View Full Version : Another SBC 406

Bobby D
12-13-2011, 01:22 PM
The plan is for this 406 to be a budget build up, my main focus is building it to run all day and have lots of torque under 5000 RPM at a certain price point. I understand you can build 406 small blocks with more HP, but doing that moves the torque/HP curve to a higher RPM range and the build cost would be higher as well, neither of which I want. That being said, I do understand you can easily turn this engine to above 5500 RPM if you would like.

Thanks to Mike (maddad) sharing information on his build over the past few months I finally took his no replacement for displacement advice and now there will eventually be two 1972 18ís with a 406 motor. I came close to buying the 383 that Phil put up on the board a few weeks ago however in the end I decided to buy a 406 for about the same cost. The motor is an older build and unfortunately we have not been able to locate the build sheet or cam card. The motor was built/ran on a dyno and than stored on a motor stand. Itís an early SBC 400 4 bolt main block bored .030 that started out as a marine build than my buddy decided to go with a BBC instead and it ended up as a stand by truck motor. Last weekend we measured the cam (flat tappet) duration with a dial indicator on the lifters since they are exposed and we came up with duration @ .50Ē lift to be 210 intake and 218 exhaust.

Iím not an engine builder so l need help figuring out if this cam is suitable for marine use, I searched comp cams website and found the X4254H extreme 4x4 hydraulic flat tappet camshaft matched the duration @ .50Ē lift. What I do know is the motor was built by Troy Dennis who at the time built motors for Reggie Fountain, the heads are world products S/R Torquer iron heads that were ported and polished by Griffin automotive and marine in North Carolina. The motor and heads are well built and have good heavy duty stuff but nothing fancy or exotic. The motor also came with an Edelbrock performer intake manifold, mechanical fuel pump, and a flex plate with 400 counter weight. I need to get organized and figure out what direction to take so my first question is this cam OK for marine use?


12-13-2011, 03:00 PM
use it as-is, but add the COMP Pro Magnum Stainless Rockers, check valve cover clearance for rockers

don't look back, it'll pull the dock down :)

12-13-2011, 06:27 PM
Is that a 7qt oil pan? I like :)

12-13-2011, 10:36 PM
Good luck with it Bob. You run an SX Volvo right? To mate the external balanced 406 to my AQ drive, I had to have a small SBC flywheel drilled so it had the right counter weight. I also use the Comp rockers and they fit under the stock size tin covers I use.

12-14-2011, 12:56 AM
I'm running the Comp Pro magnums in the 1.6 ratio on my 383 and I had to do some grinding on the valve covers, mine have the center bolts, the talls hit the exhaust manifolds and risers. So good catch Buiz! Steve

12-14-2011, 09:23 AM
if you use the 1.6 Pro Magnums on those heads you MUST drill the pushrod holes out an extra 1/8" larger in drill size or the pushrods will rub significantly, I did that setup 15 years ago on a new 1996 GMC 1500 truck with those exact heads, rockers, and cam combo, and it pulled HARD,,, peak TQ was 3200-3500 which is perfect for a boat cruise rpm

Bobby D
12-15-2011, 11:22 AM
Thanks Jim for feed back on the cam and rocker recommendation, Iíll add it to the BOM and see if it falls blow or above the line.

Mike yes I run a 1.45:1 SX Drive and 21"PLUS RAKER SS LH.

Can I use the externally balanced flexplate that came with the motor, from what I have read it may not have enough weight? Going from a SBC 350 one piece real main seal to a SBC 400 two- piece real main seal I have to solve the bolt pattern puzzle. Not positive but I think I have a 14Ē 168 ring gear teeth flywheel that will not work, also the Volvo SX rubber coupling has the wrong bolt pattern as well. I plan on ordering an externally balanced 400 flywheel from JEGS and a new two-piece SX rubber coupling

12-20-2011, 10:09 AM
Get a 14" 400 counterweighted flywheel and a engine coupler from a big block SX volvo engine.
The bolt pattern on the big block coupler is the same as the 2 piece rear main sbc.

Bobby D
01-25-2012, 05:44 PM
Any suggestions on selecting an ignition system for the build?

Thanks I ordered the 400 flywheel and the BB engine coupler today.

01-26-2012, 09:56 AM
Plus I'd worry a little about adding a new flywheel if the rotating assembly was not balanced with it. Sounds like it was balanced with the flexplate?

