I did a search, and didn't come up with much. Has anyone swapped out a 421 Three Duces set-up into 3rd Gen? Back in the old days, my dad had a 66 Bonnieville and a 66 Goat. That huge Bonnie had a 421, tri-power, turbo-400, and would almost stay with the Goat with a 389 tri-power, 4-speed Munci. At 365 Hp stock and enough torque to pull a house off it's foundation, with some modern tuning, the 421 should be a real powerhouse.

 

It's a Pontiac motor. Same as any of the rest of them. No different in any way, beyond year-model issues like the crank flange/flexplate situation and such as that. The same things do/don't fit, work/don't, etc. etc. etc. as any other size Pontiac motor; 326, 455, 400, 389, 350, whatever.

Having 3 2-barrels on top of it doesn't change the issues that wrapping 3rd gen sheet metal around it will require you to deal with.

There's no magic in a 421. Everything that one of those will do, a 455 will do better. the 3 2-bbl intake will still bolt rght up, if that's the main draw. Given how much "maze" (expense, difficulty, risk) you'll be running to get to the "cheese" (power, eye candy, personal pride, whatever) of having some Pontiac motor in your Chevrolet body (with whichever badges on it), there's no point in limiting the size of the cheese, by using any smaller than the biggest CID motor you can. Besides which, 455s are FAR cheeper and more common than 421s, thereby decreasing the amount of maze you have to run to get to that cheese.

Rule #0 of hot-rodding should be: aim at the highest cheese-to-maze ratio mods you can.

See the Pontiac swap sticky at the top of the page.

 

That's a solid quote right there, from one of the most quotable people on this forum.

Tri-power carb setups typically just add hassle and expense vs a well tuned 4bbl carb. A 455 Pontiac, Buick or Olds engine with a big carb and good cam and aftermarket heads would do very well. There are a few members on here with the 455 BOP engine in their cars here. Hassles like oil filter location, exhaust header style/location are the big ones.

 

Also, the older Pontiac engines have the engine mounts in a different place on the engine block than the 68-up engines do. You'll need something like the conversion plates that indian adventures or chief many horses sells.

If you're gonna tri-power, you should do three TBI units to keep up with the times!

Good luck!

 

Thanks to everyone for the info. I did not know about the motor mounts. I also did not consider the problems getting 3-2's under a third gen hood. You are right that a 455 can be built to be as hot or hotter that a 421, but in stock form, there is no comparison. I have owned x3 455's, all stock, and they were not even in the same league. As for tuning 3-2's, they need weekly tuning to run well.

I learned how to tune them back in the day. Still have the tools and the knowledge. It's pretty easy once you get the hang of it. When they are right, they are scary fast. I admit that it is old technology, probably best left in cars of that vintage.

As for my T/A it is a stock 86 garage queen with 27K the clock. I am thinking about buying a decent roller, possibly an 82-83 T/A, and building a street rod out of it. Thought a big block would be a kick. How about a GM crate 502?

 

Thats not entirely true, not to pke at you, but the 421 had a slighty different block and could make easy power, and yes the 455 is a lil easier when it comes to the modding and making power(SD-455 was rated at 290 for emission standards but was more like 395hp or so and torque out the ***). And you could make the horsepower go past 500 benchmark with a few mods.

 

Right; the motor mounts fall into the "year model detail difference" category. A very minor speed bump, comparatively. Buy an adapter, bolt em up, done.

I agree Dave, for a motor that is supposed to run HARD, a 455 is the way to go. It's the easiest Pontiac motor there is, to make big power with. CID is your friend. Bigger will beat smaller, every time, all else being equal. It's so easy to get all wrapped up in romantic nostalgia about the 60s and specific "memorable" products, that it's easy to forget or overlook something that simple and basic.

