OK, here's a fun one for the novice to ponder and you experts to answer:

Why is the factory mechanical CR so low?

and for reference, what is the highest mechanical CR that can be physically achieved? assume no octane limitations -

I'm just looking for the design limit for the highest CR that can be / has been in a Type 4 engine using available technology.

Thanks

Might need some context to your questions;

ie. Octane is a fuel. So what is the engine? Internal combustion and what fuel?

Diesel uses compression for the spark plug and a A bomb uses tnt to start the fission reaction.

So for reference you need to add context to the question. When you say Octane I suppose you are referring to Octane rating. But what is the fuel?

Kind of funny way of asking what is the max HP a Type 4 engine can make.

Often when these questions are asked, you have a younger guy, a novice who is only looking at the top number.

You can run at lower CR
The factory CR is about normal for the era.
Over about 9.5 you need to twin plug.
At to 12:1 your done for gas

Above has too many variables, but is ballpark for an aircooled, you can get a bit higher out of a watercooled

Compression ratio is often set by quality of fuel. Head effiency and desired results.
At the factory compression these motors are very reliable as long as maintained properly.
cant really sell someone a car that's constantly exploding.

Assuming you aren't actually trying to burn anything, and are in a vacuum to boot, the maximum compression ratio is infinite. If you have zero volume in the chamber when the piston is at the top of its travel, you will have ((swept + 0) / 0):1 compression, which is infinite or undefined (depending on who you ask).

We need some space up at the top of travel for the air and fuel, obviously. We also need space for the slop in the rod bearings, wrist pins, etc., and for things to grow as they heat up. So there is a minimum amount of space needed, but how much depends on a lot of factors.

The stock 914 compression ratio is relatively low because it is set up to avoid pre-ignition, or detonation, or pinging. Much like all engines.

The engine has a pretty primitive design. The wedge-shaped combustion chambers are OK, but not great, so you can get detonation more easily than with a more advanced shape.. The cam is very mild so you don't have compression pressure "leak out" on overlap, which means you need a lower compression ratio.

The engine management system is primitive (D-jet, L-jet) or even more primitive (carbs) so you can't tune it closer to the edge and rely on the engine management to save you from detonation.

An air-cooled motor cools the way it wants to, and it is hard to get parts of it to run cooler than they want to. Water will absorb heat a lot better than air will, and you can run fine passages where you want them to go, and control the heat in various parts of the engine better. Having specific things get hot will lead to detonation more easily than keeping them cooler, though of course there are things you want to be hot for efficiency's sake.

The 914's compression ratio is not out of the normal range for the time the motor was designed, as Mark said. There were cars that ran higher compression, and some that ran lower.

Today, there are gasoline-powered cars that run over 14:1 compression, but those are pushing things! The highest I remember hearing about in a 914 motor is about 12.5:1, and that required race gas and had a big lumpy cam and cubic dollars sunk into the heads.

--DD

13:1 at 200 hp
Race fuel only.

Could not move the car under 4500 rpms...
built tuned between 5500-7500 rpms.

stupid to drive anywhere aside from racing.

As Jake always says, its all in the combo.
He gets 200hp on pump fuel now....

The thing to remember is that higher CR creates heat...the worst enemy of an aircooled motor.

Rich

Thank you one and all.

I'm afraid I wasn't clear enough in my original inquiry -

I am modeling the Type 4 based upon other engines I have been involved with in the past.

I am not, however, familiar enough with the air-cooled engine to know if there are any hidden constraints that are unique.

I believe it is possible to increase the output to 100 - 110 hp / liter in a street driven, smooth idling engine of two valve design - but I know there are limits -

and it appears that, without going to exotic extremes that the reasonable limits would be 13:1.

Has anybody gone higher ?

Any and all info is greatly appreciated

Thanks for the input / advice / sage wisdom

IMHO twin plugging and race gas are exotic extremes.

