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Posted: **Tue Jan 07, 2014 2:01 am**

Why does using different materials for blocks and heads reduce the MTBF?

I my experience working for a major auto supplier. A few examples come to mind. The current Ford F150 Raptor uses a 6.2L engine. The engine uses a aluminium head and a cast iron block... it is my understanding that Ford chose cast iron for the block material for increased durability as it's a heavier duty truck engine. Also the older Ford triton engines... 4.6L Mustang and 5.4L F150 (and others) engine. Both used aluminium (maybe AlSi), heads and cast iron blocks. The current Ford 5.0L is aluminum block and heads. I could see using cast iron heads on an aluminium block might reduce durability as the block is the heavy torque end, but iron block with aluminium heads should be ok. There are also a few variants of some GM engines I worked on that use cast iron blocks and heads. I was also looking into the purchase of an Audi 2.0T recently, which I believe is also a cast iron block with aluminium head. I'm sure there are many other examples.

Posted: **Tue Jan 07, 2014 3:07 am**

Iron and aluminum expand at different rates when heated... in early cars this caused a tendency for head gaskets to fail prematurely. Modern advances in gasket technology among other things are why engineers have been able to make it work more reliably so the MTBF penalty is not as severe in the later years.

On a slightly different note: the most reliable engines I've owned had bi-metal construction, and the least reliable ones had the same block/head construction. :lol:

My Ford Thunderbird Turbo Coupe blew a head gasket: all iron
My Volvo 740 Turbo ran well right up until I sold it: iron block/aluminum head
My Ford Taurus SHO ran well right up until I sold it: iron block/aluminum head
My green Lincoln Mark VIII blew a head gasket on the previous owner (which gave him an excuse to buy a set of ported heads :mrgreen:

): all aluminum

So... ummm... my experiences with bi-metal engines seem to suggest the opposite, but the physics are what they are.

Posted: **Tue Jan 07, 2014 10:39 am**

Slim Jim wrote:On a slightly different note: the most reliable engines I've owned had bi-metal construction, and the least reliable ones had the same block/head construction.

Interesting. My experience with engines has only included single metal construction, my current car being all aluminium and the Ford being cast iron, and both have run very well.

However my dad had an old Nissan with an iron block and aluminium head (or maybe the other way around) for his first car and the head gasket failed, in his case leading to complete engine failure. I think it also caught fire.

I do agree with Slim Jim, advances in technology have made bi-metal engines such as the Toyota 2JZ and the Nissan RB26, both of which have a strong reliability.

Posted: **Sun May 25, 2014 9:59 am**

I think the penalty for Iron block/Aluminium head is far too harsh. It basically halves the lifespan of the engine and this is far too much.. Maybe a small decrease in reliability, and larger service costs(head gasket replacement) would be more appropriate.

I can't think of any real life engines where the use of 2 different materials made that big of a diffierence. The Nissan L series engine is a great example of this. Despite Inline 6's tending to have issues with head gaskets, these problems, and any problems really, are very rare on L series engines. I've seen L series engines with over 400,000 miles and still on the road..

I can see where a Aluminum block and Iron head could be a problem, but not so much the other way around..

stephenl9000 wrote:
Slim Jim wrote:On a slightly different note: the most reliable engines I've owned had bi-metal construction, and the least reliable ones had the same block/head construction.

I do agree with Slim Jim, advances in technology have made bi-metal engines such as the Toyota 2JZ and the Nissan RB26, both of which have a strong reliability.

I would say that newer nissan RB and Toyota JZ engines have far more issues with headgaskets from what I've read than the old L series engines. Then again that could in part be due to forced Induction.. I know RB engines are bad for headgaskets, despite the internals being able to handle large amounts of power and torque, the stock headgaskets are a common failure on tuned engines.

Posted: **Sun May 25, 2014 1:14 pm**

I'm currently driving a 22 year old 4a-fe corolla, iron block /w aluminum head. Over the 271,500 miles it's gone I've had a few problems, but never with the engine. That said I am fairly sure Toyota has a few points in engine tech, especially back in the early 90's.

Posted: **Mon May 26, 2014 9:21 am**

nialloftara wrote:I'm currently driving a 22 year old 4a-fe corolla, iron block /w aluminum head. Over the 271,500 miles it's gone I've had a few problems, but never with the engine. That said I am fairly sure Toyota has a few points in engine tech, especially back in the early 90's.

Yeah, those old 4A engines were pretty bullet proof.

MTBF will be changing to reliability in coming updates, but reliability is kinda a subjective term.. In my mind I see reliability as the potential for longevity with an engine, and its internal parts, not things that are serviced or replaced like headgaskets.. So I don't think the Iron block/aluminium head should really have any reliability malus, instead it should have small increase to service costs to offset the possible increased replacement of headgasket. It shouldn't be too much though, I doubt many cars get more than one headgasket replaced in their lifetime, and some never need it..

There are some engines that can be quite reliable, but need more regular service. Turbo cars like my Saab 9-3 are a good example of this.. They can do upwards of 400,000km which is pretty impressive for a small turbo engine, and with proper maintenance and regular oil changes the Turbo charger should last the life of the engine as well.. However, if you don't change your oil enough it will break down from all the heat and you'll start to wear things.. People who neglect oil changes on these cars end up replacing turbos, timing chains(which are supposed to last the life of the engine) and getting bad sludge buildup that eventually leads to engine failure..

