GADJIT98
I am in the process of tearing down a 401. My crank will need to be turned.
What is the limit of turning the mains & rod journals without losing durability, or weakening the crank?
I am shooting for the 400 hp range. I have heard that 10 under cranks are weak, etc. What is the general opinion of turning 10 under, 20 under, or even 30 under on a 401 forged crank? Any issues?
Thanks
Dave
jeepsr4ever
Dont worry about having the crank ground. They can go wayyyyyyyyyy under before they have any integrity issues :idea:
Holeshot
400 HP??? If you are doing all the standard things that are done to build a motor, you should easily go over 500 (with a little port work). I've seen too many people underestimate the air moving capabilities of the AMC engines and put too small of a carb on. I wouldn't use anything less than an 850 double pumper for any AM 360 and up that will be making use of the great head flow capabilities, meaning rev to 7000 or more. If that's what you want, be sure to get a cam & kit that will allow 7000 operation and use a single-plane intake (although the R4B is a GREAT 2-plane).
Of course if you are building a rock crawler you may as well sell the 401 (to me) and put a 258 in it. If you want a low speed 401, leave the ports alone and use stock exhaust manifolds and a small port intake.
Holeshot
And, I forgot to say, if you have to, or want to, replace your valves, 2.08" intake & 1.74" exhaust are easily fitted by your machinist. May as well use undercut stainless steel swirl-polished ones, they are less than $200, this mod could add 20 or 30 ponies, if the rest of your combo can move the air. Also, Total Seal zero gap rings are worth a good chunk of extra power throughout the life of your engine, allowing 0% leakage past the rings, compared to 3~5% plus for a conventional ring set when new, and way more leakage after some use. So 550 HP is not hard to reach, with a little extra dough. If you get the block O-ringed, I've been told that a 350 HP shot of NOS should be safe (on a properly built 401) for short bursts.
That's 900 HP!!!
SwampRat
I would have to disagree that a AMC is gonna move enough air to need a 850 carb on a mild build, and need a exhaust valve as big as 1.74." Your talking 230-250 CFM, that is not that superior when talking cylinder heads. If you don't have access to a flowbench you aren't gonna magically make any AMC head push 270+ CFM. Especially on a 360 where there be a greater limit to the amount of valve un-shrouding that can be done.
Holeshot
A "mild build", eh?
Totally stock heads can rev out to at least 6500 with performance springs, so long as the rest of the engine can breathe. How many CFM is that?
According to Indy, stock 291Cs flow 225 intake & 155 exhaust, 463 HP with stock heads. From what I have seen, they may be underestimating that a bit to make their heads look better.
I've seen flow sheets on ported (by BCI) AM heads that flow 275/206 CFM. That's good for between 600~750 HP, if the right parts are used.
A mild port job will reportedly easily achieve 247/177, when using the 2.08/1.74 valves. That's good for well over 500 HP.
My 360 had totally stock heads with performance springs, a 401 cam, Edelbrock intake, headers, an 850 DP, and 3.54 gears. It turned a 13.02 @ 108, through the mufflers with pipes to the bumper, street tires, breaking a traction bar on launch, & running the bowls dry in third gear (3/4 track). I crossed the finish line pumping the throttle w/o any response, out of gas. That's getting close to 400 HP at the flywheel.
That's NO bullshirt. I wouldn't even call that a mild build, just a few bolt-ons, and a fresh stock rebuild. The only non-stock innards were the biggest Crane springs that would fit the stock heads, a stock '71 401 cam, .0100" longer "service" pushrods, and Rhoades lifters.
I ran that combo for almost 15 years and was using a brand new Holley 750 3310 before I moved up to the 850. The 850 was a big boost in power, no doubt about it. There were a few 440 Roadrunners & Chargers that could attest to that back then (early '80s). We don't see many cars like that on the street anymore.
Anyway, the original question did not say anything about a "mild build", and was about a 401, which can move more air than a 360, until you consider that a 360 can rev higher than a 401, if you don't mind stressing the cast rods or have put forged ones in (are in the Mopar catalog).