The materials used in a stock 914 engine do not like high compression.
Water cooling provides more controlled cooling than does steel cylinders on an air cooled motor

It's expensive to rebuild with modern components/nickies/etc
additionally the metallurgy of the block/heads can play into high theoretical numbers

engine sealing becomes an issue. Cylinder head temperatures become an issue. Oil cooling which is important to consider separately from CHT becomes an issue.
Your numbers, 100 HP/liter are doable, but I know only a couple builders who can make that live very long. At the raw number, 200-210HP, you might as well put a 3.2-6 in it as you've spent the money...

To a point ...

100hp/liter is a crack pipe dream for a novice Type 4 builder. A Type 4 is an unforgiving bitch that will granade if you don't build it right.
Your pistons and cylinders alone will cost $3440, I'd say you are easily well over $12K in parts alone. I know look at my signature line for my '67 bug.

If the price doesn't scare you then look at my sig line again and what's going into my 914. Once you get to the cost of a super HP Type 4 in a 914, you may as well do a nice /6.

But then if HP is all you are looking for... do a V8.

The cooling, or lack of is why such low compression.


If you look at almost all street engines the lowest compression motors for car and motorcycle are air cooled.

Water cooled have a point or more higher.

Direct injection water cooled motors have even higher compression due to the fuel cooling off the combustion chamber.

A few thoughts from a novice 1 time Type 4 builder.

100-110HP/liter is not doable in a N/A Type 4 without a SERIOUS cash infusion, unless perhaps it is an alcohol burning bracket racer you rebuild after every run. That's optimistic even for a modern N/A inline 4 street motor....

I have two liter+ motorcycles that make this kind of power, but at 8-10K and no torque. Not a problem to push 700lbs, big problem for a passenger car.

I'm sure it can be done, and maybe has, but after spending the last 5 years watching, reading, learning and doing, I havent seen it..... The Type 4 is a different animal.. Do some reading and educate yourself. The CR is not really low for that era. 13:1 CR reasonable? you need to put down the crack pipe freind

Jake says he's done it, closest I've come on a slightly milder 2.6L build is 70hp/liter, but you're totally right on outrageously expensive and not a novice build.

Personally for the novice I'd start with a 2056cc build and if you are truly skilled a 2276cc would be the max. Both engines are great in a 914.
BTW just a FYI a performance /6 build is way harder than a /4. BTDT

Thank you all for all your input. I knew that the collective intellect could be relied upon for valuable insight and experience

To answer a few comments/observations made, I am trying trying to maximize the thermodynamic efficiency of the design, not just max HP numbers...

Whatever the numbers end up being, it has to be drivable, have sufficient torque throughout the range and without going to endless amounts revs - I always try to minimize frictional losses.

this is not to be a track / race engine; just a daily driver

So to sum up, the enemy that needs to be addressed is heat management, and combustion chamber limitations, correct?

and yes, this sort of stuff always costs... its just a fun project - for an old guy.

I always welcome any and all comments / observations / experiences so keep 'em coming.

and to R Towle, do you have the camshaft specifications from your 13:1, 200 hp engine? I am specifically interested in your valve timing events

thanks again.

There has been some discussion about a water cooled head, air cooled cylinders but I dont think anyone has ever done it.

I seem to recall pictures of it done on a type I engine long ago (what WASNT done to a type I in the 80s-90s ? )

If you want 100hp/liter in a 4cyl NA boxer, just get a FA20 from a BRZ (which happens to be 86mmX86mm with 12.5/1 CR)

100HP/liter cost me $14000. For parts alone. If you have to pay for the labor?
I am very happy with my 3.2 six. 220HP with manners...

Yes, in a dragster.
Only raced a few times, never amounted to much, was deemed illegal after just a few races. IIRC it's been a long time, it was a feature in HotVW's

If you're looking to improve thermodynamic efficiency, why are we talking about compression? Why are we talking about horsepower? Neither of things have any direct connection to head cooling.

You're being very cagey about what you're actually trying to do. It makes it hard to help.

And what is your budget?

We've seen our share of new members posting they want a 200hp type four, then after countless posts we find out their entire budget is $2k and a case of beer.

That's not true. Theoretically otto cycle thermal efficiency is proportional to 1-(1/CR^0.4) or so.

