This might be nitpicking but unless you have a nuclear reaction mass in= mass out. Now the chemical bonds will be different and the mass will be more excited (hotter) but it's still all the same mass just in different form.

Sorry pet peeve of mine since my father's a chemistry professor.

Tim;
I stand corrected. In hind sight I was confusing the creation of energy from braking down atoms with the breaking down of chemical bonds. I guess it is the later form of reaction which accounts for how a gasoline engine works.

Its been a long time since I took either Chem or Physics.

But I belive you're right in the end, john
If the pressure is higher in the cylinder than the port then gases are going rush out and I belive that's why you don't need such a large exhaust valve. The pressure differential between the exhaust port and cylinder on the exhaust stroke is much larger than the intake port and cylinder on the intake stroke.

The use of a flow bench has long ago been established as a valid indicator of performance. The more flow, the more power potential, that simple. The next order of analysis is the total area or volume of air that flows given the cam profile. High flows at low lifts are very important because they last a very long time. Flow at higher lifts are less important because they only flow for very brief times ( think of just the top 10 degrees of rotation over the very peak of the cam vs the total time the cam has the valves open.

There is an established intake vs exhaust flow rate (about 75% for the exhaust) that is required for max performance.

NOw to real engines. They are PULSED SYSTEMS, think Fourier series and stuff like that. If you know about them, then think about the old SineX/X in the frequency domain. Each impulse forms a series of waves, of the Sine X/X shape. These waves overlap each other and can add or subtract from each other. If everything is designed so that they add in phase in a desirable way, a process that involves the rep rate (RPM), the shape of the pulse (cam profile) intake and exhaust runner lengths, ect you can end up with 110% volumetric effenciency due to the favorable phasing, at a single RPM. Using very very advanced math you can even broaden the RPM range that this works (at the expense of peak effenciency) THis area is both simple, old, and at the same time VERY advanced (as VERY few can do the math).

A Picture is worth a thousand words...
 

Check out this automation which shows what Snowman is trying to describe. It shows the pressures across the system of a 4 stroke engine. It is read from left to right...

Top Line:
First segment is the unrestricted intake pipe
Second (small) segment is the intake plenum
third segment is the intake pipe (port)
The first circle represents the intake valve
The green and white striped rectangle represents the cylinder
The second circle is the exhaust valve
The last segment is the exhaust system

Bottom Line:
The moving lines below represent the pressures.
The blue line is the leftward wave. Note that it "leads" with the right edge and travels left.
The red line is the rightward pressure vave and note that it "leads" with the lleft edge and travels right.
The pink line is the "superposition pressure" or summation of the leftward and rightward lines.

BTW; here's the web site from the manufacturer of the software that generated this model. They also have a few more animations.

BTW, I just noticed that my first attempt at a link didn't work. I just fixed it and now it works. I've also updated the descriptions based on the most recent edition of "Race Engine Technology" which has an article about the software used to create the animations as well as the the use of the software to understand the affects of intake restricters on engines.

John

Really nifty animation, really cool.

I am looking to do the same with my 2.2t.

Do you have the part number for the 86mm JE pistons?
I'm assuming the 4032 alloy, from what I've read.

Thanks

2.2 has a 66mm stroke, compared to the '72 70mm stroke. Plus I would imagine that JE has changed it's product line since 2004.

I believe Pelican will stock a piston that will work for you. You could search their parts catalog. I tried but the catalog search feature defeated me.

I just had my 72 2.4TV engine rebuilt by a reputable shop here in Germany.
My 50 year old T cast iron cylinders were rebored to 84.50mm and now are home to respective size Woessner pistons. These are beautifully made forged pistons which also turn out quite a bit lighter than Mahles / Kolbenschmidt pistons (not sure about JE but they look heavy from the pictures).

Compression ratio was reduced to 9.7-9.8:1 by milling down the piston's top section slightly.
Cam profile was changed to E spec and Zeniths required some further jetting adaption.

Previous setup was 84mm 2.2T pistons fitted in the same stock size cylinders, with original T cams. Already quite nice due to the bump in compression and free-breathing Zeniths.

Good luck with the build(s)! :)
Jan

Thanks trackrash, will check it out 😉

Thanks for the information, this is really helpful 👍
I was wondering if the Woessner set you had milled down was the 2.2 911s one they have for sale ( 10.5 :1)
https://wossnerpistons.com/products/9103
How has your setup been working?

Thanks again

Chris.

Chris,

It was actually the 2.4 T/E/S set (strangely it only comes up for 1973):

https://wossnerpistons.com/products/9482

I am still supposed to receive the full photo documentation of the build. Hopefully I can then provide a picture of the machined pistons.

My engine builder is a big fan of reboring old cylinders (as opposed to using new cylinders) as the risk of thermal deformation is close to zero.

Cheers
Jan

I have a 2.2 with the 66mm crank.

I imagine using the 2.4 10:1 CR pistons in my 2.2 would lower the Compression into the 9s no? Anyone have an idea of what the compression would be? In the area of 9.5:1 would be great.

Any reason not to do this?

Thanks,

Chris.

The lightest pistons you can get is preferable , JE pistons are heavy and have overly fat ring sets .
The hone is the most important detail to get right . The hone must match the rings specified RA
Cast iron has very different numbers than NICKI

Thanks, this is important. I was wondering alot about this as the Woessner 2.4 piston set lists its 10:1 cr for 911t, 911e and 911s but the 911t would require different rings for the iron cylinders.

Hmmm.

I guess I could order a set of Total seal rings and specify the iron cylinders so they match.

Ideas?

Chris.

yep custom rings are the right way to go, send them a piston and cylinder

You must do a very thorough set of measurements to get the comp ratio.
piston compression height ,piston dome displacement, rod length, Stroke, head cc,
Deck height, bore dia,

don't forget "pie R squared"

I used to do all long hand math,,,,, this is much faster.................

http://www.csgnetwork.com/compcalc.html

ian

Anyone know the material the rings are made out of for the Woessner pistons posted above?
I will reach out to them and check but am curious if anyone knows.

I imagine moly or cast....once I know that then I could specify a grit for honing correct?

220-280 for cast
400 for moly?

Thanks

Chris.

I have not found that to be true. Maybe in some cases?

The 95mm 9.5-1 JE pistons I am using in my 3.0l used stock Goetz rings same as the Mahles and were lighter than the CAST Mahles.

The motor I am working on now uses 92mm JE 10.5-1 pistons that use thiner rings than came stock in the 90mm Mahles.
Left is JE, right is Mahle.
http://forums.pelicanparts.com/uploa...1673469554.jpg

Pretty sure if you are having pistons made, you can specify whatever size rings you want. This is definitely true of CP, I'd have to imagine JE could also accommodate this.

The reason I would like to use the Woessner 2.4 10.1 cr pistons in my 2.2t cylinders is because they are made of 4032 alloy (lower expansion) which matches better with the cast iron cylinders i have. I've read JE will not make Porsche pistons in the 4032 alloy.

Noob question: ring gap is based on the ring material expansion characteristics and not the cylinder, correct? Would the cylinder material make a big difference? (Woessner ring details states the rings can be used in Cast or Biral/ Aluminum Nikasil cylinders, but would it require a different gap in each?

Thanks,

Chris.