401 Nailhead engine transplant for a 1965 Buick Special - opinions?


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401 (or other Buick) engine transplant for 65 Buick Special - opinions?

Dear Buick Enthusiasts, :shield:

I have a 1965 Buick Special Deluxe wagon with a 300 cu V8 engine that is getting weary. I joined Team Buick in order to get some advice on rebuilding the engine and truly discovered how little really I understood about the whole project! :confused:

In that thread (http://www.teambuick.com/forums/showthread.php?t=19792), BigRivy suggested if I consider any alternative engine, I should try to stick to period Buick engines: specifically the 401 Nailhead. Having learned plenty in the interim, I have to confess some interest in the 401 upgrade. Aside from the obvious - more - appeal :bgrin:, the Nailhead has a much larger following and many more enhancement parts. Perhaps not so obvious is that with its stock compression ratio of 10.25:1, it should run nicely on today's anemic premium gas (the original 11:1 high-compression 300 won't). My surfing the web uncovered one more unexpected benefit: the Nailhead equipped 1965 Skylark GS got 12.2 mpg at the time. My car was rated 12.7 (and indeed that was accurate). 100 more hp and almost the same gas mileage - where do I sign! :laugh_3:

So enough daydreaming. Obviously it must be possible to put a 401 Nailhead in a 65 A-body since Buick did it. My question is: can you make a Nailhead transplant into a car originally equipped with something else? Is it "reasonably straightforward" or a pain in the whatever expletive you prefer to delete. Reading around the forum, it seems like the engine mounting points should be the same and that it should be possible to bolt the Nailhead to my transmission without adapters - true? The car already has the heavy duty radiator, would additional cooling upgrades be desirable? Looking at photos of the 65 Skylark GS engine compartment, the only difference I could see was that the battery has been moved to the driver's side. Are there other gotchas in making such a transplant that aren't obvious?

Has anybody else performed this transplant? Why or why not? What do the 1965 Skylark GS folks think about their cars and engines?

Obviously this is still more daydreaming than not and my wallet may veto the horsepower upgrade. Still, I would be interested in what folks think about the idea.

Thanks for any and all pearls of wisdom!


Edouard in Orinda

P.S. Discussion later expands to consider other late 60s Buick V8 engines like the 350 and 455 - see below:
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Much easier to install a Buick 350 than a "Nail". Although I'm a "Nail" guy there are MANY things that have to be changed in order to install a "Nail". Engine mounting plates to the frame. Engine mounts. Then the plates on the engine. A "NailHead specific trans. weather a ST300 or ST400. GS only exhaust manifolds or headers. Rear sump GS pan & GS specific oil pick-up. Crossflow radiator instead of downflow. Engine compartment wiring. And others I may have & surely forgotten about. Not just a bolt-in swap especially for someone without the nec. experience or fabrication skills. Not saying it can't be & hasn't been done by countless others. Just time consuming & $$$$$.
Just my thoughts.

Tom T.


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Okay, how about a Buick 350 transplant then?

Dear Tom,

Although I'm a "Nail" guy there are MANY things that have to be changed in order to install a "Nail"

Thanks for your feedback. My inexperience is showing, as I had hoped it wasn't that drastic an operation. Golly, you are making up my mind in a hurry!

Much easier to install a Buick 350 than a "Nail".

I may be just as sorry to ask this, but is truly "easy enough" to make aiming for a Buick 350 worth considering? The stock performance of the Buick 350 wasn't that much better than the existing 300 cu V8, but it is far more popular engine, so it offers many more possibilities.

Thanks again for your feedback,

Sincerely, Edouard


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Everything that Telriv said of the 401 swap will be the same for any engine swap. There will be lots of time and money involved. Fixing your existing engine or replacing it with another 300 is in my opinion the best option for the easiest and least expensive way to get your car back on the road. The best way to put the 401 in your car would be to find a GS donor car. That might be a little tough. Not impossible but tough especially if you are on a time schedule.
You have mentioned the 11 to 1 compression of your 300. If you have your engine rebuilt I would assume that they are going to bore the cylinders to the next oversize. You have stated the miles on this motor being very high, 200,000+ so I'm assuming this. I don't believe that the 11 to 1 pistons are still available in the general after market. So you would be using lower compression pistons and you wouldn't have to worry about using today's gas.
The Buick 350 would be another alternative. It would still be best to find a complete donor vehicle to get everything that you will need. If it is in good condition it will provide plenty of power for your wagon. Regardless of what the factory ratings were it still has 50 cubic inches on the one you have now and that usually means more torque.