What is a mild build on a 401? It sure doesn't make any sense to me to take heads that, when stock, flow almost identical numbers as the early Chrysler Hemi, in stock form make over 450 HP, and put restrictions in the system that plug up those great flowing heads.
The guy with the 401 was hoping to get 400 HP. 500+ HP is just a very small bit more difficult to attain, so why not do it?
As far as the flow bench, well yah, it will cost a few bucks to get the heads ported by a pro. How much is enough? An extra 100~150 HP would certainly be nice
The "Performance American Style" book gives all the specs to get the heads into very nice shape. Any good race machine shop can do those things and set all combustion chambers to the same volume. A flow bench can then be used to get all the ports equalized, or not. It's still gonna be a big boost if done to the book's specs.
So, if you want to put a peewee carb, a peewee intake, & peewee valves on your AMC engine, be my guest. I'm not opposed to blowing the doors off of an AMC, if I ever see one out to play.
SwampRat
To me your horsepower guesstimations are pretty optimistic but that's just me. Of course bigger carbs pick up power, but a streetmachine may not just respond to a huge carb for the engine.
You will not see a port job magically pick up 100-150 Hp, once again your being too optimistic.
I can see how you think, Peewee this and that, well I know I take into consideration much more than you do if your main concern is using the biggest valves and manifold and carb possible.
jeepsr4ever
You guys need to simmer :idea:
Holeshot
Well, I guess if somebody wants to go slow through the trails or rock crawling, they can build an AMC engine that restricts airflow, but, like you said, that's just you. They could even use the '69 heads & block and slow down to a more controllable crawl. Seems like a waste of a good design to me.
What you call "horsepower guesstimations" are derived by dyno runs and experience building AMCs. You may be trying to transfer knowledge of GM or Ford to the AMC design, it doesn't apply. The AMC design is extremely friendly to high RPM flow, which equals horsepower. A lot of "off-brand" users have been in denial for decades. I guess it would suck to get smoked by an old "Rambler" when a guy has a new Mustang, LT-1, or whatever.
As far as a street machine responding to a "huge" carb, my street 390 dynoed 518 HP to the rear wheels with a ported Torker, 2" open spacer, and 900 CFM of Holley 4 barrel. Then I put a tunnel ram on it with 1320 CFM via 2-4 barrel Holleys. That was a huge improvement all throughout the range. Never had a notion of any undriveability or softness down low.
But that's just me, and I like to go fast.
SwampRat
All throughout the rev range huh, wow even at 1500 RPM under a heavy load?
It really depends on the setup of the car, it is well known that huge carbs and intakes can make engines soggy on the low end due to poor fuel atomization, your no engineer so just because your car was fine doesn't mean another will be. What kind of gears do you have? Tranny (stall)? Tire height? Weight? Camshaft? Compression?
Holeshot
Who in the hell runs under a heavy load at 1500 RPM???
(if the answer is rock crawlers, you don't need a 401 for that)
The question was if the guy could get in the 400 HP range with his 401.
The answer is YES, getting OVER 500 HP is quite easy with a 401.
Getting to 600 HP is do-able, getting close to 1000 is do-able with a 350 HP shot of NOS.
If you don't want to go fast, put a small carb, small port intake, stock exhaust manifolds, etc. on it.
Then do your going slow thing out of my way, because I like to go fast.
SwampRat
Who runs under a fairly heavy load at 1500 RPM? Everyone does, unless you don't drive your car on the highway that is.
You have your ways and I have mine, we are both stubborn, so I suggest we shut up before we get thrown off the board
Holeshot
Not everyone does, count me as one who does NOT.
When you put together a combo that's supposed to be fast, you need to think about the gear ratios and tranny ratios, etc. You don't just bolt a 500+ HP engine into a stock chassis and expect to be ready to enjoy.
A five-speed Richmond with a 3.27 first means I never see 1500 RPM.
