2012 03:15 PM
1932bantam yes the thickness of third counterweight. 396 has a lighter rotating assembly if it is a 396 crank and making a 427 using 454 block probably should have everything balanced for longevity. you can't mistake steel crank. it has a wide parting line. just put a 3/4 end wrench on it it will either fit or not
10-08-2012 03:10 PM
66GMC
Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Can't tell because of angle/clarity of pics. Don't have my crank book with me. Looks like cast.

Rule of thumb. If the parting line on the side of the crank throw is only a line, up to 1/16" wide it is a casting. If the line is 1/4" plus and looks like it has grind marks on it. It is forged.

Stand crank on end, on a shop towel. Rap a counter weight with a hammer. If it goes "thunk" it is cast. If it rings clearly, like a bell, it is a forging.
Pics and more info fom BBC Parts Interchange Manual.
10-08-2012 01:16 PM
1986c10 I was told it was a 427 rotating assembly so i assumed he just had a 396 crank and rods laying around as well as a 454 block so he made it a 427 + .030 assembly. When you say the different sizes, you are referring to the counterweight thickness correct?
10-08-2012 09:37 AM
1932bantam third counterweight on a 396 is 3/4 on a 427 it is 7/8 hope this helps
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