Do you know what length connecting rods are in it?

Bobby D
01-26-2012, 05:06 PM

Good challenge before buying the motor I needed to figure out the crankshaft bolt pattern puzzle. I have to go from a 1986 and later crank with 3.00 ďbolt circle to a pre 86 production 3.58Ē crankshaft. I also learned that all 400ci SBC V8ís are externally balanced and must use a counterweighted flywheel (or flex plate) for proper engine balance. I found this information on GM performance parts home page:

Part number 471578 flexplate is for externally balanced 400ci SB only and is to be used with balancer P/N 6272225.

Part number 3986394 flywheel is for externally balanced 400ci SB only and is to be used with balancer P/N 6272225.

Thanks for the heads up the flywheel, the one I ordered replaces GM 3986394.
Iím following your advice my buddyís machine shop will check it and get it right.


Bobby D
01-27-2012, 08:46 AM

Yep harmonic balancer is cut and the heads have the stream holes drilled.
Rubber coupling arrived yesterday and its correct for a 2 piece seal install.

Also any thoughts or opinions on MSD Chevy V8 marine certified ready to run distributors, MSD Part no 8560 or 83606?

Bobby D

01-27-2012, 07:45 PM
make damm sure the cap and rotor has brass contacts...

Bobby D
01-29-2012, 07:58 AM
Jim if I understand you correctly youíre telling me just because it says its marine donít assume it has brass contacts?

The weather in Pennsylvania was mild yesterday so decided to pull the engine and outdrive took me 2 hours. First time evolution for me however with all the information on this site it was quite easy to do. Next step is clean up and paint the area and organize wiring and work on a new layout for whatís going back in. New parts are staring to arrive so the 406 build will start back up next weekend.

01-29-2012, 09:59 AM
from direct past experience with MSD anomoly's... check the cap for brass contacts, and also make SURE the rotor tab hits the center cap button, you can tweak the rotor spring tab for more tension, I had one rotor that didn't even touch the cap center pin at all, not going to extend here how long it took to figure that out :nilly:

Bobby D
01-29-2012, 06:25 PM
Doses anyone know what this is? It was cut to fit glued to the inside of the engine compartment. Its been there for about 12 years and the foam has designate and lost adhesion..

01-29-2012, 08:31 PM
You think it was some type of sound deadner?

Bobby D
01-30-2012, 08:23 AM
Thatís what I thought at first however, most sound barrier stuff I have seen is composite and consists of a layer of vinyl sandwiched between two layers of fire retardant foam covered by a vapor barrier facing. This material has vinyl on one side and foam on the other.

02-03-2012, 01:38 PM
Don't over look the Delco Voyager HEI kit.
It has a great performance ign curve in it.
You can get replacement parts anywhere, ie Napa, Merc/Volvo dealer.
Kit comes with everything but the sparkplugs.

Bobby D
02-11-2012, 11:53 AM
Sam thanks for the Delco tip that’s exactly what I was looking for very simple and easy to install with a good track record.

Made some progress this week I started pulling parts off the old motor, cleaning up the motor compartment, the 406 assembly starts next week and I also started reworking the existing wiring. Since I’m doing most of the work myself progress has been slow however at this point I should have everything back together by late spring. I clearly underestimated the cost associated with all the small miscellaneous things needed to do this project and that’s why I will not get everything done on the work order this year.

1972 DONZI 18 2+3 Work Order

406 SBC
SS Marine Exhaust System
Clean-up existing VP SX Outdrive
Detail engine compartment (clean and paint)
Inspect and refresh SX drive and Bennett trim tab pumps
Refurbish existing interior hardware
Replace existing interior with Built-Rite
Rework electrical system in engine compartment and consider going with (1) battery

