J20
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?
jeepsr4ever
are the pistons you are using forged, have you done any oiling mods yet, who did your regrind?
J20
Yes the pistons are forged. I am going to install the valley oil mod. There is a really good machinist here in Great Falls, MT. He has built several engines for tractor pull comps when he was in Ioha.
Lifted79CJ7
Hey J20, Welcome to the board! If you can, take lots of pics and and do a write up for us. I would love to see how this thing turns out! :sa:
Jack
J20
A write up sounds like a great idea, could prevent others from making a few of the mistakes I made in finding and purchasing an engine (fortunatly very little $ involved, mostly time). If there is a moderator reading, how and where would you like to see this? I've learned a lot about engine geometry researching a rod/piston combo, cross sectioned a head to figure combustion chamber modification, and a few other things for this build. Could post pics also. Please point me in the right direction. Does this have a spell check function?
Elliott
I've read you could do that using SBC rods and 400 pistons, don't know anymore then that other then I'm looking at a similar project with 4.150 stroke and 4.374 sleeves for 500CI. I guess it's workable. :mrgreen:
Elliott
Here's some good interchange info you may want to rat hole somewhere:
http://www.american-powersports.com/dave/image/amx/tech/amc_pi.htm
J20
I looked at the idea of sbc 400 pistons. Several problems, two of the most significant are: compression height is wrong and valve pocket angles are wrong. I called Wisco and Ross and both said pretty much the same thing. Also the 4.165 bore considered, with a 4.125 400 piston dictates for minor .020 bore on the 4.165 = 4.185. The 4.125 at .060 over is the only real possibility. But, considering the other problems, this still won't work. Another thing to consider is the clearance under the piston for the end of the connecting rod. The standard sbc dish is not big enough for the 58cc AMC heads. To get a 9.3:1 compression ratio, the piston dish needs to be 37cc. (I know there is a little room if head gaket thickness is adjusted and there is some room to work with quench) There is not enough material there for such a big dish. Combustion chambers must be opened up 4 tp 6cc to keep the piston dish at no more than 33cc and that is on the edge. One advantage of using a custom piston, is the ability to select a more efficient combustion shape. The machinist has ideas for this I'm not up on yet. As I get more info I'll post.
jeepsr4ever
how about in the how to area I will sticky it for you....wish I had pics of my builds :smile:
J20
Here is a question. Is there a production head that will fit the 71 - 78 AMC 360/401 (omit 304 to avoid valve size issue) with a bigger combustion chamber, say 64 or larger cc? I'm not aware of one.
20 May 05. The Edelbrock aluminum head is also a 58cc combustion chamber, stock valve size. I think Indy makes an aluminum AMC head with a 62cc combustion chamber. Very expensive, intended for high rpm applications.
jeepsr4ever
maybe after porting but never a stock head
ILUV2XLR8
Hey J20, just like to say hey! I may be in the Springs now, but I was borne and raised in Billings, MT. Good to have you aboard.
J20
OK, lets move this to the "How To" page. I've got pics to post.
J20
The way I figure it, I've got 9.208 inches of block to work with that being the distance from the center of the crank to the top of the cylinder. The 401 starts with a stroke of 3.68 inches, a 5.85 inch connecting rod measured from center of rod journal to center of piston pin and a 1.508 (about) compression hieght on the piston measured from the center of the piston pin to the top of the piston. Take half the stroke, 1.84 + 5.85 + 1.508 and you get 9.198. This leaves .010 at the top of the stroke for rod and piston expansion. Also consider the thickness of the head gasket so there is a little more room before the piston hits the head). Given all of that, I think of the stroke as the diameter of the circle the center of the connecting rod journal makes as it rotates around the crank center. to make this circle bigger I'm going to off center grind the connecting rod journal, reducing the connecting rod journal diameter from 2.2474 to 2.1 inch (same size as sbc rod). This will move the center of the connecting rod journal .0737 (2.2474 - 2.1 = .1474 now divide this by 2 and you get .0737). The stroke will increas by .1474 because the diameter of the circle the center of the connecting rod journal makes as it rotates around the crank shaft center will increase from 3.68 to 3.8274 (3.68 + .1474 = 3.8274). The radius of circle increased by .0737 so diameter increases by 2 times that or .1474. That is how I intend to increase the stroke of my 401. It may not come out exactly 3.8274 because the connecting rod journals have to be turned to take out a few very minor scratches. Lets say we go .010 on the connecting rod journals, I'll end up with a 3.817 in stroke. Either way, this engine will stomp all over a sbc 383!! Any body see any flaws in my thinking? I'll deal with the compression ration next because if the stroke gets longer and nothing changes with piston or head, compression ratio goes up. I'm aiming for a 9.2 : 1.
Elliott
Fella ran these 401 4x4 stroker #s for me on Dyno 2000, it's based on ICH's Bracket Master Moldex 4.15" stroke crank and std bores (I have not confirmed with ICH that this crank will stuff in a factory 401 block):
The Moldex crank used in the Indy "Bracket Master 500"
is 4.15" stroke,
probably safe to say that is probably the largest
stroke we will see for a
stock block (assuming the 401 block can be massaged to
clear those crank
throws). That nets 452.3 cubes with the 4.165 bore,
and 600 ft/lbs of
torque at 2000 RPM!!! (with Ultradyne's smallest
hydraulic (.517/.541 lift &
231/239 duration) AMC cam, stock big-valve dogleg
heads, stock intake,
600CFM 4bbl, small-tube headers w/mufflers, 10.2-1
compression). Not much
HP there, but loads of torque. I also tried adding
fully ported heads,
big-tube headers, big cam, big carb & Torker, the
rev-range is dictated by
the bore/stroke ratio, and 5500 RPM is peaked-out for
this one, no matter
how much cam, exhaust, or intake you throw at it.
Engine Power Torque
RPM (Fly) (Fly)
2000 229 600
2500 266 559
3000 304 532
3500 327 491
4000 320 420
4500 296 345
5000 256 269
5500 207 198
jeepsr4ever
thats some torque there! I know ive ripped crank bolts before but my goal this summer is a real stump puller!!!!!!!!!!
J20
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?
J20
Posted a few pics, I think. Some may find value others may not. The cross section of the head shows there is plenty of material to remove at least 5 cc.
J20
Working with Wisco for a piston. Here are a few of the things discussed: The block should be bored to a "standard" bore to make use of a "standard" ring pack. Example, 4.125 + .060 = 4.165 + .020. There are a few more examples that will work. This has a few advantages, cost being a big one. Wisco is happy that the combustion chamber can be expanded at least 5 cc. This allows a small enough dish to leave enough thickness between the bottom of the dish and the top of the connecting rod. The exact shape of combustion chamber and dish have yet to be determined. I think the compression height will come out very close to 1.2 in., close to the proven sbc 383 (1.120) with 6 in rod.
J20
A couple of new tidbits. I called ARP (very helpful) asking about AMC main studs and why they were not listed. It so happens that the AMC 401 main bolt measures 3.5 inches from under the head to end and is 1/2 in, same as ch*vy big block. I'll use a set of ch*vy big block two bolt main studs without windage tray. Saved a few $$ by going this route. Also, ordered a set of hardened push rods, just so happens ch*vy small block push rods are identical, ask for ch*vy sb push rods, saved a few more $$. The Scorpian roller rockers arrived, they are beautiful, it will be a shame to cover them. Went with the ARP 7/16 thread diameter top and bottom rocker studs. Will have to re-drill/tap bolt holes and mill down for guide plate. Have not ordered guide plates. Piston design will go final late next week.
