Thread: Offenhauser dual quad on an amc 401!

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Hello hello...

This is my first posting on this website, but I have been reading in for a while now. It seems to me that there are some solid motorheads around here that could easily handle my questions. I apologize in advance for what must be the longest post(or damn close) that any of you have even seen. But as I have seen many times before with forums, the most helpful suggestions are from people who know as much as possible about the details of the particular situation. This should not present a problem for anyone who is kind enough to read this entire thread. And again...thanks for reading!


I am in the process of building up a 1966 AMC classic convertible to be more of a true muscle car. It will be a ground up job. Everything in the driveline either new or rebuilt/modified. I intend to put together a fast CRUISER here. I have a 69 Firebird with a 12.5:1 comp 383 solid lifter chevy with a turbo 350 and a 8 3/4 mopar rear with 3.91's in a posi for scaring the @#&% out of myself around town. But we all know that combo isn't very handy for much else. So here are my plans to date.

Driveline: I have a cast iron case AMC t-85 3spd(what they used to make the t-10 out of) behind a Lakewood scattershield bellhousing and a HD Borg Warner (.7)overdrive "torque tube" tailhousing. Yes...this car believe it or not has a torque tube driveshaft for those who are not familiar with the car. I intend to KEEP the tube, well sort of. That is I will retain the original basic design. The tube itself will be replaced with a slightly larger(in diameter and thickness) main tube and use only the ends of the original tube to weld it to. This is to house a custom driveshaft that requires the slghtly larger inside diameter of the housing tube. The rear axle is a corporate model 20 that will recieve new custom Moser one piece axles and either 3.15 or 2.87 (did I mention CRUISER) gears in a posi unit. The tranny will recieve all the realistic improvements I can have done to it(basic t-10 stuff) and all parts will be rebuilt completely. With the tranny I have the option of using either a 2.99 or 2.49 1st gear along with the 1.85 2nd and 1:1 3rd. I have both sets currently. The rest of the car will recieve some obviously needed structural improvements, better brakes, sway bars, etc, etc.

My questions regard the motors' induction set up. This is what I have to work with engine wise. I intend to run an AMC 401. I have been collecting them. I may very well have my crank offset ground from the original 2.25 rod journal down to 2.00 and use custom chevy rods with a .8 width at the big end to match the AMC width on the crank. With the then 3.908 stroke and my fresh .040 bore this leaves me at 434 cubic inches. This has all been done before(and much more). Point is that I want to have plenty of torque available to pull reasonably well from a stop with say the 2.87 rear gears with a 2.49 first with 26.5in. tires(BFG Radial TA 255/60/15's) I have no intention of ever running slicks(even though I have a nice set in the garage now) drag radials, etc. Since my tranny should be the weakest link, I'd like not to break it(or anything else if I can help it). I'll assume that I will loose traction before I can really harm my tranny with basic radial street tires...So I hope. Regardless, more than 450 lbs. or so of torque would be unnecessary for my needs with this car. I do though want to be able to run around comfortably at 1500 around town and cruise at 75mph at 1800 or so with decent fuel economy(for a 3500lb. convertible with the aero of a blick!). I plan to run this thing for a lot of highway miles. To that end I am interested on using Keith Black 17.3 cc D-cup dished pistons with seriously ported Stock iron 58cc heads hogged out to 63cc's running a tight quench area and a 10 to 10.2:1 final compression for high test pump gas. I intend to use an MSD 6AL box with the matching Blaster coil and either my NOS 1978 and newer type motorcraft type vacuum advance electronic distributor(same a 80's 5.0 mustangs) or a higher end vacuum advance alternative. I intend to run dual 2 1/2in. exhaust behind ported 70's "free flow" type cast iron manifolds. It will also sport a power steering pump and an air conditioning compressor (cruising comfort) There will be oiling improvement modifications, high flow water pump, 4 core radiator, etc, etc.