406 SBC build
1. Break-down:
o 406 CID SBC Troy Dennis (Charlotte, NC) 4-bolt main rotating assembly (externally balanced, 2-piece rear seal).
o Hypereutectic dish pistons
o World Products S/R TORKER IRON HEADS polished and ported
o stainless steel valves (intake and exhaust)
o Comp Xtreme Marine XM256H Hydraulic flat-tappet camshaft kit
o Edelbrock Performer intake manifold with ARP Stainless Steel bolts
o Delco Voyager EST Marine Electronic Distributor kit
o Billet Specialities aluminum valve covers
o Edelbrock Marine Series 750, electric choke carburetor
o Holley marine mechanical fuel pump
o VP fuel filter
o Fel-Pro MLS marine gaskets & one-piece oil pan gasket
o Stainless Marine cross over system
o Melling high volume oil pump with ARP shaft
o New Fel-Pro head bolts
o Flywheel with 400 counter-weight
o Brass freeze plugs
o Stainless Marine Exhaust Manifolds
o VP alternator
o VP starter
o VP Power steering pump
o VP raw water pump
o VP 7.4L engine coupler
o Custom dip stick/oil drain tube
o VP remote oil filter system

Bobby D
02-11-2012, 12:32 PM
Poor choice of words on my part as far as I know this is first time itís been removed since original install? That being said there are no issues with this drive its has about 240 hours of use so the plan is grease the fittings, change oil, touch up the paint and put it back on.

Jim Bo
02-11-2012, 07:34 PM
Interesting, sounds like some good stuff. How do you think it compares with the Amsoil Severe Gear? Are you getting it direct or have to go through a distributor? Thanks

Bobby D
02-12-2012, 08:06 AM
My boat will take on a very small amount of water after a day of boating and I believe it may be finding it way in thru the exhaust blank-off plate. Any suggestions on how to inspect and seal would be appreciated.

02-14-2012, 09:07 PM
What compression ratio are you ending up with? Iron heads, what cc with the flat top slugs?

Bobby D
02-15-2012, 08:26 PM
Thanks for pointing out my mistake on the build sheet, it should read dish pistons. As far as compression for a 406, they could be either 8.6-1 up to 9.5-1 depending on the head CC. My buddy Mark built the motor to run on pump gas and decided on the 67 cc heads and 89 gas.

02-16-2012, 06:39 PM
Sounds swell and should sound swell!

Bobby D
02-23-2012, 05:56 PM
First coat of bilge coat and cleaned up and stamped motor mounts.

02-23-2012, 07:46 PM
Great idea. I tagged mine but the stamp is no risk. Gonna do that some how where the powder coating won't affect it.

Bobby D
02-24-2012, 10:58 AM
I have a good memory itís just not very long so I bag and tag everything. SBC blocks are cast the same so I decided to stamp all the motor mount components to insure that what I take off goes back together exactly the same way. I have access to a clean tank so the parts after painting look good as new. Iím using a product called Rust-Oleum stops rust Hammered Spray paint on things you will not see like the bell housing and motor mounts and they are turning out nice.

02-24-2012, 01:34 PM
I really like the hammered effect too--used it for my v-drives and their mounts. Just stumbled into it in Home Depot and thought the chip looked right, and it was even better in real life.

Bobby D
02-25-2012, 06:53 PM
My buddy fabricates ornamental iron outdoor artwork and 4 years ago he gave my wife a shepherdís hook for her garden. He painted it with this stuff and after sitting outside it still looks new.

Bobby D
03-05-2012, 09:45 AM
Not much SX information here but does anyone know the spec on VP coupler studs, not a lot of information in the service manual as well. It says to remove six nuts and slide coupler off. Iím installing a new flywheel and hub and tried to remove a stud yesterday to see what it looked like but it did not want to come out. I believe it a double ended stud. I want to use new fasteners, grade 8 and blue LT? I had run-out checked on the flywheel at the machine shop it was .001.

Bobby D
03-05-2012, 09:54 AM
Need help selecting a fuel filter, I found (2) two models for gasoline use which one do I need to use 110A or 120?

Bobby D
03-26-2012, 10:01 AM
The 406 is starting to look like a motor again, yesterday I started bolting on parts to see how they fit up and what will require modification. I also installed the dipstick tube on the new oil pan to match what came off the old motor. At the original drain plug hole I plan on using the mercury drain hose kit that fits thru the transom plug hole. Since the bottom plug boss is about 3/8 thick the oil below the boss will never drain and contaminants will settle so I also have the option to use the tube to change oil occasionally. Last week I drained the old oil and measured 6 quarts not including the filter, yesterday I poured 6 quarts of clean oil and it showed a half quart low on the stick, add the oil filter and it measures correct.

