jmm4jmc

First time posting. Read alot, wealth of information here.

Anyways, I have a 401 SBC stroker, had a piston ring failure in #6 cylinder in my current build, beat the piston top and head to hell, not to mention the contamination that went through the engine. So now I am pretty much starting over and rethinking a new build. This a 26ft hull, approx 4000lbs and my typical cruse speed is 3500-3900 rpm (30-35mph), running 1-2 hours at a time, with the occasional WOT @ 5000-5100 (48mph) just to confirm everything is running where it should be. Also running a Volvo 290a DP with C4 stainless props. Boat pulls hard from 2.6k-4.5k rpm and with good fuel economy from 2k-4k. Idles low and smooth. Overall pretty happy with everything, but I want just a little bit more mid to top end from the new build. Was running timing at 36 deg, never seen or heard any indication of detonation or indication of water reversion. Boat ran and pulled nicely.
Current build is/was:
401 stroker
Dart SHP 1-piece SBC block.
4.125 bore
Scat 3.75 stroke forged 1-piece crank, (int/ext ballanced)
Scat 5.7 forged rods
Icon 2618 pistons (9.3:1 CR) (1.425 CH) (.039 quench)
Comp XM 270HR-12 hyd roller (218 int./224 exh @ 050 / 112 LSA)
Comp Pro Magnum Hyd Roller Lifters
Promaxx 183 heads / 64 cc chamber (Manley extreme Ex. / severe Int. valves)
Rpm Airgap
Edelbrock 600cfm carb
DUI HEI distributor
Melling10552 oil pump
Canton 9-qt oil pan
Stainless Marine 4” stainless exhaust (thru-transom)

New “overbuilt” plan is:
401 stroker
Existing Dart SHP 1-piece SBC block (bored .010 over)
4.135 bore
Crower Enduro 3.75 stroke forged 1-piece crank (custom) (int balanced)
Crower Sportsman 5.7 forged rods
JE 2618 pistons (9.2:1 CR) (custom) (1.425 CH) (.039 quench)
Crower hyd roller (221 int./230 exh @ 050 / 112 LSA) (custom grind )
Crower Enduro Stainless Roller Rockers
Dart Pro 1 180 heads / 64 cc chamber or Profiler 185 (either with Ferrea super alloy Ex. / Comp plus Int. valves)
Existing Rpm Airgap
Existing Edelbrock 600cfm carb
Existing DUI HEI distributor
Existing Melling10552 oil pump
Existing Canton 9-qt oil pan
Existing Stainless Marine 4” stainless exhaust (thru-transom)

Here are my concerns and 2nd guessing’s. I need a 3.75 1-piece crank running 5.7 rods, and I do not want Scat this time, nor Eagle. The current Scat was magged and there are two 1/8” cracks on #1 throw. So I am now looking at Callies Magnum or Crower Enduro. Neither offer a crank in the specs I need (3.75 1-piece running 5.7 rods), but Crower will make me one for the same price as off-the-shelf, with a 6-week lead time.

My other choice is using an in stock “off-the-shelf” 2-piece crank (3.75 running 6” rods) from either Callies or Crower, but using a rear main seal adapter in the 1-piece shp block. And now I will need to run a 1.125 CH piston (JE has these in stock “off-the-shelf”).

So after the days of exhausting research I made the decision to have the custom Crower 1-piece made and run the custom JE dished pistons, and just deal with the 6-week lead time on the crank. But then I started thinking about the other options, using an in stock 2-piece crank and rear main seal adapter, while using 6” rods. (even if I wanted to run 5.7 rods Crower would still have to make the crank and they prefer to make it with a 1-piece to avoid me using a rear main seal adapter).

The questions I have are, if I go with the 2-piece crank option:
1. Do I need to worry about oil leaks using a rear main seal adapter?
2. Any problems running a 6” rod?
3. Any problems running the 1.125 CH piston (oil ring is now in up in the pin)?

Or do I just be patient and wait for the 1-piece crank?

