TheSamba.com :: View topic

Tue Sep 04, 2007 4:56 am

Hi, new to this but anyway,
Below are some jpgs of the twin cam head I designed last year for my engineering thesis.
It's meant to run on a type1 case, it uses Subaru EJ25 valve gear. It's just a model (proE) at the moment, it'll take a bit of cash to get going. I did do a 3D print of half of the head and flow tested it. With the stock EJ25 cam and valves it had half the pressure drop as my slightly ported twin port at big lift.
In the pics it's sitting on stock 1600 barrels, the valves just fit.

Any Comments/advise?

Tue Sep 04, 2007 6:03 am

Nice 3D model, and nice effort, too.

...but...

all previous efforts of creating 4-valve heads for a/c engines I know of suffered the same fundamental problem:

They all smoked their exhaust valves & seats! With the exhaust side facing downwards, that area of the head could never be cooled sufficient enough.

I think there's a reason not even Porsche got 4 valves going on an aircooled basis...

But, as I already stated, nice approach!

BugUser

Tue Sep 04, 2007 7:47 am

very nice indeed.... im currently going to school to become an engineer and that is one kick ass modeling...... damn i wish i could design like that.... (maybe someday i will) .... but anyways a few questions for ya

what will time the cams?? i dont see anything connecting to the crank.. maybe just missed it....

maybe a stupid question but what will be the major benifit of 4 vavles versus the standard 2.....

oo anther thing.. what about lubing those cams?

either way great job and great idea.... im hoping when i finish school that i can design something vw type1 related....

Tue Sep 04, 2007 8:28 am

michael1968 wrote:
Any Comments/advise?

If this is something you plan on actually creating, and not just a design project, optimize the combustion chamber, valve size and valve location for a 94mm cylinder (if you haven't already) and larger displacements (2.2L+), not an 85.5mm cylinder.

Tue Sep 04, 2007 9:16 am

looks pretty good. you might try making the heads water cooled. then you could really control the head temps.

Tue Sep 04, 2007 10:18 am

its also looks like the studs are in the way of the valves... or is just that the angle in which it is presented?? im talking about the studs used to torque the head to the jugs.....

Tue Sep 04, 2007 10:36 am

Nice CAD drawing there Michael1968.

BugUser wrote:
I think there's a reason not even Porsche got 4 valves going on an aircooled basis...

But, as I already stated, nice approach!

BugUser
Eh? Where have you been?
Porsche did make an aircooled 4-cam engine in the 904 Spyders and 356 Carrera.

Tue Sep 04, 2007 10:43 am

Oh yeah...BTW Michael1968, have you seen the VW/Subaru hybrid engine project which utilizes a VW engine case, internals, and cylinders while using a Suby heads?

Hybrid Engine Project - http://www.shoptalkforums.com/viewtopic.php?t=93249

Tue Sep 04, 2007 11:47 am

Banzai KG wrote: Nice CAD drawing there Michael1968.

BugUser wrote:
I think there's a reason not even Porsche got 4 valves going on an aircooled basis...

But, as I already stated, nice approach!

BugUser
Eh? Where have you been?
Porsche did make an aircooled 4-cam engine in the 904 Spyders and 356 Carrera.
Those porsche 4 cams are sweet,but they are not 4 valves per cylinder.Ever have one apart?If you don't have a book your screwed.The cam timing gears are tricky.

Tue Sep 04, 2007 12:16 pm

wouldn't t1 case need some modifications in order to support side loads from the belts? I remember reading about people attaching propellers to the back side of the engine (crankshaft pulley) in the AV applications and destroying bearings. This was also the case with superchargers as well...

Anton

Tue Sep 04, 2007 12:31 pm

akokarski wrote: wouldn't t1 case need some modifications in order to support side loads from the belts? I remember reading about people attaching propellers to the back side of the engine (crankshaft pulley) in the AV applications and destroying bearings. This was also the case with superchargers as well...

Anton

Probably not; any side-loading to drive the cams is going to be minor in comparison to a supercharger or a propellor.

Tue Sep 04, 2007 1:28 pm

Banzai KG wrote: Oh yeah...BTW Michael1968, have you seen the VW/Subaru hybrid engine project which utilizes a VW engine case, internals, and cylinders while using a Suby heads?

Hybrid Engine Project - http://www.shoptalkforums.com/viewtopic.php?t=93249

edit out photos for space

wow thats gnarly man!

Tue Sep 04, 2007 3:34 pm

A lot simpler option to going water-cooled is to box the head fins in, and run a separate oil supply over them, utilizing the common automatic Bug's oil pump. Jon Karcey did a couple engines like this, commenting how cool the valves ran. The valve lash never required regapping.

4 valves per cylinder of course yields great low end torque with sufficient flow for high rpm.

Tue Sep 04, 2007 11:54 pm

OK, lots of questions.
Quote: They all smoked their exhaust valves & seats! With the exhaust side facing downwards, that area of the head could never be cooled sufficient enough.