NOW FOR THE QUESTIONABLE PART:

There are some good intakes out there for me.
- Stock early 70's holley pattern 4bbl iron manifold(have one)
- Edelbrock basic performer(I have two now)
- Edelbrock SP2P (very small passage dual plane that is supposed to be good for torque and mileage, runs out of gas in the 4500rpm or so range on a stock motor)
- Edelbrock torquer
- Edelbrock RPM Air Gap(most obviously a good choice)
- Offy 360 single
- Offy 360 "high rise" dual quad. (about as "high" as an edelbrock air gap manifold)
- etc, etc

I am interested in possibly using the least likely of the bunch for my needs, the dual quad. It is a single plane "high rise" 360 "equaflow" that is set up to be completely separated from side to side. The center divider runs completely front to back in the plenum and up to the carb mount. Though single plane manifolds are known to handle "larger than necessary" carburetors without too much penalty as long as the booster signal is sufficient and so on, using two carbs would require me to use more cfm that my motor would require at a 5500 or so rpm max. I do though have two holley 450 vacuum secondary carbs that one is from the convertible's original 327 high comp motor and the other is from my 66 rebel parts car with the same motor. I have rebuild both down to the throttle shafts, professionally bead blasted, tanked, Holley trick kits, the whole nine yards. It would be hilarious(if only to me)to be able to say that I am running "correct carbs" on the car. It would sure keep a few people scratching their heads!

So to the smart ones out there.

Are a pair or 450 vacv secondary holleys too much for a 10:1 compression AMC 409 to 434 cubic inch motor that is not intended to spin past 5500 or so? (some recommend up to 600's, some say 390's)
If they'll work OK, how much of a cruising speed gas mileage penalty should I have to suck up for the privelage of running what amounts to an overcomplicated, unnecessary, inefficient, and at least mildly power robbing visual(and humor) statement.
Should the primaries be hooked in tandem or a progressive set up like edelbrocks adjustable progressive linkage.
How much low rpm grunt can this manifold really deal with. Being that it has the shortest runners possible on a v-8 motor...not the main ingredient for low rpm intake velocity for sure.
Obviously the larger displacement of the motor compared to the modest sized small blocks helps make up for some of the manifolds' shortcommings, but is there going to be a HUGE big difference if I stick with the 409 size instead of stroking to 434.
Offenhouser tech department suggested only that I not use a cam with less than a 218 duration, and other that saying that "it'll work just fine", he was not interested in going much beyond that. Any cam suggestions? I'd like not to go much beyond .5 lift and 5500rpm or so in revs. I want to keep the power in the lower rpm ranges.

If any of you are still awake...THANKS!!

ANY thoughts would be greatly appreciated! And I'll try to keep my posts short from now on.

George

The 450's will work fine. So would the 390's or the 600's. Why? Vacuum secondary diaphragm spring selection. The 390's would run a spring with less tension and the 600's would be tightest. I'd start with the tightest and loosen up 'til it starts to bog.

Dual carbs. have a certain aura. They're just flat cool. A little harder to tune (read time consuming) but worth it in my opinion.

Hard to beat the extra cubic inches and torque the stroker motor has to offer.

I say go for it.

Thanks for the thoughts friend. Yeah...and would you believe my girlfriend digs the old school menacing hot rod engine look more than I do. I like it too...but at first I was looking at going for the "ya just never know" sleeper look with the car. Who would guess from a mid sized AMC convertible? Ahh what the hell, it'll look good!

Any thoughts on the carb linkage though. together or progressive?

George

You're gonna have to open the carbs. together. The vacuum diaphragm will provide the "progressive" part with the secondaries.

Kinda what I figured...would you suggest using slightly different vacuum spring rates front and rear to stagger the secondaries' opening sequence?

Any thoughts on the sad gas mileage front with a 1800rpm 75mph cruise. Do you think I will take a sizable hit as compared to an air gap with a 600 on it on an otherwise identical motor?

Thanks,

George

I wouldn't worry about staggering the secondary springs. The joy of getting it to idle and part throttle will temper any ideas of getting carried away with the tune. Power valve selection will be important also.

As far as fuel mileage? I've only run 2 dual carb set-ups, one a tunnel ram 350 and the other was a cast iron (flat) 400. Maybe I got 11 mpg's? Once?

In my opinion single plane intakes are for race tracks. U want to build a torquer motor so I suggest the sp2p intake, as a starting point. Then a 550-600 cfm carb. Yeah I know it sounds wimpee, but u like turning wrenches so this willbe good exercise. If u still need more gusto u can tune up from that. Good luck --rdhotfrd

I suppose that you weren't interestred in mileage much with a tunnel ram. I'll assume that both were without and overdrive tranny and/or highway gears. I'm just trying to shove square pegs into round holes here. It's pretty dumb of me really to even put fuel mileage and single plane dual quads in the same thought! I so like the challenges though!!!

