401 engine advice needed

[Rogue]

i've read the AMX files and just about anything else i could find on this site and others, thanks to the peeps at this great site i found out about the oiling systems mods!!! :eek: So now fer the question - from what I understand I can buy pre - 74 pistons and put them in my 74 401 - this will change compression ratio from 8.5 - 1 to 9.5 - 1 , do I have this right?!?! :confused: is there any interference problems?!?!? :confused: how much will this limit camshaft choice?!?!? ( me wants big lift, sloppy idle, argh, ugh, ugh, ugh )TIA, Jeff and oh yea has anyone actually tried this?

[ February 24, 2002: Message edited by: RogueStar ]</p>

[sandmanb]

sounds like you have been doing some reserch,wish i could answer the question for you but i cant,i would however love to know what you find out about it though.you may want to post this quetion on an amx board.good luck

[Rogue]

thanks once again to sandman!!! IS THERE ANYONE OUT THERE?????????HELP!!!!!

[oldyellowwagoneer]

the reason for the higher compression on the earlier engines was the heads combustion chamber volume. the earlier heads were 51 cc's and the later ones were 58 cc's. The main reason to get the earlier heads ( 70-71 )was to eliminate the later rocker mounting style which doesnt allow quite as radical a cam.They could be ported larger than the later heads also. The benifit of the later heads was improoved cooling due to larger cooolant passages.If your going to use your jeep I'd recommend the later heads,and aftermarket pistons will give you any compression you desire.With a full size jeep you would be better off to use a cam thats designed for low end torque instead of high rpm.dennis

[Jerk]

AHHHH! 401 questions...at last. actually, the heads changed in '71 from 51cc to 58-61 cc due to smog regs, this is the same year that chrysler decided to hack the 426 hemi and the 440 sixpack from its car line...all for emissions regulations. early 401 and 390s had 10.2:1 compression, 70 was last year for the 390, 71 first year for 401, half way through 71, they dropped compression to 9.5:1 (approx) and by 72, it was 8.23:1. it has been there ever since on ALL post 72 AMC v8 engines. Federal mogul makes forged high performance pistons (TRW actually) from 8.75:1 all the way up to 10.?:1, and if you use 390 pistons (same bore-4.165")it can go as high as 13.?:1! other mods are required to do this. usually, early 401 heads and 70 390 heads are your best choice for hot performance. ALL dogleg 360 and 401 heads from 72 up will make really decent power and flow well! remember anything above 10.0:1 compression will more than likely require 95 and up octane fuel, which is dang expensive, I have 9.5:1 compression in my 401 and it takes 91 or 92 octane not to ping with stock mechanical distributor advance, i don't run vacuum advance for the simple reason that I had 42 degrees advance at 3000rpm with the mechanical and vacuum hooked up. with just mech, i get around 30 +/- 3 degrees, not exactly sure, haven't checked in a while. ANY way, the federal mogul catalogue will give compression ratios based on head chamber volume, so it is neccessary to find out where /how/ when your are going to use/abuse ;) the engine/vehicle, then build it for that purpose based on what you have/can get for the vehicle/engine. one other thing, the stock pistons are .375" dish, the pistons I have are .250" dish (I think) the 390s are all domed, using these in a 401 will require machining the dome down to prevent clearance problems. BTW, the piston dish is, I believe, how they went from 9.2:1 down to 8.2:1 compression w/out altering the heads even more.after all, pistons are cheap to make, heads are not!If you do go for high rpm power band, you will not like it in a jeep, you'll most likely be breaking things alot, transfer cases and u-joints were never really designed to take 500 hp! :D as my engine sits, it (on paper) makes 350hp and 450 lb/ft of torque...this is in the Desktop Dyno2000 program and uses pretty generalized numbers and flow rates for heads, exhaust systems and intake manifolds, as well as carbs. as it sits in the truck at 4500 ft. elevation, it probably loses 30% of that through driveline and atmospheric pressure drop from sea level. Hope this helps, if you have any big questions, email me. the address is in my information at top of my post. Matt

[Rogue]

thank you thank you thank you and thank you Matt, and Scoutgrl, i was basically shooting for higher compression - camshaft choice is still up in the air - but i do beg to differ about higher rpm engines in a jeep, if you're torque convertor is matched to your camshaft - and i'm not talking about an 8" 4000 rpm stall race convertor more like a 1800 - 2000 rpm( a few hundred more than stock )type convertor you'll place the take off right in the engine's sweet spot ( in the meat of the torque peak/curve ) a high stall convertor doesn't necessarily launch hard it depends on how hard you stomp the go pedal and allowing the engine to reach closer to peak efficiency before bogging it down with torque convertor action will give more availible torque to the wheels. i could be wrong but these are the kind of theories that put John Force out front week after week after week, I'm simply rehashing what I've been taught just learning about AMC in the process, don't get me wrong Matt you have given me much valuable knowledge and insight and I greatly appreciate it!!! i guess what it breaks down to for me is if I can buy pre smog era pistons for the price I can buy stock 74 pistons and not pay the extra $$$ for high compression written on the box than thats what I'm trying to accomplish, thanks again. Jeff

