"Bulletproof" Engines

In the various automotive circles, there are certain engines which everyone refers to as being the “best of the best” or bulletproof, or what have you. I’m not talking modified engines, but ones stock from the factory. Each automaker seems to produce one or two of those engines. For example, there’s a slant six engine that Chrysler put out in the 60s that I’ve never heard anyone say anything bad about. In fact, I’ve heard people say that they specifically bought that car over a V-8 equipped one, because they knew that the slant six version had the more reliable engine. Another Chrysler engine that I’ve heard positive things about is the 383, but each car maker seems to have one or two engines that no one complains about. There’s also the converse of that, people will tell you never to buy a car with a certain engine in it, because that engine’s nothing but trouble. These engines also tend to have a relatively short production life.

My questions are:

1.) What is it about those engines that makes them so more reliable than their counterparts?

2.)Is it just that there are certain configurations that are better than others?

3.) Why don’t the automakers produce more engines like that?

Well, i would have to say that toyota’s i22re is a great engine. I’ve never heard anyone complain about it (other than the timing belt guide.) I’ve heard of them lasting 300,000 miles between rebuilds and still having great compression on all cylinders.

In engineering there’s always a tradeoff between performance, strength and reliability. Make something lighter and it’ll move faster, but break easily. Increase the power and you stress the structure, reducing its life. The “bulletproof” engine is never the top-performance engine in the lineup.

Another thing is that most designs have a weak link somewhere. Even if most of the engine is overbuilt and tuned down for durability, it just takes one weak spot to make it unreliable. The perfect machine is one where all the parts are made equally strong - just strong enough to do the job but no more. Like the “One-hoss Shay” in Oliver Wendell Holmes’s poem. You can get close to that ideal if you stick with the same engine design for a long time, making minor modifications to strengthen the weak spots.

Indeed scr4, you hit the nail on the head there.

All things being equal, a 300hp engine which is 7 litres in capacity and works extremely free of stress will always, without fail, outlive and out “maintain” a highly stressed 2 litre turbo engine say, which delivers the same horsepower.

Oddly enough however, within reason both of those engines will deliver similar fuel consumption figures - and the reason for that is as follows…

Regardless of engine design, or engine breathing method, or valve actuation, or cam shaft placement - all things being equal - horsepower costs fuel. Every internal combustion engine requires a coolant system of some sort to prevent the engine block from melting. Accordingly, even in the most esoteric Formula One engine, still to this day after 100 years of development, over 60% of the potential energy in a given amount of fuel is lost to the coolant system. When you throw in mechanical friction as well, due to such factors as your gearbox and your drive train - a modern F1 engine delivers 38% fuel liberation to the back wheels. In most road going engines, that figure drops to somewhere between 32 and 36%.

Hence, the issue is not so much what engine configuration works best, but rather, how much horsepower do you truly require in your daily life? Sure, some folks like to have 500hp in an AC Cobra replica, but that 500hp still burns the same proportionate amount of fuel if you see what I’m getting at.

So, once you’ve got an idea of your horsepower and torque requirements, then in theory, an engine which delivers those requirements in a lazy non-stressed manner will ALWAYS outlive another engine which delivers the same performance, but does so in a highly stressed manner.

Obviously, a heavier vehicle will influence fuel consumption per distance travelled compared to a lighter vehicle too.

So, in short, after all these years, the consensus is this - a well tuned push rod 2 or 4 valve per cylinder engine with a modern electronic fuel injection and engine management system is going to be the winner - at least in terms of longevity. They have fewr things in them which can break - which in turn means that they have fewer “weak links”. And THAT is what we perceive as being a “bullet proof engine”.

Down here in Australia - in the late 60’s, GM, Ford, And Chrysler all invested heavily in local car manufacturing facilities. As you know, Australia’s a pretty hot and rugged place - so our locally designed engines were modelled on the American formula - as averse to the European or Japanese formula. It’s still very common to see 30+ year old Aussie made cars with “American style” engine designs working like old workhorses.

Indeed, more than a few Aussie tweaks and refinements ended up in their parent companys back in Detroit as a result.

      • Bulletproof engines are basically just relatively low-power-density engines. I had a truck that had one such “bulletproof” combo: an 82 Chevy inline 6 [258 cu. ins?] on a four-speed manual transmission (that means 3 forward speeds+reverse). The engine was so low-powered that it didn’t put near the stress on the transmission that it could handle (the same trans was used in vehicles with 8-cylinder small blocks [350 cu. ins] ), and the engine didn’t get anywhere near its redline in 3rd gear with the accellerator pedal floored (the truck would just barely go about 85 MPH tops). This was basically a full-size truck with a small-truck engine on a full-size vehicle transmission… The previous owner had even occasionally pulled light trailers with it on the bumper hitch. I gave it to someone as a fixer-upper because it wouldn’t pass emissions tests and needed an engine rebuild at 145K miles.

That truck always ran but was slow though; the engine ran fine and was kept maintained but sometimes on the highway, loaded 18-wheelers would pass me while going up big hills because I had to use second gear–>~40 MPH.

There are plenty of “bullet-proof” engines out there. Most of them are in trucks and farm machinery. This is a logical extension of what was posted earlier.

When building a car, the manufacturer is looking for performance, fuel economy and reduced weight. Hence, lighter, less durable parts. The same factors are not of much concern for industrial and agricultural applications. Most of the engines (cars) are resold after a few years so the original buyer doesn’ t care if the engine has a short life.