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I was wrong. Egge Machine still lists the 11 to 1 pistons for the 300 Buick at $300 a set. They also list the 9 to 1 pistons as well which would be a much better choice for today's fuel.
The Buick 300 engine only had 11:1 compression in the 64 engine with aluminum heads. These same pistons were used in 65 300 engine, but only produced 10.25:1 compression with the larger combustion chambers in the iron heads. These same pistons and iron heads were also used with the 340 engine (stroked 300) for 10.25 compression in 66 and 67. You can get away with 93 octane fuel in all of those engines (depending on timing). Aluminum heads allow extra resistance to detonation. Generally aluminum heads can be run one compression point over the same heads in iron without detonation. Buick knew what they were doing with the 11:1 ratio in the 64 300.

The buick 340 and 350 will bolt directly in place of the 300. The same mounts, transmission and accessory drives can be used. The 350 will require new exhaust manifolds as the head exhaust spacing is different between these engines (same crank is used in both though). The 350 was made from 68 into the 80s and has a lot of aftermarket parts available. The 340 was a two year deal in 66-67 and evolved into the 350.

Once the engine changes are made, you may not feel any difference in power without considering upgrades to the transmission and rear as well. The three speed TH350 will bolt in place of the two speed ST300 without modification to the mounting points or driveshaft. A Sport Wagon from 66 and 67 would also make a good donor for a 340, ST 400, and driveshaft that are a direct swap. Most of the wagons came with al least 3.23 rear end ratios, but standards had a 3.36 that would pick up the pick up a little. Now you have more to think about!
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Thanks, indeed much more to think about!

Dear Steve (Dr. FrankenBuick), BigRivy, and all, :thumbsup:

Thanks so much for some short but incredibly important comments! Indeed, I now have some much clearer choices and a practical path to pursue either way.

To help folks (if it can be called help! :bgrin:) I created a blog entry that describes my thinking up to roughly to this moment http://www.teambuick.com/forums/blog.php?b=134. It also has a cute picture of my Buick wagon as "moving van" :car:

The nitty gritty details that matter is that this car has gotten some modifications along the way. I can't put in a TH350 transmission without replacing the one that's already there! Also, along the way I've had miserable struggles with the original Carter AFB carburetor. Right now the car has a Edelbrock Thunder carburetor (1801). Since the car is at the body shop, I can't be sure, but I'm almost certain that the car has the crossflow radiator as its heavy-duty radiator upgrade.

Thanks to BigRivy, I now have the pointers so that I can specify the 300 cid V8 be rebuilt to its original factory specifications (or modestly enhanced.)

Thanks to Dr. FrankenBuick, I can also consider the Buick 350. The performance gains is certainly nice, but the issue will probably be decided mostly on how comfortable I am with the status of the 1965 engine being so "low" on the interest level of suppliers. Right now parts are available, but there is only so much you can do for an engine that was produced only a few years. If the goal is to keep the car as a practical vehicle, there is a lot to be said for having an engine in the car that was in production for decades.

So, it's time for me to go back and think! Certainly, part of that thinking will involve seeing if I can find an engine rebuilder who I trust to do the job correctly and will do the work for something less than an arm and a leg!

Thanks to all for all the great help and Happy New Year!! :finish:

Cheers, Edouard

P.S. Just an unfortunate "gotcha", but I just checked the EGGE machine company website and their rebuild kit for the 300 cid V8 is described as for an 11:1 compression ratio http://www.egge.com/kits?make=BUICK&year=1965. I don't know if that's a typo on the website or an error in assuming the 64 and 65 engine used the same compression ratio. The 66 340 engine kit has the correct 10.25:1 ratio.
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Team Buick data much better than faulty memory!

Thanks "Dr. FrankenBuick" ! :shield:

There is some more information on the 65 engine compression ratios and engine codes here: http://www.teambuick.com/reference/years/65/65_engine_number.html.

Let me indeed second that suggestion! Surfing the web has the hazard of dredging as much bad information as good. When in doubt, go back to the Team Buick references rather than the last spot you "surfed".

It doesn't help when you "remember" that a car was rated 270hp, when the service manual stubbornly agrees with Team Buick - it was only 250!

Optimistic dementia? :bgrin:

Thanks again to all!