03-26-2012, 11:05 PM
Fuel filter - Look up FSTperformance.com. They make a great fuel water/sep filter. 300 GPH flow rate and 3 micron filtration efficiency.
Coupler - same a Fixx, but I use 271(red) loctite on the studs and nuts.
Engine looks great...

Bobby D
03-28-2012, 01:31 PM

Thanks for all the information had to order the studs from Volvo.
Will this work Holley 712-327-11 Holley Marine Fuel Pump 110 GPH fuel pump?

Thanks as well although not much Volvo SX stuff posted here your information has been spot on.


Bobby D
04-04-2012, 09:07 PM
Can I use this filter system with a mechanical fuel pump? I planned on using the existing bracket to mount a new 320R Racor however if I remove the low pressure pump it looks like it could work?

Bobby D
04-11-2012, 06:10 PM
Fabricated a motor stand out of recycled unistrut and mounted the flywheel and hub. Also fit up the fuel/water filter head unit and it looks like it will work out. This week I will be installing the stainless marine cross over and manifolds.

Bobby D
04-14-2012, 09:31 PM
Today I fit up the stainless marine crossover and the exhaust manifolds, the exhaust fit perfect, however the cross over did not because Volvo rigs the power steering pump and alternator bracket to the recirculation pump. Since I no longer have a recirculation pump I fabricated a bracket to support the power steering pump to the alternator bracket. I also relocated the alternator bracket to the fuel/water filter bracket and drilled a hole in the alternator bracket to allow the port side cooling hose a clean path to the exhaust manifol

Bobby D
04-19-2012, 07:47 PM
Here are a few more pictures of the progress, motor is coming together and should be ready to go back in the boat next week.

Bobby D
05-07-2012, 11:05 AM
Installed the motor Saturday and took the tailpipe dimension per the layout sheet for fabrication. Existing exhaust tips are about 11Ē long and will need to be cut to allow room for riser and short piece of hose installation.

Just Say N20
05-07-2012, 01:10 PM
Very tidy.

I'm jealous of all the room you have in the engine compartment!

How long until you get the rest of the exhaust?

05-08-2012, 12:34 PM
Not that a boat engine and a car engine have a lot in common, but yesterday I had to drop some oil off to a local engine builder.

He had just run a 406 on the dyno that he had built for the street, 10:1, hyd cam, alum heads, pump gas.

He told more more of the internals, but the bottom line was 567 HP with a 600 CFM carb, and 575 with an 800/850 (I forgot which one) CFM carb. Torque was in the 535lb ft range. Oh yeah, he was spinning it 6700 RPM.

Nice piece.


05-08-2012, 01:06 PM
Wow. (Am I missing something? Sound lean to anyone? What happened to 2.2 cfm/hp?)

Bobby D
05-08-2012, 02:25 PM

The exhaust is straight forward I went with the extended risers to prevent reversion. Stainless Marine will build them to go right to the transom so I will just have a short piece of hose connecting them to the tips. Once the measurements are received they normally build and ship them about 10 days later.

Yep the engine fits in there very well and should give you a basic idea of how your new motor will look and fit when delivered. Now that the motor is simple and easy to understand and Iíll be the guy working on it moving forward I put a lot of thought into the final assembly. I moved things in, out, up, down and back again until I was satisfied with the location. I can get to hoses, belts, wires, change oil & filters, bolts, etc without much trouble and also get a wrench on all transom shield and motor mount bolts and make sure everything remains torqued down.

In addition to a finding a worn-out recirculation pump and raw water pump impeller when I pulled the old mill I also found (6) six of the transom shield bolts and (2) motor mount bolts loose. Bottom line from now on I will have a good PM program in place and look at things much more closely than before. I clearly had the ďif it isnít broke donít fix itĒ mentality thinking that low hours translated into no problems.

After we talked I remembered a motorcycle shop down the road, I stopped in we talked and he ordered a case of oil for me.


05-08-2012, 02:38 PM
Bob, I am glad, 1) I could help and 2) it all worked out.

If you have any more questions, just call.


