Stroking a 401

[MrFurious]

Updates? Pictures? Come on man...it's been a month, you're killing me!

Actually, reading through this thread has been helping me a lot in regards to stroking my 360 to a 406. Now I'm no mathematical whiz like J20 here, so I'm hoping someone can help me out with this a few things.

1) Assuming a 4.11" bore in the 360 (+0.030"), 3.827" stroke, 6" SBC rod length, and a compression height of 1.29" on the piston I'm getting a scant 0.0045" deck clearance. Dropping back to a 1.275" compression height, I'm still only getting 0.0195" deck clearance.

9.208 - 1.9135 - 6.0 - 1.29 = 0.0045"
9.208 - 1.9135 - 6.0 - 1.275 = 0.0195"

Even adding 0.050" for head gasket thickness only bumps them up to 0.0545" and 0.0695" respectively.

That sure doesn't seem like much deck clearance, and more importantly what will piston-to-valve clearance be like? Shave the deck a little to square things up and you'd really be skinny on clearance.

2) The 360 rod journal width is 1.998 to 2.004", while the 401's is 1.846 to 1.852". Would I have to comensate for this difference in some way, or won't it make a difference? I figure it wouldn't be hard to widen the 401's journals while grinding them down, but is it necessary and will it cause excessive side clearance with the SBC rods? My main concern here is ensuring the rods are centered up in the bores and not in a bind at the crank leading to premature rod bearing failure.

3) Oddly enough, when I plugged this all into a compression ratio calculator using the 33cc dish, 58cc combustion chamber and 0.050" thick head gasket, I cam up with a CR of 9.02:1.

From my understanding, you are removing additional material from the combustion chambers to gain 5cc's of volume for a total of 63cc. According to my calculations, this will net a CR of 8.65:1. Conversely, milling the heads to reduce the combustion chambers by 5cc to yield 53cc's, which by my calculations would result in a 9.43:1 CR.

Am I missing something here? If my calculations are correct (which they may not be), wouldn't it have been much easier to just reduce the piston dish by 5cc rather than working over the heads?

[J20]

MrFurious;

Glad your getting something out of this thread. I went back to page three and edited the para on compression ratio, added a 9cc value for head gasket and nothing shaved from head, stock (58cc) combustion chamber, 33cc piston dish will yeild a 9.3:1 compreesion ratio with a 3.82 stroke and 4.195 bore. I did not shave a significant amount off the heads and did open the chamber to install bigger valves. My 33cc dish finished at 9.1:1. Here is why - I finished with a 863cc bore and a 61cc combustion area and 9cc gasket. 863 + 61 + 9 = 933. Now divide 936 by 103 ( chamber, 61 + gasket, 9 + dish, 33) and you get 936/103 = 9.058. I finished a shade under 9:1. I devalued my compression ratio to improve towing (debate?) and decrease my dependency on premium gas. Here is another factor to consider and crucial to the 33cc piston dish - eventually I may want to run a little boost - I can perform a fairly simple head swap, and go supercharged. Probably won't have to but at least the option is there without having to change the pistons. The cam selected and multi port EFI (may not need a new chip or fuel adjust depending on boost level. 5 to 6 lbs may require no modification at all) will support this. Hence the Manley steel rods, forged pistons, balanced.....

[Blown7]

Not to seem too smarty pants but you are going to have to install a big CC chamber which I don't think it can be made from a AMC head if you want to add some boost. At 6 lbs of boost at 9-1 compression your around 13.4 final compression which for me is way to close to detonation with no igniton retard for even good pump gas on a a zero degree day. I have 64.4 CC chambers with 2.090 and 1.750 valves unshrouded right to the head gasket ring with a 7.75-1 compression ratio. JE pistons had all they could do to keep the top ring land sturdy with a big dish to get down that low and still have room for a .990 inch piston pin. I am very interested to find out what kind of head, and the machining it would take. What are your plans on installing a head easily to get a compression ratio down below 8-1 for even mild boost? I know going open chamber will yeild about 11 CC's or so. Thanks, Jeff

[J20]

Good point, 6 pounds is too much for this application. Not sure how to handle this one yet.

[tarior]

I'm sure I've been on this tack before, but I must say that if all the poking and stroking weakens the block and sets the rod angle too severe, then why not go small displacement with LOTS of boost? I'm not in a position to build a high dollar race motor, but I'm sure someone out there is. Just look at what people have been doing with small block Fords.

[J20]

Find an amc 327, early model, will handle a lot of boost.

[Blown7]

I'm sure I've been on this tack before, but I must say that if all the poking and stroking weakens the block and sets the rod angle too severe, then why not go small displacement with LOTS of boost? I'm not in a position to build a high dollar race motor, but I'm sure someone out there is. Just look at what people have been doing with small block Fords.

You can, but conversely now if you want a daily driver, and a weekend warrior a big boost engine will be not fun to drive on the street, act just like a radical normally aspirated engine (lousy idle, race gas, hp and torque band in the high RPM's, roller lifters that need constant adjusting, high maintenance). Every engine has a mission specific profile, I think that everyone just wants a great performing engine without all the hassle of babysitting it. Thats why a mild restroke and bore or better yet (and more expensive) a mild huffer gets the most bang for the buck. Remember NOTHING beats cubic inches either normally aspirated or blown thats why big cubic inches is a great place to start. Thats why my next build is the Indy 500 cube blown. That engine has alot of potential for big HP and Blown and still be a daily driver. I'm thinking 750 to 900 hp @ 3500 RPM and maybe 200-300 HP at idle. Torque off the scale at both ends, lots of parts downstream to modify to hold up to that engine. Jeff

[tarior]

Find an amc 327, early model, will handle a lot of boost.

I was thinking Gen II or III AMC, the small block Ford isn't as strong as any AMC, yet those guys are running 8's in "street driven" Mustangs with centrifugal blowers.

[Gremlin4ever]

Wow! I made it to the end (so far anyways) of this thread. I for one am big on large displacement engines

Didn't see any pics, but don't let that mess with your focus on details in your building process. But after you assemble, disassemble a few times to check all the clearances, a few pics would do us wonders as your final assembly takes place. Take your time with this assembly as we wouldn't want to see you miss a very important task somewhere in the build.

Attention to detail is more important than us looking at pictures

[jeepsr4ever]

401 = 50.125 cubic inches per cylinder
401 Bore x Stroke, 4.165" x 3.68"
2.54cc in one inch
2.54 X 2.54 X 2.54
16.387 cc's in a cubic inch
3.539 cubi inches in a 58 cc head
3.552 ci left over in the combustion chamber for 8.5-1 compression
Change in volume 8.5 / 9 = 5.6% of the 58cc dome in the head
.1981 CI needs be milled away or 3.246cc's to gain .5 bump in compression

hmm a liquid test will tell you how much you will need to take off...58cc's of liquid will fill the combustion chamber on the head and to gain .5 boost in compression over 8.5-1 you will need to remove 3.246cc's which at this point tonight I cant tell you how much that would be off the head. May be around .022"