The Pontiac 400 engine is a member of the famous “GM family” started with Oldsmobile. It was initially created in 1968 and used the same block as the 350 V8 – this was a tedious afternoon project to save money, making it one of the most iconic engines in history. Because it was a bored-out 350 engine with a 400 badge, not many people knew it was a 400. They also took the time to grind off part of the 350 V8’s casting number and stamp in a new one reading “400”. In the late 70s, they were only available in Trans Ams and Bonneville’s but were used in Firebirds and GTO’s into the early-mid 80s.
The Pontiac 400 engine was designed to be a luxury performance option at an affordable price – this means that it had more power than your average car but still didn’t cost close to $10,000 as most other American Muscle options did. The only other engines on the market that was almost as powerful (yet still affordable) were Ford and Chrysler’s 400 cubic inch engines. The Pontiac 400 engine had more power than both, but it also came with a few problems like any other car built back then.
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Pontiac 400 Engine Specs
The Pontiac 400 engine started in 1968 using the same block as the 350 V8. It was equipped with a 2-bolt main bearing block, bore at 4.125″, stroke at 3.75″ for 401 cubic inches. The compression ratio came in at 9.5:1 (this means that you could run this car on pretty much any gas – not like cars today). It had an aluminum intake manifold coupled with a Rochester Quadrajet 4bbl Carburetor and Comp Cams Grind camshaft. The 400 was able to make close to 300 Horsepower stock (not bad at all for the late ’60s), and this number goes up when you get into the Super Duty editions.
The 400 engine block went through many changes throughout its life, but its main features stayed pretty much the same. It was equipped with a “Rocker Arm Shaft” to make it more efficient at higher RPM’s, Oil Pumps were improved and made bigger (but still pretty pathetic by today’s standards), and the heads went from a 2-bolt design (like the 350) to 4-bolts in 1974. The 400 engine block was equipped with freeze plugs as well – this is something that 99% of car engines today don’t have. There were also plenty of other minor changes such as drillings, different types of crankshafts, etc.
The 400 engine came equipped with a 2-Bolt Main Bearing Block, Bore at 4.125″, and Stroke at 3.75″. It had an Aluminum Intake Manifold coupled with a Rochester Quadrajet 4bbl Carburetor (early models were equipped with regular quadratic carbs). The compression ratio is 9.5:1, and the 400 HP (1968-72) and 350 HP (1973) made around 300 ft/lbs of torque at 3600 RPMs.
The Pontiac 400 engine was a prevalent option from 1968 until 1979 when it was discontinued – the price tag associated with this car gave other cars such as the Buick 350 the ability to become such a popular option. It was available in Trans Ams and Bonnevilles (1968-1973), Firebirds (1974-1975), and GTO’s (1976-1979). After 1979, it was replaced by the Buick 350 V8.
Is a Pontiac 400 a good engine?
The Pontiac 400 engine is a tremendous classic engine for smaller cars. It can give you lots of power and torque at a low price. The only problem with it is that not many people know how to work on them, so finding someone who can fix it when something goes wrong may be challenging, depending on where you live. Also, because the engines are so old, they are bound to break down every once in a while.
Pontiac 400 Engine Weight
The 400 engine weighs around 575 pounds. You can find more Pontiac Engine Specs right here.
How to identify a Pontiac 400 engine?
Pontiac has been making cars since 1926. You can tell if it is a 400 by looking at the door for the engine size, or you can look at the VIN. If it’s a 1968-1973 Trans Am, it will have 350 written on the door by the VIN, 1974-1976 it will have 350 written on the door, and 1977-1979 it will have 400 written on the door. It will be noted on the VIN near where the engine size is located for any other car.
Common Pontiac 400 Engine Problems
One thing to always watch out for are Heads made from 1971-1974. They have aluminum heads that are very prone to cracking, so be careful when buying one of these cars – you might want to buy a car with the “H” Heads instead or skip this car altogether.
Another common problem is Oil Leaks. The head gasket and rear main seal can leak pretty badly if not maintained. This is pretty normal for engines this age, but if you drive it too much with lousy oil leaks, it could become a very costly repair or, even worse – engine replacement.
Checking the Valve Covers will also be necessary. If they aren’t in too good condition, you should think twice about buying them. It is pretty normal to see the inside of them rusty, and if this is the case, they can be repaired by welding – but don’t expect it to last forever.
The 400 Engine was a perfect engine for its time because so many people were buying these cars (especially in Trans Am form), but that doesn’t mean you should run out and buy one right away as soon as you get your license – do some more research first before taking the plunge!
One thing I tend to forget to mention is Transmission type. If you’re planning on doing a Pontiac 400 engine swap, ensure it has manual transmission because automatics will not work with this engine (unless it’s already been swapped for one).
If you are thinking about buying a Pontiac 400 engine, make sure to do some research on it first. It’s not the same as other engines, so don’t take these problems lightly. If you have any more questions or need help with your car, post below, and I’ll try to answer them!
Please make sure to comment and leave feedback about this article! I am also open to suggestions of what you would like to see in future articles.
Further Reading: How To Identify Pontiac Engine Blocks
Dmitry Petrov is an engineer who specializes in materials science, and has a deep passion for all things related to automotive technology. He is a true motorhead at heart, and spends much of his free time tinkering with engines and studying vehicular dynamics.