Bobby D
05-22-2012, 05:28 PM
My port side cylinder developed a small leak last year and needed to be fixed before going back in the water this summer. Although not recommended by Volvo I found seal kits for the SX and DP cylinders by going thru OMC. I wanted to share this information to help anyone with this type of cylinder decide if they want to replace a leaking cylinder as recommended by Volvo or try the OMC seal kit. OMC had a joint venture with Volvo starting in 1994 and used many of the same parts, turns out OMC makes a seal kit and Volvo does not. The 1998 OMC cobra drive trim cylinder and my SX drive are the same and since the seal kit was available I figured I give it a try. The OMC reseal kit part number is 985060 (cost is $28.25 plus tax) compared to a new Volvo SX trim cylinder which is ($472.50 plus tax each). The kit comes with easy to follow instructions to reseal the cylinder. I replaced the internal O-ring and scraper in the end cap, both external and internal O-rings from the end cap and the two split-ring retainers and O-ring from the piston. The job took 30 minutes from start to finish. Last Saturday after finishing up the wiring and final alignment checks I installed the outdrive and cycled the cylinders several times. Today I checked out the cylinder and found no leaks.
Also I followed an alignment procedure posted by MOP and several others a few years back and when I was done it was dead nuts on.

Bobby D
05-26-2012, 03:52 PM
A little more progress made today

05-26-2012, 04:18 PM
What brand cooling hose is that? I need it bad!

Bobby D
05-27-2012, 06:45 AM
Here you go, when I relocated the power steering cooler I could not find the correct 1” formed hose that would work. I originally bought the hose for the installation you see in the lower right corner however since I had a tight fit on top of the engine by the alternator I used it there as well.

Can easily be bent into tight radius, Designed to give excellent service.

Corrugated Nautiflex Silicone Exhaust Hose

05-27-2012, 08:02 AM
Excellent, thanks I am putting my engine together now!

05-28-2012, 08:38 PM
I torqued them four times, stretch was .004 last time.
Max is .006, too bad I don't have a minimum spec.
Thanks for any advice though!

05-30-2012, 04:10 PM
Talked to scat, for my length bolts the torque spec is 63 and stretch is between .0036 and .0046 so I am good to go.
Thanks for advice, sorry for hijack I will start my own thread with pics soon.

Bobby D
06-19-2012, 05:29 PM
Deck plates back on, wire loom and vent hose installed…and that’s about it. I started installing the interior and so far it’s going well about half the snaps are complete and the interior fit and look is nice. Once exhaust pipes and tips are delivered and installed she will be ready to start. The new exhaust has taken much longer than expected because I needed to provide SSM with many additional dimensions both inside, outside and finally had to have new tips fabricated because they were fabricated weird to fit the old mill.

06-20-2012, 10:35 AM
Bob, Very nice work as usual. Can't wait to see it in person one of these days.

06-20-2012, 02:16 PM
Bob, is the large diameter blue hose close to the front bulkhead and piped into the front air vent your bilge blower hose or just a hose to introduce fresh air down low?


Bobby D
06-20-2012, 02:24 PM
ADB (all done but) finishing up. I expected to have the 406 fired up, dialed in and retiring from the Dust-off by now, no doubt this has taken longer than I expected. Did you install the vent screens?

Bobby D
06-20-2012, 03:04 PM
Yes its goes directly to the blower, I asked about correct configuration a few years back and this was (MOP) Philís response:

One side forward free flow in aft hose to lower aft bilge drawing out. Other side forward hose to lower forward bilge blowing in aft drawing air out free flow. The object is to circulate the bilge air above and below in the compartment, which side really does not matter, but when inspected by the CG they look for the above!

On my boat two vents just move air (port forward and starboard aft) on and out with no hoses and two vents are hosed (starboard forward and port aft) and are the ones in and out clearing the bilge of fumes. The hoses are supported to a couple of inches above the hull bottom to insure free flow.

Also look closely at the picture i posted looking at the open exhaust holes. On the left by the red oil drain hose cap is my silver in color bilge pump hose the hose I spoke to you about the other day is the same type only itís yellow.

06-21-2012, 07:45 PM
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Bob, the vent screens came out great. One of the things that help win the "best restored classic" at the dust off. I've been meaning to take a photo of them. Thanks again.

Bobby D
06-30-2012, 09:11 PM
Productive day the exhaust was worth the wait the fit is perfect.

Bobby D
07-01-2012, 06:41 AM
Its Shields Marine Engine Hose series 262, see post # 59 for cut sheet, easily bent into tight radius, designed to give excellent service.

Just Say N20
07-02-2012, 12:34 AM
Don't make us work so hard to see that fantastic engine and exhaust!