Technically for best efficiency you want to optimize the temperature of the heads etc. to minimize heat transfer from the combustion process to the outside environment. From a thermal efficiency perspective, head cooling is considered a necessary loss (just like needed a TB is a pumping loss, etc.).

What do you mean by modeling? The past experience kind or the computer/math kind (WAVE, GT-POWER).

Eh, I'm not buying it.

Driveable? Porsche sold thousands of these cars making less than 100HP and were/are completely driveable and enjoyable. That's subjective anyhow.

All you've talked about is HP/liter and ridiculous compression ratios. Now you are looking to maximize thermodynamic efficiency?

You also seem to be ignoring the 'collective intellect'

I just finished a 2056 build (you can look at the #770 Update thread). I havent put on a dyno yet, but even in a 911 body, the car is responsive, has great driveability, power and loves to rev to redline. I'm guessing will be at the 125-130 HP range.

There are dozens of build threads all over the 914 world, aircooled.net, and if you've spent 5 minutes searching, you have found all the Raby stuff out there.

I'd like to see an example of one of these engines you've built.... or even what year your 914 is..... I think your talking in circles.... But hey, I'm just a grumpy guy. But I'm thinking TROLL ALERT here. Gonna be fun.

guys! I didn't mean to start a firestorm over this... I was just curious as to what the mechanical limitations of the type 4 engine was

no secrets here.

as for the concept, its a variation of the Atkinson / Miller cycle.

On circular intake ports it seems to be possible to minimize the pumping losses while taking advantage of a much greater expansion cycle. for example, instead of 1-2 pts, utilize 5-7 pts, allowing for a cooler exhaust and broadening the torque curve.

Years ago I took my Audi 5000 turbo and increased to CR to 11:8 +- while altering the cam timing events so the actual CR was 8:1 - that is my reference point - variations on this theme have been done to jaguar engines and a domestic v8 - all liquid cooled

I bought a 914 when I started having more time, and have become intrigued with the Type 4 engine.

as far as the modeling, right now its computer - and I'll see where that leads me.

You really cannot model the Type IV using past motor builds, completely different designs...bore, stroke, combustion chamber, port shapes and flows.

What worked on your Chevy might not work here. I seriously doubt you are going to come up with magical engine recipe that hasn't been tried before.

probably not, it may all blow up - but I do want to look at it.

This is supposed to a fun exercise. and I think it will be.

and, if it all blows up, Y'all will be among the first to know

The type 4 engine is a 50 year old 2 valve pushrod design based on a 85 year old 2 valve pushrod design. Add to this that the Type 4 has weak head sealing/bolt design for turbo or supercharging at anything but moderate levels.
The thing is unless you have made a amazing Type 4 flux capacitor breakthrough, what you are talking about would be better off started on a clean slate.

There has been all kinds of theoretical engine discussion here over the years. Not once has anything come to fruition that hasn't been already been firmly rooted in current or past technology.
Computer modeling can be great, but the Type 4 is oldschool, try building a couple of real T4 engines first. Then get back to us with some theories.

PM member veekry9, he would be a perfect muse, who knows maybe the two of you can make an amazing breakthrough.

seriously.... as a hypothetical discussion you can get 100/hp per liter for a cost of 20K (and it will be necessary to pay someone to build it)

realistically.... you can not do it
yes some people can do it... they have years of experience and development

as a "new" 914 engine builder its not likely that you will get there
after 30 years and a million worth of development you will be able to
but realistically plan on 130hp from a 2.0 air cooled -4, and plan on a conversion if you want water cooled performance capabilities

I would suggest you call around, talk with JAke Raby and the guys at FAT performance.
FInd a live customer near you that has a motor about 150HP or greater and ask them for first hand info, and possibly to take you for a ride.

You would be surprised what 150-180 HP will do in these 2500lb cars....

200hp in these cars means you need to be up to high in the RPM range to enjoy it, and have it be simple to drive. It also means a shorter lifespan than a 150hp motor...by a long shot.

Rich

Tough crowd.

What software are you using? Commercial or homebrew? I saw your post looking for cam-to-lifter geometry so I assume you're at the connecting measured cam profile to actual lift stage.

