Offshoreonly.com - Need advice on new 401 SBC stroker build

Quote:

Originally Posted by NHGuy (Post 4628481)

I think you need the bigger carburetor too. I have my OE Weber which is effectively a 650 Edelbrock. The Weber runs my 383 in a 4000 lb boat, to 5000 rpm or so. My bigger carb is a 750 Quickfuel. Since it can send more air it can send more fuel. So more rpms can be had.

If you think your plugs are good, they might be. But it's hard to shut off a boat during a hard run to pull spark plugs and get a true plug reading. An air fuel meter is your next gotta-have-it tool.

I will have to look into possibly more carb and research on a wide band.

Quote:

Originally Posted by Paxtonspeed (Post 4628488)

As far as your crank cracked, how was the engine balanced? If you are using a 400 balancer with a weight on it, that may have been your problem. Even though they will balance that way, you still have a huge chunk of weight hanging off the front shout of the crank. I just had mine internal balanced on the front, external on the rear (383). We had to put a chunk of malory in the front counter weight.

Crank was balanced internal front external rear.

Quote:

Originally Posted by Paxtonspeed (Post 4628496)

I am looking up the specs on my new rings. Wondering if maybe your rings did not but up due to heat.

FUEL APPLICATION RING END GAP FACTOR
Street Normally Aspirated .0065"
Drag Fuel Alcohol .0075"
Street Nitrous, Supercharged, Street Towing; Circle Track Unrestricted & Alcohol; Marine .0080"

So, your bore size multiplied by these numbers
Mine would be, 4.030 x .008 = .032 for my engine.

Based on the piston specs, for marine use and 2618 alloy the piston to wall was set at .0055. The ring gap I set was .018 for the top and .020 for the 2nd ring based on the recommended .0040 ring gap factor.

Quote:

Originally Posted by BillK (Post 4628553)

Jim,
Exactly how did the ring fail ? I wonder if it stuck in the bore and pulled the top ring land off the piston. Any pictures of the failure ?
I would think that 36 degrees of timing is pushing it unless everything is just about perfect as far as fuel goes.
The Scat crank should not have been a problem. I wonder if the cracks are an indication of detonation ? How did the rod bearings look, especially the upper half ?
I agree that internal balance is definitely better in this case.
Even though I do balancing if I was doing this I would have Crower balance the crank. Just give them the bob weight number.
600 cfm carb definitely needs to go.

Just thinking out loud :)

See attached image of the piston and head. (site won't let me upload images until I have 10 posts!)
The two small cracks were almost impossible to see even with the magnaflux, and that was on #1 trow. Didn't see any indication of detonation on #1 piston. I wonder if the cracks were there before install? And the rod bearings looked decent considering the trash that was embedded in them.
And yes I am having Crower do an internal balance once I get the pistons from JE and get the bob weight.
And the consensus all around seems to be bigger carb.
https://cimg3.ibsrv.net/gimg/www.off...b43ef10856.jpg

And thanks everyone for all the input, much appreciated.