I would love people’s opinions and experience on this. I know it’s an overkill build for my use but I don’t mind spending the little extra to make it right.

Thanks for your time,
Jim

SB

I really question your carburetor choice. Not only CFM very small but it is prob hard to get enough fuel thru it for this size engine. Was it on your last build ? Was it the cause of your ring failure ? If not, what was the cause ? Are you real good at reading plugs or do you have Widebands hooked up for tuning ?

That cam will be a 'tow truck' cam (not quote of course but close) for that CID. Peak HP RPM should be no more than 5K as that is where it peaks with 383's. Just asking here,not being critical yet, as I don't know what your needs/wants/goals/type of boat/etc are....yet.

jmm4jmc

Thanks SB for the reply.
Carb choice was for fuel economy basically. I always questioned the carb CFM size though, but plugs always read good. It did not seem the engine was running lean/hot. As far a CFM size this carb seemed (on paper) to be the max limit for this engine and border lining on needing a 750 CFM. And I also question " why did the ring fail". Did I run it too lean/hot which caused the breakage? I showed the piston, head and valves to 3-different long time reputable engine builders and at first everyone thought it was detonation, but then they all came to the conclusion it was just ring failure. Bad luck? Bad ring? Or did I pinch the ring on install (ring gap was within spec and pistons went in without effort)? Or did I run it lean from lack of fuel? I definitely do not want this to happen again, and I want to fix the original problem. During the new build research I was looking to replace the carb with either an Edelbrock 750 (fuel economy, if there is such a thing) or a Holley 650 or 750 marine with vacuum secondaries. But I would love to hear opinions on my previous carb choice and a carb choice.

The boat is a 26ft Wilson, stern cabin, light and likes to go fast. Boat is used primarily to fish, but my wants and goals are to get in and out as quick as I can (conditions permitting) while getting decent fuel economy. I also want decent idle while out all day. The previous cam was my choice and seemed to do very well, with max rpm/WOT @ 5000-5100, which is what that cams comp dino sheet showed, peak hp @ 5100, then falling off from there. The new cam choice was recommended by (after talking on the phone to) Comp, Crower, and Howards. All came up with the same/close cam specs. Again, I would love to hear opinions on this.

Thanks,
Jim

GPM

The Lunati Voodoo crank seems pretty nice, the 6 inch rod works well with the 3.75 stroke, AFR 195 heads may be better suited for your cubic inch, the Edelbrock marine 750 would be a good choice, seems to work well right out of the box. There again, this is only my opinion.

Trash

Cam peaks at 5300 or more. Cam is fine. Carb should be bigger.

6.0 rods will work fine too.

NHGuy

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.

Edelbrock has nice tuning jet kits. Their carbs are very easy to service. So if you find the mix needs adjusting it's pretty DIY.

Your quench is great, smart man.

You may want lifter valley vents. they are stand pipes that stick up in the lifter valley. They are there to direct oil to the pan without going by the spinning crank.

On the new engine you want to be sure the ring gaps are calculated for marine/towing. Which is a tad over normal to allow the expansion that comes with heat buildup under prolonged loads.

I don't know about the RMS adapter issue. Or the crank differences.

I'd suggest short travel lifters. I have them and they work well.

Paxtonspeed

I would be concerned about it going lean on top end with the carburetor you have. Put a 750 double pumper on it and get you a wide band 02 sensor. The cam you have should rev fine past 5000 RPM. I would also look more into why the rings broke. Rings should not just break. I had broken rings in my engine on cylinder 3, but it was becasue the boat sat for 6 years at one point and condensation rusted the ring to the cylinder wall.

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 had a Scat 9000 Cast crank in a boosted 383, 10 PSI, ran like SOB. made way more power than the crank was rated for. One of the cheap cast pistons let go (rings butted from the heat) before the crank. The motor was old and had been together for years when we decided to boost it.

Paxtonspeed

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.

BillK

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

BillK

By the way, I really do not consider your engine a "stroker" it is basically a 400 Chevy small block