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360 Budget stroker with 390 crank (Read 1955 times)
bricklin
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360 Budget stroker with 390 crank
11/02/12 at 15:12:43
 
sorry haven't been around for a while , but there used to be a bunch of discussion about offset grinding 390 cranks and using SBC 400 pistons, I did a search and really couldn't find what i was looking for.  
 I have a rusty old 390 crank sitting here and a rusty 360 block, I also have a set of sb400 pistons and a fresh pair of 291 heads, I know some were using 6 cyl chev rods, there seem to be an issue with pin position, I am now considering doing one of these for street car and after a couple of years I'm sure you guys have it all worked out. I'm just  trying to use up some used up stuff and make a decent street engine. Kn Parkman knows how cheap I am LOL
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Re: 360 Budget stroker with 390 crank
Reply #1 - 11/02/12 at 16:33:17
 
Not sure of the stroker specifics, but with custom pistons you can do anything. 410-420 cubic inches is fairly straightforward I think. I recently did some SBC 400 pistons in a 343 to 360 build and by the time you pay to have the pin bore resizes to AMC specs and cut valves releifs you might as well pay an extra couple of bucks and get some custom forged pistons made.
 
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Re: 360 Budget stroker with 390 crank
Reply #2 - 11/02/12 at 18:49:32
 
I went so far as to buy SBC pistons.  What I found was that the pin boss below the pin was going to hit the counterweights.  Not a huge deal, but I would have had to re-do the valve reliefs, and cut the pistons a little to get the right height, as well as cut the pin bosses, so I bailed and bought custom pistons.  You have to tell the piston manufacturer what the pin boss needs to be.  Using a longer rod would have solved my problem.  But then you need a custom piston to get the right compression height.
For rods, there are three choices.  Ignore the offset of the rod and just run them, buy the PEP or K1 rods that have the right offset, or re-chamfer the chevy rods and run them reversed so the offset is about right.  I guess a 4th option is to use the LS rods, which have no offset so are in between the AMC and SBC offset.  I already had the rods, so I had them chamfered.  Since then I have been using the K1 rods.  
The 401 K1 rods move the bearing over close to the crank counterweight and so you have to check the clearance of the bearing to the crank.  Moving the bearing aligns the load path of the beam and bearing, and is good engineering practice, but if the bearing is a little wide or the radius of the crank fillet is very generous the bearing might need to be trimmed.  You have to check it.  I have done two engines with the 401 K1 rods and it was not a problem on either.  But one guy on the internet used the wrong bearings and now you will read that the K1 rods have the bearings "in the wrong place".  
When I did my motor there were no quality rods with the right offset, so I made them fit with the right bearings and chamfering both the rods and bearings to fit.  I think the K1 rods are a better starting point.  But with any performance build you have to check everything.  
r.
 
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Re: 360 Budget stroker with 390 crank
Reply #3 - 11/02/12 at 20:14:18
 

 When using Chevy LS style rods you can widen the crank pins by .010 in both directions, remove .010 from the chamfored side of the rods and use the narrowed King bearings. That will place the rods on the crank and wristpins as they were origionally from the factory. If staying with the std AMC journals the K-1 rods are the ticket. At this point with those rod choices fiddling with regular SBC rods makes no sense.
 
 SKeown
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Re: 360 Budget stroker with 390 crank
Reply #4 - 11/02/12 at 22:21:51
 
Quote from SKeown on 11/02/12 at 20:14:18:

At this point with those rod choices fiddling with regular SBC rods makes no sense.

SKeown

Why?  
Can you buy an H bearing for the k1 AMC rod?  
If LS1 rods requires "fiddling" then what is the difference between them and a regular sbc rod?
"Regular" SBC can be centered..many choice of brands and materials....and have many bearing choices...brand,quality,and undersizes...
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Re: 360 Budget stroker with 390 crank
Reply #5 - 11/03/12 at 01:33:46
 
Quote from Hurst390 on 11/02/12 at 22:21:51:
Quote from SKeown on 11/02/12 at 20:14:18:

 At this point with those rod choices fiddling with regular SBC rods makes no sense.

SKeown

Why?
Can you buy an H bearing for the k1 AMC rod?
If LS1 rods requires "fiddling" then what is the difference between them and a regular sbc rod?
"Regular" SBC can be centered..many choice of brands and materials....and have many bearing choices...brand,quality,and undersizes...

 
 If grinding a crank to use Chevy 2.100" rods the journals can be widened easily to accept the .930 instead of the AMC .920 width rods. That process also allows you to achieve the desired side clearance too. Then the only modification needed for the rods is removing .010 from the chamfored side of the LS rod to center them correctly. Then the narrowed or chamfored bearings can be used without further "fiddeling". Unlike the standard Chevy rods which have to be turned around, narrowed, re-chamfored and still don't center as accurately as the LS approach. Besides with the old school fiddeling approace using std Chevy rods that must be re-chamfored, the bearings have to be modified/ fiddeled with too unlike the LS rods and bearings. Thats why it makes no sense.
 
 If using AMC spec rod journals the bearing choice is indeed quiet limited unlike the Chevy bearings. At least the K-1 rods are designed correctly for a replacement AMC rod. You do have a good point about the availiable variation in lengths of std Chevy rods that require more extensive reworking to fit. I use 6" x 2" journal LS style rods myself.
 
 If you're looking for odd rod combos, like different lengths or journal size, you can fit Ford 4.6L rods just like the Chevy LS rods. They are availiable in many different  specs, but most will require custom pistons with Ford size wrist pins. Heres one example: http://www.ebay.com/itm/Saleen-FORD-4-6-Manley-Stroker-Connecting-Rods-14044-8-H -BEAM-MUSTANG-F150-/110768157630?pt=Motors_Car_Truck_Parts_Accessories&hash=item19ca4bf3be&vxp=mtr  
 
 SKeown
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« Last Edit: 11/03/12 at 02:59:42 by SKeown »  
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Re: 360 Budget stroker with 390 crank
Reply #6 - 11/03/12 at 04:36:53
 
Read this:
Quote:
Re: hp limit for 360
Reply #7 - 01/30/10 at 07:56:04 I'm currently building a stroked 360 for my son's Gremlin that won't make 600 but could probably handle it. I bought a used and abused 390 crank with spun bearing damage(thanks Rob) and had it machined to 3.566" stroke with 2.10" big end. The block is going to 4.125" bore using SRP forged pistons and Scat 6" ProComp I beam rods. This makes it 381 ci and 11 to 1 cr.
* Crank work including stroking, mains, heat treat, and oil mods == $500 (it's now real pretty)
* Pistons from Summit ==$444 (1.425" CH)
* Total Seal tool steel rings on clearance from Summit == $125
* Scat rods from Summit == $274
This will be topped with stock unported heads and a small flat tappet cam. Should last forever.

I'm pretty confident the 360 block could handle 600. Maybe not much more.

 
The car has gone a best of 11.40 at about 119mph.  It is really a low(er) budget deal that runs great.
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