George

My younger brother (now since deceased) had a brand new 68 Javlin with a 390/4spd. He put in a Crower cam (don't remember the specs), Offy 2/4 intake with Carter 600's and a Ford 9 inch with 3.91 Locker. Wasn't a Goat, 442 or any other vehicle that could touch it. I came back on leave from the Navy with my 60 Vette (convertible) and he traded me for the weekend. Boy did I have fun. Hehehehehe

Yeah... I want to cruise fast with the top down. It weighs nearly the same as the 390 javelin, and I'll have some more cubes to rumble with. Hopefully 434 stroker! Can't wait!

Hi. I do believe that you are going the wrong way. The AMC "dogleg" heads are very good as cast. Plus, you intend on porting them. Ported, they flow as well as the early Mopar Hemis. (I know all you "off-brand guys are biting your lips". You back down from AMXs, don't you?) You need to tailor the rest of your engine to the band where your heads function the best. Stock heads with free flowing exhaust and sufficient intake flow are good to 6500 RPM. Ported heads are good to 7000. If you choke it down with a dual plane and/or dinky carbs, why even port the heads? The stock 401 puts out 430 ft.lbs of torque. With ported heads, unrestrictive intake and exhaust, 525 HP and 530 ft.lbs. torque are VERY easily obtainable. Don't be shy with the cam, either. This engine makes enough torque to give some up with a hot cam. Cam it for the redline that your heads impose, 6500 for stockers and 7200 for basic ported. Rhoads lifters will bleed off at low revs to give back some low end. Make SURE you use a new distributor gear, distributor drive gear on the cam, and run the external line to oil the dist gears. You probably already know of the extra line to be installed in the lifter gallery, do it.

If you insist on using the 401 exhaust manifolds, get them extrusion honed and bore the exit out as big as it will go, and then use that size pipe, an "X" pipe, and that ID in the mufflers. For intake, a Torker and a Holley 850 double pumper is a proven winner and easily tuned. The Edelbrock R4B is the other truly GREAT single carb intake. Though a dual plane, it runs strong to 6500, and holds a slight edge over the Torker till that level, after which the Torker tops it. The new Indy single plane is supposedly a real good RACE manifold. The air-gap manifolds are dual planes and I rule them out as a bandaid Edelbrock is using for cash flow. Why don't they recast the R4B, the STR-11, the UR-18, or their AMC valve covers? They are missing the boat, big time!!! If you go with any dual quad intakes, I would strongly suggest using Holley 4224 "Center-squirters". They were designed from the start as dual quad carbs. All four plates open together and the squirter is in the center. With all the other type carbs, the primaries open first, enrichening only half of the intake. Mixture distribution sux until all plates are WOT and even then, the secondaries are not plumbed the same as the primaries. It's a compromise. I have been using 4224s on a UR-18 Tunnel Ram for years, on the street!!! A little harder to tune, but way stronger than the extrusion ported Torker/trick Carb Shop 850DP I used before. I'm not a big Offy fan, but I'm sure good performance can be had with the one you mentioned. Just don't choke it off like some of these guys are suggesting. That 401 wants to go, and will take all the carb you can give it as long as enough gas gets mixed with the air.

As far as turning down the crank to SBC spec and offset grinding it for more stroke, don't. You will shift the mechanical power range down the RPM scale, making the GREAT AMC heads a waste. If anything, a shorter stroke will move the band up the range, where the heads can stretch out and show their stuff. I've modeled all this on the Dyno2000/DeskTop Dyno, and AMC had the bore/stroke ratio rite with the 390 and went slightly backward with the 401s increased stroke. When AMC designed their new engines (290 thru 390), they had already made the decision to change their image and go racing, then studied all the competitors best efforts, and took the best ideas and improved on them. The redesign for '70 got the heads right.

A point of fact: My '71 360 AMX turned a 13.02 @ 108 STOCK with a dealer installed AMC R4B and Holley, headers, and a dual point. It was fairly fresh and had new valve springs and a used 401 cam. Not one performance part inside. Just a stock rebuild with knurled stock 8.5-1 pistons, knurled valve guides, and a standard local Ridge Co. valve job. On street tires, through the full tailpipes, and running the float bowls dry when I hit third gear (3.54 rear). That's why the "off-branders" shy away from AMXs and Javelins on the street!!! Many a 440 Mopar and 5.0 'Stang have felt the pain, and made the quick turn off to go hide.