It is meaningless and stupid to talk about what any of those 60s motors claimed to be capable of, in stock trim. However they end up in one of these cars, they will no longer be stock. ABSOLUTELY 100% IRONCLAD GUARANTEE. If for no other reason than the exhaust. Throwing out "a so-and-so was rated at 365 HP in 1966 but a such-and-such was rated at only 265 HP in 1974" doesn't even begin to come close to giving a whiff of a hint of a glimpse of a clue of what the motors' actual POTENTIAL is, let alone the RESULTS to expect from a swap.

Keep in mind that if you can actually find either one of the remaining 421 3-2 engines that are still in totally bone-stock condition, and then if you could persuade either one of those 2 people to sell it, you will have spent enough money to buy a whole other 3rd gen in perfect immaculate flawless condition and buy a new crate LS6 to put in it; and outrun the old 60s stuff.

Then, keep in mind also that if you do that, it will not run on any fuel you can find today. No amount of lead substitute will adequately make up for the changes that have occurred in gasoline since the late 60s. Keep in mind also, that even if you DID decide to deal with that, you just added a HUGE expense to the cost of operating the car.

Finding the ORIGINAL 3-2 intake, carbs, air cleaner, linkage (!), and everything else that it takes to get one of those systems to work, is tough enough, without requiring that it still be on top of its original host cast-iron.

Torque goes with cubic inches. The reason the 455 had so much torque was NOT because it was a Pontiac motor; NOT because there was a screaming chicken on the hood; it was because it was a 455. See my recommendation above for the engine displacement to use for a Pontiac swap: that's the reason for it. Likewise, the reason the 421 made such great power for its time was NOT because the block was special somehow, or even because it was a 421; it was because the induction system flowed lots of air. But that was in 1966, and compared to other induction systems supplied by Pontiac in 1966, not the aftermarket in 2008. Fact of the matter is, if you want power, a single modern Holley or Demon 4-barrel will FAR out-power 3 40-yr-old Rochester 2G 2-barrels. And a 455 will out-power a 421, all else being equal. No other outcome in either case is possible in the RW.

Now if this whole swap deal is just going to be a car-show type thing, where it accumulates a grand total of 3 miles on it during the entire rest of its life 50' at a time pulling on and off of a trailer, then the block underneath the square inches of chrome that the 3-2 setup permits, will be irrelevant. And at that point, the 3-2 setup isn't NEAR as hard to come up with, by itself; people by and large don't really want those any more, because they're slow and troublesome for a runner, they're only good for show. It'll cost alot, but they're not particularly "rare". Kind of like the guys in car shows that show a T-bucket with all chrome front suspension, pleat-and-tuck leather interior, a steering wheel made out of chain welded together and chromed, $500 apiece chrome wheels, chrome Jaguar independent rear suspension, chrome headers and lakes pipes, a chrome 6-1 blower, some hoaty-groaty cam with a gear drive, and a stock 78 305 2-barrel long block. (Did I mention "chrome" and "show"? just in case I forgot...) Because the long block DOESN'T MATTER in that application, there just needs to BE ONE. It'll be one of those boring painted parts. You can't really chrome it, and even if you did, it wouldn't matter what one it is, you'd win the show regardless. All long blocks can hold an approximately equal # of square inches of chrome.

Again, keep the goal - the "cheese", whatever that may be, to the OP - in mind, FIRMLY; and carefully evaluate the "maze", which is the expense, difficulty of finding stuff, difficulty of getting it to fit, risk of it not working, limitations on usability, operating expense if any, etc. that the OP - not me, or anyone else - has to put themselves through to get to that goal. Analyzed logically, sensibly, and unemotionally, it should be pretty obvious that while the OP's original proposal makes a pretty pipe dream, it doesn't fit the real practical world out here in meatspace very well. And furthermore, doesn't present any technical challenges (fit, fab, etc.) that make it any different from any other Pontiac motor swap, only HUGE logistic ones (finding and paying for stuff).

So yeah, for a car-show motor, a 3-2 on top of ANY Pontiac motor would be equal, doesn't have to be a 421; for a runner, a 455 (not necessarliy ANY "stock" one, so whatever they made in "stock" trim is irrelevant) with a single 4-bbl will win, hands down; and a 421 is not the best choice for either, ESPECIALLY not in stock trim. The only "benefit" to the 421, which might or might not be part of the OP's perceived "cheese", is bragging rights, among people who care about such things. Seems like some MIGHTY EXPENSIVE bragging rights though, in the end.