Posted: **Mon May 26, 2014 5:19 pm**

I would think to get a good reliability rating in the game with multi material engines would be to really increase quality on the heads (for any era). To face the obvious it has taken many many decades of R&D to get aluminum to work to any standard to the stress of a motor. Aluminum is very unforgiving with stress, and doesn't hold up nearly as well as iron. The fact that aluminum expands and contracts at a different rate can be overcome, but it would require more time spend on R&D compared to iron block/heads or aluminum block/heads. Also aluminum wasn't a good head or block material until the 70s. Some older folks can tell you about the first all aluminum mass produced and successful V6 (The GM Fireball 215). Buick, Oldsmobile, and Pontiac started the design of the all aluminum engine starting in 1951 and started putting them in the 1961 model year. The glycol alcohol (antifreeze) corroded the cooling galleys on the all aluminum block and heads (some were iron, some aluminum). They also had problems with warped heads with higher compression on them. They got a bad rap for blowing head gaskets and over heating often. Rover then bought the tooling, and design of the 215 and I think Rover tried several variants of aluminum and iron block/heads. They were still building the 215 up until not to long ago. Goes to show the idea of aluminum as a tempting material for engine design is worth all the trouble! Proving to make a reliable multi material engine (in general) requires more attention to design.

Just my 2 cents

Posted: **Mon May 26, 2014 5:33 pm**

You make some good points.. I didn't consider the really early aluminium engines when I wrote my post, but it seems to me that by the 70's the issues with iron block/ aluminium head were mostly dealt with.. Maybe the games tech system that we have yet to see is the solution to this. So if you develop the aluminium technology enough it becomes a non issue..

The thing that does bother me though with the current system is that there is never any reason to mix materials unless you are trying to recreate a historical design, or are trying to make a bad engine on purpose.. Why choose aluminium head on an iron block when you can go all aluminium and have none of the reliability issues?.. It doesn't make for good gameplay.

Posted: **Mon May 26, 2014 10:03 pm**

90 and beyond you can go iron head aluminum block with a few tech points to the head and get better power, less emissions, and only a small hit to mtbf.

Posted: **Mon May 26, 2014 11:16 pm**

nialloftara wrote:90 and beyond you can go iron head aluminum block with a few tech points to the head and get better power, less emissions, and only a small hit to mtbf.

By the 2010s, the MTBF hit is very small, and could be considered insignificant. On a semi-related note, cast iron blocks will give you a few extra horsepower.

Posted: **Tue May 27, 2014 1:27 am**

Jakgoe wrote:
nialloftara wrote:90 and beyond you can go iron head aluminum block with a few tech points to the head and get better power, less emissions, and only a small hit to mtbf.

By the 2010s, the MTBF hit is very small, and could be considered insignificant. On a semi-related note, cast iron blocks will give you a few extra horsepower.

Of the two I've found using iron heads brings more power at a lower cost to quality slider where as aluminum block cuts emissions by about as much as heads. Of course I tend to use pushrod heads so I'm not sure if there's more of a effect with ohc.

Posted: **Tue May 27, 2014 9:58 am**

Jakgoe wrote:
nialloftara wrote:90 and beyond you can go iron head aluminum block with a few tech points to the head and get better power, less emissions, and only a small hit to mtbf.

By the 2010s, the MTBF hit is very small, and could be considered insignificant. On a semi-related note, cast iron blocks will give you a few extra horsepower.

I concur. The required quality slider for reliable multi material block/heads should decrease with each decade. By 2020 no extra quality is needed for reliable designs. Realistically the aluminum head should be offered in 1950. Every major US manufacturer was designing and testing aluminum heads and aftermarket companies were selling performance aluminum heads at that time (although suffering with reliability). Aluminum blocks should be offered to be used starting in 1950 as well but would require alot of tech points and quality to make it hold up to any decent power output.

Posted: **Tue May 27, 2014 11:15 am**

Aside from the buick 215 though I have trouble thinking of many factory production engines that really made use of aluminum blocks or heads before the 70's. They may have experimented with it but few really used it.

Posted: **Tue May 27, 2014 12:08 pm**

JayZee88 wrote:Realistically the aluminum head should be offered in 1950. Every major US manufacturer was designing and testing aluminum heads and aftermarket companies were selling performance aluminum heads at that time (although suffering with reliability). Aluminum blocks should be offered to be used starting in 1950 as well but would require alot of tech points and quality to make it hold up to any decent power output.

Remember, self-driving cars are being tested and developed in the present, but if that was to be available in the game, I would not say that it is a mass-market option. Remember, the options are unlocked as they become available to the masses.

Posted: **Tue May 27, 2014 6:42 pm**

nialloftara wrote:Aside from the buick 215 though I have trouble thinking of many factory production engines that really made use of aluminum blocks or heads before the 70's. They may have experimented with it but few really used it.

In the 40s and 50s there were aluminum heads for Ford flatheads (aftermarket), Chrysler and GM also made special low production sets in the 50s and 60s, Jaguar XK6 came from the factory with aluminum heads. I am unsure about blocks, but aluminum in motors has been around as long as the motor. Althought not in mass production until after WWII. I found out that the reason why Buick used so much aluminum on their V8s in the 50s for thermostat housings, water pumps, etc was to see how aluminum holds up to corrosion in a motor. That is where they got the information on how to design the 215! For a long while I pondered why all the 50s Buicks I see under the hood have more aluminum then 10 of any other car of the era combined! Talk about a road test! :lol:

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