Yeah, this is a bit of a concern, but 2 exhaust valves do run cooler than 1, I was looking into ceramic coating the exhaust ports to keep temps down.

Quote: what will time the cams??
I haven't modeled the cam pulleys(subaru), I'm trying to use as many ready made parts as possible.

Quote: major benifit of 4 vavles versus the standard 2
You can get a lot more effective valve area for the same or less mass ie less power loss.

Quote: If this is something you plan on actually creating, and not just a design project, optimize the combustion chamber, valve size and valve location for a 94mm cylinder (if you haven't already) and larger displacements (2.2L+), not an 85.5mm cylinder.
It's a long term project, this is only the first stage. The whole point of the project was to increase the efficency of the engine not the capacity. It was kind of concieved to run in an under 1600cc unlimited hill climb class we have over here.

Quote: its also looks like the studs are in the way of the valves...
They would be, they are designed to bolt into threaded holes in the heads, just like in a normal case.

I've heard of the hybrid but hadn't seen any pics, nice. It would be easier in some respects to just bolt on a set of sub heads but where's the fun in that.
Thanks for your comments guys.

Wed Sep 05, 2007 3:41 am

Banzai KG wrote: Nice CAD drawing there Michael1968.

BugUser wrote:
I think there's a reason not even Porsche got 4 valves going on an aircooled basis...

But, as I already stated, nice approach!

BugUser
Eh? Where have you been?
Porsche did make an aircooled 4-cam engine in the 904 Spyders and 356 Carrera.

Eh? Where have You been?
4 cams don't equate 4 valves per cylinder...

Wed Sep 05, 2007 6:40 am

Quote: They all smoked their exhaust valves & seats! With the exhaust side facing downwards, that area of the head could never be cooled sufficient enough.

Absolutely incorrect.

The 4 cam Carrera engine has underside exhaust ports, so does the Porsche 911 and the Type 4 engine, Corvairs and Pinzgauers as well..

Placing the exhaust port under the head is a MORE EFFECTIVE means of positioning a cooling charge around it- IF the head is designed to allow this, as all the aforementioned examples I posted were. Side mounted exhaust ports like the TI and the Porsche 356 have great flow characteristics, but horrible cooling characteristics as a sold 1/4 of the port is incapable of being exposed to the cooling charge.

If you need any assistance let me know, I have more experience than I'd like to have with challenges like yours having taken a solid works model of a cylinder head and manipulating it into a working piece.....

This

to this

Wed Sep 05, 2007 8:18 am

Jake Raby wrote: Quote: They all smoked their exhaust valves & seats! With the exhaust side facing downwards, that area of the head could never be cooled sufficient enough.

Absolutely incorrect.

The 4 cam Carrera engine has underside exhaust ports, so does the Porsche 911 and the Type 4 engine, Corvairs and Pinzgauers as well..

Placing the exhaust port under the head is a MORE EFFECTIVE means of positioning a cooling charge around it- IF the head is designed to allow this, as all the aforementioned examples I posted were. Side mounted exhaust ports like the TI and the Porsche 356 have great flow characteristics, but horrible cooling characteristics as a sold 1/4 of the port is incapable of being exposed to the cooling charge.

Dear Mr. Raby,

I very well know the underside exhaust ports of those engines and I never negated their cooling capabilites in a SINGLE exhaust valve scenario...

From my own experience in creating watercooled 4-valve head designs (and following mandatory logic), the highest thermal stresses occur in the web between both exhaust valve seats and the area where the discrete exhaust ports merge together. THIS is the crucial area that makes the 4-valve underside exhaust incommensurable to the well-known and proven 2-valve exhaust...

If You find a solution of striking simplicity to this issue, You'll surely take credit for its development throughout the whole aircooled world...

BTW...
in 1980's Group C series, Porsche "cheated" around that issue by putting watercooled 4-valve heads on their otherwise aircooled Flat-6' in the 956 and 962 series race cars...

Cheers,

BugUser

Wed Sep 05, 2007 8:26 am

Multiple exhaust valves CAN cause over temp issues, just as a single exhaust valve can that is too big too be suported by the port or exhaust system.

Mon Jun 02, 2014 8:34 pm

Hey i know this post is long dead but maybe the op will see.
I like that Cad image is that solid works you used?
Did you ever try creating a usable prototype?
I am in school for Mechanical engineering and am thinking some something similar but for a cam-less servo motor valve actuation.

Tue Jun 03, 2014 9:53 am

BugUser wrote:

BTW...
in 1980's Group C series, Porsche "cheated" around that issue by putting watercooled 4-valve heads on their otherwise aircooled Flat-6' in the 956 and 962 series race cars...

Cheers,

BugUser

they were also Dual Turbocharged... more heat/strain on the cooling system, at that point it was more effective to water-cool the heads.... that is a point I think you are missing.

lmao... i just realized his post was in 2007 ... lol sorry :lol: