Need advice on new 401 SBC stroker build
05-27-2018, 12:40 PM
#11
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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.
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.
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.
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.
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.
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
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.
And thanks everyone for all the input, much appreciated.
Last edited by jmm4jmc; 05-27-2018 at 01:04 PM.
05-27-2018, 03:37 PM
#19
What a mess, can't say I haven't been there. Any chance you had a vacuum leak at the intake runner, or head gasket leaking between the cylinders that over heated that piston.
05-27-2018, 07:29 PM
#20
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