Cheers, Edouard


Active Member
engine swaps........

I have had a 64 skylark in the past that originally had the 300 /2bbl engine.... that car had the same frame as the 65 GS.... down thru the years i rebuilt the original engine to the 300 ''optional'' specs..... that was the best, most fun combo that I had in the car.... broke less and raced more..... then I installed a nailhead.... and tom is right.... there are special things that you have to have.... the frame mount pieces, the engine plates, the motor mounts,,, the right radiator,,, the exhaust manifolds,,, I put in a th 400 with a switch pitch,,, and I had to fab a rear cross member.... and shorten the drive shaft 5''.... and change starters..... and some wireing to accomodate the changes that I made.... but the car was a brute and was not beaten on the street for 2 years..... then I put in a 430/ stage 2 combo... and that was the most powerfull set up..... of all... but it would not hold up because i went with 12 to 1 pistons and every time I got down on it hard the headgaskets would pop.....
If I were going to do all that over..... i would go for a engine combo that was exactly the factory set up for a GN.... except in a 65 body.... that will be reliable and get good mileage..... or....
go with a 455/ th400 combo.... and keep to stock specs.... basicly a bolt in swap ..... with lots of torq......
Rebuilding the engine that is already in there is different from engine swapping.... when you start swapping engines , you are moving into a higher level of hot rodding.....


Active Member
Talk me into a 455 swap . . . (what am I DOing!?!??)

Hi DocModisett and Buick fans, :shield:

Decisions . . . decisions . . . .

. . . .
If I were going to do all that over..... i would go for a engine combo that was exactly the factory set up for a GN.... except in a 65 body.... that will be reliable and get good mileage..... or....
go with a 455/ th400 combo.... and keep to stock specs.... basicly a bolt in swap ..... with lots of torq......
Rebuilding the engine that is already in there is different from engine swapping.... when you start swapping engines , you are moving into a higher level of hot rodding.....

Well, I'm trying to dance between something of these two extremes. I grew up with the 300 cid V8. So I know this engine right down to tuning it by sound alone. If I could get even a modest performance rebuild that I really could just would be done right, I think I would feel fine with that. However, as I noted in my blog entry (http://www.teambuick.com/forums/blog.php?b=134), this isn't a stock Buick anymore. The car has been in the family since 1968, so we made changes along the way to cope with things like the OPEC oil embargo. So the car has already a different transmission: HydraMatic TH350.

Reading other postings on Team Buick suggested that I consider another transmission mousetrap: the 200-4R. If I understand correctly, that can be mounted into the existing space with less modifications than TH400. Apparently, at least California Performance Transmission claims they harden the 200-4R to handle any horsepower you can practically stick in the car (opinions on this would also be appreciated.)

Right now the car is limping along with a sick engine that isn't producing 200hp. My hope was that I could get 300 cid V8 a bit beyond it's factory rating of 250hp into somewhere between 275-300hp. I thought matched with the 200-4R would make a pleasant but still visually authentic daily driver.

My "plan-b" was to look at the Buick 350, if I couldn't find someone who could competently rebuild the 300. The 350 is a modest horsepower bump and was built for much longer, so parts hopefully wouldn't be a problem anymore. However, it hasn't escaped my attention that I could go with a 455 instead as another esteemed member of the Buick brotherhood has done: http://www.teambuick.com/showroom/showphoto.php/photo/635

So what are you'all waiting for . . . . aren't you'all going to talk me into going whole-hog and trying to stuff a 455 into my humble workhorse 65 Special Wagon . . . .

What am I DOing!!!! :clonk:

Thanks as always for the great advice and a few smiles along the way!

