What is the largest Flat Four Possible?
 

They say there is no replacement for displacement. So is there a theoretical limit to how big the motor can get? 3l? 3.5l? Can a flat four take litre sized jugs and become a 4l? 5l? Who has built the largest (functioning) motor to date?

Just curious on a slow day at work. :D

Jake Raby has a 3.0 with Nickies in the works...

Several of the aftermarket case/cylinder/head companies make 4.0L engines but they are for drag cars where they only run for a few seconds. They are not used by a lot of racers as they use a 2L engine and nitrous and can squeeze 300HP easily out of a type one. Notice these are made after type one engines as the type four combustion design is terrible.

The poor head design is no longer a problem.

These heads are a type 1 Exhaust port. To use in a 914 you would need to change the coooling system.

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Steve, what does one of those heads cost?

I had a 2.9 for about 5,000 miles.

It would seem to be a type one then?? My 2.8L lasted about that much too, but in 30 minute race sessions....

HOLLY HEADS BATMAN!
WHERE CAN YOU GET THOSE STEVE!!!!!!

Why only 5,000 miles? I guess I don't know what the limiting factors are in an air cooled boxer motor. For instance, AFAIK, you can massively bore out a chevy small block and run it hard till the cows come home (unless you make the cylinder walls so thin that the block cracks). Why not have a five liter flat four?

You can only go so big in-regards to piston cylinders to increase displacement. I think 105's are the biggest made, anything over that would require a very different head. Stroke is what becomes the reliability factor short coming.

I now run a turbocharged 3.0 - 6 in my 914 which I find works well as a reliable daily driver.

Besides the fact that those heads cost as much as a used 3.0 6 longblock, if your in a specific class in racing, they are sweet, and needed to happen a long time ago. What i don't get is why they didn't add any water cooling jackets? These motors already have a hard time with heat, why not machine in some chambers that an electric water pump can get extra cooling to the vave guilds and other areas? Worked wonders for the 959... I understand the whole "aircooled" religion, but alittle water assistance, and wouldn't hurt the motor if not using it, would make those heads worth the money.

Those heads are nothing new... They come from a company called "Engine Plus" in Germany...

I have a set if them to test against MY Billet heads that we have been developing since late 2002. The 3.0 engine I am building now can be read about here
www.aircooledtechnology.com/research
It will be tested with heavily modified 2.0 Porsche heads, a set of The Engine Plus heads as well as a set of My Billet CNC heads that have already outflowed the engine plus heads by 11% and have attained a magical 80% E/I ratio!

To answer the question about the largest engine available:

I have been working on a 3619cc engine for several years now. Thecase is extremely modified and it utilizes a 113mm bore. I call it "Project X" and its being done simply to prove that it can be accomplished with a STOCK TYPE IV CASE! For me I have a full machine shop, and do my own work so this is easy to do.. I would NEVER sell one to a customer.

Those huge heads, unless they are coupled to a huge engine will create an engine that is not worth driving, as the powerband will be killed at anything less than 5K Rpm..

It is not how big it is, but rather how you make it big that counts!

Dayyam, thanks for replying, Jake. If we can never hope to drive your 3.6, I hope we can at least read about it on your website and dream. :D

And without asking you to give away any trade secrets, may I ask what the obstacles/challenges are in building such a beast?