 

A

 

Perfect!!! Much better plan than a 3rd gen.

Might not even be too unrealistic to consider a 1st gen Firebird.

Keep in mind, the exh valve seats in those old heads are not hardened, and the valves will eat their way right through the heads in short order, with modern fuel. IMO you'd do better to find a pair of modern heads such as 6X or one of the other "better" castings, or aftermarket; and match the pistons accordingly if necessary.

 

easy swap

 

All points taken... Thanks for taking the time to explain it to me. I never had any experience with an SD-455, just the stock generic versions of the 455. I get it. A 40 year-old engine has no practical use today.

I am not looking for a 421. I have one. The old Bonnie is hanging out in our hay barn in Georgia. It drove in under it's own power in 1976, and has not been moved since. The car has it's original and stock 365 HP 421, 3 duces, had 140K miles, and was dripping oil out of the rear main seal at the rate of a quart to 30 miles, so we just parked it. Dad bought it new. It has never been apart.

My mom gave me the car before she passed, even though I told her that the engine may have some value as a collector's item. The engine is complete, and will turn over, but will it not start. The car is a rust bucket as it spent much of it's childhood in Cocoa Beach Florida. I am trying to decide a good project to put it in. Although the car is trashed, I would like to see that engine run again. I think that I will just look for a decent Lemans or maybe luck onto a GTO, and drop it in.I am going to have the 421 rebuilt, and will probably keep her stock except to drop the compression ratio so it will run on pump gas.

No extra chrome planned or desired, don't want a show car, just a decent driver street rod, to get out on the weekends and play with. I don't care how fast it is or how much power it makes. And yeh, definatley bragging rights, because how many running 421- 3 duces do you see on a regular basis?

 

And, already having the motor and the whole rest of the setup, changes the picture, too. Not having to go out and FIND it, means that the "maze" of using one is CONSIDERABLY reduced.

Those 3-2 setups are not very user-friendly for the street, but are VERY popular with the show-car crowd. Last person I knew that had one, that's exactly what he did. If you're planning on driving whatever you build, I'd strongly recommend turning that into cash, which you should be able to get ALOT of for it; and getting something less finnicky and troublesome. Remember, what seemed "acceptable" in 1966, isn't the same as it is today: when EVERYBODY got 8 miles to the gallon and had all kinds of trouble in cold weather and had to tinker with their cars every weekend (or at least, often) and so forth, those things weren't as bothersome as they would be today, when you can get the same power or more without having to deal with all that. The "romance" of saying "421" kind of fades in a hurry when you're sitting in a parking lot somewhere with a problem or something, or when you don't ever want to drive it because it takes a gallon of gas just to get to the gas station.

 

Thanks for the tips on the heads. I understand and agree with everything you are saying about the old ill tempered Poncho, but it's been in the family since I was 10 years old, and I am not interested in selling it. I am going to get the engine running again, and just need to decide what is best to drop it in. If the Bonnie were in better shape, I would put her back on the road. I might go with a second gen, like a 74 Formula.

 

Easy swap? I live in Florida! Where's the friggin A/C?

haha Anyway, great job! It looks beautiful in there!

 

Yeah that kind of takes all the fun out of it....

I like that solid roller valve train setup you got there!

 

what's it run? or is that top secret

never got the ls1 to the track. did take out some other ls1 cars though

 

HA! You must not have t-tops, because it isnt bad if you right is heavy and the tops are off! HaHa!

 

Bull crap! It doesn't matter how fast I drive, roof or not, in Lakeland I need A/C!!