Cheers, Edouard


Active Member

Well, lets take a real hard look here,,,,having done the nailhead swap in the past, to me , it was a fairly easy swap , if you can gather up the correct parts.... that is the only real problem with going the nailhead route,,,,but if I were going to build a nailhead to go in there , it would be a 425.... with a switch pitch th400.... that way i would have a strong running , reliable, engine /trans combo that would stay with the best of them....and i would not have to do a bunch of expensive mods to make it live.....with the forged steel crank and forged steel rods and the good oil system and good cooling system it is very dependable.... + a switch pitch th4 will put massive amounts of power to the ground.... and with a gear ratio like 3.08 or 3.42 it will get reasonable gas mileage....my personal GS is set up with a 410 block, good hot cam, and my ''Doc dual plane'' intake mod and a holley 1050 cfm three barrel carb.... port matched exhaust manifolds and 2 1/4 pipes and turbo mufflers.... and my red neck ram air , air cleaner assembly....
You could adapt all the modern stuff to the 300 but that would be a expensive can of worms.... [ efi ] ect.....
If you change to a nail you will have to change the motor mounts/frame pads/starter/exhaust manifolds/rear crossmember/ exhaust pipes/ air cleaner assembly..... and you will have to change those exact same things to install a 400/430/455...... but the massive amounts of torq those engines will reliably move the car....
I consider the nailhead to be more reliable than the BBB,,,, no oil system mods need to be made, the head have 5 bolts per cyl... not 4......forged steel rods, crank ect.... nails have 2 things you have to watch for.... the harmonic balancer will very rarely crack in the keyway in the hub.... and with high mileage the factory cast pistons can fail.....they get brittle and start coming apart.... but in 50 years of messing with nailheads I can count on one hand the engines that i have found that have done those things....
as for looks,, no engine looks as good as a nailhead dressed out....period....
but nailhead or big block, either one , if done to stock specs will do fine in that car....
Hello Edouard
Here is my Wagon: 65 Special...

I installed a 455 into it a while back. There sere some complications for my swap - plumbing for radiator, fuel, exhaust and power steering. Took me a while to get done.

This i s my Skylark: it had a broken 300, and I had a 350 in a parts car. The instalation went way easier, as I used the 300's pulleys and alternator and ps pump - all bolted to the 350 easily. I have a TH350 transmission in it- kept the 2.78 rear end-and it is excellent. Almost better than the wagon for driving around.

Here is my 65 Skylark Gran Sport: I had collected ALL the parts to do a swap like Doc suggested, engine mounts, manifolds, radiator, wiring harness, etc. I used most of them to get a 401 into this car. Its not done yet...


So for ease, power increase, drivability I think of the 350.
For lots of power, 455.
For the coolest power, Nailhead...but that choice has $$$ and time considerations.

There is a fellow Ohioan that has done the Nailhead swap into his 65 Special Wagon. I have not heard from him for a while!:finish:


Active Member
Wow! such useful info! Thoughts on towing?

Hi DocModisett Ted, and Buick fans, :shield:

Thanks DocModisett for your review and thoughts of putting in a 401 Nailhead in a 1965 Buick Special. I'm a newbie to all this, but I can already appreciate how unique and attractive the Buick Nailhead engines were. However, this looks a little too involved for what I would want to get myself into. I sure am glad other Buick gurus have done it! :thumbsup: I greatly appreciate your work! :hurray:

Golly Ted you lay out for me all the possible options in some beautiful cars! :car: I'm tickled pink just to see a picture of your 65 Special Wagon! My wagon has been feeling very alone - now I know she has at least 2 sisters still alive! :waving:

The more information I collect and the feedback I'm getting from various folks, it seems to me that either getting the original 300 back or making the modest upgrade to the 350 is the best compromise for me. I'm still hoping to use the car for things like vacation trips. So inconvenient truths like gas mileage should still matter to me. I'm definitely not trying to do anything like racing.

However, the 455 has one appeal that I cannot ignore: additional tow capacity. Is anybody using a 65 Buick for towing? (besides: http://www.teambuick.com/showroom/showphoto.php/photo/635) :bgrin: Any opinions on equipping these cars for towing? I don't know if I'll ever get around to towing something heavy, but if I do, I'd better factor that into engine selection decision.

Thanks again for all the great input!! :rod:

Cheers, Edouard


Active Member
Towing for a 65 Buick Special - the upper limit!

Dear Team Buick :shield:

Cruising around the Internet, I found one example of a 1965 Buick Special Wagon being used to do some extreme towing. It is the 455 equipped wagon that in the galleries(http://www.teambuick.com/showroom/showphoto.php/photo/635) This car has a dedicated website: http://www.gmcguy.com/1965_buick_special_station_wagon.html. It shows that the humble 65 Buick wagons can pull quite a load when given the right enhancements. However, if you visit the slide show about the trip to the GSCA Nationals, you'll see that this truly extreme towing . . . .http://adobe.kodakgallery.com/Slideshow.jsp?mode=fromshare&Uc=5oqfg2z.8vcb0fj7&Uy=751q7p&Ux=0 It's a good thing that my towing aspirations are much more modest!! :car:

Cheers, Edouard