It's be interesting to see what kind of efficiency gains you can see from increasing the expansion ratio. I do wonder what the trade off in terms of power will be with leaving the intake valve open so long. Either of these cycles offer relatively good efficiency gains (though a Miller might be tough just due to mechanical strength of the head attachment), but may fall down too much in the overall WOT power part since we don't have the variable valve timing knob to tune.

If your goal is 100hp/liter T4 you're best chances are with a small bore, small displacement engine. The smaller the better.

https://www.youtube.com/watch?v=zcPGfjUO3Yg


https://www.youtube.com/user/GrasshutPerformance/discussion
https://en.wikipedia.org/wiki/Julius_Mackerle
Turbo,efi,titanium weight-loss,auxiliary head and piston cooling,21st century sensors.
The heads lifting off will need a cure,like o-ringing them on to the nickies,stiffening the heads.
Note the use of modern off the shelf rods,as an economy.( Honda B16A H beam con rods)
Maximum effort calls for maximum control of heat in fine resolution.
An aluminum liquid coolant tube inserted into the head to sink heat will work too.
Not quite HD,but a bridgeport mill op,to keep a cool head.
The use of modern coatings to reduce friction and conduction is effective.
There,I spent some money for you,as any thing is possible.Methanol/Nitro fuel engine?
CadCam a set of new three valve heads you can graphite diecast for cheap and have a prototype shop do a short run on speculation.
I'll give you their number:
http://www.armstrongmold.com/pages/graphite_die_casting.html


/
Reading,it's good fer yuh.

Julius Mackerle: Air-Cooled Motor Engines, Cleaver-Hume Press, London 1961
Julius Mackerle: Air-Cooled Automobile Engines, The Institute of Mechanical Engineers, London 1961-2

I'm not trying to be a smart ass here, but there is nothing new or innovative in any of this stuff.

Now the last comment on three valve heads, we've been hearing about 4 valve per cylinder heads since the early 2000, we're still waiting....
But even they do get made my bet is they will be nothing but a novelty due to price.

I admire what you are doing, and that you can do it.
Please share what you think might work because there are still some of us that may take a shot at it purely for fun

wow! Thanks to all for all the input.

to answer jd74914 questions: 1) initially, I just use a spiral notebook and a pen to gather info, 2) initial dynamic modeling using 'Dynomation", 3) take the data and build one... see how long it takes to blow up!

The #1 concern that pops up from the comments, after 'it can't be done', is the cylinder/head sealing - I can only assume that the Type 4 engine 'flops' around - and what about stability and flex of the crank?

That would necessitate small bore to minimize flex. But please tell me, is the head/cylinder just a registered fit under compression?

As far as air-cooling goes, does anything compare to Mr. Raby's DTM system used in conjunction with Nikasil?

Is there a book or source with all the torques, tolerances and dimensions? I know that after 40 years, there must be a lot of hard data, somewhere.

Thanks again

Look at how the 911 turbo seals the head to cylinder.
Basically a small diameter wire machined into the head and cylinder, then crushed when torqued down.

Is this thread still going? I lost interest in trying to help a while ago.

No Rich, you don't understand what I mean by fire ring .
The Fire ring that is match machined into a high performance 911 turbo head and cylinder. The ring also stops cylinder head movement or shuffle.



BTW I often work on a 500+hp porsche 911 turbo 3.8L high performance engine that has over 100hp/cyl.
The owner has well over $80K into the engine alone...this time around.

You built a Cali shroud? From the time of the Usenet RAMVA groups? Man, you HAVE been around for a while, so hat's off to you. I still have an unused original Joe Locicero DTM kit in a box somewhere, before Jake took over, with Joe's own handwritten instructions. Good man.

It might have been lost in the thread:

If you want to study how to get 100hp/L, then look at the Toyota FA20 - 4cyl, boxer, NA, 86mmX86mm with 12.5/1 CR.

How does it get to 100hp/L without a turbo?
Direct + Port Injection

That original DTM by Joe would an OPP (Oregon Performance products).

I've also used FAT and Sharpbuilt shrouds in the past.

My all steel shroud.

Yup, original OPP with Joe's handwritten instructions, in a box, never installed. He was a great guy. I used Sharpebuilt too, but never FAT.