[TimB]

That high stall convertor to find the sweet spot works good if you're racing, but these things are lead sleds. Low-end grunt is whats important for towing, everyday and off-road driving. High horsepower sounds good, but if you have to run in excess of 3000 rpm to get there, then your just being plain inefficient. Spending a lot of the time at the filling stations too. High torque figures in the 2500 rpm range are more meaningful than high HP. I had a high stall convertor on my '76 Waggie w/401 and hated it. Had to rev to 2000 rpm or so before the thing would start moving from a stop. Pulled and replaced it with a low stall convertor and man would that thing pull. A good blueprinted engine with 8.5:1 compression to run 87 octane gas and a stock camshaft will do wonders for low-end grunt, good vacuum, idle and mileage. Proper gearing for the size tires used is also paramount.

[oldyellowwagoneer]

<blockquote>quote:</font><hr>Originally posted by RogueStar:
ti could be wrong but these are the kind of theories that put John Force out front week after week after week <hr></blockquote>his car is 4000 lbs lighter than yours. I still stick to my previous recommendation DENNIS

[Jerk]

hey, been offline awhile, so...this is on paper, I have never actually dynoed my truck but here goes...at sea level even- 2000 to 4000rpm - 450 lb/ft of torque. hp comes in at about 2500 at216 and climbs to 330 at4000 rpm and peaks at 360 from 4500 to 5000 rpm. this is with 9.5:1 cr, edelbrock cam /lifters /intake / carb. pocket ported heads milled .020", small tube 4 into 1 headers and dual exhaust with mufflers. you can go a little meaner than the edelbrock cam and not have to alter everything else to match cam specs. remember long duration (lumpy) cams are used in high rpm hp engines. the longer duration, the higher the rpm the engine needs to work effectively to make hp. this is a fact. lumpy cams don't idle good, you have to generally set them up at 1200 to 1800 rpm to idle, remember, if you want drag racing amc stuff, buy a javelin and stick to 1/4 mile at a time. if you want decent torque and ok hp, stick to milder (short duration) cam. you can probably build 10:1 cr and a more meaty cam than an edelbrock, with a high rise dual plane and fuel injection, but I wouldn't(for street driveability and power train surviveability reasons ) go much beyond that. I know, probably not what you wanted to hear, but sometimes free advice is worth some money after all. look at it this way, street javelins had 10.2:1 cr and dual plain intake, iron heads, iron exhaust manifolds, etc. and were pretty kickGreat Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley Moogley. basically I've got a '71 Javelin motor in my truck, just with aftermarket parts, and lower cr. same power though. (actually 78 401, but you know what i mean,)

[Jerk]

btw, "'74 pistons"? those should be low cr pieces. all stock pistons were low cr after 72. my trw forged + .030" pistons were $350. if that helps. tongue.gif

[Rogue]

that helps A LOT very many thanks to you Matt. thanks for everyone else's advice also. what I had in mind was pretty much what Matt described. I'll REPEAT I'm not talking about building a full out race engine. Tim and Scoutgrl - if an engine makes 385 lbs/ft torque at 1200 rpm and climbs to a peak of 420 lbs/ft at 1800 rpm and then "flattens out"(on a graph) and you had your choice between a 1200 rpm stall and a 1800 rpm stall which do you think would deliver more torque to the wheels to get our heavy sleds working?!?!?!? im no mathmatician and im certainly not too bright sometimes so if you can explain to me how a less availible torque to the wheels can move an object faster than more availible torque then I'd be more than happy to agree with you 100%. there are two types of stall speeds, one is called "flash stall" this is what you get when you "stand on it" and it is higher in rpm than normal stall speed. the only reason for getting a higher stall speed convertor would be to match your camshaft as a stock convertor with a tall cam will bog your engine down at idle and cause an off idle hesitation commonly mistaken as a carburetor problem which usually goes something like this - "GodD**n vacuum secondary carb is a piece of s**t, i'm gonna throw this holley double pumper on top of this baby and mask my real problem" so anyways - i plan to stay with a dual plane intake, ported heads, camshaft slighty more aggressive than edelbrock - same lift but more lobe separation (overlap) for the loose idle, hopefully 9.5 CR as explained by AMXfiles and Matt, and topped with a Quadrajet carb - YUP A QUADRAJET - this is a seriously underated carb, small primaries for cruising and gas mileage, and huge vacuum secondaries that deliver all the power you need as your engine demands it. simple metering rod changes and vacuum secondary springs are all it usually takes to set one of these up right. this should produce an engine with a VERY strong mid-range which is where it'll be used most ( 1500 - 4000 ) once again thanks for all the replies the advice IS appreciated, Jeff Oh yea MATT where did you find forged pistons for $350?