Here's a URL of (one of) my BBO '69 'X. The page is out of date, but you'll see some cool AMC schtuff.

http://www.american-powersports.com/dave/fr_bbo.htm

Another of my BBOs....

Holeshot___again..thank you for the thoughts. Clearly you know what your talking about with AMC's. That's what I need. I'm impressed that you even have one of those rare tunnel rams never mind run it on the street! As far as my situation goes, I have a unique situation...I don't want to make too much power. I want to put together a fast cruiser. By that I mean geared up (probably 3.15s...maybe 3.54s) running a t-85 3spd with a borg warner (.7) overdrive through a moderately beefed up car. There is not much that can be done to my understanding to strengthen up the t-85 and overdrive much beyond stock(everything will be rebuilt), so that is my "power limitation"...I don't want to tear it up. That is why no slicks, no drag radials, (I would grudgingly consider leaving out my sure grip if need be) I would rather spin the tires before I can load up the driveline with evough torque to bust anything, hopefully. I am trying to put together a motor that very much favors low to mid range power as I intend to keep the cruise speed down to 2000 or below. I'm looking at putting in a cam with short duration and high(for a short duration) lift... 0.50 or so. I know what your thinking...for the time and effort(and expense) a much faster motor(and car) could easily be built. True, but I want a cruiser(around town and highway) this time. I have a 69 Firebird with a 12.5:1 comp 383, race ported 461 heads, crane gold rockers, stud girdle, big solid lift cam, Team G intake with a modified 750 double pumper, and a 8 3/4 mopar rear with both 3.91 posi and 4.56 and spool on a seperate carrier. That's plenty for me! I want the opposite this time. A 13.5 quarter would be just fine on street tires for this car. Faster would be great, but no big deal.
I was looking at going bigger (in stroke) just for the reason that you mentioned. Drop the rpm range down...and gain a bit of "free torque" in the process with a few more cubes. I'm only looking at say 5500rpm or so max here. Boring..I know! The head porting that I mentioned was to open up the chambers to allow the KB pistons that I want to run to be able to drop to the 10.2:1 or so range. The runner and bowl work would be towards low lift flow to get the most out of the short duration. Blending the backs of the valves, etc. The dual quad idea is more of a style thing that admittedly my girlfriend favors more than I do. They would go well with my vintage aluminum edelbrock valve covers. Personally, I'm very tempted to make it as stock looking as I can get away with(gold 66 290 colors and all) throw a correct air cleaner on with the typhoom 290 4v sticker on it along with a set of 290 badges ot the rear quarter panels, and not let anyone in on what's really in there. I will be running an air conditioning compressor along with a power steering pump on this motor, so that may end up looking more appropriate anyway. I am trying to hold myself back here in the all out speed department, but I admit I consider "improvement potential" when I am trying to put parts together. I have a real nice set of 291 heads if I wanted to jump into the higher compression bracket, etc, etc
I'd love to hear more of your thoughts,

George

Well, what I was really trying to say is that the dogleg heads want to flow way more than you'll be asking of them. You would get more bottom end by using '69 rectangle ports. So, if it was me, I'd try to find a 68 or 69 390, and save the 401 and 291 heads for a project that needs them. Actually, there is no reason to use the forged crank & rods in your application. You could do most of the same stuff to a 343 and end up about the same place. Then you could sell the 401 stuff to me!!!

Why don't you lose the torque-tube and 3-speed???? Nostalgia is one thing, and that has it's place. Please don't embarass the rest of us AMC-ers by mating a 401 to that driveline. I don't want to insult you, but you WILL be insulting yourself if you do that deed. You will be getting rolled-eyes not only from the off-branders but from fellow AMC-ers, guaranteed. Why not just keep the original driveline in a pile somewhere and go 401, T-10 (or 727), and 9-inch Ford? I promise that you will be glad you did. Odd combinations begin, and end, as headaches, and land on the scrap heap.

I just got my 3rd UR-18. My second one was a Wally Booth Prostock item and had his name stamped rite in it. Unuseable unless you had the Prostock heads. I offed it for $450. I just got a STR-11 that will someday be on my 401 in my '71 AMX. You don't even want to know what those are going for these days!!! They have been doubling every year for the past several years.

