Stroking a 401

[Elliott]

WOW! Those are very impressive torque values. I'd be interested to know what rod piston combo a build like that requires. My goal is not so lofty. This truck gets drove everyday. I've opted to use a 6 in sbc rod and a standard 3 ring set on the piston. A chose the six in rod to maintain a good rod length to stroke ratio. (1.59 : 1 stock 401, 1.6 :1 for 383 sbc) I know there is debate regarding the use of longer rods and I believe a longer rod is the better option primarily for the following two reasons: With the piston pin set higher in piston (There is a limit, I don't want to have to contend with supported rings. I think 1.25 in comprssion hieght is about as short as I would want to go.) the side load pressure the piston exerts on the cylinder wall is reduced, The variance in connecting rod angle in relationship to the connecting rod journal is minimized with a longer rod thus reducing the ovalating stress placed on the connecting rod bearings. I believe these two factors will increase engine life and reliability. Any thoughts?

1) Those figures were just a dyno build, so don't know if the rod/pistons are compatible with the correct quench. Essentially the rods were 6.2x2.10 Eagles and the piston would be a flat top Std AMC bore piston @10.2:1 comp. I haven't determined a combination of pistons and rods that will fit that stroke length inside the deck height, looking at Mopar stroker flat top pistons in a larger 4.375 bore.
2) From what I've been reading ( http://victorylibrary.com/mopar/rod-tech-c.htm ) you are right on all counts... except one on the longer rod and rod angle benefits, the longer rod also builds more torque down low with a sacrifice at the top end.
3) FYI, I was looking into the Wiseco pistons because ICH uses them in the 500 Bracket Master.... I've been advised against them in favor of Ross and JE. Apparently they haven't held up that well... might want to get some more opinions on that from guys that are using them.

[Elliott]

I'm having the crank of my 401 off center ground to accept a 2.1 inch sbc 6 in rod, should get about 3.817 inch stroke. Plan to use a Wisco piston, anyone else tried this? Will have to remove about 4 - 6 cc from combustion chamber to keep compression ratio down to 9.3:1. Any thoughts?

Just in case you want to crunch some more #s, that crank supposedly can be offset ground to throw a 3.93" stroke.

[J20]

Elliot, you are correct. If you start with a 2.2474 connecting rod journal and off center grind to accept a sbc small journal rod (2.0) you can get a 3.9 inch stroke. I chose not to use the 2.0 journal because the ch*vy engineers must have known what they were doing in not using the 2.0 journal on the 350/400. I think the 2.0 journal was mainly a 283/327 thing. The extra .1 inch of stroke also shortens the compression height by .1 and jeopardizes the use of a standard ring pack, raising the cost of the piston. I don’t want to take the compression height to less than 1.2 inches. Want to leave plenty of metal for the ring pack.

[J20]

Elliott (I spelled it right this time. I also miss spelled Scorpion in the previous post and I’ll bet there are still people looking Ioha. I meant Iowa.) Thanks for the data. I think a flat top piston in a standard bore 401 with a 58 cc head will yield about a 13:1 compression ratio. I think you will need to remove material from combustion chamber to get 10.2:1. I know I have to remove about 5 cc to get 9.3:1 with a 33 cc dish in piston. This 401 is for a pickup, should never hit 4000 rpm. Please explain the rod and rod angle benefit line in point two. I did a mock up of this and the rod angle to rod journal is definitely reduced using a 6 inch rod vs. a 5.7 inch rod. I would agree with your comment on piston manufacturer choice if this were a high rpm build. I do welcome and value the opinion of this forum in regards to parts selection and do rely heavily on technical advice of others. Afterall, there are those of you out there who have acturally done this and have the final results to share. Thanks.

[J20]

Lets make sure I have right idea on compression ratio. Lets start with a 4.165 bore divided by 2 then squared then multiplied by the stroke. That would give the volume of the cylinder. I'll convert to cc early. Use 1 cubic inch equals 16.387064 cubic centimeters. Now we need stroke. 3.68 x 2.54 = 9.3472. Now bore x stroke gives 87.8997 x 9.3472 = 821.6. Now add the gasket and combustion chamber area, 9cc and 58cc to get total volume or 888. Now divide 888 by 9cc plus 58cc or 888 divided by 67 and we get 888/67 = 13.25:1. Consider the stock compression ration of 8.5 ish we get 888/8.5 = 104.47. 104.47-67=37.47cc for a stock piston dish.


If the the bore turns out at 4.195 and increase stroke to 3.817, the final cylinder volume is 862.407 cc. Add to this the stock 58cc for combustion chamber and 9 for head gasket we get 929.407. Divide this by 67 and we get a 13.7:1 compression ratio with a flat top piston. If I want a 9.3:1 compression ratio I need to cram 929.407 cc into a 99.93 cc combustion area. So 99.93cc minus some for head gasket thickness, (about 9 cc) minus 58 for the combustion chamber leaves about 33cc piston dish. Piston needs 33 cc dish to finish at 9.3:1 compression ratio providing you shave nothing from the head or remove material from stock combustion chamber. Any thoughts?