A loose tq converter is what an automatic would need.
I have the VERY strong suspicion that you are looking at all this from a 4 wheeler, trail rider, grocery getter, huge (tall) tire, or rock crawling point of view.
I am looking at it from an "as light as I can get it" AMX pro street machine point of view. The 401 can handle close to 1000 HP and 8000 RPM as long as it has the oiling system ironed out and attention to the little details and all the small things that cost more money than you'd tell the wife.
SwampRat
I'm looking at this in a perspective as not a "one fits all" kind of deal. If your car was under 1500 RPM's crusing then it would just be under a heavier load, a car that to do this often wouldn't like a large plenum and large carb for this for durability and economy and other issues.
I still think your Horsepower guesses are optimistic, for a stock buttom end that is. But I guess I have seen some people on the American Motors forum say they've done it, but do I agree with it? nope. Probably a kind of ticking time bomb, so in this case a chevy guy like myself wouldn't agree with it, but it should be left at that.
Holeshot
1500 RPM is just above idle, the only vehicle I can think of that may "cruise" at 1500 RPM may be my '01 Dodge Ram 1500 4x4 360 in OD at 35 or 40 MPH. 1500 is for stop & go with an automatic granny mobile.
My '69 AMX with the Richmond 5-speed would almost never see anything below 2500, unless putting like a granny.
My horsepower "guesses" are not guesses, they are real numbers from real engines. You must shed your GM mindset. Give the 401 a try. Do all the normal mods you'd do to your 350 (except use big-tube headers, a Torker & 850+ DP). You'll never go back to a SBC!!! But I did have a fresh L-88 taken from a stock car that I put in my '68 Camaro that would crank the speedo needle past the right turn indicator in low 2, and really set you back in the seat when you did the next shift. The 401 can't compete with a well built BBC with rectangle ports, as far as I know. Maybe if ya used a 396 with oval ports (Chevy head) for cubic inch parity.
The AMC head flow is best compared to a stock to mild ported oval port BBC head (Chevy part, not AFR or whatever).
AMCs design was layed out after the factory disected the competition & took the best ideas from each competitor. The design was tested and refined on the TransAm tracks & Bonneville. When they settled on the design, they cast the blocks in super high nickel-content iron. Hard enough to make machine shops dread boring them. They usually have minimal ridge when taken down, even after 100,000+.
A stock 401 bottom end is good for 8000 (assuming parts pass pre-machining testing), if the rods are polished and shotpeened (for added reliability), crank cross-drilled, block align-bored, oil system addressed, etc., and then assembled properly. By "stock", I mean NO aftermarket parts except for maybe rod bolts, main studs would be nice, head studs could be used, you could O-ring the block. But without any aftermarket crank or rods, & four-bolt mains not needed.
I'm not saying an endurance racing engine that runs 8k for extended periods, that's where the aftermarket cranks, etc. come in, and that would likely be a funded racing program, with such parts budgeted.
I mentioned the AMCFORUM in another post because I had been on that board several years back and Coocoo, Fran, and Ollie had their own little clik and didn't appreciate anyone explaining anything that they didn't father themselves. Tinkle on that.
As for me, my dad was a lifelong "Master Mechanic" who worked for Hudson, Nash, then Rambler, and finally AMC, before he opened his own shop. I was there changing engines by myself in '69 & '70, when I was 11 & 12 years old (summer job). By the time I was 18, I was tired of leaning over the fender and went on to the local Honda cycle dealership, where I worked through all the classifications, up to "Master Mechanic" over the next 10 years. I ended up there as Service Manager for over 15 years. I did my share of multi-valve 4-stroke buildups: my CBX build won the biggest state trophy, shutting down ALL the Kawis and those XS11 Yamis, my turbo GSXR1100 build held the state record in sand drags for almost 2 years. Also did some 125cc go-carting, and a bit of mx.
I bought my first AMX in 1980, a '71 360/4-speed with "Go" pak. That's the one that went 13.02 in mostly stock condition. I've been through quite a few since then.
