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Author Topic:   421 howto?
istock59
Member
posted September 28, 2004 11:22 AM
So, obviously a 421 starts life as a 400 SBC block, and uses an aftermarket 3.875 stroke crank.

Is there an aftermarket off-the-shelf piston/rod combo that you can use?

What about block clearance problems?

Small base circle cam needed?

Thanks for info.

sixwillwin
Member
posted September 28, 2004 02:41 PM
the cheap claimer way ......stock offset ground crank, use 5.7 stock rods with brg. spacers, Speed Pro flattops with .040 milled off the top,

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The Joy of Six website


BiggerBill
Member
posted September 28, 2004 06:59 PM
You ned spacers for the mains not the rods.


rocket36
Member
posted September 29, 2004 04:56 AM
small base circle cam is required for rod clearance.
the factory reliefs cast into the block at the bottom of the cylinder walls need to be enlarged and the pan rails need to be relieved for rod clearance. the amount just depends on the type of rod being used.
if you choose to use a 6" or longer rod, you need the rings with the "retainers" as the gudgeon pin is located right where your ring landings are on the piston.

i have done all this on our current engine (3.800" x 4.165) and to tell you the truth, i'm not sure its worth all the hassles and effort (i'm a machinist and did the block work myself in a mill). you get a bunch load of low and mid range torque which is good, but it makes it alot harder to try to "hook" the car up. personally, in my opinion, i would look towards something based around a 372/383 type combination.



sixwillwin
Member
posted September 29, 2004 10:39 AM
yes, you can use the small journal rods, but i used the cheaper, more plentiful 5.7 rods with ROD brg. spacers. You do NOT need main brg spacers.....

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The Joy of Six website


BiggerBill
Member
posted September 29, 2004 06:41 PM
First off,you better have a good machinist for the crank. Grinding off center cranks is very difficult, if you get someone who has never done it before or has done it very many times, you might want to think about another approach. After you get it done, I wouldn't be to hard on it because they grind on one side to get the stroke, after that the crank gets pretty weak (we're talking cast cranks). That long of stroke produces a good amount of torque, witch will snap it preety easy if you hook it up or turn it hard. Secondly, using 5.7 rods are all right but not advisable. With that kind of stoke, you are going to have to move the pin placement higher up in the cyclinder walls, to take stress off of them. even with a good balance job, it could still easily blow. My advice would be to look around for some used sprint car parts (rotating assy)it would be more cost affective. Also you have to crind the block for clearance, witch better be done by someone who knows what there doing. You can grind through pretty easy in some of the spots where you need to grind. sleepy


sleepy 1h
Member
posted September 30, 2004 12:56 AM
Sorry about the misspellings its pretty late. sleepy


ford5
Member
posted September 30, 2004 05:59 AM
I have built several of these using stock 283 or 327 SJ rods with new ARP bolts and crank offset to 3.81 stroke, and they have run good and lasted long times without any crank breakage, but they have been in our area street stock type cars that are 2V restricted.......not sure what unlimited induction would do? Never had to grind anything for clearance either because the big end of the SJ rod is smaller, did have to shorten the pistons tho.


Kromulous
Member
posted September 30, 2004 07:56 AM
By the time you put all that money into a cast crank (offset grinding, rebalancing) just buy a seriess 9000 scat (steel) and call it a day, or even a Eagle 4330 unit. Internal balance it with some Eagle sir 6" rods and some Hyoer pistons and your lower end is set without the worry of running stock parts.



JT54
Member
posted September 30, 2004 11:47 AM
We have run a 9000 in our 355 and it has held up pretty well. But i wouldnt run a 3.75 stroke or larger and expect it to live if you are turning it fairly hard. But thats just my opinion.


Kromulous
Member
posted September 30, 2004 12:51 PM
I would expect it to be quite abit better than a stock cast crank, but like Dirtbuster said, i wouldnt twist it to hard.


Xtreme12x
Member
posted September 30, 2004 04:06 PM
gm cast over the scat any day of the week..
just took my 6 inch rod motor to get re built at a well known shop in ames (not midwest), scat crank that was ran 20 times never over 6000 rpm with flat top pistons and 6 inch rods is now junk...
meanwhile my stock bottom end 355 stock rod motor the crank is crack free and back together
now i'm spending the real money on a real crank (callies) and not going to worry about rpms next year...


2nd2none
Member
posted October 01, 2004 02:05 AM
quote:
Originally posted by Xtreme12x:
scat crank that was ran 20 times never over 6000 rpm with flat top pistons and 6 inch rods is now junk


Did you magnaflux that scat crank when you first bought it? It isn't uncommon to find cast scat cranks cracked out of the box!