Your Cali style is nice. You go to a VW show and walk past dozens of engines with slight variations, carburetors or whatever, then come to that Cali and people just stop. It's there, obviously, and it's right, but there's something about it that's wrong.... something wrong there... Crankfire too, very cool.

And 46mm Tb's made from suzuki TB's

Damn, old school! I didn't notice that, it really does look good. I have a set of GSXR TB's around here somewhere, lost the ITB itch and they were never installed. Probably in a box next to Joe's shroud. Going Subaru kind of changes that game.

https://www.youtube.com/watch?v=vmkKqVc2g0s

http://www.forestcitycastings.com/services-molds.php
https://www.youtube.com/watch?v=OLAqtLWd3HI
http://dacedace.com/graphite-mold-castings.php
https://www.youtube.com/watch?v=RiPQpiE4_qY
https://www.youtube.com/watch?v=BnDh1a0q_GI
https://www.youtube.com/watch?v=Dw6cs7opvzA
http://www.agile-manufacturing.com/

Design brief:
1) air/liquid cooled hybrid
2) 3 valve
3) uses production valves.
4) meehanite-ex/bronze-int valve guides
5) pushrod activated roller tipped,rollercam
6) T4 headbolt pattern
7) canted valves
8) induction hardened seats
9) direct injection
10) dual plug

All of these details are desirable,but the pertinent question is,how many can you sell?
There are plenty of great stories of attempts and failures.
The impetus is improving on what came before,in some incremental way.

https://www.onshape.com/
https://www.tinkercad.com/

Make a cloud cad file,3d print the prototype,analyze the result,improve,cast the part,
machine 5X,assemble,prep,install,run.
All for <2K profit each set.
Hard to do isn't it?

https://www.google.ca/search?q=custom+vw+t1...wavNTQY-geuM%3A

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http://www.apfelbeck.nl/
/
Reading through the comment sections.
However well you do making a great product or service,there will always be the naysayers.
Can't,won't,shouldn't and didn't are the words they use.
Read a book?Hell no,I can't,won't,shouldn't,didn't.
Pat them on their head in sympathy and
Send them on their way with a lollipop.
Sadly,they may procreate,great,more halfwits.
The effort they expend in negging other's labour and thought might better be used in an attempt at raising their own iq.

/

http://www.amazon.ca/Air-Cooled-Motor-Engi...%2C+London+1961

Julius Mackerle: Air-Cooled Motor Engines, Cleaver-Hume Press, London 1961
Julius Mackerle: Air-Cooled Automobile Engines, The Institute of Mechanical Engineers, London 1961-2

As a start,for your own engineering library,to like,know stuff.
These are the books,thermodynamics as applied the the aircooled internal combustion engine.
Not sure if his later books have been translated.
A few of the designers of both the GM Corvair and the VW T4 perused these tomes.
A guy trying to make his own head might want the same knowhow,for like ideas.

OK then....enough of the yakety yack...Build it!!!

https://www.google.ca/webhp?sourceid=chrome...mposite%20metal

Something new this week,a new material with unique strength and conduction properties.
There are a few requisites other than the tools I've posted about above.
Again,this is no overnite sensation,a thorough examination of the demand for a T4 head is neccessary.
Pointless to make a part,or a car you can't sell,many have tried.
Now if it provided enormous benefits,why then,a few could be flogged.
Take a look at what the 911-4 Polo guy did,he created a demand by being perfect.
Illusions of instant gratification is rainbow dreaming.
It's not easy,otherwise everyone would do it.
Discussions of air/liquid cooled cylinder head design is what we're talking about.
The constraints as above define the geometry to some extent,which is why you would start there.
Coming up with your own set of poppet pipes is part of the fun,just like at work.
As for a schedule,I'm in no particular hurry,having done many years of hard deadlines in cnc machining.
Now a contribution by any number of wanna be engine designers is possible with the cloud based cad system.
A consensus of 97% of world wide 14 people might develop a reasonable part.
What features might be possible with a new material such as described.
A basic understanding of metallurgy is needed to 'get' this.

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