Also have been through over a half-dozen late-model Zees and T/As, with their almost respectable LT-1s. Wow - a mid to high 14 second machine that costs $30k and you can't work on. Any old purely stock AMX 360/390/401 can beat that. Even that ugly little SC/Rambler 390 beats that.
SwampRat
I don't doubt the AMC's potential at all, and never did. I see you've had your share of experience with them and believe they are a great engine. I'm sure they could go to 8000 RPM's, it's just a question in my mind If I would want to make that kind of investment. Another thing with the AMC engines, tell me the truth about their oiling problems, especially for 8000 RPM use :wink:
I do really question something you said in that post, your doubting the big block chevys cylinder head capability too much. Stock big valve oval ports can flow 250-260 CFM. I personally have achieved 300 CFM @.650 with literally a backyard port job with a 2.19" valve @ 28 in H20 on a SF-900 bench with 4.25" bore. I believe Ken Parkman or Steve from the American Motors forum has arrived at this magical 300 number with a extremely dedicated, flowbench designed port with a 2.1" valve at, at least .700" lift. But they also don't advise to try that at home. :mrgreen:
=D>
jeepsr4ever
SwampRat wroteI don't doubt the AMC's potential at all, and never did. I see you've had your share of experience with them and believe they are a great engine. I'm sure they could go to 8000 RPM's, it's just a question in my mind If I would want to make that kind of investment. Another thing with the AMC engines, tell me the truth about their oiling problems, especially for 8000 RPM use :wink:
I do really question something you said in that post, your doubting the big block chevys cylinder head capability too much. Stock big valve oval ports can flow 250-260 CFM. I personally have achieved 300 CFM @.650 with literally a backyard port job with a 2.19" valve @ 28 in H20 on a SF-900 bench with 4.25" bore. I believe Ken Parkman or Steve from the American Motors forum has arrived at this magical 300 number with a extremely dedicated, flowbench designed port with a 2.1" valve at, at least .700" lift. But they also don't advise to try that at home. :mrgreen:
=D>
Ken and Steve have done thier share of tinkering thats for sure! :sa:
SwampRat
Have you ever had any experience with flowbench testing and porting AMC heads?
jeepsr4ever
yep, I am saving alot of info and tech for a small book on building different versions of the AMC smallblock
Holeshot
Remember the title of this thread? Redline of a 401?
You can get 8000 out of one with mostly AMC parts!!!
Exception being cam & kit, & at least a 2" open hole carb spacer, more if you can get it under the hood.
AMC offered an Edelbrock intake with an AMC part number, a Holley 950 CFM three-bbl. with an AMC part number, and tube headers with an AMC part number.
Make's for one quick stock car. I think there is a guy still running in a stock class that is going high 11s, but I would have to check again on that. He may be in the tens.
As far as the head flow of the stock 291C heads, the 225 & 155 numbers came directly from Indy Head Service, who has a vested interest in making the stockers look bad so their high-buck heads look better.
I have heard from others that it's more like 237/168.
As far as comparing them to BBC oval ported heads, those chevy heads have a HUGE advantage in valve size, port size, valve location, and valve angle. I think we would find that as soon as you attach a pipe to the AMC head, those flow numbers will go up, due to the swirl created by the dog-leg ports.
Anyway, the AM heads flow within 10% or so of the BBC oval port heads, and that is why I said that they are the closest comparison.
Too bad a BBC weighs 200 lbs. more than a 401, that's two tenths lost by the Chevy from the get go.
Also, that great BBC that boasted 435 ft/lbs of torque doesn't seem all that great when you consider that a lowly Rambler 401 with an Autolite carb was rated at 430 ft/lbs, as well as being 200 lbs. lighter.
As far as investment into a 550 HP 401, it's about $5000, go find a GM, Ford, or Mopar crate engine for anywhere near that, and come see me.
They are getting $12,000 on up for 500 HP engines.
I think I'll keep my AMCs
