DART BLOCK - machine main bore to take large journal crankshaft

spookypt · #1 (**permalink**) 12-12-2016, 05:13 PM

A question? Im wondering if anyone has ever done this or if its even possible???

I have emailed DART to see what their TECH says but Im chasing opinions.

I have a DART Iron Eagle Block 9.2 Deck with 302 (small journal) mains. I believe the part number is 31384295 – 351 W Short Deck Steel 302 9.200 4.125

What Im wanting to know is, is the 31385295 – 351 W Short Deck Steel 351C 9.200 4.125 exactly the same as the other except for the difference in main bearing diameters: 302 (2.249”) or 351C (2.749”) allowing the choice of small or large journal crankshafts ?

Mine has the small journal crankshaft and Im wondering if possible whether I can machine the main tunnel bore to the larger journal crankshaft? While it will cost a lot it may be cheaper to go that route if the rest of the block casting and spec is exactly the same?

Really appreciate your tech help from OZ.

Kindest regards Matt

blykins · #2 (**permalink**) 12-12-2016, 05:43 PM

I doubt there would be a machinist willing to remove 1/2" of material....

Easiest route is a custom crank. For what you're going to pay in machine work (if it's even possible, never tried it) plus a new crankshaft, it's easiest just to call Scat/Callies/etc and have a new crank made for $1300-1400.

spookypt · #3 (**permalink**) 12-12-2016, 05:52 PM

This was my first idea. Problem is Im being quoted 16week wait!!!!

Who would you recommend over there who isn't quoting 4 months??? Any thoughts?

blykins · #4 (**permalink**) 12-12-2016, 05:57 PM

I'm direct with scat and can prob have one made quicker than that.

In addition to the main line boring, you would also have to have the block cut for the larger rear main seal as well. I'd definitely go the crank route, or a new block altogether.

Gaz64 · #5 (**permalink**) 12-12-2016, 05:58 PM

Hi Matt,

I doubt whether there would be enough material to pull 1/4 inch out of the tunnel radius.

The inner main bearing cap bolt spread is more than likely different.

Gary

spookypt · #6 (**permalink**) 12-12-2016, 06:08 PM

Quote:

Originally Posted by Gaz64

Hi Matt,

The inner main bearing cap bolt spread is more than likely different.

Gary

Hey Gaz, you're spot on I believe on this. I just spoke to Superformance a DART agent in Brissy and they said this would be an issue.

Im thinking more towards a custom crank.....$5200 for a new block!

Jac Mac · #7 (**permalink**) 12-12-2016, 07:02 PM

What size 'cubic inch', do you want to end up at? Current block bore is 4.125", therefore you could use a 3.4" stroke SBF crank and get an easy 363 cu in on that 4.125 bore. Should be plenty of those cranks around.

spookypt · #8 (**permalink**) 12-12-2016, 07:08 PM

440 cubes or there about.

Jac Mac · #9 (**permalink**) 12-12-2016, 07:39 PM

302 main size aint gonna be pretty at that stroke, swap the block.

eschaider · #10 (**permalink**) 12-12-2016, 08:27 PM

I agree with the other comments about using a custom crank, Matt.

Something you might want to check out is the location of the main studs vs the main saddle bore. ICE engineers like to keep the studs close to the bore. You might find the main studs are closer together on the small journal design and prevent the block from being opened a half inch for the bigger mains.

Ed

spookypt · #11 (**permalink**) 12-12-2016, 08:36 PM

Yes Ed I agree. Its hard to know what to do when faced with such a conundrum.

Appreciate everyone's feedback though.

blykins · #12 (**permalink**) 12-13-2016, 04:11 AM

I didn't know you were aiming for 440 cubes. A 4.155" x 4.000" will get you 434 but I really don't like the thought of a 4" stroke with 2.250" mains. Lots of stresses there.

I would either go for an off-the-shelfer, like a 3.5" stroke, or switch blocks altogether. I know that you said you were working with a $5200 block....is that aluminum, or just the price of a cast iron block to your door? I can get you a new Dart or Ford Racing block to your door for considerably less than that....probably fully machined.

With a 4.155" x 3.500", you'd be at 380 cubes.

spookypt · #13 (**permalink**) 12-13-2016, 12:54 PM

Hey Brent I'll drop you a detailed email in a few hours...

CraftEngines · #14 (**permalink**) 05-08-2017, 12:01 PM

Just now saw this thread, not sure if there is still a need. I have the same block I used for my personal engine. It is a 3.500 x 4.155" (380ci). This combo worked great for my build. I have an extra Lunati 3.500" crankshaft with 302 Journals. It has Honda Rod Journals and would take a custom rod but would be quicker than waiting for a custom crankshaft. Just let me know if it will get you out of a bind.

Thanks
Lance Smith

spookypt · #15 (**permalink**) 05-08-2017, 03:18 PM

All sorted Lance. Built a whole new engine. Old block will be sold. Cheers