[Elliott]

Please explain the rod and rod angle benefit line in point two.

Right, I should have said the benefit (other then less friction and stress on the piston skirt) is the torque at mid and upper end. Low end torque benefits more from a shorter rod, however the longer rod provides for longer piston dwell time at and near TDC. That means compression is held longer and combustion improves... all of which should be magnified by excellent flowing AMC heads and a Performer intake which promote increased air charge velocity to take advantage of the higher cylinder pressure after the first few degrees of rotation past TDC... before the pistons slow in their descent.

Someone correct me if I don't have this all straight...

On the rod size being 2.0", remember that them C*vy cranks were soft (like their blocks) so they probably needed larger journals on the bigger motors. On a forged crank (not that I'm a racer, just going by what they use) I don't think the 2.0" rod journal would be an issue or Indy Cylinder Head might not be running a 2.1" journal in the AMC Bracket Master 500 cranking 800hp - 670ft/lbs 7,400/4,500rpm at 14.0:1 compression. I do wonder if a little torque isn't sacrificed in reducing the reciprocation mass that close to the crank center line though.
I don't know about the ring pack and compression height issues, I'm still looking at which BB C*vy flat tops to use if I go with the 4.5 bore.

If you know of any web sites that layout the various piston dimensions let me know, where they list the pin center line to top of the piston, ring spacing, compression height, and all that. Kinda tough to find a place that has it all laid out complete.
Cheers

[J20]

I have a .040 bored 401 block in the garage (a purchasing mistake, fortunately only cost $25). I think the bore center on the AMC block is 4.75 inch. I looked through the freeze plug hole and I don‚Äôt think the cylinder walls are much over .3 inch thick a few inches from below the top of the block. Actually, 4.75 ‚Äì 4.165 = .585. So each cylinder wall can't be over ¬? of that or .2925. I don‚Äôt see how you could bore a stock AMC block to accept a 4.5 inch piston. Even if you sleeved the block, each sleeve would only be .125 inch thick (4.75 ‚Äì 4.5 = .25. .25 divided by 2 = .125) The sleeves would have to touch all the way down to the bottom. I don‚Äôt see where there would be anything left to support the sleeve. Even if you hard filled the block, I think the torsional forces would twist the block past an acceptable limit. I‚Äôm not familiar with the Bracket Master 500, must be a very special ($$$$) block.

I also did further research into Wisco pistons, I found no case of failure due to material defect or workmanship at any rpm. If there is data out there please let me know where as I did not find it.

[Elliott]

Not sure if the block must be filled to use those 4.5" liners... I've been trying to determine that. However on wet sleeve engines I've run the sleeves were only supported at the top and near the bottom. I haven't seen a sleeved 401 so I am still trying to find someone who's done it to advise me on it.
About the Wiseco pistons, I personally do not know much about them. Possibly what you haven't heard about them in auto engines is because they are new to auto production???
Here's a quoted from a guy who deals in off road toys that advised me against them, take it for what it's worth (ICH is the only place I've seen using 'em, they have a reputation at stake so....?):
"I wouldn't give $100 for a truckload of Wiseco pistons. I've been a Honda & Suzuki cycle technician for the past 25 years, and probably replaced a hundred broken Wiseco "racing" pistons before they sold their first automotive piston." Food for thought any way.

[J20]

Thanks for the insight. I'll research further. I had not delved into the cycle piston area for failure data. Based on what I can find so far, I conclude that Wisco has built a solid reputation in the automotive piston arena maintaining a record of reliability on par with Ross and others. But, as always, if some of you have input, I'm wide open.

[J20]

Spent a little time the other day looking for bearings. Particularly the main bearings, the rod bearing will be easy because it will be a standard dimension sbc rod bearing. I was hoping to find a “performance” main bearing, not that I really need one considering the low rpm application. I looked into Federal-Mogal and Clevit.
I went to the Federal-Mogal web page,
http://www.federal-mogul.com/cda/con...3_6752,00.html
Looking for an appropriate main bearing for the 401. Not finding exactly what I was after, I called the tech line, 1-800-325-8886 and talked with Gus. There is only one choice of bearing from Federal-Mogal for the 390/401 main, their standard copper/lead bearing pn 3311CPB and 3311CPA, four of one and one of the other, the middle main has a flange. I think these are their H-24 alloy. For the rod bearing, because I’m off-center grinding to accept a sbc rod, I can use the new tri-metal aluminum bearing. The new aluminum tri-metal bearing will outlast the copper lead bearing by a considerable margin.

Clevite also offers a 390/401 main bearing in their “P” series. Description is virtually identical to that of the Federal-Mogal. In Great Falls, MT a set of Clevite Mains will cost $66 - $78. Nearly identical to the Federal Mogals. I actually found the Clevites on the shelf for $67, .010, .020 or standard.