[ March 03, 2002: Message edited by: RogueStar ]</p>

[Jerk]

you know, I'm actually sure I kinda cheated on that, My dad has a resale license and I THINK I had him order directly through Federal Mogul/TRW. they didn't mark the pistons up for retail since he was basically the retailer...I think, it was 3 years ago...my memory ain't what it should be at times! ANYway, try finding a local shop that sells fed mog or trw stuff and compare with PAW prices and maybe even summit, usually summit won't list stuff for amc engines in the catalogue but they may be able to get them anyway. make sure you know what bore size you're going with before ordering, trw makes .030" and .040" over bore pistons. and if you're having the block bored, ask them if they know if the pistons are slightly under sized (being forged, they will swell more when heated)or the block should be bored another few thousandths. If I'm correct, and I think I am, trw makes their forged pistons undersized by .005" so no special block treatment should be neccessary aside from final honing. If the machinist's don't know...find another shop. some shops don't like forged plugs, and will try to sell you cast plugs. If you get cast, then I have no clue as to what your compression will be, I've never done cast, and I know TRW does they're home work for cr finding, they didn't used to, but now they do, so you know what they say you'll get for cr, is what you'll get for cr! :D
as for the carb- a Q-jet isn't my first choice because I dislike large secondary air valves (it actually slows the air/fuel mix going through the bigger holes and MAY lead to fuel/air seperation. the way I look at it is, if your gonna have a 4 barrel, make all the venturis the same size, it aids in effeciency -just some observations from performance gurus parroted through me. Personally, I like the carter afb/ edelbrock performer setup, its simple like the q-jet yet all the venturis are the same size and will fit perfectly on the edelbrock performer intake. I think the q-jet requires an adapter plate. I did the holley thing for years, but got tired of buying expensive rebuild kits alla time. any way, have fun.

[ March 03, 2002: Message edited by: Matt W ]</p>

[Rogue]

i like the carter/edelbrocks also, $200 for a new one. Q-Jet is free for the taking!!! and stock MotorCRAP is well....a motorCRAP. i agree on the holley issue also - i've known a few lucky individuals that didn't get one built on a monday or friday but 99% of the people with holleys that i've known know firsthand how to rebuild them AND for good reason :D jeff

[Jerk]

haha! yeah, I got REALLY GOOD at rebuilding holleys! when you say "moterCRAP", do you mean the stock 4 barrel, motorcrap? if so, they are even harder to tune/rebuild than holleys, I've heard, and I don't know where you would find parts for them. I haven't looked too hard, I would rather use a new, good carb than a used/ 20 year old hard to find carb. They do resemble q-jets, but I don't know if they are related...like I said, never looked too hard. I have/had 2 of them and cannabalized to get just one to work somewhat, for about 12 seconds before a lead beebee fell out of the hole it was plugging in the float bowl., so i swapped those parts around and never got it to run right. this was on an 81 cherokee s W/T with a running 360 4bbl transplanted in it because the p.o. grenaded the 360 2bbl engine that was in the cherokee. It still doesn't run, I have to repair a junkyard edelbrock manifold($50.00) and have to have the tranny looked at when I get that done. I got the cher for $150 as is and towed it 15 miles with my j20. its sat for about 8 months since the incomplete engine swap. I want to drive it! dang it! oh well, this summer! :D

[jeepbob]

as far as stall converters GM std duty T400's use an 1800 rpm stall while the HD's and 475's use a 2200 stall spd so which is better for a heavy rig?
I use a 2200 stall converter and 4.10 gears, my 360 engine desk top dynoed at 325 hp and I have run a personal best 4.95 sec E.T. with worn out Daytona Super Stag tires at the mud drags with my 4000 lb 65 Wag. What does this all mean? It means I am still .3 seconds slower than the 460 Ford powered CJ's. Oh yeah, I run a Holley carb. :D

[Rogue]

i have the 475 torque convertor in mine, i was thinking i could get away with a little more cam than with the 400 TC, i guess i'll just have to wait and see how it comes out, hell i might have to break down and get a holley to get it tuned right ( more parts availible ) I think the most important thing to remember though is that regardless of what carbs we all like is that is long as we're JEEPIN than thats all that matters. 4.95's at the mud drags eh? that's pretty impressive!!!