Xtreme12x
Member
posted October 01, 2004 12:47 PM
i dont build many of my own motors...
ptm built it the first time so i'm sure the checked it...
scat is junk period


Ego Racing
Member
posted October 01, 2004 09:38 PM
JUNK---- See that is what I think of Eagle. I have had 3 motors with Eagle cranks brake due to crank falure, these were not there cast cranks either. I have built 2 motors now with the SCAT 9000 series and have not lost one motor. The old one is 4 yaers and is turned 20/20, it runs good and strong I just don't ask more than 6500 from them and have had NO problems.


iowatoolman
Member
posted October 01, 2004 11:47 PM
hey guys isn't 4340 steel all the same???
if not that would be like saying that not all grade 8 bolts are not the same
or like saying that nike is better than reebok it is awefully hard to prove everyone has brand preference...

come on everyone has an opinion they are like @$$#*(&S everyone has one and some of us have two LOL

drive hard or drive home


Donnie Ross
Member
posted October 02, 2004 05:54 AM
the mettalurgy may be the same but is the heat treat at the factory in china the same ? how about the attention to detail in manufacture? are the cranks all crack checked and bad ones discarded or do they check one out of ten and if it passes all the rest will to? pro engine builders stay away from them for a reason.


stockcar5
Member
posted October 02, 2004 09:18 AM
4340 can vary based on how it was forged, heat treating, oil quenching ect.. also alot of the import stuff does not use defect free 4340.
then you get into the quality of the machining ect..

there was a post on here a while back about a guy who sent in samples of scat and eagle 4340 cranks and they had a VERY low nickle content in them!

if it were me i'd buy a callies and be done with it.

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www.geocities.com/dirtstockcar5


Kromulous
Member
posted October 04, 2004 07:38 AM
From my understanding about cranks, China's 4340 and American 4340 is alot different. Basicly the American 4340 has alot tighter specs than the chinese, and this shows up in Eagle & Scat cranks. Chinese made cranks can have less nickel, heat treating etc etc.

I went searching for info about this topic after reading this thread. Apprently the metal quality is the biggest difference. also i have heard Eagle's machining is not reall good as well.

Howards makes a nice american made 4340 crank for 750, brand new ready to go, or Callies. After reading about all this, i think i'll try to stick to american 4340.

Xtreme12x
Member
posted October 04, 2004 11:24 AM
for tracy's application, he is running mainly claim racing if he runs imca again... i wouldn't be afraid to build it with turned down journals and 327 rods


istock59
Member
posted October 04, 2004 01:48 PM
Thanks for all the info guys. Lots to think about building a 421.

12x, I was thinking about it as more of an Outlaw motor. I'm pretty well fed up with IMCA's rules (more their lack of enforcing them), so I'm not sure how much IMCA racing I'll do next year. Might be time for a change.

I was thinking of using a Dragonslayer crank, with a set of Manley 6" SJ rods. Wasn't sure what pistons tho. Sounds like whatever I use would have to be milled across the tops.

Xtreme12x
Member
posted October 04, 2004 09:13 PM
come up to webster next year tracy... they are getting a lot of stock cars..


eenfield
Member
posted October 05, 2004 11:14 AM
dont forget that scat 9000 series and some eagles are CAST STEEL not forged steel. Thats why you get them for a couple hundred bucks. Not to mention that the cheap ones are imports.

[This message has been edited by eenfield (edited October 05, 2004).]

Istock66
unregistered
posted October 05, 2004 03:58 PM           
Most everyone can make a piston for that its just not cheap.

Ross, JE. would be my choices for a non claimer type motor.


Xtreme12x
Member
posted October 06, 2004 07:58 AM
what stroke crank would you need and what c.i. would it be if you took a 5.7 rod and put a 6" rod piston on it, what stroke crank would you need to get that piston at 0 on deck height and what c.i. would that be?


istock59
Member
posted October 06, 2004 01:39 PM
12x, my understanding is that the math works like this....

1/2 the crank stroke + rod length + piston compression height = deck height

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So in the case of a regular 350.

(3.48 / 2) + 5.7 + 1.56 = 9"
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Or a 5.7 rod 406.

(3.75 / 2) + 5.7 + 1.425 = 9"
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Or a stock 400.

(3.75 / 2) + 5.565 + 1.56 = 9"
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So in the case of your hypothetical motor....

(X / 2) + 5.7 + 1.125 = 9", you'd need a 4.35" stroke crank. Won't fit in any SBC block I know of.

Or the 421 I've been asking about
(3.875 / 2) + 5.7 + X = 9", you'd need a piston with 1.3625" compression height. Well, that 1.425" piston in the 406 above is only .0625" too tall.....

[This message has been edited by istock59 (edited October 06, 2004).]

istock59
Member
posted October 06, 2004 01:59 PM
And here's an interesting combo.

GM makes a powdered metal rod for the SBC that's 5.94" long. Do the math.

(3.875 / 2) + 5.94 + X = 9", for a piston with 1.1225" compression height.

A 406 6" rod piston is 1.125, for a differnce of .0025. Shoot, a little extra deck height, and let the piston hang out the bore a little....

Xtreme12x
Member
posted October 06, 2004 05:30 PM
you can get those rods at like oreileys i think istock59...
i was wonderin if you could use those for a set of 6 inch rods and then cut a little off the deck and shave your heads a little and get up to 9-1 in my case for another project motor