Dished pistons and Improved Pump Gas Performance

[rick m]

Here is an example of the type piston I was running in my 2110 motor (Green 67) doing a burnout in another post.  The only difference between this one and the one in the 2110 motor is this one is an 85.5 that I've done for another motor project coming up down the road. We use an open combustion chamber design with this style piston.  Thought I would throw this out and see who else has found the advantages of doing it. It works. You can run a lower volume in the head and put some of the chamber in the piston. VANAGON's have most of their combustion chamber in the factory pistons and tiny amount of cc's in the head.

For me the objective of the dished pistons (reverse combustion chamber) was for achieving a maximum quench area. Having part of the combustion chamber in the piston helps improve the shape of the chamber and flame travel.  It allows some piston weight reduction and allows the quench action to travel further across the chamber and the piston, creating more equal load during the ignition of the fuel, rather than the uneven shock that comes from combustion with a wedge chamber design.  When I run these, I match the open chamber of the head with the diameter of the dish in the piston and run fewer cc's in the head.

This is another tried and proven street motor performance idea. I am not the only one who has done this over the years.  The beauty of the thick crown CIMA's, that BERG once sold, is I could cut the dish in a set of 90.5s and still have about a .240 crown on the piston thickness. you will notice the top of the piston is also cut for ZERO deck clearance. I run a .060 copper gasket when running ZERO deck.

Rick M

[bedjo78]

Nice work. can we do the same to mahle pistons?

[peach_]

Here is an example of the type piston I was running in my 2110 motor (Green 67) doing a burnout in another post.  The only difference between this one and the one in the 2110 motor is this one is an 85.5 that I've done for another motor project coming up down the road. We use an open combustion chamber design with this style piston.  Thought I would throw this out and see who else has found the advantages of doing it. It works. You can run a lower volume in the head and put some of the chamber in the piston. VANAGON's have most of their combustion chamber in the factory pistons and tiny amount of cc's in the head.

For me the objective of the dished pistons (reverse combustion chamber) was for achieving a maximum quench area. Having part of the combustion chamber in the piston helps improve the shape of the chamber and flame travel.  It allows some piston weight reduction and allows the quench action to travel further across the chamber and the piston, creating more equal load during the ignition of the fuel, rather than the uneven shock that comes from combustion with a wedge chamber design.  When I run these, I match the open chamber of the head with the diameter of the dish in the piston and run fewer cc's in the head.

This is another tried and proven street motor performance idea. I am not the only one who has done this over the years.  The beauty of the thick crown CIMA's, that BERG once sold, is I could cut the dish in a set of 90.5s and still have about a .240 crown on the piston thickness. you will notice the top of the piston is also cut for ZERO deck clearance. I run a .060 copper gasket when running ZERO deck.

Rick M

I'm loving this!

[Taylor]

Rick,
Just to prove that I am not 100% contrarian, here is a rendering of the piston currently in my 80x94 naturally aspirated motor.  Although I did it out of necessity because my combustion chambers were only 28cc.  Either way, it made great power.  213hp and 180 lbs of torque.  That dish is 17.2cc

[rick m]

Check out the technical article in HOT VWs by Howard Washington in the latest issue. Howard is a local fellow VW buddy.   He lends more creedance to the discussion on dished pistons, quench, etc.  He is a die hard VW enthusiast and also an engineer.  He knows a little about the subject we've been discussing on the CLF.

Rick M

[rick m]

Taylor....

Excellent example of what we are discussing.  There are a lot of ways to skin the cat. The VW Vanagon has almost no chamber in the head and a very big dish in the piston.  It runs 9 to 1 compression from the factory.  So your motor is a great example of how quench works.  We are simply exploring some ideas on how combustion chamber design also helps with removing hot spots, detonation and runs on 87 octane gas.

Your motor currently is closer to what I did in my old 2110 motor.  It works! I am currently shopping a lot of pistons to get one close to what I want to go with on my new design combo.  I can see why your motor works well! Don't take me wrong from all these discussions.  My 2110 was not nearly as unschrouded as the head I posted this go round.  It was heavily relieved around the valves (unschrouded and the  chambers laid back) but not like the new combo I am working on.

Congrats on the hp rating and torque.  You are making our point with a different way of achieving the quench.  Frankly, your motor is a great combo based on what you've shared.

Rick M

[peach_]

Rick,
Just to prove that I am not 100% contrarian, here is a rendering of the piston currently in my 80x94 naturally aspirated motor.  Although I did it out of necessity because my combustion chambers were only 28cc.  Either way, it made great power.  213hp and 180 lbs of torque.  That dish is 17.2cc

Hi just so i can get this right, Taylor are you using these pistons with a Hemi cut head or with the standard vw cut head?

cheers

[rick m]

Sounds like Taylor has a more conventional VW chamber. Especially if only 28 CC. The VW Vanagon head works extremely well with this type of combination. In fact 80% of the quench or combustion area is in the piston.  Here are some shots to show how it looks. The factory specs state that the motor came with 9.0 to 1 compression.