 

Your right about needing the A/C in the south. Take the T-tops out in the summer, and bake.Is the engine in the pic a 455? Looks like a neat clean install.Have located a 74 base Firebird hardtop, runs, fair condition, minimal rust, 350 Pontiac engine, auto, air, PS, and PB. Thinking about building a Formula clone except for the 421, 3-2's, and the 400 auto from the Bonnie.I want to build it with all of the creature comforts desired by us old farts.A friend who builds engines, says that he can install the hardened valve seats in the 421 heads which will tolerate the nolead gas, and he says that if we use 9:1 pistons, the engine will run on pump premium and still have plenty of punch for the project. He suggested a swap to an HEI dist. The Bonnie got an honest 14 MPG if driven easy, so for a weekend driver it should be OK.

 

hey i got 2-60 a/c!! thats all i need.
thanks. its not done yet, but hopfully will be this spring
never had it to the track. but from my calculations it should be low 12s
but im defenatly limited by my 10bolt rear.
after i get my 9" rear, and actually hook up my trans brake, and a little bit of spray i should see mid 11s no problem.


the engine in the pic is actually a '66 389. it is my old mans engine for his gto
that is being restored now, so i used that for mockup.
i have a '72 455 that ill be dropping in there before spring. and its not stock.

 

I want to see that built 455 in a thirdgen. Cool! Looks like you'all do some first class work! Also like to see your Dad's car restored with the 389 back in it. Had a little experience with the 66 389. Mom's car was the Bonnie. Dad had a 66 Goat 398, 4 speed Munci close ratio 4 speed, Hurst Compitetion Plus shifter. Mom lost the GTO on a rain slicked road in 70, smacked a tree. We pulled of the 3-2's and put on a 4 barrel Holley 600, transplanted the engine into a GMC 3/4 ton LWB that came originally with the original GM V-6. That 398 powered GMC would pull anything! Quite a few old GMC's ended up with 389's because of the torque. I dropped a 409 in a 68 GMC, SWB stepside, but that's another story, and I am getting too far away from thirdgen's.

 

I live South of Tampa Its gonna have a high of 80 today and low of 69.

 

80?!!??

I'm gonna have to turn the A/C colder!!

 

Only thing you need to do to the 421 is get some hardened valve seats put in the heads to run unleaded gas. Some people believe that carb sincro is a PTA but thats untrue. You have an engine that is stock with the original carbs so the only sincro involved is adjusting the carb linkage so the front and rear carbs kick in at the same time. I had a 65 421 Catalina, w/a muncie and 3:42:1 rear posi that ran like a dream back in 75. In stock form, you would do good just to keep it from rippin' the unibody frame from the floor pan. The engine is totaly forged (rod's, pistons, and crank) and was rated at 370hp. That was under rated from the factory for reasons I can't remember, but actually, put out over 400hp. at a mear 5k rpm.

 

Those cars were pretty awsome! Bet you wished you had that car back! My parents' 66 ran trouble free, except for peroidic adjustments for 10 years, and 140K. What put in out was a leaking rear main seal, and a rusted out body from being on the beach. I drove it some after getting my license in 72, and have never driven anything as impressive since. When I bought my Shelby GT350, thinking that I really had something special, we were all amazed that the old Bonneville would run circles around that Shelby.

I am going to hold out for a 66 or 67 GTO. Looking for a nice roller. I want to put the engine in a period correct body, even though a 421 was never offered in a GTO, it will be a relatively easy swap to put that engine in one of those bodies. The Bonneville is a factory air car, and some of the A/C parts may fit the GTO also. It will not be a collector car, but should be an interesting weekend driver plus I get to keep parts of the old Bonnie around a while longer.

 

The reason for the HP underating was (1) Pontiac management, and (2) Insurance. The 365 HP model was actually close to 415HP. The SD model was said to generate over 500 HP on the dyno. The 421's made massive torque, and generated thier HP at low RPM's. They came factory with forged and balanced internals, chrome moly rings, 11.5:1 compression ratio. One of my uncles was a design enginner for GM through the 60's, and he used to keep us up to date on spec's. Of course, when I drop the comp ratio back to 9:1, It will probably detune mine to about 325HP, but that is plenty for what the car will be used for.