Stock car racing engines are the perfect example. You can take a standard car engine block, put in lighter parts, tune it and gear it differently, increase revs and get a high-performance engine out of it. Of course, it will have to be rebuilt after 500 miles but hey, its fast! The same essential design in a standard care will go for over 100K miles without a rebuild.

The old British sports cars used a tractor engine that was adapted to the car. Then, of course, the mechanics would get their hands on it and modify it for performance giving up durability in the process.

To get the quick and dirty answer you should probably look at what engines are being used in taxi’s and police cars.

For an engine to be bullet proof, it has to live up to that reputation. They don`t come out of the factory as a new type of engine with the label “bullet proof”. It usually gets the reputation after being tested for several years in different model automobiles.

scr4 - never say never. Some would argue that the 3.8 liter that GM uses (Grand National, Grand Prix) is bullet proof. That engine was the cornerstone of high performance for many years. The Chevy 350/327`s have been used as high performance motors and they tend to be very durable. I have not been able to grenade a 350 to this day.

Take a NASCAR motor, knock down the comression to about 10-1, put a mild cam in it and you would have a bullet proof motor - guaranteed. The cost would be prohibitive though.

I can’t imagine the things like the main and cam bearings would last very long. They are designed to be sacrificial, despite the lighter loading of a lower compression ratio and cam specs.

Also, driveability in sub-optimal conditions is questionable. NASCAR motors have no engine management controls, and cooling systems are not engineered to real-world specifications.

I realize I’m talking about making a rhino tap dance, but the real definition of “bulletproof” is operating within the expectations of the driver, no matter what.


Stay away, no RUN FROM an AMC 360! The distributor drive gear on the end of the cam likes to eat its partner (and vice versa sometimes, which is a REAL pain in the ass!)

Bullitproof? Not even Rubberbandproof!

For Bullitproof, I would nominate Hondas RFVC 500-600 cc singles and Suzuki’s DR 350 engine.

Fagjunk Theology: Not just for sodomite propagandists anymore.

actually… when nascar teams take motors out because they question the durability, remember they need that motor to last another 3 hours / 500 miles AT WIDE OPEN THROTTLE. These places sell the nascar parts to the average joe, and you could build a way lower compression nascar motor (who needs 800hp anyway) and it would probably last forever…

What the hell, Ive got a 401 in my AMX and a 360 as a spare. Ive never heard of this problem.

I wouldnt feel comfortable putting a brick on the gas peddle of any other car until it ran out of gas. Thats pretty much what they do to the NASCAR engines. They are way overbuilt. I dont see why the bearings would be an issue, they certainly dont want to spin one of those during a race.
These engines run at 8000+ R`sPM for 500 miles with 15 - 1 compression. I stand behind what I said about cutting back on the internal loads and these engines would run forever - like something clever said.

Many car manufacturers use WOT (wide open throttle) testing. Cadillac in particular does extensive testing on its Northstar system. An example:


On a Northstar we don’t usually bother with the LD8, we run everything at 6000 RPM, 300HP…continuous…300 hours. That is like driving 150 mph for 300 hours, or about 45,000 miles actually. If you can drive the equivalent of twice around the world at 150 MPH then you are not the average customer. /quote]

You can read the rest here:


Ouch… Glad I didn’t opt for that desktop publishing gig :smiley:

If someone could put a shine on that sneaker, it would be appreciated…

a logical extension of the idea with the NASCAR engine would be an F1rpm rather than the 9000-10000 that they usually scream along at. Motors for rally cars driven under ‘normal’ street condtions work here too. An engine/trans built up for the Dakar rally would do nicely in Phoenix idling around in gridlock with the A/C blasting. Some race engines might be considered bulletproof if they make it through a day’s worth of racing without needing to be pulled apart (ie top fuel drag).

As for specific examples the GM 3800 series of engines are a solid runner, I have a much abused 87 buick with the naturally aspirated version and associates with grand nationals (the turbo charged version) trucking along strong at over 100,000 miles with no major repairs.

The definition of bulletproof is vague though, its arguable that the 38 year old 430cui in my Lincoln is bulletproof, after almost 4 decades and 118,000 its running well enough that i have no problem using the car as a daily driver (not that i do, i just can), but if something breaks that engine could lose its bulletproof classification because parts are hard to come by. Toyota/Honda engines might be considered bulletproof because a repair entails going to the junkyard and bolting up a ‘new’ part and some gaskets where as a less common engine that is in demand (such as the AMC 360) could involve a months long part search for something that MIGHT fit after some machining. the Ford 3.8L is reliable EXCEPT for its headgaskets, can it be considered ‘bulletproof’ if the engine will need one major repair in 200K miles or not?

What im getting at is that ‘bulletproof’ is a very relative term and depends on the person who uses it and/or repairs it.

Hey, a new MPSIMS game… Sequential User Names! :slight_smile:

Whoa! Where were you in my post about bench testing!? Any other cites about engine torcher?


Bullet proof is in the eye of the beholder. I would take a $100,000 NASCAR motor over the Northstar. Why do they cost so much to build? They use the best parts that they can get while staying wihtin the NASCAR guidlines. The best of everything. I`m sure there have been a few Northstar motors that have failed during the break-in period, just as there are NASCAR motors that have not made it through Happy Hour. You could build a small block motor with 1,000 hp for much less than what NASCAR builds their motors for, but you would lose the durability contest quickly.

Here is an excellent tech page for high performance engine building - talks about all aspects of high performance racing engines. Scroll down to the tech talk part and browse the articles. Excellent reading for anyone interested in how these motors come together.

In one of the articles he discusses the durability of bracket racing engines, which are under way more stress than a NASCAR motor.