Rick M

[OC1967vw]

RickM
Excellent documentation to support both Joel's and your thinking.
When I read Taylors response and excellent picture (and his thread on his car), my first thought was that he just made your point. Maybe not by design (only he can speak to his choice of parts and his thinking behind his motor), his motors performance during dyno tests underscore and strengthen your previous comments. Without getting into other posters' thoughts about what F1 engineers thinking is or may be.

Congrats to Taylor on his motor.

Certainly your pictures of factory heads and pistons illustrate that VW was thinking well in advance of many others in this regard

[rick m]

Taylor's motor is a great way to get ideal quench.  With the head chamber opened up more towards the outside of the barrel (in the combustion chamber) and and more unshrouding of the valves, things work really well on pump gas. Notice how the VW engineers actually taper the dish in the head toward the center of the piston.  It is clear where they wanted to focus the explosion of the fuel and gas on the very center of the piston. I call it focused torque.  :-)

RM

[Fastbrit]

I'm guessing that the two Ricks (M & Z) will know that the design being discussed here is known as the Heron head/piston combo, designed way back in the First World war by Samuel Heron (a lot of the development work was carried out at the Royal Aircraft Establishment, Farnborough, where my late father worked). It was first developed for aviation use (big air-cooled motors...) but ultimately junked because of the overly-heavy pistons that were part and parcel of the design.

In the car world, the Heron design is familiar to anyone working on early VW Golf GTIs (proper European ones, not the emaciated US versions) that had flat cylinder heads and dished pistons. I remember machining the lips off the pistons to make them flat-tops when we (I ran the race workshop at Autocavan at the time) built the first turbocharged GTI engines back in 1987. The Heron design generally fell out of favour as manufacturers (Volvo, etc) made greater advances with fuel management systems. Yes it works, but it's not the be-all and end-all and a dished piston's primary appeal is really, as Taylor has demonstrated, to get round the problem of an overly-small combustion chamber. It is interesting to see this old design being discussed again, though.

[rick m]

Keith,

I agree that it is not overly optimum due to the piston mass.  I do like the way Taylor set his up.  My current combo that I am working with is an open chamber that has some advantages in the area of less surface to retain heat.  Currently finishing up some CC'ing and set up work before assembly.  I ran a slight dish in my thick crown CIMA's but nothing like a vanagon, nor would I.  Just using it as an example of different combos that have happened over the years.

There is a lot of interesting discussion points I have been involved in with motor guys regarding what the PRO STOCK (V8 watercooled) guys have learned about open chambers as well, keeping in mind that they are watercooled and we are not.  I'm just having fun trying to make a VW live in 115 degree summers  ( :-)  and road trips where the ambient road temps above the asphalt reads between 145 to 150 degrees F.  I carry around an infared gun just to keep track of all the external temps affecting my motor.

Rick M

[Taylor]

Well, given chance to work at Embee Performance, albeit 5 years ago,  I got to see pistons from every motorsport on earth.  I'll tell you that this is nothing that hasn't been tried before. The pistons I have in my motor looking sexy like some of the ones I saw back then. It might be slightly naive but if it's good enough for dale earnhardt incorporated, I'll give it a go. Taylor

[rick m]

Taylor. Sounds like you had a good opportunity. Like we've stated, the ideas are not new as the chamber piston designs have been bantered around for decades. I have a lot of V8 friends and like to learn from some of their ideas too.  Your hp and torque numbers affirm another aspect of the discussion. Thanks for sharing. We're doing a final cc and flycut to my heads to get the volume where I want it and I am then on to assembly. Will post some shots as I go.

Rick M

[rick m]

Here is the link for the parts that HOWARD WASHINGTON just wrote about in the recent HOT VWs magazine.  It is the company that can get you the 93.5 +0.50 oversize piston (94mm dished) to use in your street motor project. It takes some set up and machining to get to where you want to be but is a great part that Howard has modified and runs in his own 2332 200+ hp street car.  Some work has to be done (see his HOT VWs article) to get the clearance between the pin bosses, plus to establish the dish size you want in the top of the piston for the cc and total compression ratio you are looking to set up.

Not a theory.  This is something he has done.

http://www.store.partsdinosaur.com/product4107.html

Rick Mortensen

[rick m]

Here is a set of WEISCO dished pistons. Setting up a quech area can be done many ways. The tighter the quech the more turbulence in the combustion chamber and better the flame travel over the entire piston. Mirroring the chamber to the piston, along with setting up the proper total cc's for the overall compression desired are all requirements of an effective combustion chamber design.

RM

[andy198712]

so are there any pistons out there in a 90.5 configuration with a dish then? (apart fro customs jobs)

[rick m]

I have always had to shop for a piston with a thick crown and have someone machine the dish for me. This way I can get the recess and cc amount I am looking for in my combination.  I am sure there are shops out there who can order the pistons and do the work for you. They become a little pricey once purchased and the machine work is done.  The pistons in the HOT VWs article by Howard Washington will only run you about $170 with rings.  You still need to cut the crown down a little but they are a reasonable alternative that will work.

See the HOT VWs article at the Parts Dinosaur link in one of my posts above.

Rick M