 

I don't know about the 66 bonnie but the 65 catalina 2+2 421 was rated at 370hp from the fact. One of the car mag's did a road test on it and it recorded the fastest 0-60 of any american car for that year.
Yeah, I wish I had that car back! It's one that I never got beat in. I'm not saying that it was the fastet one out there, but I never found it or it never found me. I never got it to a drag strip but it wooped assss on the street.
Sad story? I sold it for 700 bucks in 76 because I was in need of reliability because I kept breaking stuff like, upper control arm bolts on the driver side, and axel brackets where the trailing arm conected (titainium welding rods were not cheap). I really didn't know what I had with the 421 other than it was fast. As far as not being the correct engin for a goat, tell anyone that looks at it in the car that it's a 389 tri power and they'll never know.

 

Back in 1984 there was a guy with an '82 T/A that had put a real SD-455 into. This was looooonnng before there were any companies making 3rd-gen Pontiac engine conversion kits. It appears that he used '67-69 accessory bracket and pulleys to fit everything under the hood. As you can see he retained the ram air function used on '82-84 T/As but unfortunately I don't have a picture of the underside of the hood to see how he made everything mate up.

I would think twice about robbing the engine out of the 66 bonnie. A '66 Bonneville 421 Tri-Power is a VERY rare and valuable car!

 

Thanks for the input. That SD 455 looks awsome! As for robbing the Bonneville, I would like nothing better then to restore the Bonneville, as my parents bought it new in Merrit Island Florida when I was 10. Unfortunately, the car has a bad case of beach rot, and there is little left of the body. It was pretty rusty 31 years ago in 1976 when we parked in our hay barn in Georgia. It has continued to rust inside that barn sitting on a dirt floor. You can see the engine through the rusted out hood. You can see the headliner through the holes in the roof, and you can see the trunk through the holes in the quarter panels. The floor boards are gone, and the chassis is broken just behind the front wheels. Even the bumpers are rusted through. I will do well to salvage the engine and transmission out of it for a rebuild. I almost pulled the 3-2 setup off of it to sell, then scrap the rest of it, but the engine turns over freely, so I believe that it is salvagable.

 

Spark plug changes must be a breeze, ehh.....?

Crybaby, it was freaking snowing over here last night... !!

I applaud you for wanting to install the 421 into your 3rd Gen, but understand that it doesn't matter what condition the Bonneville is in. There are people out there that will pay A LOT of money for it, just for the frame, tags, and paperwork....

 

Here ya go man, Click Here. This isn't from the car above, but the same principle was used I'm sure...


-Rob

 

I guess that I could find a low optioned 66 Bonneville Coupe to use as a donor car to rebuild mine back as original as we can get it. Then it will be correct for that engine, and would classify as a restoration. It will be easier the find a Bonneville then a GTO.

 

Sorry to resurrect this thread, but that is BAD ***! Very clean motor. must be a BLAST to drive. No doubt. Hope you beefed up that rear end. My '93 axle stock gave out from the torque of the 400 i dropped in. Wasnt as much as 10.1 counterparts but still lit the tires thru a factory tall 2.73 ratio. another project for me is in the works.....


lettin it be known. Glad a real enthusiast knows the history. All the power you need, STOCK, too bad the haters didnt hear this rare info until of course they get stomped at the track with their modifed (and exaggerated #'d) small blocks.



Gorgeous It just goes to show you Pontiac refused to die in the 80's and still, in 2016. i hope i can make my late 4th gen look this good. that alternator is gonna have to be mounted lower unless i decide to ride with no hood

 

Anybody running around in a finished one?

 

I'm wondering which direction the OP went with the 421 swap.
I'd do, EFI, OD trans and some nice ported aluminum heads, that would bring that motor combo right up into to 2000s and to 20 plus mpg with nice big drivable power.

 

I wanted to know if you have any answers regarding installing the GM 502ci? What is the largest engine that will fit in a third gen car? I've got a 1989 IROC-Z and would like to go as big as possible?