Oh, and I forgot to tell you. Don't be thinking that the only way to blow a rear end is to be stopped and popping the clutch. I blew the GoPak posi out of my 360 AMX at around 70 shifting into third gear. Broke the gear carrier in half and split the housing. Luckily, I didn't slip in my own oil. That's an indicator of how weak the AMC rear is. I have also broken the yoke off of the rear a couple of times. And there is NO aftermarket or stronger parts to fix these problems. I was overjoyed to find that a Mustang (71 in this case) rear drops RITE in to the Javs & AMXs. Only change was bigger U bolts and an adapter u-joint.

Do us all a favor, put the unstroked 401/T-10/Ford 9" in it. The 401s need no additional torque. Again, I GUARANTEE you that you will be WAY WAY better off. Or else leave it stock and find a Jav or AMX to hot rod.....Dave

Yeah I know, it's an odd idea doing a 66 convertible. And it is certainly a challenge. I want to do it for several reasons.

1- I am big into convertibles. As I mentioned, I already have a very healthly 69 firebird coupe. It drives me nuts to drive around on nice warn sunny days(here in Wilmington, NC we have plenty of them year round) with a lid. I also have a real nice condition 1976 CJ5, mildly warmed over 360, 33in BFG all terrain TKOs, 4.10's, dana 44 posi rear. I've had CJs for over 10 years, and I have grown quite fond of AMC v8s from the beginning. To give you an idea of how much I like going top down, I ran my first cj year round in NJ with no more than a bikini top and a set of half doors. Granted it was way back when I was young and busting my but to pay the mortgage on a house and stay debt free on my own in my early 20's, but with a Carhart onepiece and gloves and hat, I loved it! Not to say that I don't appreciate having the best soft top available on my ride now, but I still take the top down on plenty of 50 degree days still. I'd rather drive the jeep 10 to 1...because I can take the top off. So for a car that I intend to set up to drive alot, a convertible it must be. Obviously it must also be an AMC. I have been collecting way too much AMC v8(304, 360, and especially 401) stuff not to want to put one in an AMC where it belongs. I can't get into the Rogue, American body style. They are just not for me. The 67 or so rebel conv. is workable, but it just doesn't do it for me either. The Ambassador...we won't even go there. If the 68-70 Javelin came as a convertible.....

2- I want an overdrive tranny. the t-85 with a Borg Warner overdrive will allow the cruise gearing that I want. I like the idea of using the original "type"driveline. I have had several conversations with mostly Marlin owners who love their drivelines(love the way they ride on the highway and handle when good sway bars, shocks, springs, tires, brakes, are used) and several have either modified their 327's(one with a healthy nitrous diet) or swapped in 360/401s and have enjoyed the results. By the way, I will be saving the running original 327/auto driveline intact for storage. I'll be using the parts that I need from my 66 rebel (it also has factory air, power windows, black bucket seats, perfect console, front disc brakes, sure grip rear, t-10 tranny(very rare for a torque tube car) and a factory American Motors tach still mounted on the dash that is in great shape) Plus the drivelines' limitations will help me keep a lid on the all out performance ideas for the motor. The t-85/overderive setup is "supposed" to be as strong as the early generation t-10's that they were based off of. My very respected tranny builder seems to think that it will all survive with no problem as long as I don't go too crazy with the 401 and I keep street tires on it. Not entirely convinced, I suppose it all depends on what exactly "too crazy with the 401" means!

3- I think with the right treatment, the car could have a nice look to it. A member of the AMC club in Finland(of all places) did one up in Red with a white top, stripped the side molding, put nice aluminum rims and BFG radial ta's of respectabvle size on all corners, lifted the rear about 2" for a better stance and it looks good. (kinda mid 60's hot rodded chevelle/nova..ish!) Plus I like the fact that it is for all intents and purposes a forgotten car. I like the idea of putting together what AMC should and could have put together in 1966 to compete in the mid sized, 400 cubic inch, square bodied muscle car market...and using as many AMC parts as realistic in the process. I guess that I'm a dork for something different this time around!

As far as selling you all my 401 stuff...not so much. I have been hoarding for a reason. Seriously, if you need something, let me know, I just might have it, and POSSIBLY part with it. As for doing a total driveline swap, I looked into it. Actually it was my original intention. Modern HD aftermarket overdrive manual trans, rear disc ford 9" 32" ladder bars(fit quite nicely) etc, etc. Total swap outs have been done to several 65-66 classic/marlins that I know of with good success. Perhaps I like going the hard way. I believe the 57 rebel was only beaten by the fuel injected corvette that year in the 1/4. Yeah, it had factory 4.10s but it was still a turque tube. So ya think people will mock me?

George